Part 23 - cd3wd423.zip - Offline - Excreta Disposal for Rural Areas and Small Communities

Part 23 - cd3wd423.zip - Offline - Excreta Disposal for Rural Areas and Small Communities
A project of Volunteers in Asia
by: E.G. Wagner and JON. Lanoix
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i
EXC TA DISPOSAL
FOR RURAL AREAS AND
SMALL COMMUNITIES
.E. 6
WAGNER
J, N. LANOIX
World Health Organization
Geneva
L-
I958
FOR RURAL
EXCRETA
DISPOSAL
AREAS AND
SMALL
COMMUNlTlES
EXCRETA DISPOSAL
FOR RURAL AREAS AND
SMALL COMMUNITIES
EDMUND G. WAGNER
J. N. LANOIX
WORLD
HEALTH
ORGANIZATION
GENEVA
r958
Authors alone are responsible For views expressed in the Monograph Series of the
’
world Health cJrga&alsoa.
The menth
of specific companies or of certain manufacturxs’
products does not
imply that they are eudorsed or recommended by the World Health Organization in
prrlhwcle to others of a similar nature which are not mentioned. Proprietary names are
d&in
by initial capital letters.
PRJNTED
I
IN SWITZERLAND
CONTENTS
Page
Introduction.
. . . . . . . . . . . . . .
.
l
.
‘
.
.
.
7
tustc CoNStDERATtoNS
Public health importance of excreta disposal
Social and psychological implications of rural sanitation
.
progammes
.
L
L
.
.
.
. . . . . . . . . . . . . . . . . . . .
9
17
THE PRIVY’ METHOD QP EXCRETA DM43SAL
Factors influencing privy design . . . . . . . . . . . . .
Evaluation and selection of various excreta disposal systems
The
The
TIE
The
pit privy . . . .
aqua privy . . .
water-sea4 hmine
bored-hole latrine
The bucket latrine . .
The
The
The
The
f&11&s or trench
overhung Iatrine .
compost privy
.
chemical toilet .
WA’IER-URRJED
.................
.................
.................
..‘.
..............
.................
latrine
.............
.................
.................
.................
25
38
42
76
87
9s
103
Ill
114
115
119
METHODS OF EXCRETA DlSPQSAL
FOR RWRAL AREAS
Some problems in the disposal of water-borne wastes . . .
The septic tank . . . . . . . . . . . . . . . . . . . .
The disposal of eihent. . . . . . . . . . . . . . * . .
121
125
138
EXCRETA DZSPOSAL PROGRAMMES FOR RURAL AREAS
The planning of excreta disposal programmes ......
Training and function of the sanitation staff .......
156
165
Annex 1. Education and training of sanitarians .....
Annex 2. List of reviewers ...............
References ......................
INDEX ........................
175
177
181
185
[email protected] the past sewrd
there have ken many developments in the
#ehl of&posul of httmun wastes,and many books have been written on this
subjmt. X&egreat majority of these books, however,d~l abnost ex&sive&
with sewerageand [email protected] as qplicable to cities and Iarge townsand
communities. A survey of the relevant pnblications and of the few books
&wted to rumI sanitation r-is
important shortcomiings: in virtually all
instantxs, they are anjEtted to the SW of one or a limited group of [email protected]
wtitatioll problemsBsuch as latrines, wel/s, septic tanks, or a particnjar
method of r+se dv
adequatefor small communities. Veryfew ptibtications dd anyehe&vely with the me&m&s of getting sanitary excrete
&posalfaciliti&s cwutrueted and usedproyxrh, and wirh thefactors invotved
in the process.
I%e persotu p&[email protected] responsiblefor these aspects of ruIQI satritatiort
are the public h&h adMnistmtors, the medical oflcers of health, the civil
or sanitay engrratts engqgedin public health, and the sanitarians. It is
to these that this monogrqh is addressed. l%ey will f%td in it not onty
techniazl &a re&&tg to particular rurul excreta dispsal facitities, but also
&formation on what is beti& to be ne&d or to be done in order to achieve
successinp rogtpnvnes of excreta &ml
in mra$ areas and small comtin&tie&. l%e role of the health deptment, the needfor secnrbtgthe active
purtidpion
of the mmmunity und of the fm*iJ, theplanning of programmes,
und the twtidng of the neeessurypeuonnel are 60vered~us welt as the latest
accqptedpm-c&es in excmta disparPrfor rural ttrea~.
Fmm the& owtt eqerience attdfmm their dIscussionswith others of tong
eq+=ienceand stam&tg in rural sanitation work, the unthors haveformulated
thefollowingpriitciples which apyxar to them to be essentialin most cotcntr:es
to the successof sanitary excreta diynual programmes:
yeas
1. The object of any priwy prqmmme shotdd be to get the family to
as.~~v reqo&bility for9 and to solve, its own excreta disposatproblems.
2. l%e health deFtment shouId contributefimds for materials or tabour
or bath rir o&r to encouragethefw‘Iy to kitd thejbst tutrine and thereby
to take the jirsr important step in l&[email protected] a new habit.
3. Tire h+h +artment must trail sanitary inspectors to work with
the fmniies in the commWties on the e&cational and technical aspectsof
latrine construction, use, o)id maintenance.
EXCRETA DISPOSAL FOR RURAL AREAS
8
4.
7% smitafim
work skotrld fw timfer
the gmernf
rfirection
cj‘ II h*ol!-
trained sanita<~* engineer who must be able to umferstamf the problem of
excreta disposff/ in its mash ebementarl* terms anif the processes in vofwf
in eflectiug Sqnwement ill ihis fkndamentaC of’ rural sanitation.
This [email protected] written karge(i+on the basis of these four points. Aithough
it is obvious that evur;v problem is dtyerent and must be solved on the basis
of each local situation, it is hoped that the irtformation given herein will sheaf
some new and herrp$irllight on a problem which is very oki, no matter in
what part of the world it is found. An eflort has been made to give enough
detail to [email protected] those U&U are beginning in this work and, at the same time,
to present some ideas and approaches which mq be new to those with
e-Vperiencein rural sanitation.
It is hoped, too, that this monograph
will serve as one oj’ tile /ids
it1
the chain of eflorts being pursued by the Workf Health Organization to
stimulate environmental sanitation progrummes at the Iocal level in member
countries.
A preliminary text covering certain aspects of excreta disposal without
water carriage wasfirst drafted b\p Mr E. G. Wagner, Q short-term cottsultant
to WHO,
and was issued in 19i.5 as a mimeographed cfocument. This test
was circulated to forty experts in direrent parts of the worlcifor their comments
anii suggestions. The thirty-eight replies received were much appreciatelf,
and have greatly assisted in amending and revising the original text. (A
list of the reviewers wil/ be found in Annex 2, page I77. The Worfd Health
Organization wishes to express its gratitude to these reviewers. Also, to
the Service Especial de Satide PMica of Brazil and the Institute of InterAmerican Aflairs, and to their staffs, the Organization gives sincere thanks
for the use of their vast experience and for their frank and helpfkl criticism
j
of the material.
BASIC CONSIDERATIONS
PUBLIC HEALTH
IMPORTANCE
OF EXCRETA DISPOSAL
Excreta disposal is an important part of environmental sanitation. Its
provision is listed by the WHO Expert Committee on Environmental
Sanitation 44 among the first basic steps which should be taken towards
assuring a safe environment in f’.- A L :eas and small communities, the
others being the provision of an adequate supply of safe drinking-water
and the control of insect and animal vectorsof diseasein placeswhere these
are of significance. In large areas of the world, and indeed in parts of
every country, proper excreta disposal is among the most pressing public
health problems.
The inadequate and insanitary disposai of infected human faecesleads to
the contamination of ihe ground and of sources of water supplies. It
often affords an opportunity for certain speciesof flies to lay their eggs,
to breed, to feed on the exposed material, and to carry infection. It also
attracts domestic animals and rodents and other vermin which spread the
faeces; and it sometimescreates intolerable nuisances.
Relationship to Health
Poor excreta disposal is often associated with the lack of adequate
water supplies and of other sanitation facilities and with a low economic
status of the rural population. These conditions, all of which affect health,
make it difficult to assessthe role played by each component in the transmission of disease. However, it is well known that there is a relationship
between the disposal of excreta and the state of health of the population.
The relationship is both direct and indirect in character.
The direct effect is exemplified by the reduced incidence of certain
diseaseswhen proper disposal of excretais practised. This group of diseases
includes cholera, typhoid and paratyphoid fevers, the dysenteries, infant
diarrhoeas, hookworm disease, ascariasis, bilharziasis, and other similar
intestinal infections and parasitic infestations. These diseaseslay a heavy
hand on infants, whose immunity is low and whose vigour is often not
great enough to cope with an infection after it becomesestablished. Further
-9-
18
EXCRETA DISPOSAL
TABLE
I.
INFANT
YORI-ALITY
AND ENTERITIS
I
FOR RURAL AREAS
AND MORTALITY
FOR THE YEAR
deaths,
O-;oLyr.
81497
48734
14302
1669a
107653
3a29
4482
1745
48194
24p8
5923
7a944
33353
t 4t7
2288
EoW
Colombia
Guatemakn
-Portugal
Mexico
Costa Rica
Puerto Rico
Panama
Italy
ny, Federal Republic
deaths from
rate per
1069
live-births
deaths a
179 b
103
a6
a6
60
79
56
53
53
51
48
45
43
35
33
13 a41
2759
10679t
2651
228Q
32
31
27
27
27
17 160
25
21
20
18
dia:%enteritis (%I
43517
6 277
1392
5126
21052
772
1088
241
5168
440
391
5669
443
196
277
I
554
199
3599
64
42
54.7
12.8
9.7
39.3
19.5
20.2
24.3
13.8
11.2
la.1
7.8
7.2
1.3
13.9
12,o
,
4.0
7.2
3.3
3.1
1.8
Britain
Nomay
I
fbw Zeafand (exclusive of Maoris)
Sweden
DIARRHOEA
Infant diarrhoea
and enteritis
Infant mortality
--
C%untry
nion of South Afrka
(European popuhtkm)
Canada
Flnlenci
!?C,A
lhfllrlark
Switzerfend
United Kingdom of Great
and Northern Ireland
FROM
lW*
t343
Q&9
tQ6a
428
37
17
21
* Tahen from Ann&
EpkkmWa!
and Yitd Shalhtks, w.#.~~
(0 Flgufer gtven in this column do not Include deaths due to enteric Infectlonr
Wabke less Wan four weeks old).
b Fiaure for le53.
2.5
2.7
1.7
1.0
In the newborn
evidenceof this direct relationship may be found in a comparison of figures
for infant mortality from diarrhoeas and enteritis in various countries
(seeTable I).
A good exampleof the effect of sanitary excretadisposal on the incidence
of typhoid and paratyphoid is given by Fair & Geyer : I3 In the State of
West Virginia, USA, when a privy construction programme war;undertaken,
the death-rate attributable to these diseaseswas cut by two-thirds and
eventually was reduced to nil (see Fig. 1). It is stated, however, that
improvements in other sanitary conditions probably occurred at the same
time.
BASIC CONSIDElLUIONS
II
The indirect reiationships of exereta disposal to health are many,
but they are generally associated
1
with other components of environmental sanitation. Here mention
may be made of the following :
1. The improvement of hygienic
conditions promotes a state of wellbeing in the population which is
conducive to its social development.
2. There is considerable evidencethat the diminished incidence
of excrementaland water-borne diseaseswhich results from improvements in environmental sanitation
is accompanied by a marked decreasein morbidity from other diseases the etiology of which is not directly related to either excreta or
FIB. 1. REDUCTION IN THE DEATH-RATE
FROM TYPHOID
BY SANITATION
OF EXCRETA DtSPOSAL
contaminated water-supplies.
3. Various economic benefits, such as those resulting from an increase
in life expectancy, arise in connexion with the implementation of sanitation
P’ogrammes*
4. Morbidity resulting from lack of even the simplest sanitation facilities adversely affects deployment of labour. When they are healthy,
unemployed persons who are unable to find work in one place may readily
emigrate to another where work is available. The sick cannot do sop4
How Dlperse is car&d from bereta
+&Ianis the reservoir of most of the diseasesthat destroy or incapacitate
him. The faecal-borne infections and infestations already mentioned are
the cause of tremendous losses in death and debility. It is interesting to
note that all these diseases are controllable through good sanitation,
especially through sanitary excreta disposal.
In the transmission of these diseases from the sick, or from carriers
of disease, to the healthy, the chain of events, as shown in Fig. 2 A, is
similar to that for many other communicable diseases. Anderson &
Amstein l state that, in order to transmit disease, the following factors
are necessary:
(1) a causative or etiological agent ;
(2) a reSeNOir or source of infection of the causative agent ;
12
EXCRETA DISPOSAL FOR RURAL AREAS
FIG. 2. TRANSMISSION
CHANNELS
OF DISEASE
OF TRAHSM~SSLON
FROM EXCRtTA
OF CslSE4SE FROM EXCRCTA
STOPPING THE TRANSM&SION
OF FAECAL.f?.=G:
BY MEANS OF S4NilATION
LXEAIE;
B
(3)
(4)
host ;
(5)
(6)
a mode of escapefrom the reservoir ;
a mode of transmission from the reservoir to the potential new
a mode of entry into the new host ;
a susceptible host.
The absenceof a single one of these six conditions makes the spread
of diseaseimpossible. As may be seenfrom the diagram in Fig. 2 A, there
are many ways in which the causative agent of emeric disease reaches a
new host. In diff’erent parts of the world, different modes of transmission
may assumevarious degreesof importance : in some areas, xater, food,
and milk may be most important; in others, flies and other insects; and, in
still others, direct contact may assume a major role. What is most probable
is a combination of all, and the sanitary worker must asx;‘me thai this
BASIC COffSIDlXATIONS
13
is the case and guard against all modes of transmission. The technical
objective of sanitary excreta disposal is therefore to isolate faecesso that
thz infectious agents in them cannot possibly get to 3 new host. Fig. 2 B
shows the place where the sanitation officer might choose to erect a barrier
to break the chain of disease transmission from excrete.
Extent of the Problem
A rapid investigation of sanitary conditions throughout the world
would show how vast and important is the problem of excreta disposal.
Even in countries such as Great Britain, France, and the USA, which
by world standards may be considered prosperous and healthy, much
remains to be done in this field. J. A. Scott 32states that in Great Britain,
where 20% of the population live in rural communities, 23% of households
do not have the exclusiveuse of a water-closet. In France, of 38 000 local
authorities (municipal authorities) only 80 have sewage-treatmentplants,
and fewer than 1500 have any kind of seweragesystem or refuse-disposal
organization. In the USA, it was conservatively estimated in 1943 that
4 000 000 sanitary privies were needed in rural areas to serve 16000 000
people, who lacked these fundamental necessitiesand who, for the most
part, resided in areas having the highest incidence of typhoid fever,
dysentery, and hookwormp6
While similar figures are not available for other areas of the world,
sanitary surveys and statistical data collected from a large number of
countries give useful indications as to the extent of the problem. In India
and Pakistan, faecal-borne diseasesrank high among the most important
communicable diseases. In the decade between 1940 and 1950the record
shows that 27 438 Ooo persons died in India from the enteric diseases.
The incidence of hookworm was between40% and 70% of the population,
and it was estimated that more than 200 million people were infected.
In Ceylon, it was estimated in 1943 by the health department that 70%
of the population was infested with hookworm. In rural areas of North
China, 81% of the population has been found positive for Awaris, and
76% was estimated to be positive for Entamoeba histolytica (amoebiasis)F3
A similar situation prevails in British Honduras, in Central America,
where the incidence among village schoolchildren was found to be over
60% for Ascaris and 50% for hookworm. Similarly, high incidences of
enteric and helminthic diseaseshave been reported for large populations
in countries of the Middle East, South-East Asia, the Western Pacific,
Africa, and the Americas by J. C. Scott 33 and by Simmons et a1.34
In 1951, Dr H. van Zile Hyde 22wrote :
“The dire effect of this upon a rural nation was clearly brought home to me by a
statement recently made by an American medical observer who stated that the worms
TABLE II.
ESTIMATED
Country
COST OF TVPHOIO FEVER AND OF DIARRHOEA AND ENTERITIS
IN CERTAIN COUNTRIES FOR THE YEAR 1W
Income
par caput
N’s $1
Typhoid
fever
Dlsrrhoea
and enterttlo
deaths
deaths a
cases
deathr 8
TOtd
cams
cases
F”tiJat
pgy)
Medical
care 0
‘I (US S)
Value
POPULATION
(US $1
t!Bn;f
time
lost a
(US $1
(US S)
o:OE
I
I
USA
Tots’
PER WOW
2’
1 452
0.1
1
5.7
285
5.8
285
115tr
21 4M)
17 765
14635
55 040
France
450
2.0
20
21 .I
1070
23.4
1 020
1450
25800
28500
17256
73ooo
Portugal
140
0.6
86
195.2
9760
203.8
0846
3930
72305
66800
48200
191 130
98
1.3
13
88.0
4 400
86.3
4 413
1200
22 850
18560
15200
57 750
200
12.4
124
i28.1
6405
140.5
6529
3 875
66ooo
76800
46200
195 775
83
12.0
126
56.5
3 475
81.5
3595
930
15700
22ooo
10566
48135
5 810
131.7
6645
1706
2Q Qoo
35 356
19956
55666
32M
124.4
3 524
925
0840
40700
5800
58 265
Japan
Colombia
Ceylon
Dominican
India d
Republic
84
13.5
135
116.2
54
58.6
234
65.8
a Typhoid fever mortality rate assumed to be 10%.
b Dlarrhoea and P’ ‘eritls mortality rate assumed to be 2%.
c Funeral expensea based on E265 In USA ; *D medical care costs based on $75 per case in USA ; ra value of llves lost bges g-45) from typhoid and
paratyphotd fevers estimated at $15 500 and from diarrhoea and enterltls (ages O-45) at S28fiClfor USA .I# Worklng time lost per case assumed to be two
weeks, with a value of $50 In USA. The estimated unit cost of funerals and medical care and the value of llves and working time lost for countries other
than the USA were assumed to be in the same ratio to similar costs and values in the USA as the per capuf income for those countries to that for the
USA.
d Mortality rates for typhold fever and for diarrhoea and enteritis are not available for India. The rates and values listed are those for cholera and
for diarrhoea and dysentery.
BASIC
TABLE
Ill.
CONSJDERATJONS
IS
ESTIMATED
PER CAPUT
COST OF RURAL WATER
SUPPLIES
AND LATRINES
AND COST OF TYPHOID
FEVER AND OF DIARRHOEA
AND ENTERITIS
PER [email protected] POPULATION
FOR CERTAIN
COUNTRIES
IN 1948
cost per caput of
Hater supplies (US $1 a
Cost per cam/t at
latrines (US S) a
Country
USA
France
Portrrgal
Japan
Colombia
Ceylon
Dominican
Republic
India 8’
capital
cost
maintenance
17.00
5.25
1.65
1.15
2.35
0.98
0.55
0.17
0.05
0.04
0.08
0.03
14.00
4.35
1.35
O.QS
1.25
0.50
5.75
1.50
0.55
0.40
0.50
0.33
1.10
0.63
0.04
0.02
0.94
0.52
0.38
Cost of
yp;t$ Fer
Total cost
per 100000
PO(p&a$”
diarrhoea
rnd enteritis
per 100000
population
(US $1
req$S? for
amortization
of water
supply and
sanitation
facilities
from savings
3730000
1157ooo
35otmo
254ooo
518000
214000
55 720
73000
191230
57 750
195 775
49 130
68
16
2
5
3
4
246 000
135000
85800
55255
3
3
maintenance
091
Approximate
number of
-I
u This includes the cost of labour, materials, and equipment.
These costs could be reduced considerably by the use of voluntary labour and materials available locally to the householder.
infesting the people of a certain semi-tropical
country
metabolize
more of the produce
of that country than do the inhabitants. Half the work of a sick peasantry, therefore,
goes into the cultivation of food for the worms that make them sick.”
It should be noted that, in many countries, more than 80% of the
population live in rural areas and small communities and, as a general
rule, have a low income. In most cases, all the elements of rural sanitation
are absent, and indiscriminate fouling of the soil with human excrement
is common. Such conditions are also often found in rural areas near
towns, and aggravate the urban sanitation problems. The menace of
inadequate excreta disposal is present so long as sanitary privies are lacking
in a community.
The economic losses resulting from insanitation often reach staggering
proportions. Atkins,” analysing data available for several countries in
1949, found that infant mortality and mortality from typhoid fever,
diarrhoea, and enteritis were in inverse proportion to the income per
caput. He estimated the cost of these three diseases (see Table II) and
the per caput cost of rural water-supplies and latrines (see Table III).
He concluded that in each of the countries considered, except the USA.
and France, it would be possible to amortize within a period of five years
a Atkins. C. H. (1953) Some economic aspects of sanitation programmes in rural areas
and small communities (Unpublished
workiog document WHO/Env.San./56)
16
EXCRETA DISPOSAL FOR RURAL AREAS
the cost of rural sanitation facilities from the savings which would accrue
from the reductions in typhoid fever, diarrhoea, and enteritis. Other
advantages would result from the control and reduction in incidence of
cholera, the dysenteries, ascariasis, guinea-worm, hookworm, and other
enteric and parasitic diseases. In addition, there would be several indirect
benefits, such as the convenience and saving of time which the facilities
would offer.
Collateral Bene6ts of Proper Excreta Disposal
Certain public health programrnes, when properly carried out, often
yield important side benefits quite apart from those which they were
expected to produce. Programmes of excreta disposal belong to this
group. An example of this was given by Tisdale & Atkins 35 in 1943 :
“ The sanitary privy has a definite relationship to public health and in this connection
the following points are significant :
* 1. In areas [of the USA] where water carriage sewerage systems are impracticable the privy is the facility relied upon to break the transmission chain of intestinal
diseases.
“ 2. Privy construction programs, originally undertaken in the hookworm and
typhoid fever regions in the South thirty years ago, contributed substantially to the early
development of full-time local health services. At present more than 1,800 counties in
the United States have such services.
*‘ 3. The 3,ooO,OOOsanitary privies constructed under the various work-relief
programs have had an important effect in reducing the incidence of intestinal diseases.
“ 4. The close association of U.S. Public Health Service officials with state health
departments in rural sanitation campaigns over a period of 30 years has been instrumental
in developing the esprit de corps which now enables local, state, and federal health
services to cope successfully with problems of sanitation, malaria. venereal disease, and
industrial hygiene in critical war areas in America today.
I‘ 5. The fundamental principles of federal-state cooperation, successfully demonstrated in the rural sanitation programs, are now being applied throughout the field of
public health. In addition, cooperative plans for public health work among selected
population groups have been developed by the Public Health Service with other federal
agencies. The Farm Security Administration’s health and sanitation program is an
example of federal cooperative health work.”
l
Similar examples may be drawn from the experiences of Scott 33 in
China and the World Health Organization in Taiwan, where attempts at
solving the excreta disposal problem have been found to be linked with
the development of satisfactory composting procedures. In these countries,
as well as in Latin America, programmes of excreta disposal have led
to the recognition of the need for team-work between the medical officer,
the public health engineer, and the public health inspector.
BASIC CONSIDERATIONS
17
SOCIAL AND PSYCHOLOGICAL IMPLICATIONS
OF RURAL SANITATION PROCRAMMES
commlmity Pruticiption
Expetience available from all parts of the world leads to the conclusion
that a programme of rural sanitation, of which sanitary excreta disposal
is an essential part, cannot be successfulwithout the participation of the
local community. To be truly effective, environmental sanitation, which
is a basic function of every integrated health service, needs the understanding, the support, and the active participation of the people concerned.
Mere technical improvement of the environment without public education
in hygiene and sanitation, based on local customs, traditions, and beliefs,
has again and again proved futile.
One measure of the successof a rural sanitation programme is its
power to sustain itself and grow. In order to achieve this success,it is
necessaryto find ways of gaining popular support and of overcoming
popular objection. In both, health education of the public plays a major
role. In the former instance, attention must be given to the structure and
organization of a programme which will fit into the local social and economic
system. More important still is the desirability of bringing the people
into the programme as partners. In the pursuit of the second objective,
the assistanceof a competent health educator may be required. It is very
likely that, even before reaching the stageof overcoming popular objection,
the sanitarian may have to undertake the task of disturbing the age-old
apathy and inertia which grip the people. For example, the fact that a
community is without adequate excreta disposal facilities immediately
suggeststo a health worker the need for providing latrines. However,
the community may not be ready for, or interested in, such facilities, or
may be even hostile to them. To insist upon the immediate introduction
of latrines into a community under such circumstancesis not a wise move
on the part of the sanitarian, who should always remember that “ doing
things to people and for people is easier, though in the long run more
costly, and lesseffective,than fostering greaterindividual and local initiative,
responsibility, and self-reliance on a well-informed basis “.’
This health education stage is admittedly the most difficult in the
evolution of a privy scheme. Once it is successfullypassed,the programme
will move at a faster rate. For example, in the rural areas of severalLatin
American countries where community health programmes have been
‘a Martikainen. A. H. (1956) Co-operation for future progress in heulth education of the
public. In : Report of the Third Conference of the International Union of Health Education of
the Public. Rome. vol. 1. (This pamr also exists as a WHO unpublished document : WHO/
MH/AS 124.56.)
2
I
18
EXCRETA DISPOSAL FOR RURAL AREAS
going on for some time, privies are constructed almost exclusively by
the families, with the health department supplying the necessary guidance
and the concrete privy slab either at cost or gratis. In many places the
demand for slabs is always greater than the supply.
Experience shows that the most important factor in getting the community to participate is to bring members from all its segments into the
programme as partners. The people must, however, understand what
the programme is all about. This may be achieved by working through
ihe village council, if one exists, and if not, through a village committee
set up at the plann& 0 stage and comprising prominent and respected
leadersof the community. Further proqess will come from the assimilation
and use of scientific excreta disposal principles by the villagers themselves,
and this can be realized only if they take part in the survey, planning,
and conduct of the programme. One should expect that initial progress
will be rather slow and that it may be necessaryto plan the programme
in successivestages stretched over a period of time.
The relation of health education of the public to the important subject
of community participation in rural sanitation programmes has been
studied by various authors, in particular by Foster,‘* Derryberry,** o and
Ramakrishna.”
In recent years the expression “ community development” has come
into popular international usage to connote a complex of processesof
which the two most important elements are the following :
“The participation by the people themselves in efforts to improve their level of
living with as much reliance as possible on their own initiative ; and the provision of
technical and other services in ways which encourage initiative, self-help and mutual
help and make the+ more effective.” a6
As stressedearlier, thz practical application of theseprinciples is essential
for lasting progress in rural sanitation. In addition, field experienceshows
that a specific local project or activity in sanitation initiated in response
to a local demand can serveas a very practical basis for stimulating local
interest and participation in attacking other basic problems, and thus
act as an important spearheadfor the promotion of community development.
Family Participation
Since one of the ultimate objectives of a sanitation programme in a
community is to get the family to solve its own excreta disposal problems
(within reason, of course), it is important that each family unit participate
= Ramakrishna. V. (1956) Role of health education in environmental sanitation programmes
(Unpublished paper prepared for the WHO Seminar on Environmental Sanitation. Beirut.
Oct.-Nov. 1956)
BASIC
CONSIDERATIONS
19
in some way in its execution. Whatever the nature of the sanitation needs
and related heairh problems, health workers can gain the interest of people
by a sympat?.cric and practical approach to their problems. People who
come to a health centre or dispensary (mobile or stationary) seeking treatment of intestinal disorders are usually receptive to suggestions as to how
to avoid dysentery and diarrhoea. Full advantage should be taken of
such opportunities to help make the people aware of the measures which
can be applied at home and in the community to prevent these conditions.
Practical demonstrations and discussions of latrine construction, aided
by the use of visual media based on local situations-e.g., photographs,
slides, posters, film strips, film exhibits, and others-may be particularly
rewarding.
Once the family is willing to participate in the scheme and to learn a
new habit, the public health inspector must be ready to offer a solution
which is acceptable and as simple and economical as possible. When
sanitation and personal hygiene become habits, the health programme
will have made tremendous progress.
The sanitation work cannot be considered completed, however, after
the construction of the first privy or latrine ; in fact, it has just begun.
The public health inspectors or public health nurses, as the case may be,
must remain continuously in touch with the family to stimulate and educate
its members into using and maintaining this facility, which often has been
constructed after hard and time-consuming labour. The continued
educational process involved requires the co-operation of the whole health
department staff, which can consider that success has been achieved only
when the family has accepted the privy as a part of its way of life, and is
willing to maintain it, to rebuild it, and to move it to a new location, as
necessity demands, and even to become a disciple in teaching the neighbours.
It will be noted that time and continuity of staff and organization are
essential for successful rural sanitation development.
Mention has been made of simple and economical solutions to the
family’s excreta disposal problems. Finding reasonable solutions is considered to be one of the keys to active family participation. These are
not always easy to find. Undoubtedly there are places where nature,
aided perhaps by man, makes it very difficult, if not impossible, to devise
simple and economical facilities. In these situations, the sanitarian’s
ingenuity and ability are taxed to the limit. He must be resourceful in
making use of available materials and in organizing the people of the
community for the difficult tasks at hand. In some instances extra technical
and financial assistance may be required from the health department.
The family cannot be expected to perform difficult and complicated
construction operations. Sanitarians and public health officers should
strive to propose and design solutions that are within the means and ability
of the people to operate, maintain, and replace. This is true of a simple
20
EXCRETA
DISPOSAL
FOR RURAL
AREAS
family privy, a village well, a public water-supply system, or large waterand sewage-treatment works.
As to actual modes of obtaining family participation, several systems
have been tried in different countries with varying degrees of success.
The best methods are those in which initial work and expenses are shared
by the family and the health authorities or other agencies. Family contribution either may be financial in character or may take the form of
labour and materials. Although financial contribution by the villagers,
or by the local authorities, is highly desirable, it will be found advantageous
in the early stages of a programme to secure the actual participation of
the people in the work, which is being executed for their own benefit.
People are more likely to put into daily practice those learning experiences
in which self-initiative and self-help have played a part. The psychological
advantages of self-help are considerable, even if the extent of the self-help
is limited to the provision of manpower and locally available material.
In an effort to give proper importance to the construction of privies,
use has been made in Latin America, with remarkable success, of simple
contracts between the health -department and the head of the family.
The contracts state in simple, direct terms the obligations of each party,
so that no misunderstanding can arise. This impresses on the family
the importance which both parties attach to the privy as a vital element
in household health. The application of this technique depends on a
patient and enthusiastic health department representative, for it takes time
to talk to each family and explain over and over the need for a sanitary
privy and the benefits which can be derived from its daily use.
Another technique used with success in some countries in South-East
Asia consists of “ selling ” the programme to respected leaders of the
community and helping them, first, to install their latrines. The possession
of a sanitary latrine thus becomes associated with a position of prestige
in the community.
Role of the Health Department and Other Agencies
It is accepted as axiomatic in environmental sanitation that governments
should take the initiative both in stimulating action and in providing the
essential technical guidance .44 For excreta disposal programmes the
primary responsibility and authority for surveying, planning, organizing,
and implementing wide-scale measures obviously rest with the health
department. To do this job with any chance of success, however, the
health department must secure the understanding, the support, and
the participation of the villagers, as previously mentioned. It is also the
responsibility of the health department to seek the cu-operation of various
interested government or private agencies, such as agriculture, education,
BASIC CONStDEBATtONS
21
and public works departments, or large plantation estates, and to coordinate their activities in this field in order to ensure proper integration
of their activities into the general health and community development
programme planned for the area concerned.
When excreta disposal programmes are contemplated for the first time
in a community, the health department should he prepared to spend more
than the mere cost of required staff. The sum to be spent need not be
large but will make it possible for the department to win the co-operation
of individual families for the construction of the initial facilities. Experience
shows that, if the health department does not enter into the programme
with adequate funds, it may take many years to get to a point of complete
community participation. On the other hand, by giving the sanitation
work a good start in the form of partial financial assistance,the time can
be greatly reduced. The funds spent in this manner will pay great dividends
in the future. With money to buy materials, es-pzciaIlythe types of materials
unavailable locally, the public health inspector is in a position to offer
something concrete, beside technical advice, to the family. He may then
say : “ If you will provide the Iabour for your privy, I w1l1provide materials.”
Or he may offer part of the labour and part of the materials.
The health department is also responsiblefor organizing demonstration
or pilot schemes of excreta disposal. Such demonstrations should be
carried out first in health and welfare centres, in schools, and in residences
of local health and sanitation officials. A demonstration plot of land
suitably located and provided with sanitary excretadisposal units in various
stagesof completion is a desirableitem in a planned sanitation improvement
and training programme. The health department should also prepare
and make available to the people and their leaders leaflets and manuals
covering the design, construction, and operation of excretadisposalfacilities
that fit the conditions encountered in the areas concerned.
“ Wherever
bodcanstrucrion,
poorventitatiunandlighting,tackof washingfacilities,
insanitaryloiters,or similardeficiencies
exist [in schools], children will be absorbing
wrong ideas and teaming harmful habits which may never be eradicated . , . Similarly.
a well-built and welt-kept latrine may be far safer as welt as of greater fundamental
education value than a porcelain and tile toilet which is allowed to become dirty and a
nuisance.” Is
Mere classroom teaching of sanitation, unaccompanied by actual
demonstration, will have little-if any-effect on children ; but this is,
unfortunately, common in many parts of the world. It is well known that
children learn by doing and through example, two facts which can be
used to advantage in leading schoolchildren into the practice of a sanitary
way of living. It goes without saying that health workers should lead
the way and give the proper example 10 the people by living and working
in sanitary surroundings.
22
ESCRETA
DlSPOSAL
FOR RURAL
AREAS
Under certain circumstances which require the use of communitycontrolled IaCrineconstruction services, the role of the health department
may assume increased scope and importance. Such situations would
arise, for example, in areas where crowding of houses or hard ground
conditions make it necessary to put in some kind of collective sanitation
facility, deep-bored holes inside houses, precast hand-flush installations
in houses, or other types of excreta disposal systems which, because of
physical circumstances, cannot be erected by the families themselves. In
these cases a government, through its health department, may need to
set up and maintain an efficient organization to carry out excreta disposal
construction work. Here also the active participation and contribution
of the local populations in the form of labour, materials, and money are
absolutely required for the ultimate success of the excreta disposal pro+mmme. The people should never be led to rely entirely on the health
department for the provision, maintenance, or renewal of their sanitary
facilities, even when these must be built for them for special reasons, as
explained above. An alternative solution which may sometimes be used
involves the formation of construction co-operatives or health leagues by
the people themselves under the sponsorship of the health department,
which may supply financial and material assistance in addition to providing
technical guidance.
In order to achieve efficiency and rapidity ot execution, it is often
tempting to carry out latrine construction work on the basis of campaigns.
This method has a definite place in health programmes, and experience
has shown that it can be successfulunder certain conditions. Campaigns
will prove useful, however, only when there is good follow-up and continued
health education and sanitary inspection. Under these conditions, t’ e
health department still has an opportunity to convince the families \i.,f
the worth of the latrine and to persuade them to maintain it and replace
it when the need arises.
In areas where there is a lack of organized community services in
addition to a low economic level, there will be no follow-up inspection
or health education, and the programme is likely to be a complete failure.
It is uneconomical to spend money on latrine campaigns under such
conditions, for rarely do the people use the privies in sufficient numbers,
and even more rarely do they maintain or replace them. It has been
reported, for exampie, that even where public acceptance of privy campaigns
in areas of Latin America has been good, the privies have frequently been
used as chicken-coops or grain silos. Experience after experience can be
recounted in which a great deal of money and effort was expended only
to have the situation return to its original unhygienic status after a rela-
B.&SIC CONSlDEiRATIONS
23
tively short time because of the lack of continued health education and
inspection by a well-organized and integrated sanitation service of a health
organization.
One important aspect of latrine campaigns is the community interest
and attention that are focused on the excreta disposal problem. Parallel
situations exist in connexion with other health campaigns, such as malaria
control and yaws campaigns. If advantage can be taken of this interest
and if an adequate and permanent follow-up organization can be set up,
the campaign technique can be a very successfulmethod of getting latrines
built and used. Under most conditions, however, the education and
family participation method, although slow, is best.
Public Versus Individual Latrines
Publiz latrines, or ” multiple units +’ types, are usually constructed
in markets, camps, schools, factories, slum districts, and similar localities.
They are also useful in other placeswhere large numbers of personscongregate occasionally, provided that permanent and close attention is available
to ensure cleanliness and proper operation.
Experience in all parts of the world indicates that, except in unusual
circumstances,multiple units should never be substituted for the individual
family fatrine . True, it is cheaper and less troublesome to construct a
few communal latrines in a community than to build a large number of
individual latrines at the rate of one unitper family. In addition, a good
solution to each family’s excreta disposal problem is not always easy to
fmd. For such reasons the construction of the communal type of excreta
disposal facility was accepted in the past, even in urban communities.
Mowever, it was discoveredafter a few years’ use that thesepublic latrines
were employed by only a portion of the population for which they were
intended, the remaining group continuing the original practice of defaecating
anywhere. It was then believed that two reasons for this situation were
inadequate design and the lack of cleanliness. Attempts were made to
improve these elements; but, in most instances, communal latrines,
irrespective of the type of design, proved to be failures.
It should be pointed out that the community is generally made responsible for the maintenanceof public units. Usually communal administrations are notoriously poor and ine&ctive at maintaining even the
utilities that offer great convenience, such as water works and electric
light systems, let alone a communal privy which many do not consider
essential in any case. This does not mean that the construction of public
latrines should be disregarded; but one should be warned against their
limitations and the illusion that they mill be automatically and efficiently
maintained by the community. The truth is that the communal authorities
24
EXCRJXTA
DISPOSAL
FOR RURAL
AREAS
must be prodded on this important matter of maintenance as much as,
or more than, the family. So long as the effort to ensure good maintenance
must be made, it is decidedly better to spendit on the family, on whom there
is hope of its eventually having the desired effect. Families will usually
keep their own latrines clean and in proper operaticn with only occasional
guidance from the public health inspector.
Public latrines, therefore, should be built only where absolutely necessary
and should be designed to facilitate maintenance and constructed for
permanence, as far as possible. They must be kept clean at all titnes,
for, unless cleanlinessis observed, they will not be used. Water and other
materials must be available for use in keeping the latrines clean.
Since the objective of this monograph is the promotion of rural excreta
disposal by the individual family, no attempt will be made to describe
types of public latrines or urinals which are usually associated with them.
THE PRIVY METHOD
OF EXCRETA DISPOSAL
FACTORS
INFLUENCING
PRIVY
DESIGN
A rational approach to the problem of collecting and disposing of
human excreta in rural areas assumesthat the engineering aspects, while
not as extensiveas those associatedwith urban engineering schetnes, still
require the samecareful marshalling of facts and application of painstaking
analyses for their solution. There are several factors which influence
the choice and the design of a systemapplicable to a particular community.
Some are biological in character ; others are of an engineering nature ;
and still others, which are of no less importance, involve careful consideration of human behaviour.
Deco~~po&ion of Excretr
Excreta, wherever deposited, immediately start to decompose,and are
ultimately converted to an inodorous, inoffensive, and stable product.
In the design of excreta disposal facilities it is important for the health
worker to know and understand how this processtakes place and how it
affats the material itself and the, harmful organisms such material may
contain. The sanitarian, in particular, is often called upon to explain
in simple terms what actually happens to faeces and the health hazards
involved in inadequate disposal systems.
The main actions of decomposition are to break down the complex
organic compounds, such as proteins and urea, into simpler and more
stable forms ; to reduce the volume and mass (sometimes as much as
80%) of the decomposing material by the production of such gases as
methane, carbon dioxide, ammonia, and nitrogen, which are dissipated
into the atmosphere, and by the production of soluble materials which,
under some circumstances, leach away into the underlying soil ; and to
destroy pathogenic organisms which in some instances are unable to
survive the processesof decomposition or attack by the rich biological
life of the decomposing mass.
BacteGa play the major role in decomposition ; and bacterial action
may either be aerobic-i.e., carried out in the presenceof air-or anaerobic
-
25 -
26
ESCRETA
DISPOSAL
FOR RURAL
AREAS
-i.e., carried out in the absence of oxygen, generally in a fluid or saturated
environment. The process may be entirely anaerobic, as it is in aqua
privies, septic tanks, or at the bottom of deep pits, or entirely aerobic,
as it is in certain cornposting operations. On the other hand, decomposition
may consist of more than one stage, some anaerobic and some aerobic,
depending upon the physical conditions encountered. For example,
anaerobic processes may take place in a septic tank ; but, as t+e liquid
effluent is discharged into an underground tile distribution system, the
water drains away, leavin g much organic matter in the upper layers of
the soil to be decomposed by aerobic saprophytic bacteria, which thrive
in the top 60 cm of the soil.
FIG. 3. CYCLE
OF NITROGEN
The process of decomposition applies to all dead organic matter of
vegetable or animal origin, and particularly to their nitrogenous, sulfurous,
or carbonaceous constituents. In the case of human wastes, a mixture
of faeces and urine, which are relatively rich in nitrogenous compounds,
the decomposition process is typically represented by the nitrogen cycle,
which is shown in Fig. 3. In this cycle compounds are broken down
Grst into ammonia and other simple products, and are then converted
by nitrifying bacteria into nitrites and nitrates. The strong smell noted
during the decomposition of urine is due to ammonia, which escapes
before it has been converted into a more stable form. Decomposition
may proceed very rapidly, the period varying from a few days in the case
THE
PRIVY
MlXHOD
OF EXCRETA
DlSPOSAL
27
of very carefully controlled mechanical cornposting to several months,
perhaps up to nearly a year, under averageconditions in a pit privy.
Conditions prevailing in decomposingfaecesare generally unfavourable
to the survival of pathogenic organisms. Not only do the temperature
and moisture conditions inhibit the growth of pathogens, but also the
competing bacterial flora and protozoa are predatory and destructive.
Pathogens tend to die quickly when the humus-like end product of
decomposition is spread out and dries. The bacterial pathogensprobably
do not survive more than two months in undisturbed privy contents.
The ova of hookworm will remain viable for much longer periods, depending
on moisture and air temperature : they may live up to five months in cool
climates, much less long under tropical conditions. They will eventually
hatch in the presenceof air, and will produce larvae which may survive
for several weeks in moist, sandy soils. Ascuris ova may live for two
or three months in pit-privy material.
The final products of decomposition contain valuable soil nutrients
and may profitably be used as fertilizers. Sometimes farmers complain
of the small nitrogenous content of digested or composted night-soil.
Indeed fresh excreta do contain more nitrogenous matter which, however,
cannot be used by plants in their original composition. Plants can utilize
nitrogen only as ammonia or as nitrites or nitrates, which are only produced
during later stages of decomposition. When raw excreta are spread on
the land, much of the nitrogen is transformed into volatile matter, which
evaporates into the air instead of being used by plants.
Quantities of Human Faeces
The public health engineer or inspector is interested in the amount
of the raw material which must be processed. Most studies on quantities
of human waste have been made chiefly on a physiological basis and have
given some information on the rangesand mean values of the quantities of
excreta produced by individuals. A small amount of information based
on actual field observations is also available but is of varying reliability.
It is recognized that the quantities of human excreta produced may be
iafluenced by local conditions, not only physiological, but also cultural
and religious. An example may be the use of ablution water or other
personal cleansing materials.
A review of published data shows that in Asia the amount of faeces is
about 2OO-400g (7-14 oz.) per person per day (wet weight), as compared
to 100-150g (3.5-5.3 oz.) per day for European and American countries.
In North America a figure for pit-privy design is basedon 1.5 cu. ft (42.4 1)
per person per year where urine may leach away, and a figure of 19.5 cu. ft
(552 1) per person per year for water-tight containers such as the vault
28
EXCRJZTA DISPOSAL FOR RURAL AREAS
privy. In India, according to the Manuul sJ [email protected] fbr the armed forces,
1953,915
the amount per person per day is 400 g (14 oz.) for faeces and
2300 g (81 oz.) for urine and cleansing water. According to 0. J. S. Macdonald,‘s in the tropics faeceswill range from 280 g to 530 g (10-19 oz.)
per person per day, and urine, depending upon temperature and humidity,
from 600 g to 1130 g (1.3-2.5 lb.).
H. B. Gotaas,‘8 in a worldwide summary, gives the following data
. collected from various sources:
Grumslpersontdav
wet weight
dry weight
Fmces . . . . . . . . . . .
Urine
. . . . . . . _ . . .
Total
. . . _ . . . . _
t35-270
1000-1300
35-70
50-70
1135-IS?0
85-140
A study in the Philippines indicated an average production of 665 g
(1.5 lb.) of total excreta per person per day. it was noted that probably
only a fraction of the urine was included in this figure.
It has been recommended that controlled observations be made in
each country or portion of a country where there is reason to believe
that deviation from the established norm may occur. These observations
should be of such duration as to allow the measurementof possible seasonal
variations, should include an adequate sample, and should be carried
on under the direction of a responsible officer.
The available data beiig admittedly meagre, it has been suggested for
design purposes that for total excreta the figure of 1 kg (2.2 lb.) (wet
weight) per person per day should be used.
Soil and Ground-Water Pollution
The study of methods of pollution of the soil and water by excreta
also provides useful information concerning the design of disposal facilities,
especially their location with respect to sourcesof drinking-water supplies.
After excreta are deposited on the ground or in pits, the bacteria, unable
to move much by themselves, may be transported horizontally and
downward into the ground by leaching liquids or urine, or by rain water.
The distance of travel of bacteria in this way varies with several factors,
the most important of which is the porosity of the soil (see Fig. 4, 5, 6).
Their horizontal travel through soil in this manner is usually less than
90 cm (3 ft) and the downward travel less than 3 m (10 ft) in pits open
to heavy rains, and not more than 60 cm (2 ft) normally in porous soils.27
Gotaas and his ceworkers,a studying the artificial recharge of aquifers
with reclaimed sewageand other waste waters in the State of California,
THE
PRIVY
METHOD
OF ESCRETA
DISPOSAL
29
USA, found that bacteria were transported to a distance of up to 30 m
(100 ft) from the recharge well in 33 hours, and that there was a rapid
resression of bacteria1 count over this distance due to effective filtration
and to bacterial die-off. They also found that chemical pollution travelled
twice as fast. Recently, other t.vorkers,l5 studying ground-water pollution
in Alaska, noted that bacteria were traced to a distance of 15 m (50 ft)
from the dosing well into which test bacteria were introduced. The width
of the path of bacteria1 travel varied between 45 cm and 120 cm (1.5 ft
and 3 ft). Reyeession ther, took place and, after a year, only the dosing
well remained positive for the test organism. These investigations confirm
the findings of other workers f?7to the effect that the contamination from
excreta dkposal systems tends to travel downward until it reaches the
water table, then moves along with the ground-water flow across a path
which increases in width to a limited extent before gradual disappearance.
FIG. 4. MOVEMENT
OF POLLUTION
IN DRY SOIL
In dry soil there is relatively little migration of chemical and bacterial substances.
Laterally
there is practically no movement; and with excessive washing (not common in privies or septic
tanks) the vertical penetration is only about 3 m (IO ft). Where the contamination does not enter
the ground water, there is practically no danger of contaminating water supplies.
i,
FIG. 5. BACTERIAL
cmIAL
SOIL
AND
PoLumON
c
-GROUND
CHEMICAL
PATTERN
CHEMICAL
SOIL POLLUTION
Based
SOIL
POLLUTION
WATER FLOW-
on data from Caldwell
--.
AND
MAXIMUM
MIGRATIONS
l
4
1 to 3 m/dq
l
PATTERNS
& Parr % 6 and Dyer. Bbaskaran & Sekar.*“* II o
PATTERN
-I
The source of contamination in these studies was human
excreta placed In a hole which
enetrated the ground-water
table. Samples positive for coli Porm organisms were picked
up quite soon between 4 m and 6 m (13 ft and 19 ft) from the
source of contamination.
The area of contamination widened
out to a width of approximately 2 m (7 ft) at a point about 5 m
(16 ft) from the privy and tapered off at about 11 m (36 ft).
Contamination
did not move “ upstream ” or against the
direction of flow of the ground water. After a few months the
soll around the privy became clogged, and positive samples
could be plcked up at only 2 m to 3 m (7 ft to 10 ft) from the plt.
In other words, the area of soil contamination had shrunk.
The chemical pollution pattern is similar in shape to that of
bacterial pollution but extends to much greater aistances.
From the point of view of sanitation, the interest is in the
maximum migrations and the fact that the duection of migration
is always that of the flow of ground water. In locating wells, it
must be remembered that the water withln the circle of influence
of the well flows towards the well. No part of the area of chemical or bacterial contamination
may be within reach of the
circle of influence of the well.
THE
PRIVY
FIG. 6. MOVEMENT
A = Top soil
METHOD
OF EXCRETA
OF POLLUTION
B = Water-bearing
formation
31
DISPOSAL
IN UNDERGROUND
C = Direction
WATER
of ground-water
flow
In the Netherlands, Baars 2 found that, unless accompanied by a considerable amount of water, bacterial contamination did not travel more than
7.5 m (25 ft) through fine sand.
On the surface of the ground, only the earth immediately surrounding
the faeces is likely to be contaminated, unless it is carried further by surface
water such as rain and irrigation water, blown away by the wind, or picked
up by the hair and feet of flies or other insects and animals. It has been
observed in pit latrines, however, that hookworm larvae, although unable
to move sideways to any appreciable extent, are likely to climb upwards
along the pit walls and reach the top surface of defective wooden or
earthen floors, where they lie in wait for a person with bare feet.
Depending upon conditions of humidity and temperature, pathogenic
bacteria and ova of parasitic worms will survive varying lengths of time
in the ground. Pathogenic Lcteria do not usually find in the soil a suitable
environment for their multiplication, and will die within a few days. On
the other hand, hookworm eggs will survive as many as five months in
wet, sandy soil, and three months in sewage. Hookworm disease is
transmitted through contact of the skin, usually bare feet, with soil
containing hookworm larvae. Other parasitic diseasesare also transmitted
when fresh faeces or sewage is used, during the growing season, to fertilize
vegetable crops which are eaten raw.
If ground water is located near a source of infection within the distances
mentioned above, it may become contatinated by harmful bacteria and
by putrid chemical substances originating in faecal decomposition. A
32
EXCRETA
DISPOSAL
FOR RURAL
AREAS
source of infection may be some excreta deposited on the ground near by,
a pit latrine, a cesspool, or a leaky sewer or sewage disposal pipe. The
contaminated ground-water, which is usually shallow, may be tapped by
a well used for drinking-water and other domestic purposes and may
lead to further human infection and diseases such as diarrhoeas, typhoid
and parathyphoid fevers, cholera, and the dysenteries.
The effects of proximity of wells to latrines and the travel of faecal
pollution through ground water have been investigated by various scientists.
The studies of Caldwell & Parr 4*5 and of Dyer, Bhaskaran & Sekar lo, l1
are classics which should be studied by all interested public health workers.
Location of Latrines and Other Excieta Disposal Facilities
Regarding the location of latrines with respect to sources of water
supply, the following conclusions may be drawn from up-to-date information.
1. There can be no arbitrary rule governing the distance that is necessary
for safety between a privy and a source of water supply. Many factors,
such as slope and level of ground water and soil-permeability, affect the
removal of bacteria in ground water. It is of the greatest importance
to locate the privy or cesspool downhill, or at least on some level piece
of land, and to avoid, if possible, placing it directly uphill from a well.
Where uphill locations cannot be avoided, a distance of 15 m (50 ft) will
prevent bacterial pollution of the well. Setting the privy off to either
the right or the left would considerably lessen the possibility of contaminating the ground water reaching the well. In sandy soil a privy may be
located as close as 7.5 m (25 ft) from a properly constructed household
well iP it is impossible to place it at a greater distance. In the case of a
higher-yielding well, not less than 15 m (50 ft) should separate the well
from a latrine.
2. In homogeneous soils the chance of ground-water pollution is
virtually nil if the bottom of a latrine is more than 1.5 m (5 ft) above the
ground-water table. The same may be said if the bottom of a cesspool
is more than 3 m (10 ft) above the level of the ground water.
3. A careful investigation should be made before building pit privies,
bored-hole latrines, cesspools, and seepagepits in areas containing fissured
rocks or limestone formations, since pollution may be carried directly
through solution channels and without natural filtration to distant wells
or other sources of drinking-water supplies.
Regarding the location of latrines with respect to dwellings, experience
shows that the distance between the two is an important consideration
in the acceptability of the sanitary facilities. The location of latrines,
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
33
private or communal, at a considerable distance or away and uphill from
dwellings has been observed to mitigate against their regular use and
proper maintenance. A latrine will more likely be kept clean if it is close
to the house or other building which it serves. Fig. 7 gives an example
of proper location of latrines with respect to wells and dwellings.
FIG. 7. WELL
AND
PRIVY
LOCATION
IN A RURAL
COMMUNITY
Other considerations are as follows :
1. The site should be dry, well drained, and above flood level.
2. The immediate surroundings of the latrine-i.e.,
an area 2 m
(6.5 ft) wide around the structure-should be cleared of all vegetation,
wastes, and other debris. This recommendation may be ignored, however,
in the initial stages of sanitary development of rural areas where it is
necessary, for example, in order to secure acceptability of the latrine
by the local population, to avoid disturbing the natural bush-type surroundings which were previously used for defaecation.
Fly Breeding in Excreta
The role of flies in the transmission of faecal-borne diseaseshas already
been mentioned. The common housefly lays its eggs preferably in horse
and stable manure, but will also do so in exposed human excrement and
any other decaying organic matter. It crawls and feeds on this material,
picking up filth and live organisms on its hairy body, as well as bacteria
which pass unharmed through its alimentary tract and are often deposited
later on human food. Besides the housefly, various other flies (bluebottle
fly, greenbottle fly) may also breed in human excrement and decaying
matter. In temperate climates, excreta-borne diseases are usually more
34
EXCRETA
DISPOSAL
FOR RURAL
AREAS
prevalent during the warmer months when flies are most numerous and
most active.
In designing a latrine, attention must be paid to means of preventing
fly breeding. In so doing advantage may be taken of the fact that flies
have a positive phototropism and, therefore, are attracted by light and
shun darkness and dark surfaces. The best latrine is one in which the
excreta are promptly flushed away into a closed pit or tank underground.
Other types of latrine would also be effective in this respect if all openings
leading to the excreta, including the seat, were kept clean and closed when
not in actual use. This is not usually the case.
Attempts have been made to attract and trap flies which have hatched
in latrine pits. These attempts have apparently not been successful, as
the mechanisms involved (inverted glass bottle, perforated cans, or others)
do not seem to last or stay in place very long.
Disinfectants are of little use in pit latrines because they are quickly
neutralized by the organic matter. They also have the disadvantage of
interfering with bacterial decomposition and reduction of excreta:
Certain inorganic chemicals may be added to latrines as larvicides
to control fly breeding-namely, sodium fluosilicate, sodium arsenite, or
borax (sodium tetraborate). A 2.5cm (l-in.) surface layer of 10% borax
in each latrine has proved highly effective in India.
Among the organic chemicals, either PDB (paradichlorobenzene) or
ODB (orthodichlorobenzene) has proved an effective larvicide and ovicide ;
the latter is used in home latrines in Japan. The use of aldrin, dieldrin,
chlordane, BHC, or DDT in faecal matter leads rapidly to the development
of resistance to these chlorinated hydrocarbon insecticides by the larval
and adult houseflies. Spraying of inside walls of latrine superstructures
with aldrin and dieldrin has been found to increase housefly production
by as much as fifty times.26
Hole Covers
The subject of a cover for a hole or seat is an interesting but controversial point in the design of latrines. There is no doubt that a cover is
desirable, and in some places necessary, to prevent ingress of flies and
other vermin and, also, to reduce odours. However, in all the literature
on public health subjects, and on excreta disposal in particular, no case has
been reported where covers have been successfully used and kept in place
over a period of months or years. Even in countries, such as the USA,
where people in general are highly conscious of sanitation, the problem
of seat covers has not been solved.
Self-closing covers have not been successful because the condensation
which takes place on the under-side of a closed seat is objectionable to the
users. Covers that are hinged to the slab or riser are usually left in the
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
35
open position. Covers not hinged to the slab are seldom replaced on
the hole and are soon carried away by children. Hinges of even the most
rugged design soon become broken. More complicated types of cover
have been tried, the principle being that the door of the privy will not open
to let the user out if the cover is not
closed. This type has failed because
FIG. 8. SIMPLE HOLE COVER
it is too complicated for the people
and discourages them from using the
privy, or they soon learn to get rid
of the cover in some way.
In view of the above, the drawings in this document do not include seat or hole covers, except for
Fig. 8, which shows a simple type
of cover. This problem is left to
each health department to weigh
and try to solve in the light of
the local situation. In the Amazon
Valley of Brazil some 20 000 installations have been constructed ; and, A = Long handle is a special feature. Top
part is likely to remain clean.
because the fly population is not too
B = Width and length to suit size and shape
great, no attempt has been made to
of hole, which will be covered, not
plugged.
put hole covers on the squat type
of privy slabs. But where there are
many ties, some attempt should be made to cover the holes and prevent
the flies entering and breeding in the pits.
The successful use of hole covers will probably result only from a long
and concentrated educational programme.
Engineering Factors
The selection, design, location, and construction of excreta dis’posal
installations require the application of some engineering knowledge. Such
knowledge may assume major importance in certain areas because of
peculiar physical factors and difficulties. The nature of ground formations
is often the governing factor in the selection of a type of installation.
In areas containing rocks, boulders, or fissured limestone and, also, where
ground water is high or caving of pits occurs, the public health officer
and the sanitarian may require the assistance of the engineer to find adequate
and economical solutions to these engineering problems.
The selection and proper use of local materials are also of engineering
significance in the construction and cost of privies on a mass scale. The
use of bamboo for pit curbing and for the reinforcement of concrete
35
EXCRETA
DISPOSAL FOR RURAL
AREAS
slabs li and the use of sand-stabilized earth ” are examples in point. In
every area it is desirable that field research and experiments be carried
out to discover the best possible use of cheap, locally available materials.
Finally, the selection of design features which can be handled by local
labour is an important engineering consideration. Local skills should be
utilized to the greatest possible exlent. It is fairly obvious that, if the
type of installation selected cannot be built by the villagers themselves,
the privy scheme will be limited to the construction of a very few installations
by imported labour.
This brief outline of the engineering problems which are likely to be
faced by most health departments in the execution of large-scale privy
campaigns and other sanitary installations points to the need to have
a few full-time public health engineers on the health department staff.
These engineers may be detailed from the centre as required to assist
rural health units in solving such problems.
Human Factors
In all matters of excreta disposal, human factors are as important as
technical features. People, especially inhabitants of rural areas, will not
use a latrine of a type which they dislike, or which does not afford adequate
privacy or, finally, which cannot be kept clean.
Regarding the type of latrine which should be selected, the preliminary
sanitation and sociological survey will indicate the types of facilities, if
any, in use in the area. The first step in design will therefore be to ;iry
to improve the existing system, retaining as many as possible of its “ soc;iological ” features. Two examples may be cited to illustrate this important
point. Water-flush-type latrines with risers and seats, though best from
the sanitary standpoint, have not normally been found acceptable by
people who are used to defaecating in the bush in a squatting position.
In another instance, people readily accepted pit privies which were built
within a thatch and bamboo enclosure without a roof, as they preferred
to squat in the open air. Everywhere in the world people have certain
taboos with respect to the collection and disposal of human faeces. While
it is impossible in one document or textbook to study them all, the health
worker should pay much attention to them and should avail himself at
all times of the assistance of experienced health educators, social anthropologists, or sociologists to discover the right approach to the solution
of the excreta disposal problem of rural communities.
The next important human factors to be considered are the matters
of privacy and of separation of the facilities provided for men and for
a Youssef. M. S. (1953) Suggestions for improving building materials used by Egyptian
Wnuublished Paper prepared for the Egyptian Government)
farmers
THE PRIVY
METHOD
37
OF EXCRETA DISPOSAL
women. Various systems have been designed to provide privacy ; they
are shown in Fig. 9, together with those for separating the sexes. I?.,will
be noted that latrine doors should preferably open invards.
A latrine, whether of the family or communal type, the design of which
does not allow easy cleaning will also not be acceptable to most people.
FIG. 9. PRIVY
DESIGNS
ENSURING
A = These two layouts ensure
6 = Semi-private
installarion.
passage when latrine floor
C = Preferred types, ensuring
PRI VACY
AND
SEPARATION
complete separation of the sexes.
Defaecation
Snail-type entrance.
is dirty.
complete privacy.
OF THE SEXES
may take place
in corridor
I
38
EXCRETA
DISPOSAL FOR RURAL
AREAS
In this respect, smooth, hard-surface floors of concrete, cement, brick,
or similar material are best because it is easy to flush them with water.
A latrine which is designed for too large a number of people will
probably get dirty quickly and remain so, with the result that late callers
will prefer to go and defaecate around the latrine building or in a neighbouring bush. A one-hole latrine is adequate for a family of five or six
persons. For communal latrines in camps, markets, and similar places,
one hole should be provided for every 15 persons ; and in schools, one
hole for every 15 girls and one hole plus a urinal for every 25 boys.
Cost Factors
As pointed out before, the type of latrine to be recommended to a
community or to a family should be simple, acceptable, and economical
to build, to maintain, and to replace when the need arises. While there
are simple and acceptable types of latrines fulfilling the three conditions
mentioned, there are none which are at the same time cheap to build,
to maintain, and to replace. Oddly enough, the systems which are most
expensive to build (water-flush latrines) are the cheapest in the long run,
because of their long life, and are the easiest and most economical from
the maintenance standpoint.
General experience reveals one very important fact : in selecting or
designing a type of latrine, cost should not be the dominant factor. It
is necessary to strike a middle way after careful consideration of all the
elements involved, giving preference to those factors which are conducive
to a sanitary environment and to acceptability by the family.
EVALUATION
AND SELECTION OF VARIOUS
DISPOSAL SYSTEMS
EXCRETA
Criteria for Selection
j
The problems of selecting a type of sanitary installation for a particular
rural community are manifold and without a clear and simple answer.
It has become evident that, in planning a permanent solution to an excreta
disposal problem, many inter-related factors must be considered, among
them cultural patterns, religious customs, climatological and geological
conditions, economic standards, political and social organization of rural
communities, general and health education, skills of local populations,
and the availability of construction materials and personnel for technical
supervision. What originally may appear on the surface to be a simple
THE
PRIVY
METHOD
OF JZXCRETA
DISPOSAL
39
problem has often, upon more careful examination, been found to be a
relatively complex one.
The selection of the type of installation best suited to local needs must
take into account the element of cost. Water-carried sewerage systems
with flush toilets are very expensive and far beyond the economic possibilities
of most rural areas. At the other extreme, it is possible for everyone to
relieve himself in the most primitive manner at no cost whatsoever ; but
this method is disastrous in terms of sickness and death and resulting
economic loss. Therefore, between these two extremes a solution should
be found that will give the most in health protection and, at the same time,
will be within the economic possibilities of the people to construct and
maintain. Every sanitation worker should carefully consider this aspect
of the problem, not only as it applies to privies, but also as it relates to
every other type of sanitary improvement. The health department, through
its staff, should assist each family in finding the proper solution, by painstaking efforts where necessary. Of course, it is relatively easy to decide
on a privy campaign for a rural area from a health department office
situated far away in the state or provincial capital simply by choosing
a design that appears to be satisfactory because it has been used somewhere in the world. This is the kind of privy programme which has resulted
in empty, abandoned, and unused installations in so many places.
As might be expected, a review of the Literature reveals that a great
variety of excreta disposal methods are in use in the world. Latrine
characteristics are often very different. However, from a purely technical
standpoint, it is generally agreed that a latrine or other disposal method
should satisfy the following seven requirements (adapted from Ehlers
& Steel 12):
1. The surface soil should not be contaminated.
2. There should be no contamination of ground water that may enter
springs or wells.
3. There should be no contamination of surface water.
4. Excreta should not be accessible to flies or animals.
5. There should be no handling of fresh excreta ; or, when this is
indispensable, it should be kept to a strict minimum.
6. There should be freedom from odours or unsightly conditions.
7. The method used should be simple and inexpensive in construction
and operation.
Main Types of Installation
The two types of installation which come closest to fulfilling the above
seven requirements are the pit privy and the aqua privy.
40
EXCREiTA
DISPOSAL
FOR RURAL
AREAS
The pit privy is used almost exclusively throughout the Western
hemisphere and Europe and is common in parts of Africa and the Middle
East. With a minimum of attention to location and construction, there
wiII be no soil pollution and no surface- or ground-water contamination.
The execreta will not be accessible to flies if the hole is kept covered ;
but, even when the hole is left open, the fly problem will not be very great
since flies are not attracted to dark holes and surfaces. A good superstructure helps to keep the sun’s rays and light from shining into the pit.
There is no handling of the material. Odours are negligible, and faeces
are normally out of sight. The pit privy is simple in design and easy to
use, and does not require operation. Its life span will vary from five
to f8teen years, depending upon the capacity of the pit and the use and
abuse to which it is put. Its chief advantage is that it can be built
cheaply, in any part of the world, by the family with little or no outside help and from locally available materials. It has few disadvantages, and it can play a major role in the prevention of filth-borne
diseases.
The aqua privy is a modification of the “ septic privy “, which originated
in the USA about fifty years ago. It is being used in increasing numbers
in countries in Africa, the Middle East, and South-East Asia. If the tank
is water-tight, the soil as well as the surface- and ground-water cannot
be contaminated. Flies are not attracted to the tank’s contents, and there
are no odours or unsightly conditions. It may be located close to the
house. Faeces and sludge, together with stones, sticks, rags, and other
debris which may be thrown in, accumulate in the tank and must, of
course, be removed at intervals. If the tank’s capacity is sufficient, however,
handling of its contents can be kept to a minimum. The aqua privy requires
daily additions of water to keep it operating properly. The small amount
of water needed is normally supplied by the water used for anal cleansing
and for cleaning the slab and the drop pipe or funnel. This privy needs
a little maintenance, but it is a permanent type of installation. It is more
expensive to construct than the pit privy.
Mention may be made here of the water-seal slab which gives its name
to a latrine called “ water-seal ” or sometimes “ pour flush ” latrine. In
actual fact, it is not a separate type of excreta-disposal installation but
is rather an interesting modification of the usual latrine slab or floor.
The water-seal slab may be installed over a pit (such as that of a pit privy)
or a water tank (such as that of an aqua privy). With proper operation
and maintenance, the water seal will keep both flies and odours away.
For this reason it may be installed advantageously as a j3dCt of the dwelling,
preferably near the back of the house and with an outside entrance. It
is obvious that its small trap will not withstand abuse. The water-seal
slab is extensively used in the South-East Asia region, where anal cleansing
with water is widely practised.
THE
PRIVY
MJXHOD
OF EXCRETA
DISPOSAL
41
Less Desirable Types of Installation
The bored-hole latrine is a variation of the pit privy. The pit is smaller
in cross-section but deeper. Its capacity, however, is much less than
that of the usual pit privy, and this results in a shorter useful life. Because
of its depth-as much as 6 m (20 ft)-the pit often penetrates the ground
water, which it contaminates easily. There is no soil or surface-water
pollution, however ; and no handling of excreta is involved. The fly
hazard is increased because of the chances of pollution of the upper walls
of the hole, immediately below the opening. Caving of the pit’s walls
often constitutes a serious disadvantage. It is cheap and easy to construct
when the necessary tools are available. It is widely used in many parts
of the world, especially in the Middle East and in South-East Asia.
The bucket latrine, or box-and-can privy, has been extensively used
in the past in Europe, the Americas, and Australia ; it is still used in many
countries of Africa, South-East Asia, and the Western Pacific. Its use
is decreasing, however, even in these areas. Although, theoretically and
under unusually efficient control, it should be possible to devise and operate
a bucket-latrine system in a hygienic manner, experience everywhere
shows that, in actual practice, this is not the case. As usually operated
the bucket-latrine system attracts flies in enormous numbers, not just
at the latrine site but all along the conveyance route to the disposal ground
itself. There is considerable handling of the excreta. Regarding this
system it may now be safely stated that insanitary handling of the buckets
and night-soil is the rule, although exceptions may be found in a few
properly operated and supervised systems. The hazards of soil pollution
and of surface- and ground-water pollution are ever present. There are
usually considerable odour and unsightly conditions. Although the initial
cost of a bucket latrine is not high, the cost of operation makes it, within
a few years, the most expensive type of installation. Its use is justified
only in areas, the Western Pacific, for example, where excreta are needed
as soil fertilizer. Even here it is believed that the conventional bucketlatrine system should be considerably improved or replaced by a latrine
such as the compost privy mentioned below.
FeuilZkes and trench latrines are commonly used in some territories
in Africa, in camps, and at times of emergency. As stated by MCdecinGeneral Sanner,sl the fed&es are installations which may be relatively
satisfactory or grossly insanitary, depending upon whether certain precautions are observed or neglected. These precautions (which will be
described later) depend for their application upon the user and, in most
cases, are not followed in actual practice. The system thus frequently
results in violations of the most fundamental standards of sanitation,
the most important of which are, in this particular instance, soil pollution
and accessibility to flies and animals. Its use is not recommended.
42
EXCRFXA
DISPOSAL
FOR RURAL
AREAS
The “ overhung privy ” is often used in limited areas that are frequently
or periodically covered with water, especially the sea. This applies to
coastal fishing villages in some countries of South-East Asia and the
Western Pacific and in a few other places. The criteria listed above do
not apply exactly. New criteria were considered at the WHO Seminar on
Sewage Disposal held in Ceylon in August 1955. The most important
factors in this case are the degree of salinity of the receiving water, its
depth, and the degree of possible dilution. This type of installation should
be considered only as a last resort under unusual circumstances.
Installations for Special Situations
The compost privy has been used in areas where it is desirable to
compost safely in the privy itself a mixture of faeces and other organic
wastes (straw, kitchen wastes, grass clippings, etc.). To serve this purpose,
two or more pits are required, and consequently the cost is greater than
for ordinary pit latrines. If poorly constructed and operated, this privy
may attract flies, which may breed in the material. Also, odours may
be a problem. The compost privy is simple to build but requires some
operation and maintenance. Since the pits are used alternately, handling
of their contents is kept to a minimum and is done after their decomposition
and reduction by anaerobic bacteria. The humus-like product is stable
and safe and is a good soil fertilizer.
The chemical toilet is an efficient installation which fulfils all the abovementioned criteria except the one which pertains to cost. It is, relatively
speaking, very expensive both in initial cost and in operation. Its chief
advantage is that it may be placed inside the dwelling. It is frequently
used in rural houses and schools of the economically more favoured areas
of the world.
THE PIT PRIVY
Description
The pit privy (as shown in Fig. 10 and 11) consists of a hand-dug hole
in the ground covered with either a squatting plate or a slab provided
with riser and seat. A superstructure or house is then built around it.
Design and Function of Its Parts
‘The pit
The function of the pit is to isolate and store human excreta in such
a way that no harmful bacteria can be carried therefrom to a new host.
The pit is usually round or square for the individual family installation
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
43
and rectangular for the public latrine. Its dimensions vary from 90 cm
to 120 cm (36 in. to 48 in.) in diameter or square. Common figures for
family latrines are 90 cm (36 in.) diameter or 1.06 m (42 in.) square. For
public installations, the pit will be 90 cm to 100 cm (36 in. to 40 in.) wide ;
its length will depend upon the number
of holes provided. The depth
FIG. 10. VARIOUS PARTS
OF A SANITARY
PRIVY
is usually about 2.50 m (8 ft), but
may vary from 1.80 m to 5 m (6 ft
to 16 ft). In Iran, and elsewhere,
some pits have been dug to a depth
of 7-8 m (23-26 ft) in soils which
are very stable (see Fig. 12-15).
Life
of a pit
One of the very important aspects of the pit is its useful life.
The longer a pit privy will serve
a family without being moved or
rebuilt, the more certain is the
health protection which it can give
and, therefore, the more value it
has to the family and community.
It is important, by increasing the
capacity and efficiency of privy pits,
to extend their useful life and
thereby to reduce the annual cost
per person of the installation. The
life of a privy depends on the care
A = Pit
E = House,
with which it is built, the materials
including door
= Base
F = Ventilation
used in its construction, and the
ii = Floor
G = Roof
D = Mound
time required for the pit to fill.
The critical factor, usually, is the
time required for the pit to fill ; this, in turn, depends on the method of
anal cleansing and on the volume of the pit and the conditions within it..
By the word “ conditions ” are meant the efficiency of bacterial decomposition and the degree of abuse to which the pit is subjected (i.e., the
stones, sticks, mud balls, garbage, coconut husks, etc. thrown into it).
In deciding on the volume of a pit, it is necessary to consider whether
the pit will be wet or dry, i.e., whether it will penetrate the ground-water
table or not. In either case, however, it is essential to remember that
the decomposition process starts as soon as the excreta are deposited in
the pit and that, through decomposition and compaction, the volume of
the slowly accumulating sludge is smaller than the total amount of excreta
44
EXCRETA
DlSPOSAL
FIG. 11. THE PRINCIPAL
PARTS
FOR RURAL
OF TWO
TYPES
AREAS
OF SANITARY
PRIVY
C
D
D
E
A = House
B = Mound
C = Floor
-
D = Base
E = Pit
deposited. Strictly speaking, the rate of accumulation of digested sludge
and of partially digested excreta is not directly proportional to the amount
of excreta added each year. This phenomenon is illustrated graphically
in Fig. 16. From this graph, which is based on approximate data only,
it will be noted that, after the digestion process has been well established,
the actual volume of material in a wet pit might be reduced in time to
approximately 10 % of the total waste (faeces and urine) deposited. This
graph is very approximate, however, and may need to be substantially
modified in the light of experience in different areas. These data should
be developed in each country by controlled field observations carried out
over a number of years. Only in this way can reliable figures be obtained
as a basis for Ptiture design of latrine capacity. The following considerations
are based on data contained in the report on the aforementioned WHOsponsored seminar on sewage disposal.”
a Report OR Seminar on Sewage Disposal (Rural ad Urbatrl. Kandy. Ceylon.
(Report issued by rhe WHO Regional Office for South-East Asia, New Delhi)
1955
THE
FIG. 12. VARIOUS
PRIVY
COMBINATIONS
METHOD
OF EXCRETA
OF DIFFERENT
AND FLOOR
TYPES
45
DISPOSAL
OF PIT,
PIT LINING,
BASE.
T
-A-
a
b
A
B
C
=
=
=
=
=
Open joints
Joints laid with mortar
Square pit with brick lining and base and wooden floor
Round pit with partial lining of cut tree limbs, soil-cement
Bored pit with concrete lining, base, and floor
FIG. 13. LARGE-VOLUME
PITS WITH
SMALL
FLOORS
C
.w ,*,o
base, and built-up
AND
floor
SUPLRSTRUCTURES
A = Large diameter or square pit with soil-cement cone at top to reduce size of opening and
accommodate small floor (Cone may be of any material which will provide the strength to
support the weight on top.)
B = Similar to A, Lut with brick
C = Pit showing enlarged lower portion to provide increased volume ; practicable only in very
stable soil
46
EXCRETA DISPOSAL FOR RURAL AREAS
FlG. 14. TYPE
OF PIT. PIT LINING, BASE, AND FLOOR
BY THE US PUBLIC HEALTH SERVICE
A = bWzgtn
it lining, 2.6 x 15 cm (1 x 6 in.)
1 bout 1.2 cm (0.5 In.) space left
betwee; boards below top two
B = Concrete sill
C - Concrete floor and riser
RECOMMENDED
Ada~tcd. by permission. from United Stares Publtc
Health Service (1933) l7te sanitary prfvy. Washington.
D.C. (Revised type No. IV of Publ. Hlrh Rep.
(Wad.).
Suppl. 108).
FIG. 15. TYPE OF RURAL PIT PRIVY
DEVELOPED BY TCA’
IN IRAN
In wet pits, assuming that the
daily pioduction of one litre (approximately one quart) of excrement contains 100g (3.5 oz.) of dry
solids and that digestion for one
year under wet-pit conditions will
reduce this mass by 80”/,, a total
of 20 g (0.7 oz.) of dry solids will
remain. Further assuming an 80%
moisture content in the digested
sludge, one arrives at the figure
of 100 g (3.5 oz.) of wet sludge
after a one-year digestion period.
A = Round, reinforced concrete slab. Can
be easily raIled to priv site without
brzrkage. Water is used r or anal cleans6
C
0
E
F
l
=
=
=
=
=
Lime-mud mixture
Brick or stone masonry
Floor of prtvy
Steps leading to entrance
Original ground-level
Technical
~tion
Akimhhation
door
or
the
USA
THE PRIVY METHOD OF EXCRETA DISPOSAL.
FIG. 16. SLUDGE
ACCUMULATION
47
IN PIT LATRINES
0
I
4
S
b
II
Years
A 6 C 0 -
Human waste (liquid and solid) deposited in pit by a family of flue (at the rate of one litre,
or quart, per pereon per day)
Compondtng
amounts of solid wa8tes alone (approrimately)
Rate of accumulation of sludge, by volume, in dry pit
Rafe of accumulafion of sludge, by volume, in wet pit
This amounts to 36.5 l(l.3 cu. ft) per person per year. Thus, z family of
five would require sludge-storagespace of 184 1 (6.5 cu. ft) per year.
Actual observations on wet-pit latrines in West Bengal, India, where
ablution water is used, gave a figure of 25 1 (0.88 cu. ft) of sludge per
person per year. In the Philippines, where solid deansing materials are
used, a wet-pit figure of 40 1 (1.4 cu. ft) was obtained.
It is recommendedthat for the design of the effective capacity of wetpit latrines a provision of 37 1 (1.3 cu. ft) per person per year should be
allowed. If cleansing materials such as grass, stones, mud balls, coconut
husks, or similar solids are used, it is recommended that this figure be
increased by 50% to a total of 57 1 (2.0 cu. ft) per person per year.
It is recognized that digestion of solids is less rapid and less complete
in dry-pit latrines than in wet-pit latrines. Actual observations in the
Philippines indicate a reduction by dry-pit digestion of about 50% in
volume .peryear. In the absenceof more accurate data, this rate is tentatively accepted. In Brazil, a privy of one cubic metre (35 cu. ft) of effective
capacity will servean averagefamily of five for four years ; this represents
a capacity of 0.05 m3 (1.75 cu. ft) per person per year. Somewhat lower
figures have been found in the USA, but higher figures are reported from
areas where different types of anal cleansing materials are employed. For
48
EXCRETA
DISPOSAL
FOR RURAL
AREAS
design purposes, a provision of 0.06 m3 (2 cu. ft) per person per year is
recommended, to be increased by 50% in cases where the types of personal
cleansing materials normally employed might indicate that such an allowance
is necessary.
It is further recommended that, where practicable, wet pits should
have a minimum depth of 3 m (10 ft). With regard to pit storage capacity,
it is desirable to design for as long a period as possible, i.e., for lo-15 years.
However, it is recognized that, from the standpoint of cost, or because
of difficulties in supporting pit walls in unstable soil formations, it might
sometimes be impossible to attain this objective. Nevertheless, it is
strongly recommended that pits should be designed for a life of at least
four years.
TABLE IV. WET-PIT
VOLUME
AND DEPTH l FOR RURAL LATRINE
WITH AN ASSUMED
CROSS-SECTIONAL
AREA OF 9 SQUARE
FEET
AND INTENDED
FOR A FAMILY
OF FIVE
Personal
Service
cleansing
material
water
life
solid
volume
(cu. ft)
d%;h
4 years (minimum)
26
3
40
4.6
8 years
52
5.8
80
9
97
11.8
150
16.6
15 years (maximum)
volume
(cu. ft)
l
Depth given is effective pit depth, and 1-2 ft (30-60 cm) are usually added to obtain overall depth of pit.
Table IV shows the pit volume and dimensions for household latrines
for families and gives varying periods of service life based on wet-pit
conditions. Table V presents similar data for dry-pit conditions.
These tables show that, where there is little possibility of maintaining
water in pits or holes, a pit privy with the largest possible volume is best.
From the economic standpoint, the deep pit 5 although higher in initial
cost, wiIl prove to be a profitable investment.
Finally, one factor that also influences the cross-sectional area of the
pit, although to a lesser extent, is the size of the floor that covers it. The
size of the floor slab depends much on the type of material from which
it is built. This matter is discussed in a later section (p. 52).
When the level of excreta comes to within 50 cm (20 in.) of the ground
surface, the pit should be closed and filled with earth. A new pit should
be dt,;g, preferably near the old one, and the superstructure moved over
it (or rebuilt, as the case may be). The faeces in the old pit should be left
49
THE PRIVY METHOD OF EXCRfirA DISPOSAL
TABLE V. DRY-PIT
VOLUME AND DEPTH*
FOR RURAL
LATRINE
WITH AN ASSUMED
CROSS-SECTIONAL
AREA OF 9 SQUARE
FEET
AND INTENDED
FOR A FAMILY OF FIVE
Personal
volume
(cu. ft)
solid
d;gh
4 years (minimum)
46
4.6
6 years
60
150
l
Depth given is effective
all depth of pit.
material
water
Service life
15 years (maximum)
cleansing
volume
(cu. ft)
d;fgh
60
6.7
9
120
13.3
16.6
-
pit depth, and l-2 ft (30-60 cm) are usually added to obtain over-
to decomposeanaerobically for 9 to 12 months, after which the digested
material may be easily removed and utilized as soil fertilizer. The cleaned
pit may then be reused.
To prevent mosquito breeding in wet pits, it may be desirable to add
a cupful of keroseneeach week to the pit, or to spray it with Malarial ’
or a 5% solution, emulsion, or suspensionof BHC (benzenehexachloride)
or dieldrin. No disinfectants should be added to the pit.
Lining
of pit
It is often necessaryto provide a pit lining to prevent the sides from
caving in. This is true especially in rainy seasonswhere privies are dug
in fine-grained alluvial soils, sandy soils, and similar formations, or when
they penetrate deeply into ground water. Even in stable soil formations,
it is desirable to line the top 40-60 cm (16-24 in.) of the pit in order to
consolidate it and to prevent it from caving in under the weight of the
floor and the superstructure.
Materials commonly used for this purpose include bricks, stones,
concrete blocks, laterite blocks, adobe materials, lumber, rough-hewn logs,
split cane, and bamboo. When the Grst five materials mentioned above
are used, they are laid with open joints over most of the walls’ height
and with mortar near the top of the walls, the reason being that with
these materials the lining also servesusefully as a basefor the floor. Brick
linings (see Fig. 13) should preferably be round, not square, as they then
develop arch action and are much stronger for the same wall thickness.
Wooden logs and bamboo should be used exclusively to support the walls
= Malarial is the proprietary
name for a blend of oil (70% diesel oil and 30% gas oil).
ofteu referred to as “ anti-makuial mixture ” ; it is made by Shell Chemicals Ltd. London.
4
50
ESCRETA
DISPOSAL
FOR RURAL
AREAS
of the pit, not as a foundation for the floor. Rough-hewn logs will, of
course, last longer than bamboo linings ; both, however, may be tarred
in order to increase their useful life. The use of rot- and termite-resistant
woods is recommended wherever possible.
Where a lining is necessary, it is often given to the family by the health
department) along with the floor or slab.
The base (Fig. 17-19)
The base serves as a solid, impervious foundation upon which the
floor can rest. It also helps to prevent the egress of hookworm larvae.
Properly made of a hard, durable material, it helps to prevent the entrance
of burrowing rodents and of surface water into the pit. Pit lining in most
cases will serve as a base although it may need to be strengthened at the
ground surface.
FIG. tf. TYPICAL
ROUND AND
(BUILT WlTH SOIL-CEMENT
SQUARE BASES
OR CLAY)
Measuremenu
shown are in ccnrimctres.
THE
PRWY
METHOD
OF FXCRETA
FIG. 18. A HEWN-LOG
PRIVY
Measurements
DISPOSAL
51
BASE
shown are in centimetres.
The foundation should be at least 10 cm (4 in.) wide on top in order
to provide a good surface for the floor to rest upon, and 15 cm (6 in.)
Fi6.19.
WITH
HEWN-LOG BASE
WOODEN FLOOR
Meaapcavms
sltowrt are in ccntimetres.
or more at the bottom in order
to give a stable contact with the
ground. Its shape will be that which
will fit the pit (see Fig. 17 and 18).
The base should be high enough to
raise the float 15 cm (6 in .) above
the level of the surrounding ground,
thus, with the mound, protecting
the pit from flooding.
The following materials may be
used in the construction of the
base :
(a) plain or reinforced pre-cast
concrete-same mix as floors ;
(b) soil cement-5%-6x cement
mixed with sandy clay soil and
tamped at optimum moisture content ;
(c) clay-tight clay, well tamped
at optimum moisture content ;
52
EXCRETA
(n) brick-mud-dried,
DISPOSAL
FOR RURAL
AREAS
burned, adobe, etc.
(e) stone masonry ;
(f) rough-cut logs-hardwood,
termite-resistant.
FIG. 20. HEWN LOGS TO FORM HOLE
AND FOOT-RESTS
The floor (Fig. 20-32)
The floor supports the user and
covers the pit. It should be constructed so as to fit tightly on the
base, with a minimum of small
cracks and openings between the
surfaces. The squat-type plate or
slab for pit privies has been found
to be the most suitable for rural
conditions in most parts of the
world. However, in many countries a slab provided with a riser
and seat may be found to be more
acceptable. This aspect of slab
design requires careful consideration. An eminent health educator
and social anthropologist has stated
that customary posture in defaecating is perhaps the single most important fact bearing on the acceptance or rejection of privies.
The floor or slab should normally extend to the superstructure
walls, as a peripheral earth strip
might be soiled and become a
medium for hookworm infestation.
It should be made of a durable, impervious material with a hard surface which will facilitate cleaning.
Materials commonly employed include :
(a) reinforced concrete ;
(b) reinforced concrete with brick
filler ;
(c) wood ;
FIG. 21. HEWN LOGS FORMING HOLE
AND FOOT-RESTS,
ASSEMBLED
AND UNASSEMBLED
.m ,110
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
53
(d) built-up floor of small-diameter wooden poles with chinks filled
by mud or soil-cement mixture.
The consensus of opinion is that concrete is, in the long run, the most
practicable, most acceptable, and cheapest material for the privy floor.
Wooden floors come next in the line of preference. “ Built-up ” floors,
as shown in Fig. 22-24, are less desirable because they are difficult to
keep clean and, as they get soiled (especially by children), are likely to
spread hookworm.
FIG. 22. HEWN LOG FORMING
UPON SECOND LAYER
HOLE AND FOOT-RESTS
SHOWN IN PLACE
OF TREE LIMBS IN BUILT-UP FLOOR
.A
,
Measurements
shown are in centimetres.
A = Limits of pit
Latrine slabs or floors may be round, square, or rectangular. When
slabs are to be made or cast at a central shop, it is advantageous to adopt
a standard shape and size in order to facilitate production. The size of
concrete slabs, which influences to a certain degree the cross-sectional
area of the pit and the size of the superstructure, is governed by their
weight and by the difficulty of transportation (where this applies).
54
EXCRETA DISPOSAL FOR RURAL AREAS
FIG. 23. BUILT-UP FLOOR OF SMALL-DIAMETER
PLACED OVER HEWN-LOG BASE
TREE LIMBS
Fill in with compact earth all around after the base is placed and before covering with tree
limbs
B = First layer of limbs is covered with 5 cm (2 in.) of dense earth, followed by another layer of
tree limbs
A=
FIG. 24. COMPACT
EARTH
FINISHING
THE BUILT-UP
FLOOR
AU factors considered, appropriate dimensions for concrete slabs may
be 100x 100 cm (39 x 39 in.) in over-all size. Such a slab will weigh
approximately 136 kg (300 lb.) if the average thickness is 6.35 cm (2.5 in.).
Smaller slabs, 91 x91 cm (3 x 3 ft), have been built where it is easy to
complete the floor at the site with a cement surface. Round slabs, 91 cm
(3 ft) in diameter, have also been used. Their advantage is that they may
be rolled to the latrine site instead of being transported. Fig. 25 and 26
show various types of floor made of lumber, wooden poles and reinforced
concrete. Fig. 27 shows a round concrete slab 91 cm (3 ft) in diameter.
The thickness of slabs also varies a great deal in practice. In order
to reduce weight, the tendency, of course, has been to reduce the thickness
THE
PRIVY
IMXHOD
OF EYCRJZTA
DISPOSAL
55
to a minimum consistent with safety. In this respect, however, much
depends on the quality of the concrete and the reinforcement available
(see p. 73). When these factors are satisfactory, the slab may be 6-7 cm
(2.3-2.7 in.) thick on its edges and 5 cm (2 in.) thick at its centre. A slab
1 m square will then weigh approximately 130 kg (286 lb.). The surface
FIG. 25. VARIOUS
TYPES
OF FLOOR
c
;=
=.
_..-:
_Q
.
‘.
~:
A
I3
C
D
=
=
=
=
Reinforced concrete
Relnforced brick-mortar
Wood
Floor built up with tree limbs and earth
of the slab will slope towards the hole, which is an advantage in Asian
countries where water is used for anal cleansing. Where solid cleansing
materials are used, the slab may be of uniform thickness throughout,
but not less than 6 cm (2.3 in.) thick.
Where it is not possible to cast concrete slabs in place and where the
problem of transportation is serious, the possibility of casting the slab
in four parts may be considered. Fig. 28-32 show how such a slab may
56
EXCRETA DISPOSAL FOR RURAL AREAS
be built and installed.
This procedure is particularly
useful for large
concrete slabs.
The shape and size of holes for floors with seats are fairly standard
in European and American countries. With respect to squatting plates,
FIG. 26. SQUARE
CONCRETE
SLAB
FOR PIT AND
BORED-HOLE
LATRINE
IO0
-ib
7-7----T-r-
metion a-a
__
M~~rentents
SEOWn are in centimetres.
however, the literature shows a wide variety of hole dimensions, often
with conflicting claims regarding their particular merits. The important
considerations are :
1. The opening should be large enough and shapedso as to minimizeor better, prevent-soiling of the floor. An opening having an effective
length of about 38 cm (15 in.), preferably more, will satisfy this requirement.
2. It should not be so large that small children may fall into the pit.
An opening having an effective width or diameter of 18 cm (7 in.) or less
will satisfy this requirement.
THE PRIVY METHOD
FIG. 27. CIRCULAR
SLAB
OF EXCRETA
DiSPOSAL
FOR BORED-HOLE
Measurements
57
LATRINE*
shown arc ;n cenrimetres.
A = Centre open hole 2.5 cm (1 tn.) back of centre if slab is 60 cm (31 in.) In diameter ; centre open
hole 8.0 cm (3 in.) back of centre if slab is SO cm (36 in.) in diameter
6 = Between back centre foot-rests
c=
Reinforcement
Notes on construction of slab
Concrete for slabs should be not weaker than 1 part cement to 6 parts aggregate, with a mfnlmum of water.
Slab is reinforced with strips of bamboo of timber quality. Reinforcing atrlps are about 2.5 cm
(1 in.) wide, have had inner, weaker fibres stripped away, and have been soaked In water overnlght
before use.
Slabs are cast upslde down in one operation. Base of form 1s of wood with lndentstlons for
foot-rests.
Bare of form is encircled by sheet metal strip which makes outer wall of form. Slde
walls of hole form and foot-rests are made with slight slope so as to come out easily. Form for
open hole is removed when concrete has taken fnltlal set. Slabs are removed from form In about
40 hours and stored under water* preferably for 10 days or more. Since these slabs are round, they
may be rolled some distance when conveyance is difficult.
In communal installations, the number of openings will depend on
the number of people to be served. It is good practice to provide one
hole for not more than 15 users, preferably one for each 10-12 persons.
It is often recommended that squatting plates should be provided with
slanting foot-rests to minimize the possibility of soiiing the floor. Foot-rests
usually form an integral part of the squatting plate and should be designed
to be used by both adults and children. When foot-rests are not properly
built-for
instance, when they join the floor at a sharp angle or are
excessively long, etc.-they make it difficult to clean and scrub the floor.
58
EXCRETA
-- +
DISPOSAL
FOR RURAL
AREAS
THE
FIG. 29. DETAILS
PRIVY
METHOD
OF FOUR-PART
OF EXCRETA
PRIVY
SLAB
DISPOSAL
59
100 CM (39 IN.) SQUARE
Section a-a
--id
Section
d-d
Weasurememsshown are in centimetres.
A=
Finished floor
B = Floor form without foot-rests
C = Complete set of forms
ready for pouring
but with reinforcement shown in place
60
EXCRETA
FIG. 30. DETAILS
DISPOSAL FOR RURAL
OF FOUR-PART
PRIVY SLAB
(CONTINUED)
AREAS
100 CM (39 IN.) SQUARE
F
Section f-f
Measurements
D = Floor form ready for pouring, with foot-rests
E Z Form for holding
F = Beam forms
steel in place while pouring
shown are in centimetres.
included
beams
THE PRIVY
METHOD
OF EXCRETA
DISPOSAL
61
Another factor which bears upon the acceptance or rejection of a
privy by the users is the free distance from the opening to the back wall of
the latrine. When this distance is too small, the back of the user will
rest against the wall, which may nit at all times be very clean and free
FIG. 31. FOUR-PART
PRIVY
SLAB,
SHOWING
FORMS
Me~uremenls shown illc in cemimctres.
A=
B =
C =
D =
Wooden outside form, showing reinforcing steel for one part ready for pouring
Three parts of floor ready for installation
Metat dividers separating ffoor for pouring
Foot-rest and hole forms
from ants or other insects. Also, there is a chance that excreta may soil
the upper portion of the pit wall. Yet this distance should not be too
large ; otherwise there is a likelihood that the back part of the floor will
Ek soiled. The minimum distance between the rear edge of the opening
and the superstructure wall should be 10 cm (4 in.)---preferably 15 cm
(6 in-)-and the maximum, 18 cm (7 in.).
62
EXCRETA DISPOSAL FOR RURAL
FIG. 32. FOUR-PART
PRIVY
SLAB
WITH
Measurements
BASE
shorn
AREAS
AND
REINFORCEMENT
are in centimetres.
Brick base
Reinforced concrete beams to support four-part floor
Plan of ftoor reinforcing
Floor showing forms for foot-rests and hole as well as metal dividers
its four parts
separating
floor
Into
This ftoor can be easily carried to the point of installation since it is divided Into four parts
and the slab is very thin. More labour is required for construction and installation, but materials
are fewer.
The mound
The function of the mound is to protect the pit and base f?om surface
run-off which otherwise might enter and destroy the pit. It should be
built up to the level of the floor and be very well tamped. It should extend
50 cm (20 in.) beyond the base on all sides. In exceptional cases in flood
plains and tidal areas, the mound may be built up considerably above
the ground for protection against tides and flood waters. It will normally
be built with the earth excavated from the pit or surrounding area, and
THE PRIVY METHOD
dm
ti
ii
OF EXCRETA
DISPOSAL
63
64
EXCRETA DISPOSAL FOR RURAL AREAS
FIG. 35. WATTLE
FIG. 36.
HOUSE
HOUSE
WITH
PALM
THATCH
OF CUT LUMBER WITH
CORRUGATED
OR ASBESTOS
CEMENT ROOF
ROOF
METAL
THE PRIVY METHOD OF EXCRETA DISPOSAL
65
may be consolidated with a stone facing to prevent it from being washed
away by heavy rains. In front of the entrance door, it may be preferable
to supplement the mound with a masonry or brick-built step. This helps
to keep the latrine floor clean.
In the Philippines, where the dwelling is often built above the ground
on piles, the latrine floor is also elevated; and a drop-pipe leads the excreta
downward to the covered pit below. This is called the “ antipole ” system.
The house affords privacy and protects the user and the installation
from the weather. F*g. 3238 show various types of house and a typical
wooden house frame for use in rural areas. From the sanitary viewpoint,
the house is less important than the pit or the floor. For this reason,
when latrine programmes are undertaken on a campaign basis, the house
is often left for the people to erect in the manner which is most satisfactory
to them, only general advice being offered by the health inspector. Standctures are desirable, however, from many standpoints,
nomy of construction and durability are most important.
ilk superstructure should conform to certain rules, the
most signiticant of which are :
1. Size. It should preferably fit the dimensions of the floor or slab
and should never be too large, lest people be tempted to defaecateon any
part of the floor at times when the area around the opening has been
soiled by previous users. The height of the roof over the slab near the
entrance door should be 2 m (6.5 ft) or more.
2. Ventilation of superstructure. It is desirable to provide openings
IO-15cm (44 in,) wide at the top of the house’swalls to facilitate constant
ventjlration.
3. Lighting. Natural light should be available wherever possible.
However, the superstructure should provide su5cient shade over an
uncovered seat or hole in order not to attract flies.
4. Cleanliness. A superstructure which is left dirty and in a constant
state of disrepair will soon be abandoned and unused as a latrine. It is
therefore extremely important that the house be kept clean-at all times,
both inside and outside, and that no poultry or animals be housed in it.
White or colourcd washings of the superstructure should be encouraged,
and the vegetation immediately surrounding it should be trimmed. The
roof should cover the house completely and have a large overhang to
protect the mound and the walls from rain and roof drainage. One of the
duties of the health department staff, especially the sanitarians and health
educators, is to provide constant advice to the family regarding the cleanliness and the proper use of the latrine.
66
EXCRETA DISPOSAL FOR RURAL
AREAS
When it is expected that a latrine will not last long because of small
pit capacity, the slab and superstructure should be so designed as to
facilitate their removal to a new pit when the existing pit is filled.
Materials used in the construction of the superstructure include, among
others, the following :
(a) wood-cut lumber, may be expensive in some areas ;
(6) asbestos cement sheets-expensive in most places but durable
and portable ;
(c) metal-expensive but serves for long period ;
(n) palm or grass thatch-easily available in many places, cheap, and
quite durable (When it is placed on a properly constructed frame, this
house can be moved.) ;
FIG. 37. TYPE OF SUPERSTRUCTURE
RECOMMENDED
BY US PUBLIC
HEALTH
SERVICE
Adapted. by permission, from United States Public Health Service
(1933) The sunitury
P&Y.
Washington. D.C. (Revised type No. IV
of PubI. HIth Rep. (Wash.), Suppl. 108).
A=
Vent pipe with lateral outlet
THE PRIVY
METHOD
FIG. 38. HOUSE
OF EXCRETA
OF BRICK
WITH
DISPOSAL
67
TILE ROOF
(e) brick-mud
dried, adobe, burned-permanent
but not easily
portable ;
(fl mud-if placed on proper form and protected from rains, makes
a durable house ; not easily moved ;
(g) protective fence-in some areas where there is little rainfall a
fence or screen is built around the privy for privacy in place of a house.
Pit ventilation
The provision of a pit or seat vent may be considered under certain
circumstances. In temperate climates or during cool seasons, there is
often an appreciable difference in temperature between the air in the pit
and the f.utside air. This temperature difference provokes condensation
on the under side of the seat (or hole) cover. It is also believed that a
vent induces a draught of air which helps to keep the pit materials dry
and small in bulk (completion of aerobic stage of decomposition).
In tropical areas, however, evidence seems to indicate that venting
serves no useful purposes. The temperature difference mentioned above
is negligible, and the openings are uncovered in most cases. (See Fig. 37
for a typical vent installation.)
68
EXCRETA DISPOSAL FOR RURAL
AREAS
Location of Pit Privy
The general rules given on page 32 apply to the pit privy. It may be
added here, however, that pit privies should preferably be built at some
distance, about 6 m (20 ft) or more, away from a dwelling.
cost
The cost of pit latrines varies considerably from country to country,
depending on the design and local costs of labour and materials. Several
figures have been quoted in the existing literature on sanitation, but only
a few representative examples are given below since absolute cost figures
do not mean much. In order to appreciate their real meaning and value,
it is necessary to have information on the local per CU,UMincome. For
countries of South-East Asia and the Western Pacific, it has been recommended that the maximum cost of an earth-pit latrine, including all labour
and materials, should not be more than th$ average monthly income of
a manual labourer. This rule might well apply to rural areas everywhere.
It is extremely desirable that the cost be reduced to the lowest possible
amount consistent with the criteria of health protection, structural safety,
and acceptability.
In countries of South-East Asia, the earth-pit privy cost, in 1955, between
30 and 125 Indian rupees (US $6.30 to $26.29, including labour and
material for the pit, squatting plate, and superstructure. A lower cost
of US $2.30 has been obtained on a WHO-assisted project in Thailand
for a latrine with water-seal slab (see p. 87). This cost, however, does not
include labour for the pit and superstructure. In Nigeria in 1940, a pit
latrine was developed with a pit 91 cm (36 in.) in diameter and 1.83 m
TABLE
VI. AVERAGE
LABOUR
COSTS
PER UNIT
FOR 1600 PRIVIES
BUILT IN THE AMAZON
IN TIME
VALLEY,
Cost in
cruzeiros
Slab
Pit
Base
Mound
House
I
l
US $1.00 = 20 cruzeiros
0.42
1.60
1.10
0.78
3.21
I
5.9
22.5
15.5
11.0
45.1
8.68
21.04
21.57
11.52
46.61
7.11
I
100.0
109.42
AND CRUZESROS
BRAZIL
% of total
l
cost
8.0
19.2
19.7
10.5
42.6
I-
100.0
at the time of this construction.
Reproduced, in translation. from Revista do Service Especial de Saride Ptibiica. 1947. 1,
87. by kind permission of the editors.
THE
PRIVY
METHOD
TABLE VII.
AMALYS1S
IN AYAZON
VALLEV,
6RAZlL:
OF EXCRETA
OF ALL
AVERAGE
COSTS
COST
DlWOSU
69
FOR lQ10 PRIVIES
PER UNIT IN CRUZElROS*
House
Mlecelianeous
% of total cost
Sttao - 20 wuzeirou at the time of this construction.
Remoduccd.
in tnmshtioa. from Rev&a do Service EWcial de Satidt- Phblica. 1947. 1,
87. by irind txtmksion of the editors.
l
(6 ft) deep and with a dried mud cover supported on sticks. The contract
price for such a latrine was I/- (US $0.25). In Brazil between 1945and
1952, the average cost of pit and bored-hole privies was found to be
244.59 cruzeiros (US $12.23) per unit. These latrines (two-thirds of
which were pit privies) had reinforced concrete, squat-type floors, soilcement bases, tamped earth mounds, and either wooden or palm-thatch
houses. The analysis of labour costs and of total costs is shown in Tables
VIandVII.
Advantages and Disadvantages
These have been discussed on page 40. Suffice it to say here that, out
of the heterogeneous mass of latrine designs produced over the world,
the sanitary pit privy emerges as the most practical and universally applicable
type*
c-on
MBteriBls
The types of material which may be used to construct various parts
of the pit privy have been mentioned above. It is extremely important,
in designing privies for rural areas, to plan for the maximum use of local
materials. It has been stated earlier that the ultimate objective in any
privy project is to get the people of the community to solve their own
excreta disposal problem in a sanitary way. The people should therefore
be shown a method and means that they can adopt. If the privy units
70
EXCRETA DISPOSAL FOR RURAL AREAS
are difficult to build and full of expensive, imported material, the people
cannot be expected to take over by themselves in the future. It should
be recommended also, of course, that only good materials be employed.
In some casesthis may be almost paradoxical, but it is obvious that an
installation which begins to fall apart soon after it is constructed is useless.
Good materials mean those which will build a sound unit.
In selecting the materials some consideration should be given to the
importance of the various parts of the privy ; and, if there is a possibility
of employing materials brought in from the outside, such materials should
be used on the most important parts. The floor is probably the most
vital single part of the unit ; if it can be constructed of reinforced concrete,
many subsequentproblems are thereby solved. In the first place, concrete
makes an impermeable surface that facilitates cleaning ; secondly, if well
constructed it will last indefinitely, which is extremely useful for the future
when the privy must be moved over a new pit. A good floor is perhaps
the biggest stumbling block in getting families to build sound units by
themselves. In many countries, especially in Central and South America,
there is no further need for intensive privy promotion and construction
work in rural areas; yet health departmentscontinue to fabricate concrete
floor slabs, and either to sell them at reduced prices or to give them to
the families, who build their own units under the supervision and guidance
of the sanitarian. It should therefore be noted that materials can play
a valuable role in the rural sanitation programme, and that they should
be chosen with care, due consideration being given not only to the initial,
but also to the future cost and use.
Mass production
Mass production methods are extremely useful in the construction of
sanitary privies whether theseare built a few at a time or in great numbers.
It is well for the health department to decide on a limited number of types
and then to prepare standard plans not only for the unit, but also for
its various parts. This procedure has the advantages of:
(u) economy of construction in time and materials ;
(b) setting the design, i.e., limiting to a considerable extent the variations which inexperiencedstaff are apt to introduce into the construction
if plans are not made in detail ;
(c) facilitating procurement of materials ;
(d) facilitating tremendously the training of workmen to construct the
units.
It follows, of course, that where a better selection of materials is possible
more use can be made of production in series. In areas where each unit
must be constructed of native materials collected locally, there is less
THE PRIVY
METHOD
OF EXCRETA
DISPOSAL
71
opportunity to apply mass production methods ; but even here some standardization is possible.
The most common and easily mass-produced part of the unit is the
concrete floor slab. Forms can be constructed at a central point according
to detailed plans to assure uniformity and then he Pent to the point of
manufacture of the slabs. Here, with a crew of four or five men and ten
forms, floors for several hundred privies can be produced in a short time.
With proper care, each form can be used hundreds of times. The secret
of long form-life lies in careful packing for shipment, keeping them well
soaked with oil at all times, and careful handling when in use. A metal
form has a fairly high initial cost, but it will last almost indefinitely if
properly cared for. In places where transportation facilities permit, floors
have been manufactured at a central point and distributed over long
distances. This is rather uncommon, and breakage has been found to
be high.
After most of the floors have been constructed, one form can be kept
at each health centre or wherever an inspector has his headquarters. With
the necessary materials, he can usually keep up with the demand for slabs
without any special help from his supervisor or any formally organized
construction project.
Cribbing of various materials for pits and bored holes has been prefabricated in the same way as floors. Houses or parts of houses also lend
themselves to production in series.
In many areas, concrete slabs are cast on the spot. This method also
has its advantages, which are as follows :
1. There is an opportunity to educate villagers by demonstration.
2. Local voluntary labour and aggregates may be used to reduce unit
cost.
3. There are savings in the transportation cost of heavy slabs (about
300 lb. each).
4. There are fewer breakages due to transport.
5. Little technical knowledge is required.
The choice between the two methods must be made by those in the
field, and will depend on the type of project, the family’s contribution
in terms of materials and labour, and other factors.
Use of jigs and forms
In any fabrication process, whether simple or complicated, standardization is always desirable to make each part of each unit exactly the same.
Building privies is no exception ; and, in order to ensure-reasonable
similarity, jigs and forms are employed. In digging pits, for example,
72
EXCRETA DISPOSAL FOR RURA!, AREAS
it is well to make a simple form marking the limits of the pit where excavation should start. Then, to guide the digger, another form can be made
to fit exactly inside the pit, thus assuring that the latter is reasonably
close to the size intended.
After the pit is completed, a form can be used to make the base (see
Fig. 39). It fits the pit exactly (and facilitates the construction of the base)
because the size has been dkfined by the previous form.
FIG. 39. WOODEN
FORM FOR CONCRETE OR SOIL-CEMENT
ON 80-CM-(3%IN.-)
SQUARE PIT
Section
TO USE
a-a
,
,
1
B
Measurements
A = Plan
BASE
1
WHO
5203
shown arc in centimetres.
B = Front view, placed on pit
The engineer will find it well worth his time to study carefully the design
of the unit to be built and to break it down into its components, using
forms and jigs wherever possible to control the work in the field. If, for
example, the pits are not started with guides, they will vary from 5 cm
(2 in.) to 10 cm (4 in.) or more in either direction, in which case the base
and floor may not fit.
THE PRIVY
METHOD
OF EXCRETA
DISPOSAL
73
These devices are useful to the inspector when he is working alone.
He can accomplish more in his supervisory work because the forms guide
and control the work to a great extent.
The labour force
It will be found advantageous to spend a little time training a labour
force when parts or all of the units are to be constructed in any number.
In a reasonably short time men can be trained to do good work and to
be consistent in their labours. Their success,of course, is directly dependent
on the instruction and on the control measures utilized. A small crew
for mixing concrete in floor construction, for example, can be made to
understand some simple rules for controlling quality. If they have carefully
calibrated cans or boxes for measuring the aggregates and are well drilled
in concrete mixing and placing methods, they will produce good products
with a minimum of supervision.
It is always advisable to appoint one man in a group as its foreman.
A little extra pay will usually bring out supervisory ability. This same
procedure applies to the fabrication of a part or of the entire unit. Very
often it will pay the health department to hire a person who has had some
experience as a construction foreman and to train him in privy construction.
Working under the technical supervision of a sanitarian, such a man can
often do a great deal of work. With this kind of assistance the sanitarian
has time for the important job of contacting and winning the support
of the families. This type of organization applies to any kind of construction
project ; it is especially useful in the execution of privy projects when the
health department is contributing money and material.
construction
procednres
Procedures used for the digging of pits and the construction of latrine
floors and superstructure vary a great deal from one country to another.
No attempt will be made to describe them all or to ind’cate which method
is considered best. As pointed out before, the design of latrine features
must take into consideration local skills. The following technical information, however, may prove useful in most instances.
Fig. 19 shows a method of constructing wood in floors out of green
logs and wooden planks or wooden poles. Fig. 39 illustrates a simple
wooden form for building a concrete or soil-cement base. Typical wooden
and steel forms for concrete slabs are shown in Fig. 40 and 41. Wooden
forms can be built anywhere to suit the particular slab design and dimensions desired.
Concrete made of one part cement, two parts sand, four parts broken
stone (not over 2 cm (0.75 in.) in diameter), and just enough water to
74
EXCRETA
FIG. 40. WOOD
DISIQSAL
FORM FOR PRIVY
FOR RURAL
SLABS
AREAS
100 CM (39 IN.) SQUARE
Section d-d
View d-d
-,j
Section h-b
detail
@
I
h
Placement
C
i
!2
1
f
t
details @
of steel
d
-6
ed
cc-I
. I.
Section c-d:
b
Measurements shown arc in cadmews.
A = Slightly concave slab upside down
B = Board to support form for foot-rest
only
THE PRIVY
METHOD
OF EXCREiTA DISPOSAL
75
produce a stiff but workable mixture should be used. The concrete may
be mixed by hand or by machine. The sand and gravel used should be
clean and free from dirt and other excessively fine matter. Reinforcement
may be made of hog-wire, 6.35mm (l/4-in.) steel, or bamboo li (after
satisfactory field trials).
Concrete should be carefully poured in the form and should be well
tamped or spaded, as this operation will make it flow well around the
reinforcing bars. The fresh concrete should be covered with a dsmp mat
or straw, which should be sprinkled with water and kept constantly in
a moist condition for seven days. This is very important to prevent the
concretefrom losing part of its water by e . aporation and, hence, its strength.
In mass production operations the slab is removed from the form after
one or two days and is immediately immersed in water for five to six days.
The slab may also be cast on the sround, or rather on a layer of sand
FIG. 41. STEEL
FORM FOR CONCRETE
PRIVY
SLABS
100 CM (39 IN.) SQUARE
Section a-a
Measurements
A = Anafas
welded to bottom
shown xe in cemimetres.
76
EXCRETA DISPOSAL FOR RURAL AREAS
spread flat over the ground. This eliminates the need for heavy forms.
The slab’s surface may then be trowelled to a smooth finish from its upper
edges towards the hole.
When sand and cement only are available, a mixture of one part cement
to three parts sand can be used with brick and reinforcing bars, as shown
in Fig. 25 B.
THE AQUA PRIVY
Description
The aqua privy consists of a tank filled with water into which plunges
a chute or drop-pipe hanging from the latrine floor (see Fig. 42-44). The
faecesand urine fall through the drop-pipe into the tank, where they undergo
anaerobic decomposition as in a septic tank. The digested sludge, which
is reduced to about a quarter of the volume of the excreta deposited,
accumulates in the tank and must be removed at intervals.
FIG. 42. SQUATTING
PLATE
FOR AQUA
PRIVY
Rcmoduced from Macdonald. 0. J. S. (1952) Small sewuge disposal
systems.
p. 138. by kind permission of Messrs. H. K. Lewis
London.
A = Glazed earthenware pipe cut to 22 cm (9 in.) length
B = Reinforcemenl, 0.9 cm (3/8 in.) rod
C = Reinforcement, 0.6 cm (114 in.) rod
THE PRIVY
METHOD
OF EXCRETA DISPOSAL
FIG. 43. FAMILY-TYPE
Section
AQUA
PRIVY
a-a
Adapted from Macdonald. 0. J. S. (1952) Smull sewage dispoJa
systems. p. 140. by kind permission of Mesrs H. K. Lewis.
London.
Measurements shown
are in centimctres.
A=
B =
c =
D =
Outlet to soakage trench or soakage pit
Removable, reinforced coxrete
cover slab
2.5cm- (l-in.-) diameter pip- *rentilator
Capacity of tan! 1340 litres (253 Imp. gal.!
77
FIG. 44, PUBLIC
AQUA
PRIVY
BUILT
BY UNRWA’
IN REFUGEE CAMPS
Mcusuremcnts
\
I
A = Inspection manholes, 40 x 40 cm
(16 x 16 in.)
6
Inspection box, 40 x 40 cm (16 x 16 in.)
CI
Soakage pit or soakage trench
D= Capacity of tank : 22.3 m3 (4900 Imp. gal.)
E=
Drop pipe 10.5 cm (4 in.) in diameter
F = Q;nlng
15 X 15 cm (6 x 6 in.) In partition
G = For shape of hole, see Fig. 45
I
* United Nations
shown nre in centimctrcs.
Relief and Works Agency for Palestine Refugees in the Near East.
THE PRIVY
MmHOD
OF EXCRETA
DISPOSAL
79
Design irnd Function of Its Parts
Tbe tank
The function of the tank is to receive, store, and digest the excreta.
to keep them away from flies and other vermin, and to render them innocuous. The shape of the tank depends on local construction facilities
and materials ; it may be round, square, or rectangular. Concrete tanks
built in place are usually square or rectangular since forms for those
shapesare easierto construct. Round tanks may be made of plain concrete
sewerpipes 90 cm (36 in.) or 120cm (48 in.) in diameter placed vertically
in an earth pit and sealed at the bottom with concrete.
The size of the tank varies with the number of persons for whom it
is designed and with the time interval allowed between sludge removal
operations. From information gathered and analysed by Macdonald,2s
it appears that the capacity of a family-size aqua privy should Freferably
be not less than one cubic metre (35 cu. ft), allowing for 6 years or more
betweencleaning operations. Other data indicate, however, that a smaller
tank may also operate efficiently if the precaution is taken to add water
to it daily, but that such a tank requires more frequent removal of sludge
and undigested debris thrown into the tank. For public latrines of this
type, experiencedictates a design figure of 115 1 (4 cu. ft) per person for
the maximum number of persons to be served.
With such sizes, tanks of aqua privies need not be very deep. This
is a decided advantage from the viewpoint of construction, especially in
areas where ground water or rock level is high. The usual practice is to
provide a water depth of 1.0-1.5 m (39-60 in.), 1 m being considered
a minimum.
For proper operation of this type of latrine it is important that the
tank be water-tight. Should there be any leakage, the water level in the
tank will fall below the lower opening of the drop-pipe, and as a result,
flies and mosquitos will have accessto the tank, odorous gasesof decomposition will escapedirectly into the superstructure, and, finally pollution
of the soil and ground water will occur.
Materials commonly used for the construction of the tank include :
(a) plain or reinforced concrete, or (b) brick or stone masonry with plaster
cover. Concrete is admittedly the best material to ensure water-tightness;
in addition, it is permanent and relatively easy to work with. In areas
where bricks and stones are abundant, they may be cheaper to use ; but
they require a coat of rich cement plaster to make them water-tight.
The floor or slab
The floor or slab of aqua privies is usually of the squat type and is
provided with a short length of pipe as shown in Fig. 42 and 43. Depending
upon its design, it may or may not include a bowl. The earlier type of
so
ESCRETA DISPOSAL FOR RURAL
AREAS
septic privy was provided with a riser and seat but had no chute. As :I
result, the water and scum in the tank were accessible to flies and mosquitos,
which bred in it ; septic odours were also noticeable. The use of this type
of privy is being progressively abandoned in certain bztter developed
countries in Fdvour of better, wtlter-carried, sewage disposal systems.
The floor or slab may be made of concrete, wood, or other material.
Since the aqua privy is permanent in nature, the floor is usually made of a
durable material such as concrete. This material lends itself well to mass
production methods, as previously noted in connexion with the construction of pit-privy floors and slabs (pp. 52 and 71). Typical slab designs for
aqua privies arc shown in Fig. 42 and 45. The size and thickness of the concrete slabs are governed by the same considerations as those already mentioned for pit-privy slabs. The slab surface is provided with a small slope
from the edges towards the hole or bowl to ensure drainage into the tank of
the water used for cleaning and flushing the slabs, in addition to the water
normally used in certain- parts of the world for ablution or cleansing
purposes.
The bowl is usually made of cement and is pre-cast with the slab,
while the chute or drop-pipe is made of earthenware or vitrified clay pipe.
Cement pipes may also be used, but will not last as long as the other types
mentioned since the lower extremity will tend to disintegrate along the
line of contact with the liquid in the tank. The size of the pipe varies
from 10 cm (4 in.) to 20 cm (8 in.) in diameter, depending on the anticipated
use and maintenance of the privy. If the privy is properly used, the smaller
size will be satisfactory ; but, in places where stones, mud balls, or sticks
are likely to be used for personal cleansing, the larger size will tend to
reduce blockage of the pipe. The smaller pipe size will prevent the water
from splashing and will normally be free of crust-forming scum when
the latrine is in constant use. Pipes larger than 20 cm (8 in.) expose too
much of the water surface, over which mosquitos may lay their eggs;
in addition, there is an increased nuisance of splashing water.
& to the depth of submergence of the drop-pipe, practice varies a
great deal. On this point also Macdonald 2g has made a study of the
practice followed in many countries and has experimented with 15-cm
(Gin.) and lO-cm (4-in.) diameter pipes set with a 15-cm (6-in.) and IO-cm
(4-in.) submergence or water seal. He concluded that “ the best results were
obtained with a 4-inch pipe having a seal of 4 inches, as a narrow pipe
and a short seal increases the effectiveness of flushing “. A 10-l 5-cm
(4&n.) submergence should be sufficient in most cases provided there
is reasonable assurance that the tank is absolutely water-tight and that
the liquid level will not drop.
In these latrines, perhaps more than in pit privies, there is a great
need for foot-rests, the reason being that the floors of aqua privies are
likely to be wet from splashing of cleansing and ablution water. As in
THE PRIVY
METHOD
FIG. 45. BOWL
I
11
l
See
rho
OF EXCRETA
FOR PUBLIC
AQUA
PRIVY
l
50
39
Fis. 44.
81
DISPOSAL
Measurements
1
shown are in ccntimetres.
A - Drop pipe
B = Rich sand-cement mixture
c = Reinforced concrete floor
the case of pit privies (p. 57), foot-rests should be properly designed to
ensure prompt and easy drainage of such water towards the hole,
The home or soperstntctnre
The function and design of the house or superstructure for aqua privies
are identical to those for pit privies, as discussed above (p. 65).
Tank ventilation
In aqua privies, where the decomposition of excreta is entirely anaerobic
in nature, it is necessary to provide for the escape of the large volume of
6
s2
EXCRETA
DISPOSAL FOR RURAL
AREAS
gas which is normally produced by fermentation. For this purpose a
vent pipe should be installed, as shown in Fig. 43. Its opening in the
tank should be just below the slab and away from the scum which might
choke it. Its outside opening should be above the roof of the superstructure
and away from doors and windows of neighbouring houses, if odours
are to be avoided. A 7.5cm (3-in.) pipe will be satisfactory under most
circumstances.
The disposal of effluent
For each litre of water added to the water-right tank of an aqua privy,
a corresponding amount of “ sewage ” must be evacuated and disposed
of as effluent. The latter is septic in character and is loaded with finely
divided faecal matter in suspension and in the process of decomposition.
It may also carry harmful bacteria and the ova of parasitic worms.
Furthermore, because of the small size of the tank, the possibility of
water’s short-circuiting from the chute to the outlet pipe is obvious. For
these reasons, the effluent, though small in volume, should never be
permitted to run freely over the ground or in open ditches ; nor should
it be used for irrigation of garden crops eaten raw.
The average aGo&: of water to be evacuated from an aqua privy
has been estimated at about 4.5 1 (1 Imp. gal.) per person per day.“”
However, a capacity of 9 1 (2 Imp. gal.) is recommended for the design
of the disposal system. This figure will vary with the degree of availability
of water for cleaning purposes and should be corrected by field observations.
For example, when an aqua privy is provided with a water tap inside the
superstructure, the tank may be expected to receive much more water
than is mentioned above and even to be less efficient in its operation.
An effluent disposal system designed for a rate of 9 1 per person per day
will soon be overloaded under such circumstances and will ceaseto function.
The effluent is carried away through ,a IO-cm (4-in.) pipe inserted at
the proper level into the side of the tank. In order to prevent the scum
from entering the disposal pipe, the outlet is fitted with a tee or an elbow,
as shown in Fig. 43 and 46. For small installations the disposal of effluent
is usually done by seepage pits or subsurface irrigation.
These methods of disposal are discussed later (p. 138 et seq.).
Location of Aqua Privy
A properly operated aqua privy is a clean and odourless installation
which may be safely placed close to a dwelling. If proper operation and
use cannot be guaranteed, the distance from the dwelling should be increased.
Other factors influencing the location of privies in general have been
previously discussed (p. 32).
THE PRIVY
FIG. 46. FAMILY-TYPE
METHOD
OF EXCRETA DISPOSAL
83
AQUA PRIVY USING go-CM- OR 120-CM- (3-FT- OR 4-FT-) DIAMETER
CONCRETE SEWER PIPE FOR THE TANK
Section a-a
A=
B =
C =
D =
E =
Outlet to soakage trench or soakage pit
Removable, reinforced concrete cover slab
B.!&cm- (l-in.-) diameter pipe ventilation
Tank capacity varies with diameter and length of sewer pipe used
g&cm- or W&cm- (3-ft- or 4-f&) diameter concrete sewer pipe, 90 cm (3 ft) long or more,
sealed with concrete at lower end
84
EXRETA
DISPOSAL
Operation
FOR RURAL
AREA!3
and Maintenance
The Crst operation in starting an aqua privy is filling the tank with
water up to the invert level of the effluent pipe. Some digested sludge,
bailed out from another privy, may be added in order to seed the water
with the right types of bacteria and micro-organisms to carry out the
decomposition process. This is not absolutely necessary ; but, if the tank
is not seeded, some time (68 weeks) is required to reach an efficient
level of operation. Once established, satisf%ory action will maintain
itself theretier, provided the privy is in daily use. In areas where anal
cleansing with water is not practised, the tank will still receive the small
amount of water necessaryfor its proper functioning through a daily cleaning
and flushing of the dab and bowl with two or three buckets of water-i.e.,
approximately 25-M 1 (5-8 Imp. gal.).
As in the case of the wet-pit privy, the human waste deposited in the
tank will, when digested, be considerably reduced in volume. After several
years” operation (6-8 years, approximately), the digested sludge in a familysize installation will occupy 40%-50x of the tank’s water capacity and
should then be bailed out. Sticks, stones, mud balls, coconut husks,
and similar cleansing agents will not disintegrate and will cause the tank
lo fill more rapidiy, which requires more frequent cleaning. Provision
should zherefore be made in the design of an aqua privy for periodic sludge
removal through a manhole. Such a manhole may be located either inside
or outside the superstructure. It should provide for easy accessto the
sludge and to the outlet tee and the ventilation opening, both of which
may need to be cleaned of the scum or other solids accidentally lodged
in them. The manhole should be tightly fitted to prevent the ingress of
flies and mosquitos. It should also be easily accessible, and not be buried
under an earth cover and forgotten.
The sludge b&d out will, of course, contain some undigested matter
which is still oRens&. This should be buried in shallow trenches 40 cm
(16 in.) deep.
One dirscukty often experienced with poorly maintained aqua privies
is that the droppipe gets choked with fresh faeces upon which flies lay
their eggs. Maggots then hatch and migrate all over the house’s interior
walls and ceiling and create a considerable nuisance to the users. An
attempt has been made to alleviate this trouble, apparently with success,
by providing an arrangement for lifting the chute 20 cm (8 in.) before
and during flushing. By this procedure the seal is broken for a short
period. Another method is to use a plain stick to push the faeces down
the chute.
Cost
As previously mentioned, the aqua privy is receiving increasing attention
in Asian and African countries. If, as recommended, the maximum cost
THE PRIVY
METHOD
OF ESCRETA
DISFOSAL
85
of a latrine should not be more than the average monthly income of a rural
labourer, the aqua privy could not reasonably be considered acceptableor
economical in the rural areas of thesecountries. It is true that this type of
latrine has not seen extensive application in the rural villages of SouthEast Asia and Africa, chiefly becauseof its high original cost ; it has
rather been usedin urban or suburban areas, often as a public convenience,
and on large plantations and estates.
Few reliable data are available on costs of aqua privies in various
countries. In Ceylon, Macdonald D found in 1952 that the average costs
of aqua privies built with permanent materials and including the superstructure were f22 (US $61.60) for the single unit shown in Fig. 43,
and f39 (US $109.20) for a double unit. The construction of aqua privy
parts by mass production methods-would undoubtedly reduce these costs.
Advantages and Disadvantages
From the foregoing considerations, the advantagesand disadvantages
of the aqua privy can be summarized as follows :
Adwmtages:
1. If properly used and maintained, the aqua privy satisfies the seven
criteria, set forth on p. 39 relating to health hazards and aesthetic considerations.
2. The aqua privy is a permanent type of installation which is relatively
simple and inexpensive.
3. It can be placed near a dwelling.
4, It will withstand abuse.
Disudwntege~:
1. Its rather high initial cost may prevent its extensive use in rural
areas in certain parts of the world.
2. It may not be successfulin rural areas where there are no organized
.
sanitation and health education services.
3. It requires water (although a small voiume only will suffice) for
its operation.
4. It requires operation and maintenance C:I a daily basis.
5. It cannot be used in cold climates.
Among the various types of latrine the aqua privy ranks high, with
the pit privy, as a desirable excreta disposal system in areas where the
water supply is limited.
86
EXCRETX
DISPOSAL FW. RURAL
AREAS
Construction
Materials
As in the case of the pit privy, locally available materials should be
used to the greatest possible extent in the construction of the aqua privy.
However, the aqua privy is a permanent installation which should preferably
be built of durable materials. Also, the vital part of an aqua privy is its
tank, which must be water-tight. This implies that cement must be used
for concrete walls, or for joints in stone masonry or brickwork, and for
the all-important plaster coat. Cement is not available in every rural
area, and often its cost is prohibitive. This consideration alone may
preclude the use of the aqua privy in some instances, and the solution of
the escreta disposal problem will then be found in the use of the pit privy
with a water-seal slab, or another type of installation suitable to local
conditions and meeting local acceptance.
Concrete is to be preferred for the construction of the aqua-privy
floor, although wood may also be used. For the house, any locally available
material may be used, to suit the owner’s taste.
Mass production
The small, family-size, aqua privy lends itself well to construction
by mass production methods. The use of large-diameter concrete sewerpipes, where possible, eliminates the need for forms, which involve lumber
and skilled labour, and may result in an appreciable saving of money
and construction time (see Fig. 46). The slab, or floor parts, may also
be standardized (see p. 71).
Construction prucedures
The training and use of a small crew drawn from local craftsmen for
building aqua privy tanks are a decided advantage even in areas where
pre-casting of parts is done at a central plant.
The essential steps in the construction of the tank are as follows :
1. Dig a pit to fit the size of the tank and place therein a IO-cm (4-in.)
layer of gravel, which should be well tamped to make a firm foundation.
2. Pour at one stretch the bottom concrete, at least 10 cm (4 in.)
thick, together with 20 cm (8 in.) of bottom wall, using a 1 : 2 : 4 cementsand-gravel mix with not more than 23 1 (5 Imp. gal.) of water per bag
of cement.
3. Continue the wall, inserting the outlet tee and vent pipe connexions
at the proper levels. Then plaster the inside surface of the tank with a
1.25-cm (0.5-in.) coat of a rich 1 : 3 cement-sand mixture, paying particular
care to the joints in the concrete walls.
THE PRIVY
4.
filling
5.
6.
METHOD
OF EXCRETA
DISPOSAL
87
After the concrete has set, test the tank for water-tightness by
with water for 24 hours.
Lay the floor, and complete the superstructure.
Dig the seepage pit or disposal trenches as designed.
The construction of concrete slabs has been described above (p. 73).
The only difference to be noted here is that aqua privy slabs are always
cast in an inverted position to facilitate the casting of the bowl and the
proper placing of the drop-pipe.
THE WATER-SEAL
LATRINE
Description
The water-seal latrine, also called the pour-flush unit, consists of an
ordinary concrete slab into which a specially made bowl is incorporated,
as shown in Fig. 47. Usual practices call for a seal 1.25-3.75 cm (0.51.5 in.) deep. Such a slab may be installed directly over or at a close
distance to, a pit, bore-hole, or septic tank. In the case of the septic tank,
the bowl is connected to the tank by a short length of pipe. One to three
litres (or quarts) of water are sufficient to flush the contents into the pit.
Because of the water seal, ties cannot gain access to the contents of the
pit, and odours cannot escape.
Design and Construction
The squatting plate
Various methods have been developed to cast the slab, and bowl (see
Fig. 48 and 49). Sometimes the trap assumes a P-shape or an S-shape,
depending upon the location of the slab with respect to the pit.
The following description 42 is drawn from experience at Chiengmai,
Thailand, where latrine bowls were formed from cement mortar and
incorporated in concrete slabs. The Chiengmai technique, which is
applicable everywhere, was found to be more practicable and to result
in lower costs than most of the previous methods of casting. The dimensions
given are intended merely as a guide, since the size and shape of latrine
bowls and slabs are subject to local variations. In particular, the inclusion
of raised foot-rests is a debatable point (see p. 57).
The general method of manufacture is as follows. A form is prepared
in the shape of the interior of the bowl and trap ; the form is plastered
with a mixture of Portland cement and sand ; and the bowl is left to harden
and cure at the point of manufacture. The finished bowl is then transported
88
EXCRETA
DISPOSAL FOR RURAL
FIG. 47. WATER-SEAL
AREAS
LATRINE
A
Measurementsshown are in centimetres.
A = Plan
B = Form for casting
water-seal
bowl
THE PRIVY METHOD
OF EXCRETA DISPOSAL
89
to the latrine site ; the latrine slab is cast, with the bowl forming an integral
part of it ; and the finished slab, after hardening, is lifted into place over
the latrine pit.
A longitudinal profile of the form for the interior of the bowl is shown
in Fig. 47 B. Each form consists of two parts, the main portion being
made of a rich cement mortar (two parts Portland cement to one part
sand), or of solid wood, carefully finished and oiled ; the other part of the
form-for the interior of the trap-is made of clay. In Chiengmai, the
wooden form costs the equivalent of US $3.40 and is much preferred to
concrete, both because of its superior durability and because of the greater
ease with which it allows the bowl to be removed.
The clay to be used in making the form for the interior of the trap
is kept covered with water until needed. When it has been brought to
a workable consistency by the addition of ash, it is moulded into a U-shaped
roll in a curved pipe-mould. An essential part of the form is a shelf, which
is used to support one end of the U-shaped roll of clay ; the other end of
the clay roll rests upon the main part of the bowl form. The shelf is located
20 cm (8 in.) above the base of the main form. When the U-shaped roll
is set in place, it is carefully smoothed to the main form with a small
trowel, so that no irregularity is left on the interior surface of the finished
bowl. The whole assembly is then oiled.
A thin cement-sand slurry is pressed over the form by hand, and dry
cement is dusted on to provide the bowl with a dense, smooth interior
surface. Finally, a stiff mortar, consisting of one part Portland cement
to three parts sand, is pressed on by hand and trowelled smooth to a
uniform thickness of 1.25 cm (0.5 in.). The bowl is left in place for 24 hours
or longer, and is then removed from the form, taking the clay core with
it. The operation of preparing the form and making one bowl requires
about 25 minutes. After the bowl has hardened, the clay core is dug
out of the trap with a small trowel, the entire surface is washed with a
cement-water slurry, and the finished bowl is set aside and kept wet for
about one week to cure. One 50-kg (1 lo-lb.) bag of Portland cement,
costing about US !§1.50, is sufficient for 27 to 30 bowls.
One advantage of the Chiengmai bowl is that the trap discharges
forward, beneath the mid-section of the bowl. Experience with traps
that discharge towards the rear has shown that the back wall of the pit
is liable to be washed away. Such a danger is minimized when the discharge
is near the centre of the pit.
The details of the slab used at Chiengmai are shown in Fig. 47 A. The
size of the slab must be adapted to the dimensions of the pit Whether or not
a special foundation is needed to support the slab edges depends upon the
nature of the soil. The finished bowl is transported to the site of the latrine
and is cast into the squatting slab. A hole is dug, and the bowl is inserted
so that its rim is level and 5 cm (2 in.) above the surface of the ground.
90
EXCRETA DISPOSAL FOR RURAL AREAS
FIG. 48. METHOD
7s
i
20
OF CASTING
WATER-SEAL
SLAB
IN CEYLON
I
CASTING
Cement ccmrete
&ced tn POS,,,O~
cd well rommsd
BOARD
727
BACK VIEW OF
CASTING BOARD
B
PLANDFMDULD
I
51
I
t
VIEW AFTER
BACK vlEw OF
MOULD
REMOVING
Gr~ova to ho filled
with csmsn, mz.r,w
THE MOULD
/
SECTION OF TWO
HALVES PLACED
TOGETHER
.
COMPLETETRAP
Measurements
Details
shown are in centimetres.
of casting
The casting boards A and B with the moulds fixed should be placed in position and cement
concrete 1 : 2 : 2 (0.6 cm or 0.26 in. gravel) should be deposited into position and well rammed.
Twenty-four hours should be allowed for setting.
Remove the two halves and apply neat cement to the edge of one half and place the other half
in position and fill up the groove with cement mortar.
The Inner surface should be smoothed off with a coating of neat cement.
After completion, the trap should be cured in water for a period of at least one week.
THE PRIVY METHOD
FIG. 49. WATER-SEAL
TRAP
91
OF EXCREZTA DISPOSAL
AND
SQUATTING
PLATE
WATER SEAL TRAP
13
ELEVATION
SECTION A - B
SECTIONAL
ELEVATION
THROUGH CENTRE
;pjq
1.5
PLANOFCORE
90
1.5
PLAN OF WATER SEAL
2 5 dishing
SECTION A-B
I
\
5 cm thick concrete reinfmced
with one layer of hogwire
SECTION
C-0
\
’
6 cm theck concrete reinforced
with one Ioycr of hogwire
90
A -!-
1
-
B
8
~
/
DETAIL
OF SQUATTING
PLATE
DETAIL
OF SQUATTING
Measurements
PLATE
““2
IV51
shown are in centimetres.
Siphons made of a cement-sand mixture (1 part cement to 1 part sand). Upper portions and
lips 1 cm (I/, in.) thick; lower portion, 0.9 cm (3/S in.) thick. Finished weight about 26 kg (12 lb.).
Cast inverted in one operation by plastering over core and expendable clay mould (for trap).
92
MCRJZTA
DISPOSAL FOR RURAL
AREAS
Loose soil is packed around the bowl, and a wooden frame, 5 cm (2 in.)
high, is set in place, with its upper edge level and 2.5 cm (1 in.) above
the rim of the bowl. The ground inside the frame is then smoothed and
tamped, so that it slopes downwards from the frame towards the bowl ;
thus a uniform thickness is preserved in the finished slab. Some kind of
reinforcing material-chicken-wire, for example-is then laid, and 5 cm
(2 in.) of concrete, made with one part cement, two parts sand, and four
parts broken stone (not over 2 cm (0.75 in.) in diameter), is poured on
and trowelled to a smooth finish from the upper edge of the form to the
edgeof the bowl. The slab mtut have an evenfinish to ensureeasy drainage
into the bowl. If foot-rests are required, separate small wooden forms
may be used. It should be noted that casting on the bare ground eliminates
the need for the heavy and expensive base-boards and ribs which are
commonly used. After the slab has hardened, the pit is prepared, and
the squatting plate is lifted by hand and set in place over the pit.
The cost of such a slab, based on 1955 prices, has been calculated in
Chiengmai as follows :
us s+
item
Bowl. ..............
Slab :
cement (l/3 bag). .......
iabour +* ...........
reinforcement .........
sand acd gravel ........
Total
.........
0.25
0.50
0.23
0.23
0.14
-__-_
Sl.35
l
Exchange rate of 22 bahts to the dollar
** Daily wage of US SO.68
This estimate includes the overhead costs for casting bowls at a central
plant, but not, of course, the cost of digging the pit or building the superstructure. According to Chiengmai experience, when a householder
suppliesthe labour for theselast two items, his total expenditureon materials
for the squatting plate and the superstructure amounts to approximately
US $2.30, that is, about one-sixth of the monthly income of the lowest
paid worker.
Tbfi disposd system
When the squatting plate is placed over the disposal pit, the latter is
designed and built in the same manner as for ordinary pit privieq (see
p. 42). If the squatting plate is installed inside the dwelling, the pit is
dug outside and assumesthe shape and design of a leaching cesspool
(seep. 123),or of a bore-hole. In this case,the distancebetween the cesspool
or bore-hole and the squatting plate should be as close as the building
foundation permits ; otherwise, the drainpipe becomes too long and tends
93
THE PRIVY METHOD OF EXCRET-A DlSPO!SAL
q
to clog within a short time becauseof the small volume of water used to
flush the faeces from the bowl (see Fig. SO). The drain pipe is usually
10cm or 15cm (4 in. or 6 in.) in diameter and made of cast iron or ordinary
ccmemtsewer pipe laid with a steep slope (not less than 5%). Becauseof
the added expenseand di!Eculty in laying this pipe, it is often preferable
to place the squatting plate directly over the pit or bore-hole.
Another system makes use of a septic tank in lieu of a pit or borehole in areaswhere the ground water is high and interferes with the proper
functioning of deep pits. This system is, of course, very expensive for
ordinary rural areasand communities. It should be noted that, in addition,
a subsoil disposal field is required in such systemsfor the effluent of the
septic tank.
Location
If properly operated, latrines equipped with the water-seal-type slab
fulfil all sanitary requirements and may be placed inside the dwelling
itself. Some engineering factors goweming the location of the disposal
system often prevent such an ideal arrangement. However, even then it
is pssible to locate such latrines very close to the houseswhich they serve,
a condition which ensures its daily use in bad as well as good weather.
Advantages and IBisadvantages
These may be summarized as follows :
.
Atiwmtuges:
1. The water-seal (pour-flush) latrine, when properly operated and
maintained, satisfies all sanitary and aesthetic criteria (see p. 39).
2.
3.
4.
5.
6.
It can he installed near or inside the dwelling.
It minimizes contact with flies and vermin.
The odour nuisance is kept to a minimum.
It is entirely safe for children.
With improved construction techniques, it is simple to build and
cheap for use in xral
areas.
Disdnzntages :
1. It can be used only in areas where water is obtainable (a small
volume will &Ike) the year round.
2. It requires a period of intensive education in its proper use and
cleaning and continued follow-up by sanitation authorities.
EXCRETA
DISPOSAL
FIG. 50. WATER-SEAL
FOR RURAL
LATRINE
USED
AREAS
IN CEYLON
i
:
I
I
I
Matsorcments
lowo
arc in ceotimctrcs
A = Watar-seal bowl with S trap
6 = Water tank, filled by hand and provided with plug cock and overflow pipe
C = Water pipe leading from tank to bowl for flushing purposes
0 - Drain pipa embedded in concrete leading to seepage pit
E==s%epageDlt
F -- Venlifation pipe for pit
6 - Distance betnteen bowl and pit should be as short as possible
THE
PRIVY
METHOD
OF ESCRETA
DISPOSAL
95
3. It costs slightly more than ordinary pit privies, but less than aqua
privies.
4. in many rural areas of the world, it would require a change in
customary use of cleaning IlliktWiitfS.
5. It is not readily applicable in areas with impermeable soils.
6. It cannot be used in freezing climates.
In countries of South-East Asia, latrines with water-seal slabs have
been used for more than twenty-five years, and appear to have been readily
accepted by the rural people of the region, as they fit in welt with their
customs and reiigious patterns. Experience shows, however, that the
water-seal latrine should be used oniy ia familv-I installations, that it is
not suitable for use in public conv : Gences.S
THE
BOREBHOLE
LATRtNE
Description
The bared-hole latrine is only it vLlriation of the pit privy, from which
it differs by the much smaller cross-sectional areit of its pit. The latrine
floor, or slab, and the superstructure are the same for both types of
installation. The bored-hole latrine, which was developed 30 years ago
in the Dutch East indies,‘t6is now extensively used in countries of Africa,
the Middle East, South-East Asia, the Western Pacific, and South America.
Design rrMt Functian sf Its Parts
This consists of a circular hole usually 40 cm (16 in.) in diameter bored
vertically into the ground by meansof an earth auger, or borer, to a depth
of 4-8 m (13-26 ft), most commonly 6 m (20 ft) (see Fig. 51 and 52). Holes
of 30 cm (12 in.) and 35 cm (14 in.) have also been used extensively, and
are easier to bore than is the larger, 4U-cm (l&in.) size ; but experience
shows that their capacities are much too small. En fact, the volume of
the 4tkm- (16in.-) diameter hole is considerably smaller than that of
the pit privy of same depth, the ratio being I to 6.5 in favour of a pit
90 cm (3 ft) square. The samepit privy, 90 cm (3 ft) square, is 11.5 times
larger than a 3&m- (12-m.-) diameter bored hole of the same depth Becauseof its small capacity, the bored-hole Iatrine dug into dry ground
and used only by a family of 5 or 6 persons does not last more than
I$$-2 years in most instances, and less where bulky cleansing materials
96
EXCRETA MSPOSAL
FOR RURAL
AREAS
are used. The solution in such a caseis to build two holes a short distance
apart and to use one at a time. When the first hole is filled, it is covered
with 50 cm (20 in.) of well-tamped earth, and the slab and superstructure
are skidded over the other hole. After about one year, the well-digested
material in the first hole is removed, making the hole available for the
next move. The life of a bored hole
(like that of the pit privy) is appreciFIG. 51. TYPICAL
BORED-HOLE LATRINE
ably increased when it penetrates
1-2 m (3-6 ft) into ground water,
for reasonsalready discussedunder
LLlife of a pit ” (p. 43). Chiefly
because of its small capacity, the
bored-hole latrine is a family type
of installation and cannot be used
as a public convenience.
The greatest engineering dificulty encountered in the design and
construction of bored-hole latrines
is the collapse or caving of the pit
Walk.
Ctlving is rather frequent
with this type of latrine, especially
in sandy or alluvial soils, and is
sometimes so severe as to obstruct
the hole completely. in some instances,holes have been bored into
dry and firm ground requiring no
casing and have caved in during
the next rainy season when the
ground water rose and flooded the
pit. To avoid such occurrences,
casings or linings should be pro*a0 w9
vided to support the walls of the
Measurements shorn BIG in centimetres.
pits. Much care must be taken,
Squatting
slab.
Note sides sloping
when planning bored-hole latrine A= towards
hole
installations, to study ground for- 8 = Impervious clay-tile lining
lining
mations and the fluctuations of CD == Woven-bamboo
Earth mound, well tamped
ground-water levels in the area
under consideration.
Becauseof the small dimensions of the bored hole, the upper section
of the pit is likely to be soiled by both excreta and urine. This may resu!t
in offensive conditions, and flies may be attracted and breed in the earth
below the squatting plate. To alleviate this situation, it is good practice
to line the upper 30-60 cm (12-24 in.) of the bored hole with a tight,
impervious lining (e.g., concrete, baked clay).
THE PRIVY
METHOD
OF EXCRETA DISPOSAL
FIG. 52. BORED-HOLE LATRINE
SUITABLE
FOR FLOOD PLAINS
l BuiltiJlEilsIPakhan.
97
IN ALLUVIAL
SOILS,
AND TIDAL AREAS l
Meas-eats
shown are in centimctres.
A=
6 =
C =
D =
Round slab with slope to centre, as shown in Fig. 27
Original ground
Bamboo lining required in mound
Bamboo lining full length if required
E = Tamped earth mound
Tbe floor or slab
Tl;k floor of a bored-hole latrine is identical in size and shape to that
of the pit privy (see p. 52). When the floor is built of concrete, it needs
little or no reinforcement because of the small unsupported span (40 cm,
or 16 in.) of the bored hole latrine slab. The thickness of the concrete
7
98
EXCRETA
DISPOSAL FOR RURAL
AREAS
slab may be safely reduced to 5 cm (2 in.) on the slab edge and to 4 cm
(I 5 in.) at the centre. It is desirable to use hog-wire or similar reinforcement, chiefly for the purpose of preventing cracks caused by temperature
differences and by shocks during transportation. The floor is usually
raised 15-20 cm (6-8 in.) above normal ground level, but a specially built
base is generally not necessary.
The mound
A mound of earth should be built around the floor to protect it against
run-off. The mound should be at least 50 cm (20 in.) wide and well tamped.
In flood plains and tidal areas, the floor should be elevated above the
highest water level, and the mound solidly built. As shown in Fig. 51,
it may be built of moist earth, well-tamped in small layers of 15 cm (6 in.) ;
but where necessary,the mound should be revetted with flat stones. As
in the caseof the pit privy (p. 65), it is preferable to supplementthe earth
mound in front of the entrance door with a masonry or brick step to help
prevent dirt from being tracked into the privy on the user’s feet.
‘Ibe sqmstrueture and the ventilation
The superstructure is identical to that recommended for pit privies
(p. 65). While the house should be ventilated in order to minimize the
odour nuisance, the ventilation of bored holes is generally considered to
be unnecessary. It may be noted that, thus far, the bored-hole latrine
hasbeenusedalmost exclusivelyin the tropics, where temperaturedifferences
betweenthe air in the pit and the outside air are slight ; as a result, any
draught of air through a vent pipe would be negligible.
Location of Bored-Hole Latrine
The basic considerations regarding the placement of latrines in general
with respectto sourcesof water supply and dwellings have been previously
discussed (see p. 32). In the case of the bored-hole latrine, the danger of
pollution of the ground water is obvious since it is generally desirable
that the bored hole penetrate it deeply for more efficient and durable
operation. However, the rules governing the location of bored-hole latrines
are the same as those for the pit privy.
Advantages and Disadvantages
The advantagesand disadvantagesof bored-hole latrines are in anany
respects similar to those of pit privies. Given proper construction and
location, they satisfy most of the requirements set forth under “ criteria
for selection +’ (p. 39).
THE PRIVY METHOD OF EXCRETA DISPOSAL
99
In particular, the bored-hole latrine is cheap and easy to construct in
ordinary soils. In a WHO-aided rural sanitation project in East Pakistan,
the cost of a bored-hole latrine in 1955 was found to be Rs. 11/15 (US
$3.58), plus Rs. 6/- (US $1.80) for a woven bamboo lining. In Egypt,
the estimated price in 1952 was US $5.60.
Penetration of the ground water may be either an advantage or a
disadvantage,as previously noted. In addition, the formation of a thick
scum above the water level in the hole may seriously impair the operation
and life span of the latrine. In such situations, and especially in areas
like the Nile delta in Egypt, where heavy fluctuations of the ground water
bring the water table within a few feet of the ground level, the bore-hole
fills up quickly since the solids deposited float over the scum. By breaking
the scum layer with a pole (a procedure which is admittedly impractical
in many instances),the efficiency of the latrine may be restored. However,
recent investigations have shown that proper location is more important
than a great distance between a latrine of any type, including the boredhole latrine, and the source of water supply.
The bored-hole latrine has been classified among other less desirable
types of excreta disposal installations for the following reasons:
1. It requires special equipment for its construction.
2. If it does not penetrate ground water over approximately onethird of its depth, its life span is extremely short (set discussion on
“ life of a pit “, p. 43), a most seriousconsideration in the successor failure
of an excreta disposal programme.
3. In many countries it is difficult to secure cheap but strong and
durable materials for supporting the walls of the bored hole against caving.
Coll!stmction
Mate
For the construction of linings, or casings, the following materials
are most commonly used : wooden strips, bamboo, split cane, and baked
clay. In addition, it is often possible to find in rural areas some kind of
material which may be woven or made by the rural artisans themselves
for use in the construction of casings. In large areas of Asia, bamboo
is plentiful and used for this purpose. It has the great advantage of lasting
for years under water without a preservative (although tar is used in Indonesia for this purpose). However, untarred bamboo and other wooden
linings in dry pits or above the water line in wet pits are sometimesattacked
by insects, although it is possible that they may last as long as the latrine
&4f (in the case of dry pits, at least). In areas where pottery is made,
100
EXCRETA DISPOSAL FOR RURAL AREAS
cheap linings can be manufactured for bored-hole latrines in the form of
perforated clay pipes. In the Americas, split cane has been used with
success in the same manner as bamboo.
Whatever the material used, it must be remembered that the purpose
of a lining is only to prevent caving. The perforations, or holes, in the
lining should be as large as the soil permits, in order to allow for prompt
leaching of liquid waste and dissolved solids out of the pit into the ground.
In areas where the ground-water level is high, or which are subject to
flooding, the latrine floor is elevated above the surrounding ground in
the manner shown in Fig. 52. In such a case, the portion of the lining
which passes through the elevated mound and penetrates the first 50 c!;x
(20 in.) below the normal ground level should preferably be impervious
and built of strong material, such as concrete.
Boring the hole
Equipment
One 4O-cm (16-in.) earth auger, one auger shaft, one handle, one
tripod, one pulley block, and one auger guide.
There are many types of auger which can be purchased on the market
for different purposes. Fig. 53 and 54 show various types of auger and
equipment which are suitable for bored-hole construction. A good latrineboring auger for ordinary soils (not containing boulders, rock, or hardpan)
might fulfil the following specifications:
Double-bladed, hand-operated earth auser, with a nominal diameter of 40 cm
(16 in.), capable of boring through moderately difficult soils to a depth of 6 m (20 ft).
The blades to be high carbon steel, 5 mm (*Ita in.) thick, with the points strapped to
preventthe blades from springing apart. The yoke and plug to be malleable iron cast
as one piece, the plug having an external diameter of 37.5 mm (t*/, in.) to tit into a
stat&Cd it/s in. diamcicr iron pipe .a The piug to be cast with holes, each 10 mm (8/8 in.)
in diameter through the body of the plug at right angles to its axis, with bolts to fit.
In use, the operating shaft, consisting of standard lllrin. iron pipe, fits over the plug
and is secured by the bolts through corresponding holes in the pipe shaft. The auger to
be furnished completely assembled, pipe shaft excluded.
An additional remark which may be made about double-bladed auger
design is that the edgesof the blades should not be so far apart as +o leave
large ~ipc;i spxes through which silting sand and soft mud may fall out
when the auger is being raised. Earth augers of the disc, helical, or
worm types may be used in boring through clay and softer soils without
stones.
0 lo many countries where the metric system of measurement is used. this would be replaced by a 40-mm-diameter pipe, and the other specifications would be altered accordingly.
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
101
The auger shaft may be either round or square to fit the yoke of the
auger selected. To fit the auger for which the above specifications are
given, ordinary Is-in.-diameter iron pipe will be used. -This equipment
will include : (a) one length, 6.70 m (22 ft), of standard 11/2-in. iron pipe
FIG. 53. AUGERS
B
FOR BORING
a
HOLES
0
a,
J
0
d,
0
A=
“Lang” earth borer. Note edge cutter which can slide up
to 3.2 cm (lb in.) to Increase diameter of hole
B = Worm-type earth auger
C = “Iwan” earth auger
perforated across its barrel every 60 cm (2 ft) with IO-mm (3/8-in.) holes ;
(b) one IO-mm (3/8-in.) bolt or steel pin 9 cm (31/2 in.) long ; (c) one
coupler (which may be required) for connecting two separate lengths of
11/2-in. pipe, preferably an inside or plug-type coupler, with holes 10 mm
(318 in.) in diameter, at right angles to the axis of the coupler, with bolts
to fit.
The handle will include a pipe cross, 50 x 30 mm (2 x 11/* in.) fitted
to slide along the lI/2-in. round shaft, tapped to take two handle branches,
each consisting of a standard 30-mm (11/4-in.) diameter iron pipe 75 cm
102
EXCREI’A DlSPOSAL FOR RURAL AREAS
(30 in.) long, threaded to fit the cross. The cross is to be drilled with one
hole 10 mm (3/8 in.) in diameter through the centre at right angles to
both branches, with a bolt to fit. In operation, the handle is slid along
the operating shaft, and is pinned through successivecorresponding holes
in the shaft.
The tripod may also be made
FIG. 54. COMBINATION
AUGER AND SAND
of I*$$-in.-diameter iron pipe or of BALER
FOR BORING HOLES IN SOFT SOILS
wood or bamboo poles, as shown
in Fig. 55. The pulley block, single
sheave, for 20-mm (3144~) rope
will usually be sufiicient. One auger
guide as shown in Fig. 55 and 56
will also be required.
The procedure to be used with
the equipment described above is
fairly standard all over the world.
The following suggestions are offered by Mr J. C. Carter, of the International Health Division of the
Rockefeller Foundation : f
“ (a) Set up the tripod over the spot
where it is desired to bore the hole and
attach the pulley block in place. (@ Directly under the pulley block, excavate a
hole about 6 inches (15 cm] deep and of
the same diameter as that of the auger.
(c) Place the auger, equipped with shaft
and turning handles, in the hole which
A=
Sand baler
has been excavated and adjust the turning
handles to the desired height on the shaft.
Lock the turning handles in place by
the use of the set screw in the cross tee, or by the use of a steel pin if a round shaft is
used. (& Thread the hoisting rope through the pulley b!cck and attach one end to the
auger, or to the auger shaft. (e) Turn the auger in a clockwise direction until it is filled.
Care must be exercised to ensure that the shaft is kept in a vertical position while turning
until the hole is deep enough to put the auger guide into use. (f) When the auger is
filled. lift it out of the hole by hauling on the hoisting rope, swing it to one side and
empty it. Then let the auger swing back over the hole, lower it, and proceed as before.
(g) When the hole has reached 3 depth of about 3 feet, place the auger guide in position
and Gx it in place by the use of an iron or wood peg at each comer. With the auger
guide in place no further diisculty should be experienced in boring a vertical hole.
(h) After the desired depth has heen reached remove the auger from the hole and set the
tripod aside. Insert the lining (if one is required) . . .*’
THE PRIVY METHOD OF EXCRETA DISPOSAL
FIG. 55. TYPICAL
A
B
C
D
E
=
=
=
=
INSTALLATION
FOR BORING
Tripod made of bamboo poles
Pulley block
2-cm &in.)
manila rope
Earth auger
Auger guide
THE BUCKET
LATRINE
De5cliptiorl
This system of excreta disposal is also referred to as box-and-can
privy, conservancy system, pail latrine, or earth closet in English-speaking
countries, and as tinettes in French-speaking areas. In principle, it consists
of a bucket in which excreta are deposited and which is removed for emptying
and cleaning at frequent intervals (see Fig. 57). In the earth closet and
tinette types of bucket latrines, a mechanical device is available from which
dry earth, sawdust, or ash is released by the user to cover the excreta.
These types of latrine are in use in rural towns and urban areas without
sewers in many countries of Africa, South-East Asia, and the Western
Pacific. They were also used extensively in the past in Europe and the
Americas but have almost completely disappeared in favour of better
and more sanitary types of excreta disposal installations, especially the
pit privy and the water-borne systems.
EXCRETA
FIG. 56. DETAILS
DEPOSAL
OF TRIPOD
FOR RURAL
CONSTRUCTION
AREAS
AND
AUGER
GUIDE
llsfld
L##u 51
Thne
hints
BORER AN0
fRlf=Oo
,. -\,
ELEVATION
Reproduced from Carter, J. C. (1938) B~dl. Hyg. (Lotad.), 13,
596. 597. by kind permission of the Bureau of Hygiene and
Tropical Medicine.
A=
B =
C =
D =
E =
F =
G =
H =
Iron pipes for tripod
Iron pipe for auger shaft
Plate
Auger
Cross-T and handles
Pulley block
Rope
Auger guide
THE
PRIVY
METHOD
OF EXCRETA
FIG. 57. THE BUCKET
DISPOSAL
105
LATRINE
The measurement shown is in centimetres.
A = Collection chamber built of impervious material ; note bucket
B = Fly-proof door
C = Elevated floor or slab
D = Paved surface and drain
E = Soakage pit or trench
F = Orlglnal ground-level
Design and Function of Its Parts
The bucket or receptacle
The bucket or receptacle is usually made of seamless galvanized iron,
rubber, or white enamel. It is about 38 cm (15 in.) in diameter at the top
and 30 cm (12 in.) deep and has adequate handles for lifting and carrying.
In some cases it sholrld be provided with a removable, tight-fitting lid
held in place by clamps. It is the practice to make two buckets, painted
different colours, available for each latrine hole or seat so that a clean
pail may be placed in the latrine when the other pail is taken away for
emptying.
106
EXCRETA
DISPOSAL
FOR RURAL
AREAS
The collection chamber and the superstructure
The bucket is placed in a collection chamber (or box) situated below
the squatting plate (or seat). The chamber may be built of brick or concrete,
with rounded corners and is so shaped as to help centre the pail. Most
chambers open to the rear of the latrine, into the service lane used for
collection. Where seats are used, the space beneath constitutes the box,
and the pails may be removed through the hinged latrine seats. In any
case, it is important from the sanitary standpoint that the collection
chamber be fly- and animal-proof. Good practice also calls for ventilation
of the chamber by means of a pipe vent carried to roof level of the superstructure. The vertical distance between the bottom surface of the floor
slab and the rim of the bucket should not be greater than 2.5 cm (1 in.).
The superstructure itself is built in the same manner as for an ordinary
pit privy, except that the floor is raised above the collecting chamber and
the ground level. In some countries the floor is designed in such a manner
as to separate solid faeces from urine and ablution water, which tend to
fill up the buckets quickly and to keep their contents in a semi-liquid state.
Urine and other liquid wastes are directed by troughs either to an impervious catchpit, which is emptied periodically, or to a soakage trench.
Collection and Conveyance of Buckets
Collections are usually made daily, although in some places they are
made only weekly or bi-weekly. The collected pail should be sealed with
a fly-tight lid and replaced by a clean and disinfected one of different colour
(to facilitate routine sanitary inspection). It is sometimes emptied into
a tank carried by a vehicle, and then taken away to be washed. The practice
of emptying buckets into a tank or wagon and immediately returning
them to the latrines must be unreservedly condemned. The time of collection, whether night or day, may be decided by the community concerned.
The method of transportation varies greatly among countries, from
the coolies’ “ basket ” system in the Far East to push-carts or bull-carts
and to motor vehicles elsewhere. Care is seldom taken to avoid spilling
the contents of the buckets during collection and transportation to the
disposal grounds.
In Asian countries, the amount of night-soil (faeces and urine) collected
per pail per day is roughly 4.5 I (1 Imp. gal.) ; in Ceylon, where faeces
only are collected, the collection amounts to 1.4 1 (0.3 Imp. gal.) per pail
per day,
At the disposal site, the buckets are emptied, thoroughly washed,
and disinfected with a phenol or creosol type of disinfectant before being
stored away and re-used. The wash water is disposed of underground
by means of soakage pits, and should not be permitted to run freely in
I
THE
PRIVY
METHOD
OF EXCRETA
107
DISPOSAL
open ditches or used, without adequate control by local health authorities,
for farm irrigation. It goes without saying that the disposal sites should
be located as far away as possible from human habitations and all sources
of drinking water.
The collection system is best carried out by the community administration
and under the direct supervision of the health authorities. A fee is usually
paid by the family for this service, and is sufficient to cover the costs of
operation and replacement of the equipment.
Methods of Night-Soil Disposal
The methods of disposal of night-soil were reviewed at the previously
mentioned WHO seminar on sewage disposal for South-East Asian and
Western Pacific countries. The following is based on the report on that
seminar.’
Night-soil collected by the conservancy system may be disposed of
by a number of methods, varying widely in efficiency, in sanitation, and
1 in cost.
Various methods used
(a) The use of water transport, where available, to convey night-soil
to its ultimate disposal point in a sufficiently large body of diluent water
is acceptable from a public health standpoint. This is, however, relatively
expensive and may become entirely inoperative during even moderate
stoims.
(b) Burial in earth pits or trenches, which has the advantage of being
extremely simple, is rather common. It requires a considerable amount
of hand labour.
(c) Incineration of night-soil along with other types of refuse fulfils
sanitary requirements but is expensive.
(a) Detention in specially designed tanks is practised in some Asian
countries in which it has long been the custom to use human excreta to
fertilize giowing crops. If the detention period is sufficient to permit the
“ die-away ” of pathogens, public health criteria for using this material
are met. The cost of this operation depends on the cost of storage and
transport and the selling price of the material.
(e) In some countries, raw or partially decomposed night-soil is used
for agricultural purposes. This practice, however, is universally condemned
on public health grounds.
= Repot-r OR Seminar on Sewage Disposal (Rural and Urban).
port
issued by the WHO
Regional
Office for South-East
Asia.
Ceylon.
Kandy,
New Delhi)
I
1955 (Re-
108
EXCRETA
DISPOSAL
FOR RURAL
AREAS
(f) lx~“a~
directly into sewers is practised in a number of urban
areas throughout Asia. This is an accepted method of sanitary disposal
if “ depots ” are properly constructed, maintained, and operated. It is
a relatively inexpensive method but has the disadvantages of producing
odours, placing shock loads on treatment plants, and sometimes creating
septic conditions within sewers which produce deterioration of the sewers
and sewer structures.
(g) The anaerobic digestion of night-soil in closed tanks is a relatively
new disposal technique. Digestion plants may be designed and located
so as to be used later as a part of proposed conventional water-borne
sewage-treatment plants.
(12) Finally, experiments have been carried out, in Japan, on developing
methods of heating night-soil for sterilization. One method that has been
tried is using the strong heat from municipal refuse incinerators.
Details of several methods
1. Trenching-method
(tp)
Costs of the pit or trenching technique include the cost of suitable
land located at a reasonable distance from the collection points and the
costs of labour and transportation.
Sanitary considerations associated with this technique include subsoil
conditions, the possible utilization of ground water for water supplies,
gross contamination of surface waters, and depredations of domestic or
wild animals.
A common method of trenching at the present time is to use a trench
60 cm (24 in.) deep, filled with 45 cm (18 in.) of night-soil and covered
with 15 cm (6 in.) of earth. This amount of coverage is considered inadequate for two reasons : (I) according to parasitologists, hookworms can
work their way through 10-13 cm (4-5 in.) of soil ; and (2) during monsoon
weather, the bulking of the faecal matter can cause oozing through the
cover. It is therefore essential that the trench should contain only 30 cm
(12 in.) of night-soil, with a 45-cm (l&in.), tamped earth-cover, 15 cm
(6 in.) of which is a mound of earth above ground level.
The bottom of the trench should be above the highest water-table and
preferably above the layer of soil likely to be moistened by capillary action.
In areas of excessiverainfall a ceeper trench should be provided, if possible.
Grass may be grown to assist digestion and prevent erosion, so long as
there are no cattle.
The service life of trenching areas will vary from about two months
(the time necessary for digestion) to two years (the time for which they
are used in present normal practice). It is believed that further work on
this problem may result in a reduction of this two-year service life. Service
life, utilization, and land values are inter-related ; and, if a reduction in
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
109
the trenching time were effected, less land would be required, and the
area might be utilized in a better way.
2. Disposal into sewers-method
(f)
Satisfactory depots for the disposal of night-soil into sewers should be
located at convenient points away from very populous areas. The buildings
should be fly-proof and always kept clean and sanitary. The public should
not be allowed to enter the premises to obtain water or to wash clothes.
An abundant water-supply under pressure is most important, and a storage
tank of adequate capacity should be installed. Without water the night-soil
would be inadequately flushed, the screenings exceedingly difficult to
handle, and the condition of the pails, trucks, and depots a serious public
health hazard. The receiving hopper should be made of concrete with
rounded corners and should be installed with a bar screen, through which
the night-soil may be flushed. A trap should be installed between the
dumping hopper and the sewer main. In all water pipings, care must be
taken to see that there are no cross-connexions or possibilities of backsiphonage.
The seminar participants did not endorse the collection of night-soil
in lieu of the extension of sewers. They felt, however, that, where the
practice had to be continued, collected night-soil could be disposed of
into the sewer if proper precautions were taken to prevent damage to
the sewer or interference with treatment processes.
3. Digestion plants-method (g)
The disposal of night-soil by digestion is being practised in Japan,
where, in different areas, about 20 plants, to serve populations ranging
from 3500 to 100 000, are under construction or in operation.
This process essentially involves the same digestion process of sewage
sludge as occurs in conventional sewage-treatment plants ; the digestion
plants are usually designed so that they can become component parts
of complete treatment plants when water-borne sewage schemes become
possible.
The night-soil is carried to the plant by hand or by motor transport
and is discharged through a screen chamber into the digestion tank. The
containers are cleaned, and the wash-water goes into the digestor.
Digestor gases are collected, stored, ‘and used for maintaining the temperature of the digestor contents at 30°C (86°F) for about 30 days. Digested
sludge is withdrawn to drying beds, and dried sludge used as fertilizer.
Supematant liquors are diluted and treated by biofiltration.
Screenings
are usually incinerated.
A review of the operation of one group of seven digestor installations
indicated that they had capacities ranging from about 28 1 to 39 l(1 .O cu.
ft to 1.38 cu. ft) person served.
110
EXCRETA
DISPOSAL
FOR RURAL
AREAS
Operational and cost data are unfortunately not yet available for this
method of night-soil disposal.
Comments on the Bucket Latrine System
In theory, a properly designed and operated bucket latrine system
will fulfil all sanitary requirements. In actual practice this is far from
being the case, and satisfactory conservancy systems anyvhere in the
world are rather rare exceptions. Experience gathered in every country
shows that the bucket latrine system, though cheap in initial cost, is in
fact the most expensive type of installation to operate and maintain. In
addition, it has obvious health hazards for the community and for the
scavengers, in particular ; by its very nature, it inevitably leads to difficulties
rT a social nature because of the stigma attached to the scavengers who
engage in this filthy type of work. In fact, in most countries of the world
it is becoming increasingly difficult to recruit labour for scavenging. In
rural areas it may still be possible to secure the co-operation of interested
farmers for this job.
It has been noted that the use of dry earth, sawdust, or ash is often
ignored even in areas where the latrine still bears the names of “ dry earth
closet ” and tinette. As a result, the contents of the buckets are highly
odorous and attractive to flies, which lay their eggs in them at the first
opportunity. The door of the collection chamber and the squatting hole
or seat are seldom fly-tight and closed. In spite of active supervision, the
contents of buckets are often spilled carelessly near the latrines or along
the road to the disposal site. The bucket lids are rarely kept in place ;
and it has been reported that, in a major town, the buckets are left exposed
for hours without covers on sidewalks pending collection ! The system,
which depends on the separation of urine and faeces, is seldom built and
maintained properly, as a result of which the urine simply runs over soaked
ground and through unsightly pools. Conditions at the disposal sites are
often intolerable due to spillage, lac k of an abundant supply of water,
intense fly-breeding, odours, and rodent infestation.
Owing to the enormous difficulties in operating this system in a sanitary
manner, the bucket latrine usually violates most, or all, of the sanitary
requirements set forth on page 39.
The cost of operation of the conservancy system is, in most instances,
staggering, although not often so recognized by town councils. In countries
of South-East Asia, present costs range from Rs. 20/- to Rs. 70/- (US $4.21
to $14.70) per pail per year for poor to “ good ” conservancy systems. In
Hong Kong the cost is H K $56 (US $9.82). These are only direct operating
costs of collection and disposal and do not include latrine structure,
maintenance and replacement of pails and other transportation equipment,
or gratuities to scavengers, which are additional costs borne by the family.
THE
PRIVY
MJZTHOD
OF EXCRETA
DISPOSAL
111
A rural community of 1500 persons, for example, having a conservancy
system of 320 pails may be spending up to US $3200 per year for a
never-ending insanitary excreta disposal system, without realizing that this
annual cost could finance an immediate capital expenditure of US
$41 600. This is calculated on the reasonably safe assumption that
the community would reimburse this capital by equal instalments of $3200
a year for twenty years, the interest rate being 4.5%. It is strongly recommended that communities which possess conservancy systems should
undertake a thorough sanitary and financial study of the operation of these
systems with a view to changing them to better and more economical
types of excreta disposal installation.
The only thing which may be said in favour of the bucket-latrine system
is that it offers a means for collecting night-soil, which, in some areas,
is ultimately used as soil fertilizer. There is, however, another type of
latrine-the compost privy-which is better adapted to this purpose and
which is described later.
THE “ FEUILL~ES”
OR TRENCH
LATRINE
Description
In French-speaking countries, the term feuz%es applies to very small
and shallow pits dug into the top layer of the ground. The pit is usually
square, about 30x 30 cm (12x 12 in.) in cross-section, and 40 cm (16 in.)
deep. The excavated earth is piled loosely around the hole (Fig. 58).
Each user is expected to throw a scoopful of loose earth over the faeces
deposited. The urine normally falls outside the pit and drains away. It
is estimated that a pit of this size will receive 100-150 droppings, after
which it is thoroughly covered with an equal volume of earth. 1Jn+
tropica: conditions, the decomposizlon 01 raeces 1s completed in about
eight weeks, and the resulting humus may be dug out and utilized to
fertilize garden crops. A new hole is dug at a minimum distance of one
metre (39 in.) away from the first pit and is used in the same manner.
The trench latrine operates under the same principle as the fezdIkes,
i.e., the excreta are deposited in the top layer of the soil, in which the
aerobic saprophytic bacteria are most numerous and active and reduce
the offensive material in the shortest possible time (seep. 25 “ decomposition
of excreta “). The trench is often dug to a depth of 60 cm (24 in.), which
is acceptable from the biological standpoint, with a length of about
l-3 m (3-10 ft).
While the trench latrine is designed for temporary use only in such
places as military bivouacs, scout camps, temporary building or mining
EXCRETA
DISPOSAL
FOR RURAL
AREAS
FIG. 58. A “ FEUILLEE”
Measurements shown are in centimetres.
A = Flow of urine over the ground or in a furrow
B = Fiat stones forming foot-rests
C = Loose earth used for covering faeces
sites and similar locations, feuiZZ&esare used as a permanent measure in
rural and suburban areas, and even in urban areas of large towns, especially
in Africa. The Bureau Central d’Etudes pour les Equipements d’outreMer, Paris, France, in a publication dated February 1955,16describes one
type of feuiZZt!esapplicable to soft ground (into which they are dug) and
another type applicable to hard soil (over which they may be installed).
An improved type has also been designed by this French government
office and is described by M&decin-G6nkal Sanner 31 as follows :
“ The system includes [Fig. 581 :
“ (a) a pit 0.60 x 0.40 x 0.40 m (24 x 16 x 16 in.);
“ (b) above the pit a Turkish-type squatting plate provided with two foot-rests, two
handles, one hole, and one gutter to divert urine towards a small pit or a drain ;
“ (c) a rought superstructure ;
“ (d) an open box or pitcher full of loose earth.
‘* When the pit is full, it is covered with an iron sheet held in place with four stakes
(against animals, rain run-off, and soil pollution with worm larvae) ; and the squatting
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
113
plate and superstructure are moved over another hole. After six to eight weeks, the iron
sheet may be removed, the faeces having been transformed into humus and pathogens
having been destroyed. Squatting plates of this type may be built of wood, metal, or
concrete. They could be mass-produced and given away to poor communities following
proper health educatiori of the people as to their use.” [Trans.]
Advantages and Disadvantages
Feuillbes and trench latrines offer serious disadvantages and health
hazards for villagers and rural communities as a whole. The improved
type of jhui&!es described above might constitute a considerable sanitary
improvement and might be used in rural areas if the people could reasonably
be expected to observe faithfully the few steps involved in the latrine’s
construction and operation, especi&y the step which prescribes the covering
of the full pit with an iron sheet for a period of two months. General
experience with respect to hole covers in latrines, the maintenance and
operation of the bucket latrine system, and the possible alternative uses
of sheet metal in villages leads one to believe that, despite routine inspection
and supervision, the full pits would not be kept covered in the majority
of instances.
The most significant hazards caused by these latrines are :
(la) the inevitable pollution of the soil surrounding the feuillkes or
the trench latrine, since there is virtually no protection against the access
of worm (especially hookworm) larvae to the ground surface ;
(b) the breeding of flies in enormous numbers, and the access of flies
and animals to uncovered or lightly covered faeces in the pits ;
(c) the danger of pollution of both surface and ground water ;
(d) the easy access to and scattering of the material by rodents and
other animals.
To these may be added the odour nuisance and, from the aesthetic
point of view, the unsightly conditions generally attached to these types
of latrine. On the credit side, it may perhaps be said that they are easy
and cheap to build and fit in well with the primitive habits of village folk
in many areas. However, in countries where they are used, the cost of
sickness and debility and the losses of productive power and of life-capital
through premature death generally are a heavy burden not only on the
people concerned, but also on whole regions and their governments.
Often the actual value of these losses cannot be assessed. In one instance
at least, thefeuiZZ&essystem has shown how expensive it can be : in a large
city in Africa comprising densely populated suburbs where the @.dZ~e.s
had been adopted, chemicals (DDT, diazinon, etc.) were sprayed regularly
from the air, at a heavy cost to the health authorities, in an attempt to
reduce the enormous fly infestation over the whole city.
8
114
EXCRE3’A
DISPOSAL
FOR RURAL
AREAS
Both thefilrillres and the trench latrine occupy a place among excreta
disposal installations as temporary devices to be used by moving groups
of individuals for a few days at a time.
THE OVERHUNG
LATRINE
The overhung latrine consists of a superstructure and a latrine floor
built on top of wooden piles above water along the banks of rivers, ser:
beaches, or coastal flats. This type of latrine, which is found occasionally
around seaports and fishing villages in every continent, is very common
in large coastal areas of Asian countries. The severity of the health problems
raised by this system of excreta disposal was recognized by the participants
in the WHO-sponsored seminar on sewage disposal, in the report (1 on
which the following views were expressed :
Throughout Asia many people are forced to inhabit land areas that
are frequently or periodically covered with water. The coastal fishing
villages where, it is claimed, some adults have never set foot on solid
ground would be typical examples. For people living in raised huts with
cat-walks for streets, the problem of the disposal of human excreta has
rarely been given thought or attention. In the case of brackish rivers
or tidal fiats, drinking-water is difficult to obtain ; most of the inhabitants
rely on rain-water or carry well-water from some distance by small boats.
T!!e health hazards under such conditions are difficult to evaluate, especially
in the light of the existing knowledge of the epidemiology of certain
environmental diseases.
Under such circumstances a carefully located “ overhung ” or “ drop ”
latrine might be the only measure which could be applied. Such a latrine
might be acceptable, provided the following general conditions are met :
(1) the receiving water is of sufficient year-round salinity to prevent
human consumption ;
(2) the latrine is installed over such water depth that the bed is
never exposed during low tide or the dry season ;
(3) every effort is made to select a site that will provide for carrying
floating solids away from the village and will furnish dilution ;
(4) there is a stream flow of 14 1 (0.5 cu. ft) per second per family
for adequate dilution ;
(5) the walkway, piers, squatting openings, and superstructure are
made structurally sa.Gefor adults and children.
0 Report on Seminar on Sewage Disposal (Rural and Urban). Kandy,
issued by the WHO
Regional
Office for South-East
Asia.
New Delhi)
Ceylon.
1955 (Report
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
115
There was reluctance on the part of the seminar participants to give
support to this technique, however. This reluctance was based on :
(a) the relatively long survival rates of pathogenic organisms in fresh
and brackish tropical waters ;
(b) the universal habit of prolonged contact with water in bathing
and fishing; and
(c) the possibility that the practice of using this type of latrine would
become established upstream, where it would empty into smaller and
fresh-water courses.
Such latrines should be considered only in places where the conventional
terrestrial type cannot be built. (It is recognized, however, that reluctance
to accept the overhung type of latrine, when properly situated and constructed and discharging into a stream or harbour of sufficient flow, is
not entirely consistent with the accepted practice of urban sewage disposal
by dilution.)
It should be stressed that the practice of drinking from any surface
stream in the populated areas of Asia is not safe at present, and that
surface waters are expected to become progressively more contaminated
as cities and towns become more highly developed and populated.
THE COMPOST
PRIVY
Use of Night-Soil as Fertilizer
The use of night-soil as soil fertilizer has been sMied by several
scientists, in particular by Gotaas la and Scott 99 in recent p*.tblications.
Scott states that in many countries of the Western Pacific “ fdecal-borne
diseases are very definitely related to agricultural practices in that nightsoil is used as fertilizer “. Both authors point to the important relationship
between sanitation and agriculture in all parts of the world and review
modem composting methods which are capable of producing a safe and
valuable fertilizer from mixtures of human and village wastes. Many
investigations cited by these authors have shown that pathogenic bacteria
and worm eggs are unable to survive temperature conditions and biological
antagonisms prevailing during composting processes. In rural areas where
from time immemorial excreta have been used by the farmer, it is recommended that health authorities work hand in hand with those concerned
with agriculturaI development in order to solve the problems involved
in the safe utilization of human wastes.
As has been previously noted, one problem which has not yet found
a satisfactory solution is the collection and transport (i.e., handling) of
116
EXCRETA
DISPOSAL
FOR RURAL
AREAS
night-soil from the latrine to the cornposting site. The health hazards
involved in these operations are considerable, not only for the scavenger
group, but also for the whole community ; and they cannot be ignored
by either health or agricultural authorities. Because of these hazards,
modern composting procedures, which would make possible the recovery
of the vast amounts of plant nutrients contained in human faeces and urine
cannot yet be applied everywhere.
In urban areas of many countries, pit privies, vault and aqua privies,
and septic tanks are periodically emptied by mechanical means, generally
by use of a closed metal tank, carried by a truck, into which the liquid
and semi-liquid faeces are pumped. The truck may even carry the water
necessaryfor liquefying the solid contents of the latrines. Such an operation
is, of course, expensive in initial cost and not readily applicable to every 1
rural area of the world.
The collection and transportation methods involved in the so-called
conservancy or bucket-latrine system cannot be recommended, for reasons
already discussed. There is a great need for further research and field
experiments to discover an economical and adequate solution to this
sanitation problem. It is very likely that, when such a solution is found,
human wastes from over a billion rural inhabitants will be returned to
the soil to fertilize it for the benefit of mankind.
Description and Operation of the Compost Privy
A reasonably safe way for a villager to prepare exzreta for us: as
fertilizer is for him to compost it in a privy pit. After the required period
of composting, the pit can be emptied, thus eliminating the handling of
the raw excrcta.
The privy pit, slab, location, hetnd other features would be no different
from those described above (pp. 42-68) for the pit privy. However, the
compost privy should be provided with the largest possible capacity
so that it will not fill too fast. For this reason it may be necessary to
enlarge the cross-section of the pit. This may be done by using a large,
four-part, concrete slab as shown in Fig. 28, or by giving the pit an oblong
qhape, in which case part of the vault extends outside of the superstructure
and is covered with a tight-fitting and durable cover. A pit 80 cm (32 in.)
wide, 1.80 m (6 ft) long, and 2.50 m (8 ft) or more in depth may be used
for the compost privy.
The method is a modification of the Bangalore cornposting process l8
and is based on anaerobic decomposition rzf organic wastes which are
left undisturbed during a period of at least six months to ensure destruction of pathogens and ova of helminths. The procedure would be
as follows :
THE
PRIVY
METHOD
OF EXCRETA
DlSPOSAL
117
1. Dig a pit of required size, the bottom of which should always be
above ground-water level.
2. Before the slab is placed, cover the bottom 50 cm (20 in.) of the
pit with grass cuttings, fine leaves, garbage, paper, etc. ; but allow no
rubbish such as metal cans, glass bottles, or similar materials to be deposited
therein.
3. Place slab, and complete superstructure, keeping in mind that
they will both be moved periodically to another site.
4. In addition to depositing human excrement, throw the daily garbage
into the pit, along with cow, horse, sheep, chicken, and pig manure, as
weli as urine-soaked earth or straw. The latter materials are important,
as urine is rich in nitrogen, an essential plant nutrient.
5. About once a week throw a few kilograms of grass clippings and
fine-texture leaves into the pit. After some experimentation, one can
arrive at a pit mixture which will provide a good fertilizer.
6. When the pit’s contents reach a. level 50 cm (20 in.) below ground,
a new pit is dug 1.50-2 m (5-6.5 ft) away (more if desired), and the superstructure and slab are moved over it. The first pit is levelled, finally,
with 15 cm (6 in.) of grass clippings and leaves, and the top 35 cm (14 in.)
with well-tamped earth.
7. When the second pit is filled as indicated above, the first pit is
uncovered and the compost removed. It should be stable, and will provide a good fertilizer which can be applied immediately to the fields
or stored.
The volume of the pit depends on the needs for fertilizer and the number
of people using the privy. The proportion of night-soil that can be added
to refuse for satisfactory composting should be about 1 to 5 by volume.18
From the data given above (pp. 43-48), it will be noted that a family of five
will produce, on the average, one cubic metre (35 cu. ft) of partly digested
excreta in about four years. On this basis, one-fifth of a pit of one cubic
metre (35 cu. ft) capacity would be filled with excreta in approximately
9-10 months, which would be a good composting cycle for such a pit.
(The other four-fifths of the contents would consist of refuse and other
wastes thrown in as explained above.)
Before applying or recommending this method in a rural area where
it is not familiar, it is desirable to try it first on a pilot scale under adequate
control in order to determine the proper operating schedule and materials
suitable and available in the area under consideration. The collaboration
of agricultural officials and of local leaders among the farmers of the
area is necessary.
To obviate moving the superstructure and slab back and forth over
two separate pits, the system may be amended by building what may be
118
EXCRETA
DlSPDSAL
FOR RURAL
FIG. 59. DOUBLE-VAULT
AREAS
LATRINE
Sectlon a-a
Measurements shown are in centimelres
A = Two vaults
6 = Squatting
C = Removable
slabs
covers
D = Step and earth mound
I
Section b-b
called a “ double-vault ” latrine (see Fig. 59). This latrine consists of
a large vault divided into two compartments, each of which is topped
by a slab and a hole. The superstructure is likewise partitioned into
two houses with separate entrances. In practice, the vaults are filled
and emptied alternately in the same manner as described above for
the compost privy. They should be large enough to allow sufficient time
for the materials to compost thoroughly before their removal. The vaults
need not be water-tight but should be built well above the ground-water
THE
PRIVY
METHOD
OF EXCRETA
DISPOSAL
119
table. The difficulty with the double-vault privy is that often both compartments are used simultaneously, thus defeating their purpose. Constant
inspection and advice by health and agriculture staff are necessary.
Advantages and Disadvantages
Proper composting in privy pits is rather complicated and may well
be, in the beginning, beyond the comprehension of most rural families.
Close supervision by health and agriculture officials and systematic education
and follow-up are required during the first two or more years of application.
Furthermore, privy pit composting is not free of hazards and requires
attention. Proper placement is essential to prevent pollution of ground
water supplies and the entrance of water into the pit.
Under proper conditions of operation, this method will satisfy most
sanitary requirements laid down on page 39. It is, of course, somewhat
more expensive than the ordinary pit privy since it involves the construction
of two or more pits. One further disadvantage is the loss of a portion
of the liquids (especially urine), which seep away into the ground, carrying
with them nitrogenous matter held in solution. However, it offers a
reasonable means of conserving most of the fertilizing value of excreta
with a minimum of health risks.
THE CHEMICAL
TOILET
Description
The chemical closet consists of a metal tank containing a solution of
caustic soda. A seat with cover is placed directly over the tank, which
Is ventilated by a flue rising through the house roof (see Fig. 60). The
tank is made of a special steel alloy capable of withstanding corrosion
and has a capacity of about 500 1 (110 Imp. gal.) for each seat served
by it. A charge of 11.3 kg (25 lb.) of caustic soda dissolved in 50 l(l1 Imp.
gal.) of water is applied to the tank for each toilet seat. The excreta
deposited in the tank are liquefied and sterilized by the chemical, which
also destroys all pathogens and worm eggs. To facilitate this action, the
tank is usually provided with an agitator which helps to break the solids
and to speed their disintegration by the chemical. After several months
of operation, the spent chemical and the liquefied matter are drained
or removed and are deposited in a leaching cesspool, suitably located.
This toilet is non-odorous and suitable for use inside dwellings, isolated
houses, schools, etc. It is also employed in the form of a movable commode
of about 40-l (9 Imp. gal.-) capacity on boats, aircraft, motor caravans,
120
EXCRETA
FIG. 60. CHEMICAL
DISPOSAL
CLOSET
FOR RURAL
AREAS
and other vehicles. It is oIYz;~~!;~,
from commercial establishments and
is fairly expensive in initial cost and
in operation.
Advantages and Disadvantages
With proper operation the cheinical toilet is a very satisfactory
type of excreta disposal installation which fulfils all sanitary and
aesthetic criteria. It has the further
advantage that it can be placed inside the dwelling.
The primary disadvantage is its
price and the recurring cost of the
chemical. It does require attention
A=
Closet seat inside house
B = Tank containing solution of caustic soda
and will not stand up to abuse.
C = Ventilation flue
Only toilet paper (and no other
D = Inspection opening
rubbish) should be thrown into it.
E = Drain
If poorly operated and maintained,
which is usually the case when the
chemical is spent and not immediately replaced, there are odours and an
increasing amount of floating matter over the liquid contents of the tank.
For these reasons, the chemical toilet cannot be used at present in most
rural areas of the world.
WATER-CARRIED
METHODS OF
EXCRETA DISPOSAL FOR RURAL
AREAS
SOME PROBLEMS IN THE DISPOSAL
OF WATER-BORNE WASTES
General Considerations
Experience has shown that, when running water is available, the watercarried system of excreta collection and disposal is most satisfactory and
convenient under both urban aud rural conditions. It fulfils all sanitary
and aesthetic criteria. In particular, contamination of the soil and of
surface water is avoided ; potentially dangerous wastes are rendered
inaccessible to IIies, rodents, and domestic animals ; and the mechanical
transmission of faecal-borne diseases to man is prevented.
One serious disadvantage, however, is the difficulty of disposing of
the large volume of wastes resulting from the addition of water. While
in cities the liquid wastes are usually carried away by means of sewers,
in most rural areas of the world sewerage systems do not exist, and liquid
wastes are conveniently discharged into the ground. Since in such areas
ground water is often tapped as a source of domestic water-supply, there
is an obvious need for proper location and construction of the excreta
disposal system, with a full understanding of the hazards involved (see
p. 32).
Such a situation is frequently found in suburban areas, in which case
the possibilities of linking up the drainage of these areas with the public
sewerage of the near-by town should Grst be investigated. Individual
waste disposal is often more costly and troublesome in the long run than
public sewerage. In densely populated rural areas of some countries in
Europe and North America, the sewerage problems of communities sufficiently close to each other have been solved through the creation of special
“ sewer districts ” administered in common by the municipal authorities
concerned.
In developing ruraI villages and communities with scattered dwellings,
it may be desirabIe for the local government to take the initiative and
responsibility in order to ensure the adoption and construction of the
most satisfactory installations, keeping in mind future conditions in the
-
121 -
122
EXCRETA
DISPOSAL
FOR RURAL
AREAS
developed and fully inhabited areas. In some instances, the government
may decide to undertake the planning, construction, management, and
supervision of the individual sewage disposal systems This procedure
is not recommended for application in rural areas, for reasons already
explained. However, satisfactory waste-disposal will be achieved by
individual families if the local health authorities are prepared to supply
the necessary guidance and the continued attention and supervision after
the facilities are installed.
Various methods may be used in rural areas to dispose of liquid wastes.
They include disposal by dilution in large bodies of water, the use of
cesspools and seepage pits, and the septic-tank systems, which involve
settling tanks with single or multiple compartments followed by subsurface
irrigation fields, filter trenches or sand or trickling filters. Sdection of
methods will depend primarily upon the degree of sewage treatment to
be provided, upon the location of the system and other local factors,
and, finally, upon costs. Local factors which bear upon the selection
and design of the disposal installation include, among others, the nature
of soil formations, the presenceand levels of ground water and the direction
of flow, topography, the proximity of sources of water supply, the quantity
of sewage, and the area available for the disposal works.
Disposal by Dilution
Where large bodies of surface water, such as the sea, lakes, or large
rivers, are available nearby, the liquid wastes from dwellings or communities may be discharged into such waters directly or after septic-tank
treatment only. The outfall pipe conveys the sewage to a point well below
the lowest water or sea level, preferably near the bottom of the receiving
water, in order to ensure adequate dilution of the warmer and lighter
sewage, which will normally rise and disperse through the diluent water
body.
This system of disposal is designed to take advantage of the natural
ability of water for self-purification, which is based primarily on the availability and amount of oxygen in solution in the receiving water. This oxygen
reacts with al;d stabilizes the organic matter in the sewage by oxidation.
If there is not enough oxygen in the receiving water or if the volume of
this water is too small to supply the quantity of oxygen required, anaerobic
decomposition will begin and proceed at such a pace that the normal
biological balance of the water may be upset. As a result, the receiving
water will become foul and black, and its normal fauna (especially the
fish, which require oxygen to survive) will be totally destroyed.
Another hazard created by the disposal of sewage in this manner is
;he possibility of contamination of the receiving water with pathogenic
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
123
bacteria and the eggs and larval forms of harmful helminths, such as
those of bilharziasis and liver flukes. In rural areas where such water
is used for bathing, washing clothes, irrigation of foods to be eaten raw,
and other purposes, the dangers involved are obvious. This explains why
liquid wastes from rural dwellings, institutions, or communities should
never be discharged into public bodies of water without the permission
of local health authorities. Where the objective is simply the avoidance
of nuisance, health authorities usually prescribe the desirable ratio of
volume of sewage with respect to- the amount of receiving water. For
natural waters, the amount of sewage should not be more than onetwentieth to one-fortieth of the amount of water flowing.12* l3
The Cesspool
A cesspool is essentially a covered pit which receives raw sewage.
It may be of the water-tight or of the leaching type. In some cases,especially
in Europe, it is made water-tight and is designed to hold the liquid wastes,
which must be removed periodically, about every six months. The leaching
cesspool, on the contrary, is dug into pervious soils in order to allow the
liquid portion of the waste to seep off into the ground. The solids then
accumulate in the pit and gradually seal the pores of the ground.
Water-tight cesspools are usually designed for a capacity of 68 l(l5 Imp.
gal.) per person per month, or 408 1 (90 Imp. gal.) per person when they
are emptied every six months .% Leaching cesspools have diameters of
90 cm (36 in.) or more, and are provided with an open-joint lining below
the inlet level (see Fig. 61). The top part of the lining, which is within
60-90 cm (2-3 ft) of ground level, should be impervious and laid with
mortar. Covers with inspect’on manholes are usually provided. After
the pores of the ground become clogged and the pit fills, an outlet tee
and an overflow pipe lead the supematant liquid to a seepage pit.
As previously stated (p. 32), a cesspool should be located downhill
from a well ; in any case, a distance of 15 m (50 ft) will prevent bacterial
pollution of the well. To prevent chemical pollution, too, the distance
between a well and a cesspool placed directly uphill from it should be not
less than 45 m (150 ft)- Cesspools of the leaching type should be located
at least 6 m (20 ft) away from dwelling foundations. Their construction
is not permitted by health authorities in densely inhabited communities
where wells are used as sources of drinking-water supply.
The Seepage Pit
The seepage pit receives the eHuent from aqua privies, cesspools,
and septic tanks and allows it to percolate away into the ground. It is
sometimes used for the disposal of laundry, bathroom, and kitchen wastes.
124
EXCRETA
DISPOSAL
FIG. 61. CESSPOOL
--__
-- _ ~- .A=
B =
C =
D =
E
F
G
H
I
=
=
=
=
=
-~
~.
-
FOR RURAL
LINED
A
-___--
WITH
LARGE
AREAS
STONES
-__~~.-.-_
““9 ,,*o
Measurements shown nre in centimetres.
Ground water
Depth 2 m (7 ft) or more to pervious soil
Inlet pipe
Outlet pipe to another cesspool. This pipe serves only when first cesspool is clogged and
stops working
%-cm &-in.) layer of coarse gravel
Inspection manhole, 50 x SO cm (20 x 20 in.)
Stones laid without mortar
Stones laid with mortar
Ground level
In the latter case, a grease trap may be necessary on the house sewer-line.
The seepagepit may also be built at the lower ends of subsurface disposal
tile lines in order to catch the septic-tank effluent which may have gone
through without percolating away.
As shown in Fig. 62, the s=-~--~
cry’+ pit consists merely of a round hole
in the ground dug deep enough to penetrate 1.8 m (6 ft) or more into a
porous layer of the earth. Diameters of l-O-2.5 m (39-100 in.) and depths
of 2-5 m (7-l 6 ft) are common. The side walls are lined with bricks or
stones laid without mortar below the level of the inlet pipe. The hole
may be filled with stones, in which case a lining is not required. The
seepage pit should be closed with a tight cover which will prevent access
to mosquitos and flies and to surface water as well.
If the soil through which the pit has been dug is not sufficiently porous,
the effluent will slowly accumulate and will ultimately overflow. Even
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
125
in porous soils such a situation is common, as the pores of the earth walls
become choked by the deposit of the finely divided matter carried by the
effluent and by the solids built up by the life activities of zoogloeal organisms
which thrive on the grains of the
soil in contact with this effluent.
FIG. 62. SEEPAGE PIT
These phenomena, in fact, govern
the life span of a seepage pit, which
should normally last for several
years (perhaps 6- 10 years) if the
effluent is only slightly turbid as a
result of efficient primary treatment
of the raw sewage.
When a seepage pit ceases to
operate, a new one should be dug
u
several metres away. In order to
increase the life span of the disposal system, it is possible to dig
two or three seepage pits and to
connect them at the top. The distance between any two pits should
be at least three times the diameter
of the larger pit.
The obvious disadvantage of
seepage pits is the danger of polA=
Variable depth of soil
lution of ground water. For this
B = Cement joints
reason they should be carefully
C = Open joints
D = Rock fill, 15 cm (6 in.) or more
located ; the general rules governing
their location have already been discussed (p. 32). It will be recalled here that seepagepits should preferably be
located downhill and, in any case, at least 15 m (50 ft) away from drinkingwater sources and wells. As in the case of cesspools, the construction of
seepage pits is not usually permitted by health authorities in cloezly built
communities where ground water is used for domestic purposes.
THE SEPTIC TANK
The septic tank is the most useful and satisfactory unit among all
water-carried systems of disposal of excreta and other liquid wastes from
individual dwellings, smi;ll groups of houses, or institutions located in
rural areas out of reach ol sewer systems. It consists of a covered settling
tank into which the raw sewage is led by the building sewer (see:Fig. 63-65).
The processes which take place inside the septic tank constitute the
126
EXCRETA
DISPOSAL
FOR RURAL
AREAS
“ primary treatment ” of the raw sewage, and those which occur in the
disposal field form the “ secondary treatment “. It should be noted that
all liquid wastes, including those from bathrooms and kitchens, may be
sent to the septic tank without endangering its normal operation. Recent
research has shown that, contrary to former belief, s&age wastes can
and should be discharged into septic tanks.
FIG. 63. TYPtCAL
A=
B =
C =
D =
E =
F =
G =
LAYOUT
OF SEPTIC-TANK
Private house or public institution
House sewer
Building sewer
Grease interceptor on pipe line from kitchen
Manhole
Septic tank
Dosing chamber and sit hon
H
I
J
K
L
M
N
=
=
=
=
=
=
=
SYSTEM
Pipes laid with tight joints
Distribution
box
Drop-boxes or terracotta L’s
Absorption tile lines
Seepage pit, when required
Slope of ground surface
Topographic
contour lines
WATER-CARRIED
METHODS
FIG. 54. TYPfCAL
OF EXCRETA
HOUSEHOLD
A
B
C
D
E
F
G
H
I
J
K
=
=
=
=
=
=
=
=
=
=
=
SEPTIC
127
DISPOSAL
TANK
inlet
Outlet
Baffie
Floating scum
Sludge
Scum-clear space
Sludge-clear space
Depth of water in tank
Clearance
Depth of penetration of baffle
~~,mb$
of baffle to wall, 20-30 cm
L = Top of baffle 2.5 cm (1 in.) below roof
for ventilation purposes
M = Tank covers, preferably round
N = Ground level, less than 30 cm (12 in.)
above tank (if less, raise tank covers to
ground surface)
The Biological Processes Involved
Primarpeatment
stage
In the tank, the incoming sewage is held quiescent, being retained for
a period of one to three days, according to the tank capacity. During
this period the heavier solids settle to the bottom as sludge. Most of the
lighter solids, including grease and fats, remain in the tank and form a
scum over the water surface, while the rest is carried away by the effluent
into the final disposal system.
The solids which are retained in a septic tank undergo anaerobic
decomposition through the activity of bacteria and fungi. The significant
result of this process is a considerable reduction in the volume of sludge,
FIG. 655. SEPTIC
A=
6 =
c =
6 =
TANK
WITH
TWO
COMPARTMENTS
Inlet compartment
Outlet compartment
Dosing chamber
Manhole covers (raised when earth cover
AND
DOSING
CHAMBER
D = Dosing siphon
E = Drawing depth of liquid
F = Discharge pipe
greater than 3g cm (12 in.) )
128
EXCRETA
DISPOSAL
FOR RURAL
AREAS
allows the tank to operate for periods of one to four years or more,
depending upon circumstances, before it needs to be cleaned. This
decomposition involves not only the sludge, but also the dissolved and
colloidal organic content of the sewage.
The effluent of a properly designed and efficient septic tank is only
slightly turbid, due to finely divided solids in suspension, and has a relatively
low biochemical oxygen demand (BOD). However, it is still offensive
in character ; on standing, it yields little sediment but has a characteristic,
putrid odour. In addition, this effluent is potentially dangerous to health, as
it may contain pathogenic bacteria, cysts, and worm eggs which have passed
unharmed through the tank during the relatively short detention period.
As the sludge decomposes, gas is produced and constantly rises to the
surface as bubbles. The gas bubbles carry with them particles of decomposing organic matter which inoculate the incoming sewage with organisms
which are necessary for putrefaction. These particles reach the scum
which, in time, becomes thick and heavy and partly sinks below the water
level. The floating cover of scum may attain such dimensions that its
lower surface extends into the main sewage current. This usually coincides
with a thick accumulation of dense and compact sludge over the bottom
of the tank. As a result, the flow-through section becomes so small that
adequate sedimentation of the suspended matter is no longer possible.
At that time large amounts of floating matter will be noticed in the effluent.
This condition can be prevented by regular cleaning of the tank.
The bubbling of gas through the liquid interferes to a certain extent
with the normal sedimentation of sewage solids. This interference may
be minimized by the addition of a second compartment to the septic tank.
The lighter, suspended solids carried from the first compartment find
quieter conditions for settling in the succeeding compartment. This is
especially valuable at times of rapid anaerobic decomposition when sludge
solids are found in greater quantity in the tank’s first compartment. The
sludge in the succeeding compartment is usually more homogeneous and
flocculent than that in the first compartment, and there is also less scum
production. The efl8uent of such a tank will contain a lower proportion
of suspended matter than that from a single-compartment system.
For the efficient development of the biological processes, turbulence
should be avoided, and the disturbing effects of surge flows should be
reduced to a minimum. Turbulence and surge flows may be so serious in
small or overloaded tanks as to cause a complete breakdown of tank operation and of secondary-treatment processes. The space available for clarification in the larger tanks has a certain compensatory or equalizing effect.
~a order to ensure and to speed up the establishment of the biological
processes at a high level of efficiency, newly constructed septic tanks are
usually seeded with a quantity of ripe sludge bailed out from another
tank already in operation. This sludge, which is in an advanced state
which
WATER-CARRIED
METHODS
OF
EXCRETA
DISPOSAL
129
of decomposition, provides the bacteria and fungi necessary for rapid
alkaline fermentation, which succeeds the initial breakdown of the raw
organic matter by anaerobic bacteria. The addition of yeast is not effective
in starting digestion in a new tank or in rejuvenating a sluggish tank.
Secondary-treatment stage
The secondary treatment of septic-tank effluent is based on the oxidation
of organic matter through the activity of aerobic bacteria. These bacteria
thrive in the upper layers of the soil and in sand or stone beds whose pores
are naturally aerated by oxygen from the air. In subsurface irrigation
and in filter beds, the effluent is spread as uniformly as possible over the
grains of soil or sand, or over small stones. A biological slime develops
in which the aerobic bacteria and micro-oraganismsare active. It is important
that these biological media should not be overloaded or submerged for
any great length of time, * otherwise, the aerobic bacteria will die and
anaerobic conditions will develop. In larger installations, aeration is
achieved by intermittent dosing by means of a dosing siphon installed
next to the septic tank. In this way, the soil or filter bed recuperates,
and air penetrates anew in the interstices of the filtering medium during
the intervals between flushes of the siphon. Natural aeration of the soil
is facilitated in the case of filter trenches through the drain pipes and, in
the case of subsurface irrigation, through a vent pipe or seepagepit installed
at the lower end of the disposal field.
Ventilation of the filtering medium may be arrested if the pores are
allowed to become clogged by suspended matter carried by the effluent
or by excessive slime growths. In either case, the trouble may be traced
to defective or inefficient operation of the septic tank itself, although
excessive slime growth may also be due to overloading of the disposal
field. In subsurface irrigation in particular, the need for efficient primary
treatment and. a clear effluent is greatest. Of course, much depends upon
the porosity of the soil, fine-grained sand being best from the standpoints
of both permeability and ventilation ; impervious soils, such as clay, are
totally inappropriate. Where ground water is close to the surface, it may
not be possible to dispose of the effluent through subsurface irrigation,
since the pores of the soil above the water table are clogged with water
held by capillary action. Experience shows that tile pipes should not be
laid closer than 90 cm (3 ft) to the ground-water level.
Design of the Septic-Tank System
The grease interceptor
Liquid wastes from large kitchens, such as those found in hotels, small
hospitals, and similar institutions, are likely to contain much grease, which
9
130
EXCRETA
DISPOSAL
FIG. 66. TYPES
FOR RURAL
OF GREASE
AREAS
INTERCEPTOR
/ /--,
/L,, _
v;:
\ ,-3
‘\ --’
-0
Plan
Section
\
’
((7
,.lJ
//
-
Plan
Section
WHO 7'+70
Adapted, by permission, from Mannal of septic-tank practice.37
Measurements shown are in centimetres.
may pass through the septic tank along with the effluent and may clog
the pores of the filtering medium of the disposal field. In such cases, a
grease interceptor is installed outside the building just before the building
sewer (see Fig. 66). It is designed as a small skimming tank provided with
submerged inlet and bottom outlet. Its operation is based on the principle
that the incoming liquid waste is warmer than the sewage already in the
interceptor and is cooled by it, causing the grease content to congeal and
rise to the surface, from which it is skimmed off and disposed of by burial
at periodic intervals. For this reason, grease interceptors should be easily
accessible for inspection and cleaning.
Grease interceptors are not considered necessary in sewage disposal
systems for dwellings and other small installations. Their size depends
on the type of building and the volume of sewage to be handled. For
a single-family dwelling (when it is desired to install one), the interceptor
capacity should be about 110 1 (30 US gal.) .*% Other interceptors should
preferably have a capadty equal to five times the volume of waste water
that is liable to be discharged into them at any one time.% They may
be constructed of metal, brick, vitrified or concrete pipe, or concrete. The
inlet and outlet should be placed as far apart as possible in order to avoid
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
131
a direct flow between them, and the depth below the outlet flow line should
not be less than 60 cm (2 ft).
The building sewer
The U.S. Joint Committee on Rural Sanitation 38 has the following
recommendations to make :
“ The building sewer is that part of the horizontal piping of a building drainage
system extending from a point usually 5 feet [1.50 m] outside the inner face of the foundation wall to the public sewer connection or individual sewage disposal unit (septic tank,
cesspool, or other type of disposal).
“ The building sewer should be constructed of bell and spigot pipe made of cast iron,
vitrified clay, concrete, or other durable material. Portland cement mortar or bituminous
compounds should be used for all joints on pipe lines other than cast iron ; lead or other
suitable joint material should be used on all cast-iron pipe lines. Where the septic tank
or primary unit of the disposal system is located within 25 feet [7.50 m] of the building
or dwelling, it is desirable to construct the building sewer of extra heavy cast-iron pipe
throughout its entire length because cast-iron lines are less susceptible to clogging and
are easier to clean. Vitrified clay or concrete pipe should not be used in sizes smaller
than 6 inches [15 cm]. When cast-iron pipe is used in the building sewer it may be the
same diameter as that of the building drain, provided that it is not smaller than 4 inches
[lo cm] in diameter. Whenever the building sewer is a different size than the building
drain the connection therewith should be made with the proper type increasing’fittings,
assuring a watertight joint and satisfactory construction to eliminate clogging at the
connecting point.
“ All joints on the building sewer should be made by using a ring of oakum (jute)
and such joint material to provide water tightness. Whenever the building sewer line is
laid within root-growing distance of large trees or dense shrubbery and constructed of
material other than cast-iron pipe with lead-caulked joints, the joints should be made
with a bituminous compound or other root-proofing material. Special copper rings may
be used with cement mortar or the cement mortar may be treated with copper sulfate or
coarse salt to prevent roots penetrating the joints, entering the pipe line, and eventually
clogging the sewer.
“ The most essential features to be observed in construction of the building sewer
line are as follows :
” 1. Minimum size of pipe : 6 inches [15 cm] if sewer is of vitrified clay or concrete,
4 inches [lo cm] if sewer is of cast iron.
“ 2. Minimum grade-l percent . . . However a fall of [2 percent] is preferable
and should be provided wherever feasible.
“ 3. Grade of building sewer for 10 feet [3 m] immediately preceding the tank
should not exceed 2 percent approximately . . .
“ 4. Cast-iron pipe with lead or other comparable joint material used when within :
50 feet [15 m) of a well or suction line from a well.
10 feet [3 m] of any drinking water supply line under pressure.
5 feet [1.50 m] of basement foundations, and when laid tzneath driveways with
less than 3 feet [90 cm] of earth cover.
“ 5. Cleanout at every change in line of 45” or more and at every change in grade
in excess of 221/2O.Bends of 90“ should be avoided wherever possible or such bends made
with two 45” ells or a long-sweep quarter curve. (Cleanouts are desirable within 5 feet
[1.50 m] of the septic tank where tanks are located more than 20 feet [6 m] from the
building. An economical cleanout may be provided by inserting a tee in the line with
132
EXCRETA
DISPOSAL
FOR RURAL
AREAS
the vertical leg extending to ground level and plugged with a brass cap. If the line is
deeper than 4 feet 11.20 m], manhole construction should be required for cleanout
purposes .)
“ 6. All joints made watertight and protected from damage by roots wherever
necessary.”
The tank
A review of the literature shows a multiplicity of designs adopted in
various countries for septic tanks. Many of the designs recommended
for dwellings and small institutions are cumbersome and complicated
unnecessarily by the provision of special features claimed to achieve a
better effluent. As a result of extensive research carried out between 1947
and 1953 by the United States Public Health Service,3l 3Q.4o most of the
problems involved in the design of septic tanks have been clarified. The
following information includes several of its findings, in addition to data
resulting from well-accepted practice in the USA,37 Europe,23 and elsewhere .2s
Size of tank
The principal factors to be considered in deciding on the capacity of
a septic tank are :
(a) the average daily flow of sewage ;
(b) the retenti.on period, from l-3 days, usually 24 hours ;
(c) adequate sludge storage, for desludging every 2-3 years.
The average daily flow of sewage depends on the average water consumption in the area under consideration. In rural areas and small
communities the water consumption per person is likely to be lower than
in municipalities. As a result, sewage flows of less than 100 1 (26 US gal.)
per person per day may be expected in most rural areas of the world.
However, experience indicates that such low figures cannot be used for
the design of small septic tanks, which should be provided with ample
capacity since such tanks are seldom cleaned before trouble develops.
It is therefore important that their capacity be ample to permit reasonably
long periods of trouble-free service and to prevent frequent and progressive
damage to the effluent absorption systems due to discharge of sludge by
the tanks. For this reason the capacity of residential, single-chambered,
septic tanks should not be less than 1900 1 (500 US gal.) below water-level.
The liquid capacities of the septic tanks described in Tables VIII and
IX are based on a sewage contribution of:
190 1 (50 US gal.) per person daily in dwellings ;
95 1 (25 US gal.) per person daily in camps ;
64 1 (17 US gal.) per person daily in day schools.
WATER-CARRIED
TABLE
VIII.
METHODS
OF EXCRETA
REQUIRED CAPACITIES
* FOR SEPTiC
SERVING
INDIVIDUAL
DWELLINGS
I
Mny..lN$
of persons
served
Recommended
Nominal
liquid
capacity of
tank (US gal.)
1
width
ft
in.
length
TANKS
dimensions
(
ft
133
DISPOSAL
in.
i$f
1
$?$,
ft
in.
ft
in.
4
4
4
4
4
4
4
0
0
0
6
6
6
6
5
5
5
5
5
5
5
0
0
0
6
6
6
6
-4
6
8
10
12
14
16
500
600
750
900
1100
1300
1500
3
3
3
3
4
4
4
0
0
6
6
0
0
6
6
7
7
8
8
10
:o
l
Liquid capacity based on number of persons
total depth includes air space above liquid level.
0
0
6
6
6
0
0
served in dwelling.
The volume based on
The capacities indicated in Table VIII should in most countries provide
sufficient sludge-storage space for a period of two years or more, and an
additional volume equal to the sewage flow for 24 hours.
It should be noted, however, that, in a few countries, small garbage
grinders are being installed more and more frequently in the kitchens
TABLE
Maximum number
of persons served
camps
day schools
IX. REQUIRED
CAPACITIES
FOR SEPTIC
SERVING
CAMPS AND DAY SCHOOLS
Recommended
y?$y
capacity of
tank (US gal.)
width
ft
in.
/
length
ft
TANKS
dimensions
/
in.
$$E
ft
/
$$$,
in.
ft
in.
5
6
6
6
6
6
7
7
0
3
3
3
6
6
0
0
-40
a0
120
160
200
240
280
320
60
120
180
240
300
360
420
480
1000
2600
3000
4000
5000
6000
7000
8000
4
5
6
6
7
8
8
8
0
0
0
.O
6
0
6
6
a
11
13
18
18
20
20
23
6
0
6
0
0
0
0
0
4
5
5
5
5
5
5
5
0
0
0
0
0
0
6
6
Note : Tanks with capacities In excess of 8000 gallons should be designed for the specific
requirements involved ; however, In such cases the necessity for a mote complete type of treatment should receive consideration,
134
EXCRETA DISPOSAL FOR RURAL AREAS
of dwellings for the purpose of grinding garbage or wastes, which
are then discharged into the house sewers. This adds an appreciable
load of settleable organic solids to the sewage and to the septic tank.
Where such grinders are used, the capacity of the septic tank should be
increased by 50% to allow for additional sludge-storage space.
The capacities shown in Table IX are based on a 24-hour flow of sewage
without allowance for sludge-storage space, since it is expected that septic
tanks serving camps and schools will receive regular inspection and maintenance, including more frequent cleaning than those for residences.
In the case of public institutions, such as rural hotels and hospitals!
and groups of houses, such as housing projects, the figures given in Table:,
VIII and IX may not apply. It will first be necessary to secure the advice
of a competent engineer whose duty it will be to determine the probable
daily water consumption and sewage flow, both of which are likely to be
much higher than the figures cited above. Most recent information indicates
that :
1. For flows between 1900 1 and 5700 l(500 US gal. and 1500 US gal.)
per day, the capacity of the septic tank should be equal to at least 1% days’
sewage flow.
2. For flows between 5700 1 and 37 850 1 (1500 US gal. and 10 000
US gal.) per day, the minimum effective tank capacity should be 4260 1
(1125 US gal.) plus 75% of the daily sewage flow, or :
V = 1125 + 0.75 Q, where
V is the net volume of the tank in US gallons, and Q is the daily sewage
flow, also in US gallons,
or :
V = 4260 + 0.75 Q, where
V is the net volume of the tank in litres, and Q is the daily sewage flow
in litres.
3. For flows greater than 37 850 1 (10 000 US gal.) per day, Imhoff
tanks may be more satisfactory than septic tanks for primary treatment.
Multi-compartmszt
tanks
Research by the US Public Health Service 3l 39*4o has demonstrated
that properly designed, multi-compartment, household septic tanks give
a performance as good as, or better than, single-compartment tanks of
the same total capacity. This is especially true of the smaller tanks. As
pointed out previously, the effects of fluctuations of flow and of surge
flows are disastrous to the efficiency of the primary-treatment processes
in small, single-chambered septic tanks. It is therefore desirable that
small household tanks, i.e., those serving, say, less than 20-25 persons,
WATER-CARRIED METHODS OF EXCRETA DISPOSAL
135
be provided with two compartments. The inlet compartment should have
a capacity of one-half to two-thirds of the total tank capacity, and the
liquid capacity of such an inlet compartment should be not less than
1900 1 (500 US gal.) for the minimum installation. For the larger tanks,
i.e., those serving more than 20-25 persons, the need for compartmenting
the tank will depend upon the degree of treatment required by local health
authorities and by the degree of permeability of the soil (where this applies).
The research cited above shows that there is not much to be gained by
an excessive number of partitions, and that a well-designed, single-chambered tank will result in a suspended solids removal efficiency of over 60%.
Outlet and inlet arrangements
Various outlet and inlet devices have been used in septic tanks. Recent
experimental research 3914o indicates that the baffle system or the arrangements shown in Fig. 64 and 65 are quite satisfactory and offer simplicity
and ease of installation. The depth of penetration of these devices into
the tank’s liquid is very important, as it influences the volumes of clear
space and of sludge accumulation. The research cited above shows that
for best results the outlet device should penetrate below the surface to a
depth of 40% of the liquid depth. In the case of horizontal, cylindrical
tanks, this figure should be reduced to 35%. The inlet baffle or tee should
extend 30 cm (12 in.) below water level.
Both devices should permit free ventilation through the tank and through
inlet and outlet pipes. They should extend at least 15 cm (6 in.) above
the water line and leave at least 2.5 cm (1 in.) clearance below the tank’s
cover for ventilation purposes. Baffles are usually placed 20-30 cm (812 in.) away from the inlet and outlet pipes, whose ends are flush with
the tank’s walls.
The invert of the inlet pipe should be at an elevation not less than
2.5 cm (1 in.), preferably 7.5 cm (3 in.), above water level. Connexions
between two compartments are best made by means of an ell whose
lower end does not penetrate into the liquid at a depth lower than the
outlet device.
\
Shape of tank
The shape of the tank is important inasmuch as it influences the velocity
of flow through it, the depth of accumulation of sludge, and the presence
or absence of stagnant corners. If the tank is too deep, the other dimensions
will be small, and a direct current from inlet to outlet will occur, greatly
shortening the retention period. If the tank is too shallow, however,
the sludge-clear space will be too small, and the effective cross-section of
the tank will be unduly reduced. When the width is too great, there will
be dead pockets of appreciable size at the corners where little, if any
136
EXCRJZTA DISPOSAL FOR RURAL AREAS
water movement takes place. Finally, if the tank is too narrow, the velocity
of flow will be so great as to interfere with efficient sedimentation.
Research 39 shows that “ in a two-equal-compartment arrangement, there
is no difference in performance between rectangular and cylindrical shapes,
if equal solids storage capacities are provided “. Rectangular tanks should
be designed with a length not less than two, but not more than three,
times the width. The liquid depth should not be less than 1.2 m (4 ft),
but not more than 1.7 m (5.5 ft) in the large tanks. Clearance above the
water level is usually 30 cm (12 in .)
Location of tank
The septic tank should be so located as to permit easy drainage from
the dwelling and to the effluent disposal system. When the latter makes
use of subsurface irrigation, the location of the tank should be such as
to ensure that sufficient area is available for disposal of the eflluent and
that tile !:es may be laid on a gentle slope and at a depth not exceeding
75 cm 0 in.) at any point.
Sine periodic inspections are necessary, the tank should not be buried
more than 30-45 cm (12-18 in.) below ground level. Inspection manholes
should preferably be extended to reach ground level. Precautions should
be taken to prevent the entrance of surface run-off into the tank.
Because of the possibility of leakage, especially around the inlet and
outlet pipes, the tank should be located preferably downhill and at least
15 m (50 ft) away from wells and other sources of water supply.
Construction of tank
Septic tank systems belong to the category of works which require
for their construction the direct assistance and supervision of engineers,
or at least of experienced construction foremen. No attempt will be made
to describe here in detail the steps which should be observed in the actual
construction of a tank in a rural community. The following information
and data may, however, be useful to the engineer entrusted with the
/
construction of these systems.
Tanks are usually built of concrete, a material which offers a guarantee
of strength and imperviousness. Sometimes the bottom and the cover
of the tank are made of concrete while the walls are built of bricks, cutstone, or cement blocks laid with rich cement mortar and plastered (on
the inside tank surface) with a 1 : 3 cement-sand mixture. A concrete
mixture of 1 : 2 : 4 cement sand-gravel containing 23 1 (6 US gal.) of water
per bag of cement (94 pounds or 43 kg) should be used. Concrete walls
and bottom should not be less than 10 cm (4 in.) thick, with adequate
reinforcement.
WATER-CARRIED METHODS OF EYCRETA DISPOSAL
137
The tank cover should be strong enough to withstand the weight of
earth cover and occasional extra loads. Sectional slabs may be used where
the tank is protected against surface water run-off. If not, the cover should
be cast monolithically with the walls and raised manholes provided. For
small tanks, one manhole placed above the inlet is sufficient. For large
tanks, two manholes-one above the inlet and the other above the outletare necessary. The minimum size of the manholes should be 50 cm (20 in.)
square or 61 cm (24 in.) in diameter.
The circular cover, although more difficult to build than the square
or rectangular cover, is sometimes preferred as it cannot fall through
the opening in the course of handling and tank-cleaning operations. In
an area in India where filariasis was a serious public health problem, it
was found that Culex fatigans, the local mosquito vector of the disease,
was breeding in many septic tanks in households and institutions owing
to the fact that the rectangular covers had fallen into the tanks through the
manhole covers along their diagonal axis at the time of cleaning and had
not been replaced.”
Concrete septic tanks can be pre-cast either monolithically or in small
parts at a central shop and erected quickly in the field. They are also
made commercially of metal to which a special coating is applied to prevent
corrosion.
Operation and Maintenance of the Septic Tank
As previously indicated, a newly built septic tank should first be filled
with water up to outlet level and then should be seededwith several (5 to 8)
buckets full of ripe sludge (or decomposing stable manure ripe enough
to give off an ammonia odour).
Although the designs recommended provide for desludging about every
two years or more, the tank should be inspected every 12-18 months in
the case of household installations, and every six months in the case of
tanks serving schools and other public institutions. The inspection should
be directed towards the determination of:
(a) the distance from bottom of scum to bottom of outlet (scumclear space) (see Fig. 64) ;
(b) the depth of accumulation of sludge over tank bottom.
The scum-clear space should not be less than 7.5 cm (3 in.), and the
total depth of scum and sludge accumulations should not be more than
50 cm (20 in.).
Sludge may be bailed out by means of a long-handled, dipper-type
bucket, or it may be pumped out by a specially equipped cesspool-emptying
0 Personal communication from Dr T. R. Rao. Assistant Director of Public Health
(Malaria). Bombay State, India
138
EXCRETA DISPOSAL FOR RURAL AREAS
vehicle. Where large tanks are provided with ‘bottom hoppers, cleaning
is sometimes done by flushin g and pushing the sludge out of the tank
towards a drying bed by the hydrostatic head available in the tank. Even
if care is taken, undigested sludge is likely to be removed also from the
tank in this way. On the other hand, digested sludge is fairly dense and
does not flow easiiy. This procedure is not recommended for application
in rural areas.
The scum and sludge removed from ordinary septic tanks will normally
contain some undigested portion which is still offensive and potentially
dangerous to health. Such sludge should not be used immediately as
crop fertilizer, but may be profitably composted along with other organic
wastes (garbage, grass clippings, etc .). Otherwise, it should be buried in
shallow, 60-cm- (2-ft-) deep. trenches. Provision should also be made
for‘more frequent (perhaps every 3 to 6 months) inspections of the
distribution box.
In a few instances, local health authorities may require that the effluent
from septic tanks or disposal fields be disinfected before discharge into
a small stream or public pond. This is especially true of hospital effluent,
which is likely to contain live germs of transmissible diseases. Chlorine,
as calcium hypochlorite, is commonly used for this purpose and is applied
by means of hypochlorinators.
Because of the need for regular, intelligent care to ensure the proper
operation of septic tank systems, it is desirable that some persons in the
rural community be instructed in thei; maintenance and repair. Local
health authorities should stimulate the formation of “ co-operatives ” or
the setting-up of private concerns willing to undertake the maintenance
work. These authorities should also stimulate requests from the people
for advice on septic tank construction and maintenance and should be
prepared to give technical guidance to all interested persons.
T,XE DISPOSAL
OF EFFLUENT
The quality of septic-tank effluent and the biological processesinvolved
in its purification have already been discussed. One conclusion +o be
drawn from this discussion is that septic-tank effluent should never be
permitted to run in canals and open ditches, or to be disposed over land
for the irrigation of crops or into small fishponds without the permission
of local health authorities.
In rural areas and small communities, the choice of methods available
for treating and disposing of the effluent is usually limited to (a) dilution,
(b) seepagepits, (c) subsurface irrigation, (n) filter trenches, (e) sand filters,
or (f) trickling filters.
I
WATER-CARRIED METHODS OF EXCRETA DISPOSAL
139
In order to be able to select the method which is mosL appropriate
to the particular location under consideration, it is necessary to determine
the nature of the ground, the depth of the ground-water table, the degree
of permeability of the soil, the proximity of wells and other water-supply
sources, the volume and the rate of renewal of surface water available for
dilution (in streams, ponds, and other bodies of water), and the uses made
of this surface water (e.g., water supply, fishing, bathing). Among other
factors to be considered are the land area available for the disposal works,
the proximity of houses, the prevailing directions of the wind, the vegetation
cover of the disposal land, and probable future extensions of the system.
The methods of disposal by dilution and by seepage pits have already
been described in connexion with the disposal of raw sewage (see
pp. 122-125).
Disposal by Subsurface Irrigation
This is the method most often employed in connexion with smali septic
tanks serving households and institutions. It consists simply of dispersing
tank effluent into the top layer of the ground by means of open-jointed
drain pipes laid in trenches and covered. In this way the effluent is purified
through the action of the aerobic saprophytic bacteria of the soil and
percolates away into the ground. It is obvious that this method cannot
be used where the subsoil is not porous, where the ground-water table
rises to within 1.2 m (4 ft) of the ground surface, or where there is the
danger of pollution of water supplies (in fissured limestone formations,
for example). In particular, it is not applicable in impervious clay soils
an’d swampy lands.
Percolation tests
In order to calculate the length of pipe required in the disposal field,
it is necessary to determine the degree of permeability of the soil by making
percolation tests. The method for performing such tests has been recently
improved as a result of numerous field investigations.3* 3gl4o The following
is quoted from Part III of Studies on household sewage disposal systems : 39
Percolation
Test Procedure
“ Because of the great number of factors that may affect a percolation test and the
variability that can be expected in the rate-time relationship, it appears unlikely that a
short-time procedure can be developed, applicable to all soils and all conditions.
“ It is thought best at this time to concentrate on developing a fundamental and
objective test procedure which can be applied to a wide range of soils and which, as has
been pointed out, would be essential in clay-type soils. Such a test would also be essential
where no experience with test methods or a particular soil is available. As experience is
gained, the test might be modified to suit local conditions. The fundamental test might
also be used to check modified procedures from time to time.
140
EXCRETA DISPOSAL FOR RURAL AREAS
“The following percolation test is suggested as a fundamental and objective procedure :
” 1. Ntunber and location of tests. - Six or more tests shall be made in separate
test holes spaced uniformly over the proposed absorption field site.
“ 2. Type qf test hole. - Dig or bore a hole, with horizontal dimensions of from
4 to 12 inches [IO-30 cm] and vertical sides, to the depth of the proposed absorption
trench. In order to save time, labor, and volume of water required per test, the holes
can be bored with a 4-inch [lo-cm] auger.
“ 3. Preparation of test hole. - Carefully scratch the bottom and sides of the hole
with a knife blade or sharp pointed instrument, in order to remove any smeared soil
surfaces and to provide a natural soil interface into which water may percolate. Remove
all loose material from the hole. Add 2 inches [5 cm] of coarre sand or fine gravel to
protect the bottom from scouring and sediment.
“ 4. Saturation and swelling of the soil. - Carefully fill the hole with clear water to
a minimum depth of 12 inches [30 cm] over the gravel. By refilling if necessary, or by
supplying a surplus reservoir of water, such as in an automatic siphon, keep water in
the hole for at least 4 hours and preferably overnight. Allow the soil to swell overnight.
This saturation procedure insures that the soil is given the opportunity LO swell and
approach the condition that it will be ill clurir,,: the wettest season of the year. Thus,
the test will give comparable results in the same soil whether made in a dry or a wet
season.
‘* In sandy soils containing little or no clay, the swelling procedure is not essential
and the test may be made as described under item 5C, after the water from one filling
of the hole has completely seeped away.
” 5. PercJatiotz rate measurement. - With the exception of sandy soils, percolation
rate measurements shall he made on the day following the procedure described under
item 4, above.
“ A. If water remains in the test hole after the overnight swelling period, adjust the
depth to approximately 6 inches [15 cm] over the gravel. Frcm a fixed reference point,
measure the drop in water level over a 30-minute period. This drop is used to calculate
the percolation rate.
“ B. If no water remains in the hole after the overnight swelling period, add clear
water to bring the depth of water in the hole to approximately 6 inches [I5 cm] over the
gravel. From a fixed reference point, measure the drop in water level at approximately
30-minute intervals for 4 hours, refilling 6 inches [15 cm] over the gravel as necessary.
The drop that occurs during the final 30-minute period is used to calculate the percolation
rate. The drops during prior periods provide information for possible modification of
the procedure to suit local circumstances.
“ C. In sandy soils (or other soils in which the first 6 inches [I5 cm] of water seeps
away in less than 30 minutes, after the overnight swelling period) the time interval
between measurements shall be taken as 10 minutes and the test run for 1 hour. The
drop that occurs during the final 10 minutes is used to calculate the percolation rate.
“ 6. Additional criteria for judgitlg soil suitability. - In areas of shallow ground
water, the depth to the water table shall be determined. If, for any extended period
during the year, the water table is normally at a depth of less than 4 feet [1.2 ml, the
results of the percolation test should be applied with caution. The case also warrants
special consideration if impermeable layers are found at depths of less than 4 feet [ 1.2 m] .”
The effective absorption area required may then be found from the
Table X.
WATER-CARRIED METHODS OF EXCRETA DISPOSAL
TABLE
X.
ABSORPTION-AREA
AND
Percolation rate
(time required for
water to fall 2.5 cm
(1 in.), minutes)
FOR
RESIDENCES
Required absorption area (square metres
of absorption trench bottom per person served)
2 or less
3
4
5
10
15
30
45
60
Over 60
* Adapted
REQUIREMENTS
SCHOOLS
l
141
from table given in Studies
residences
2.30
2.80
3.25
3.50
4.65
5.35
7.00
8.45
9.30
Unsuitable
on housztiold
schools
for shallow
sewage
absorption
disposal
0.84
0.93
1.12
1.21
1.67
1.86
2.70
3.10
3.50
system
systems.39
As indicated by Table X, a percolation rate of 60 or more is an indication
that the soil is unsuitable for effluent disposal by subsurface irrigation.
In such a case, the possibility of constructing seepage pits which may
penetrate into a deeper, permeable layer of the ground or the use of sandfilter trenches may be considered.
It may be emphasized that effective absorption area means the flat
area in the bottom (only) of trenches. Attention is drawn to the fact that
the figures given in the Table X ale based on a daily flow of 190 1 (50 US
gal. j of sewage per person in residences. In many parts of the world,
the daily flow of sewage will be found to be substantially less than this,
in which cases the figures in the table might be reduced on the basis of
actual field experience.
Construction an6 layout of‘dispwal field
Distribution
box
As its name implies, a distribution box is a chamber which ensures
an even distribution of the effluent to the subsurface disposal field through
the drain pipes (see Fig. 67). If easily accessible, it may also serve as
an inspection manhole for checking the amount of suspended matter in
the effluent from the septic tank as well as the proper distribution of effluent.
It requires care in its design and construction ; and, for efficient operation
-i.e., the equal distribution of flow among its various outlets-occasional
inspection and maintenance are needed. Experience shows that an outlet
may become partially obstructed by floating matter from the septic tank,
142
EXCRETA DISPOSAL FOR RURAL AREAS
if the latter needs cleaning, or by other solid matter (twigs, small stones,
etc.), which may have fallen accidentally through the manhole. As a
result, a portion of the disposal field may be inoperative and the rest
overloaded, becoming “ sewage sick ” within a short time.
FIG. 67. TYPES
OF DISTRIBUTION
BOX
A
Adapted, by permission. from
Manual of septic-tank gracfice.a7
A = Baffle in wood or brick
B = Inlet from septic tank or dosing chamber
C = Outlet to absorption lines
The general practice followed in the design of distribution boxes may
be described as follows : a*
“ The inlet pipe should enter at one end of the box about 2 inches [5 cm] above the
bottom. Sides of the box should extend approximately 12 inches 130cm] above the invert
of the inlet pipe and the box should be provided with a removable cover. Since frequent
inspection is not necessary, the cover of the box may be placed 12 to 18 inches [30 to
46 cm] below the surface of the ground. Drainage lines should be constructed with
WATER-CARRIED METHODS OF EXCRETA DISPOSAL
143
inverts at bottom level of the box or approximately one inch [2.5 cm] above the bottom
and all should be set at the same elevation. They should run straight in the desired
direction. Horizontal bends should be avoided where possible ; when necessary, however,
they should be made with tight joints. When set at the same elevation and operating
under the same head, pipes all of the same size are more likely to receive an equal flow.
Lines may be run from an elevation several inches above the bottom of the box, but care
must be taken to insure that all lines leave the box at the same elevation.
“The box need not be more than 18 inches [46 cm] in width, nor longer than is
necessary to accommodate drains for eft‘ective outlet capacity. Diversion baffle boards
should not be installed in distribution boxes on systems serving individual dwellings.
However, such construction may prove advisable on systems serving public buildings
where constant supervision and maintenance are provided and where the purpose of
such baffle boards may be realized. Lines may be shut off at will for repairs or to rest
the field when it comes waterlogged, provided a distribution box is installed. Flow diversion devices may be installed in the properly designed distribution box to facilitate rotation of use of the distribution lines where adequate and proper maintenance is assured.”
Pipes and trenches for septic-tank
efluent
Plain-end tile pipes, 10 cm (4 in.) in diameter and 30-60 cm (12-24 in.)
in length, are commonly used (see Fig. 67). Bell and spigot sewer pipe
of the same diameter but 61 cm (2 ft) in maximum length may be preferred.
A small stone or cement fillet may be used in the bottom of each socket
FIG. 68. ABSORPTION
A=
B =
C =
D =
E =
TRENCHES
Coarse gravel surrounding pipe
Bell and spigot pipe
Building or tar paper
Wooden stakes supporting grade board E
Longitudinil
boards, nailed to stakes and laid at exact
grade selected for absorption lines
F = Abs.orption tile pipes resting over grade boards
G = Tar’paper covering upper half of open joints
H = Earth-tamped backfill
144
EXCRETA DISPOSAL FOR RURAL AREAS
joint to centre the spigot in the bell. Plain-end tiles need a firm support
to remain on an even grade and, hence, to effect uniform distribution of
the septic-tank effluent. Such a support is provided by means of a flat
board-for example, 2.5 x 10 cm (1 x4 in.) in size-which is set on edge
and nailed to stakes driven at intervals in the bottom of the trench. The
top of the board can be laid accurately to the desired grade (see Fig. 68).
Both types of pipe are laid in such a way as to leave an open space
of 0.6-1.2 cm (0.25-0.50 in.) between pipe lengths for the effluent to run
out. When plain-end pipes are used, the upper half of the joint must be
covered with a strip of asphalt or tar paper to prevent entrance of fine
sanb and silt which might interfere with the flow of effluent. Ball and
spigot pipes do not require this protection, since the joints are protected
by ‘the bell ends. In either case, however, the joints should be covered
with at least 5 cm (2 in.) of gravel. Some authors 21even recommend that
irrigation trenches be filled to the ground surface with filter material
(gravel), thereby reducing the risk of silt’s entering the drain. The portion
of the effluent drain located between the septic tank and the distribution
box and a length of, for example, 1.50 m (5 ft) of outlet line from the
distribution box should be laid with tight cement joints.
The depth of pipe-inverts should not by less than 30 cm (12 in.) nor
more than 75 cm (30 in.). An earth cover of about 30 cm (12 in.) is desirable
to protect the pipe against injury. Under roads, or paths followed by
heavy agricultural machines, it may be necessary to use cast-iron pipes
or strong vitrified sewer-pipes, laid with tight joints, in order to maintain
line and grade.
The grade of the disposal pipelines should not be too small or too
great : if too flat, only the upper area of the disposal field will receive
the effluent ; if too steep, there will be a rush of liquid in the upper
portion of the pipelines towards the lower portion of the disposal field,
which will soon be waterlogged. Experience dictates a slope of 0.16%
to 0.320/,-i.e., 2-4 in. per 100 ft--with a maximum of 0.5%. In order
to maintain such grades on steep&ping lands, disposal pipes should be
laid, along the contours of the ground, and changes of direction should
be made by means of drop-boxes or terracotta L’s laid with cemented
joints. At such points special precautions should be taken to cut off
the undergratund flow of sewage which is normally running above the
upstream trench bottom and which may cause erosion of the ground
around the drop-boxes and terracotta L’s. This may be done by filling
with well-tamped clay soil the last 30 cm (12 in.) of trench preceding each
drop-box or L-pipe.
The size and lengths of trenches ,required should be calculated on the
basis of the figure previously obtained for effective absorption area. The
size and minimum spacings recommended may be obtained from the
Table XI .3R
145
WATER-CARRIED METHODS OF EXCRETA DISPOSAL
TABLE
Xl.
SIZE
AND MINIMUM
FOR DISPOSAL
SPACING
TRENCHES
REQUIREMENTS
Effective absorption
area (sq. ft/ft)
Spacing of tile
lines + (feet)
Width of trench
at bottom (inches)
Dept(bncohfetr;nch
I
18
18 to 30
1.5
6.0
24
18 to 30
2.0
6.0
30
18 to 36
2.5
7.5
36
24 to 36
3.0
9.0
* A greater spacing
is de$irable
where available
area permits.
Trenches should not be too long, * otherwise, the effluent will not be
evenly distributed over the disposal field. No trench should be longer
than 30 m (100 ft). The smallest household disposal system will consist of
two trenches 45 cm (18 in.) wide at the bottom and 30 m (100 ft) long,
irrespective of calculated findings.
So far as possible, trenches should be laid along straight lines. The
herringbone type of layout is no longer used since Y-branches do not,
in actual practice, ensure even distribution of the effluent over the disposal
field. Parallel lines issuing individually from a common distribution box
are now preferred.
After the trenches are dug to the required size and depth, a layer of
15 cm (6 in.) or more of filter material is placed over the bottom. The
pipes are then laid to the required grade, as previously described, and
are surrounded by more filter material, at least 5 cm (2 in.) thick above
the top of the pipe. The rest of the trench is then backfilled with earth.
The filter material may be washed gravel, crushed stone, slag, or clean
clinker ranging in size from 1.2 cm to 6 cm (0.5 in. to 2.5 in.), although
one single size (e.g., 1, 1.5, 2, or 2.5 in.) is sometimes preferred.21
Surface run-off should, of course, be diverted away from the disposal
field in order to avoid waterlogging of the soil, especially at times of heavy
rains.
Finally, trenches should be laid at least 7.5 m (25 ft) away from large
trees to avoid blockages due to the penetration of roots into the pipes.
For the same reason, the land area above the disposal field should not
be cult-ivated, but may be planted with short-rooted grass.
Seepage pits
Depending upon the layout of the
one or more seepage pits at the lower
serves to catch excess effluent and,
through the piping system. The last
10
trenches, it IS good practice to build
ends of the absorption lines, as this
possibly, to ventilate the trenches
1.5 m (5 ft) of trench preceding the
146
EXCRETA DISPOSAL FOR RURAL AREAS
seepage pit should be filled with well-tamped clay soil in order to stop
the flow of sewage above the trench bottom and to prevent erosion,
Pipes and trenches for aqua privies
Subsurface irrigation is also convenient for the disposal of the effluent
from aqua privies. T11c principles of design, the size and types of pipes
used, and the width of trench recommended are the same as above indicated.
However, the essential difference rests in the fact that the volume of aquaprivy effluent is much smaller than that of septic tanks. As a result, the
length and grade to be given to trenches and pipes will differ from those
recommended for the disposal of septic-tank effluent. The required length
of trench may be calculated from Table XII, which is adapted from figures
suggested by Macdonald .2g
TABLE
XII.
REQUIRED
ABSORPTION-AREAS
FOR AQUA
PRlVlES
Required absorption area (square metres of
absorption trench bottom) for aqua privies serving :
Percolation rate
(time required for
water to fall 2.5 cm
(1 in.), minutes)
10 persons
25 persons
I
-
60 persons
I
2 or less
2.80
5.60
9.80
5
3.75
7.00
11.70
10
4.65
9.80
16.20
15
6.00
11.70
19.50
30
8.00
16.70
25.00
45
9.00
18.00
30.80
60
10.25
19.50
33.50
For absorption areas less than 7 m* (75 sq. ft), trenches may be 30 cm
(12 in.) wide at the bottom ; other trenches should have a bottom width
of 45 cm (18 in .). A minimum slope of 1% is recommended.
Dosing Siphons
The importance of the penetration of air into the pores of the subsoil
has been previously stressed (p. 129). In order to enable the soil to recover
between doses of effluent and to obtain uniform distribution of sewage
through the entire distribution line, a dosing chamber equipped with one
automatic siphon is recommended for a large septic tank, i,e., one of more
than 3785-l (lOOO-US-gal.) capacity. For tanks having a capacity exceeding
7570-9463 1 (2000-2500 US gal.), a dosing chamber equipped with two
WATER-CARRIED METHODS OF EXCRETA DISPOSAL
147
siphons is recommended. These siphons will operate alternately, and
each will serve half the distribution field. The dosing chambers are usually
installed at the outlet of septic tanks, and ry:eive the effluent which accumulates over a calculated period of 2-3 hours before being discharged
into the disposal field. (See Fig. 65 and 69.) The effective capacity of
these chambers is equivalent to the volume of water required to fill all
the disposal pipes from one-half to three-quarters full at one time.
FIG. 69. TYPICAL
A
B
C
D
E
=
=
=
=
=
DOSING
SIPHON
Miller siphon
Diameter of siphon, dependent upon population served
Maximum drawing depth of water in dosing chamber
Discharge to distribution box and absorption lines
Overflow pipe
The discharge capacity of the siphon should be less than the capacity
of the disposal line leading from it to the subsurface irrigation field. A
IO-cm (4-in.) siphon may be used for plants serving 20-40 persons, and
a 12.5-cm (5-in.) siphon for those serving up to 100 persons.
Dosing siphons are particularly useful on systems involving sandfilter trenches and sand and trickling filters. They are not usually recommended for small, household types of installations, because of their cost.
a+
Sand-Filter Trenches
Sand-filter trenches may be built in soils which are tight and impervious
(clayey soils) and which have a percolation factor exceeding 60. They
may also be considered for installation in places where ground water
148
EXCRETA
DISPOSAL
FOR RURAL
AREAS
occasionally rises and reaches a level 90 cm (3 ft) below the ground surface,
or when the area available for subsurface irrigation is too small for this
purpose.
As shown in Fig. 70, a sandFIG. 70. SAND-FILTER
TRENCH
filter trench is wider than a regular
I
absorption trench and includes :
(1) an effluent distributing pipe,
usually 10 cm (4 in.) in diameter ;
(2) a sand-filter bed not less
than 60 cm (24 in .) deep, preferably 75 cm (30 in.), through which
the septic-tank effluent percolates
and undergoes biological filtration ;
(3) an underdrain, also 10 cm
(4 in.) in diameter, surrounded by
a layer of gravel laid in the bottom of the trench. This underdrain
receives the filtered effluent and discharges it into a ditch or similar
Adapted. by permission. from
Manual of septic-tank
pmctice.37
watercourse. It also prevents the
ground water from interfering with
Coarse gravel or crushed stone
the biological processestaking place AB == fluun,dne:drain
for collection of filtered efin the sand bed mentioned above.
C = Coarse filter sand
D = Coarse gravel or crushed stone
E = Effluent distributing
pipe, made of tiles
&or of perforated long pipes
F = Building or tar paper
G = Backfill, tamped in moist layers 15 cm
(6 in.) thick
H = Top soil
I = Original ground-level
Special care will be needed to
ensure that the effluent-distributing
pipes are laid on a uniform grade.
When grade boards are not used,
the sand bed should be flooded to
ensure thorough settlement before
the distribution pipes are laid.
Clean, coarse sand should be used as filtering material, as fine sand
will be quickly clogged and will lead to failure of the system.
The distribution piping and the underdrains may be built of the same
pipes as are used for the construction of the standard absorption trenches
already described, i.e., plain-end tile pipes or bell and spigot sewer pipes.
Long, perforated pipes have the advantage of maintaining the desired grade,
and may be preferred for use in the distribution of septic-tank effluent
over the sand bed. The slope of the effluent distribution pipes may be
the same as that previously mentioned for standard absorption trenches,
while the slope of underdrains may be as much as 1%.
The loading rate for sand-filter trenches is estimated at about 38 1 per m2
( 1 US gal. per sq. ft) per day of filter surface.
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
149
Sand-filter trenches usually produce a highly purified effluent which
may be disposed of in open ditches or streams. There is, however, no
certainty that the filtered effluent is bacteriologically safe. When the
receiving stream is used as a source for domestic water-supply, the effluent
should be chlorinated. In any case, sand-filter trenches should never
be constructed without the prior approval of the local health department.
Sand Filters
Subsurface sand filters
Subsurface sand filters operate under the same principles as sandfilter trenches. They “ constitute a maximal artificial development of the
filtering capacity of the subsurface [soil] “.13 The area required for
filtration, as found by the engineering design, is dug up to the required
depth and is filled in artificially with coarse sand, after the effluent distribution pipes and the underdrains have been placed. (See Fig. 71.)
The loading rate for subsurface sand filters and the pipes used are the same
as those mentioned above for sand-filter trenches. Their effluents compare
favourably with the effluents from filter trenches and may be disposed
of in the same manner.
For large installations, subsurface sand filters are likely to be cheaper
than filter trenches and should be selected over the trench system when
dosing siphons must be installed. Siphons have the advantage of ensuring
adequate dosage and of providing a long rest-period for the filter sand.
Dosing tanks equipped with single siphons should be installed where the
total filter area exceeds 17 m2 (1800 sq. ft) and where the distribution
pipes exceed 90 m (300 ft). When the length of these pipes is greater than
245 m (800 ft), the filter bed should be divided into two or more sections
and dosed separately by alternating siphons.33 Lining of the bed (or beds)
is not necessary except in very wet, soft soil.
Subsurface sand filters, like sand-filter trenches, may be built in most
rural areas of the world. They require no attention. However, since they
cannot be maintained, they eventually become clogged and must be rebuilt,
Open sand filters
In areas where the ground water remains permanently close to the
ground surface, or where subsoil conditions are unfavourable (e.g., rock
formations) for the construction of disposal systems already described,
open sand filters may be considered. These filters are built above ground
or partly below ground as the local circumstances dictate. In both instances,
masonry or concrete walls are needed to support the sides and to retain
the sand. Earth embankments may also be used for the same purpose.
150
EXCRETA
DISPOSAL
FOR RURAL
FIG. 71. SUBSURFACE
SAND
AREAS
FILTER
Section
I
------II-.
Plan
‘6+:
I
----m---s
IV’
I
9 VII
WHO 71)15
Measurements shown are in centimetree.
Section :
A =
B =
C =
D =
=
E =
G =
H =
I =
Plan:
I
II
III
IV
Coarse gravel or crushed stone
Underdrain for collectlon of filtered effluent
Coarse filter sand
Coarse gravel or crushed stone
Effluent distributing pipes made of tiles or of perforated
Backfill, tamped In moist layers 15 cm (6 In.) thick
Top sol1
Orlglnal ground-level
End line of subsurface filter
pipes
=: Septic tank
= Discharge line
= Siphon chamber
- Distribution
boxes
E;: Effluent distributing pipes (= E In section)
;I
= Underdrain for collection of filtered effluent (= B in section)
VII = Collection plpe to final point
VIII - Limits of subsurface filter
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
‘151
In open sand filters, purification of the septic-ta.nk effluent is due to
the action of aerobic bacteria in the interstices of the sand bed and
to mechanical straining. Since these bacteria require oxygen in order to
survive, the titers are usually operated intermittently so that air is drawn
into the filter bed during the intervals between dosing. For this reason,
these filters are frequently referred to as intermittent sand filters. If
properly constructed and operated, open sand filters produce an effluent.
of high and stable quality.
FIG. 72. OPEN SAND
----
FILTER
,_---,----~==E~
Adapted, by permission, from Manual of septic-tank wactice.a7
A=
B =
C =
0 =
E =
F =
G =
H =
Cast-iron pipe lines from dosing chamber
Control valves, allowing for cleanIn and repalrs of filter beds without interrupting operation
Concrete splash slabs; top surfaces are left in rough state
Underdralns, laid 1.8 m (6 ft) or more apart, with open joints to receive ftltered effluent
Collector to disposal. Pipes laid with tight joints
Coarse gravel or crushed stone
Coarse filter sand, 75-108 cm (30-42 in.) thick
Orlglnal ground-level
Open sand filters are usually divided into two or more compartments
in order to facilitate regular cleaning of the beds and to regulate operation
(see Fig, 72). As in the case of subsurface sand filters and of filter trenches,
152
EXCRETA
DISPOSAL
FOR RURAL
AREAS
a bed of clean coarse sand 75-105 cm (30-42 in.) thick, underlaid with
gravel will be used. Sand material possessing an effective size of 0.2-0.4 mm
and a uniformity coefficient of 4.0 will give satisfactory performance.
(By effective size is meant the size of the sand particle that is coarser than
10% by weight of the material. The uniformity coefficient is found by
determining the size of the particle that is coarser than 60% by weight
of the material and by dividing that size by the effective size.)
In small installations, the underdrainage system and the effluent distribution pipes may be arranged in the manner shown in Fig. 72. The
larger systems are built and operated on the principles of municipal sand
filters.
The loading rates for open sand filters are greater than those allowed
for subsurface sand filters. They depend primarily upon the degree of
treatment achieved in the septic tanks, the size of the sand particles used,
and, also; the temperature. Loading rates applicable in warm climates
are higher than those allowable in temperate and northern countries. As
an example, the loading rates on open sand filters with uniformity coefficients
not over 4.0 recommended for application in the USA are as follows, in
litres per m2 per day : 37
Region
Southern USA
Northern USA
. .
. .
0.2 mm
Effective size of stlttd
0.3 mm
0.4 mm
0.5 mm
0.6 mm
378 000
300 000
493 000
378 000
756 000
606 000
606 000
455 000
6!2 000
530 000
The intermittent operation of open sand-filter beds is usually achieved
by the use of dosing siphons. Depending upon the volume of sewage to
be treated, these siphons are operated in such a manner as to supply one
dose per day or a single dose in several days. Most commonly one to
four doses per day are provided, the bed being covered each time to a
depth of 5-8 cm (2-3 in.). The best practice calls for the installation in
the same &amber of two siphons operating alternately and discharging
upon different beds.
Open sand filters need not be covered in most instances. However,
in order to prevent odours and nuisances which may arise when operation
>,isdeficient, or to avoid freezing in northern climates, it may be necessary
to cover the beds of sand with a layer of 15 cm (6 in.) of earth.
The great disadvantage of these filters lies in the fact that they require
considerable attention. Constant maintenance and cleaning of the sand
surface are required ; otherwise, the ventilation of the beds is interrupted,
and the nitrifying bacteria die away. Cleaning is done by raking the beds
and, when necessary, by removing the top 2.5 cm (1 in.) of dirty sand.
This sand is washed and returned to the bed in order to maintain the
depth of the filter bed,
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
153
Because of the care needed in their construction and, especially, in
their operation, open sand filters are recommended only for use in communities which can afford the services of competent sanitary engineers
and sewage-plant operators. The advice and approval of the local health
department should be sought prior to their construction.
Trickling Filters
Trickling filters, also called percolating filters, are used as a means
of secondary treatment of septic tank effluent in the more economically
favoured rural areas, where sanitary engineering advice may be obtained
for the construction and operation of such units. In this method the
effluent is trickled intermittently thro lgh a thick bed of crushed stone,
metallurgical coke, lath, or even brush (twigs cleaned of leaves and bound
in bundles). (See Fig. 73.)
The rate of application of sewage to small installations is governed by
the volume and strength of the sewage to be treated. In the USA the
rates recommended range from 175 000 US gal. to 225 000 US gal. per
acre per day for each foot of depth of bed 2o (i.e., 558 1 to 718 1 per m3
of filter medium). In the United Kingdom of Great Britain and Northern
Ireland, where the domestic sewage is L..ually stronger than in the USA
due to a smaller per person consumption of water, a figure of 45 Imp.
gal. per cubic yard of filter bed (268 1 per m3 of filter bed) is recommended
for design purposes by the Royal Commission on Sewage Disposal.
The depth of a trickling filter bed usually varies from 2 m to 3 m
(6 ft to 10 ft). The bed should consist of clean, durable material of the
quality mentioned above, and the stones should have angular shape and
rough surfaces. In such a filter, air must circulate freely in order to maintain
the zoogloeal flora which thrive over the stones in the presence of oxygen.
The larger stones, 8-10 cm (3-4 in.) in size, will form a layer 15-20 cm
(6-8 in.) thick at the bottom of the bed ; the smaller stones (not less than
2.5 cm or 1 in. in size) will make up the filter bed.
In small trickling filters, distribution of the septic-tank effluent over
the bed is accomplished by means of static distributors fed intermittently
by a tip trough or a dosing siphon (see Fig. 73). The tip trough allows admission of the sewageto half of the bed at a time. It is usually not more than
4.20 m (14 ft) in length and serves a filter area not more than 1.50 m (5 ft)
wide on either side of the trough. Trickling filters larger than this require
additional tip troughs. However, the latter should not be used when the
bed exceeds 47 m2 (500 sq. ft) in area.30
The distributors may be made of cast iron, concrete, or plain 2.5 x 7.5 cm
(1 x 3 in.) boards. Cast iron and concrete distributors often assume the
shape of channels whose bottoms are perforated with small holes, or
..
154
EXCRETA
DISPOSAL
FIG. 73. SMALL
FOR RURAL
TRICKLING
AREAS
FILTER
i-“B
b
Plan
H
inlet
Outlet
Two-way tipper
Air-vent
“Aeration tiles
F
G
H
I
J
A
C
Section
c-d
=
=
=
=
=
J
WHO 1477
&in. (15~cm), half-round, aeration tiles
T-iron support
Distribution channel with serrated sides
l-in. to l*ln-in. (2.5-3.&m)
graded media
3-In. to 4-in. (7.5-lo-cm) graded media
WATER-CARRIED
METHODS
OF EXCRETA
DISPOSAL
155
whose sides are notched at close intervals in order to let the sewage out
in the form of rivulets above the bed.
Trickling filter units should be constructed of concrete or other suitable
materials and should be located at least 45 m (150 ft) away from human
habitations. Such filters are usually uncovered and are likely to produce
odours. Also, they breed large numbers of a small, moth-like fly of the
genus Psychoda, which may be carried away by the wind into human
habitations. Psyclzoda flies do not bite but are a serious nuisance to man.
They are controlled by operating the filters for a while at a very high rate
of filtration, thus reducing by sloughing the thickness of the zoogloeal
film in which the fly larvae develop. Chlorinated lime may also be applied
once a week to the bed with similar results.
The effluent of trickling filters normally contains humus-like materials
which, in large installations, are removed by passing the effluent through
a secondary settling tank. In small systems serving, for example, less than
100 persons and where the effluent can be disposed of without nuisance
or danger to sources of domestic water-supply, humus tanks are usually
not provided. When needed, such tanks should have a detention period
of four hours and be designed like a septic tank, except for the cover. The
floors of these tanks are designed to slope down to a sump at the inlet
end to permit periodic removal of sludge by scoops or by pumps.
EXCRETA DISPOSAL
FOR RURAL AREAS
THE PLANNING
PROGRAMMES
OF EXCRETA
DISPOSAL
PROGRAMMES
Essential Elements
In planning an excreta disposal programme for rural areas, it is important to remember that such a scheme should be considered only as a part
of a general sanitation plan for the country concerned. An excreta disposal
programme is not an end in itself and, even if successful, cannot be expected,
alone, to produce a considerable reduction in morbidity and mortality
due to enteric infections. Often a long-range plan of general sanitation
does not exist either because there are still doubts among health officials
as to the benefits of sanitation, or because these officials do not have the
knowledge and the desire to face the sanitation problem, which in many
countries assumes staggering proportions.
As a result of experience acquired in many parts of the world, Baity ’
has suggested that the governments concerned might take the following
progressive steps :
1. Recognize the real benefits of sanitation to the health and well-being of their
people.
2. Establish a sanitation unit within the national health service of the country,
commensurate with the country’s needs and resources, and staff it with personnel competent to plan and direct all phases of work in this field.
3. Integrate sanitation properly with other public health undertakings, and see
that “ fist things come first ” in the assignment of priorities.
4. Develop a long-range plan of sanitation for the country as a whole, into which
projects and programmes may be logically fitted as to time and place.
5. Realize that it is possible to do something helpful in environmental sanitation
under any conditions and under any budget-and that the simplest things are usually
the most important.
6. Select a point of beginning, always the most difficult step in such an undertaking,
and outline an orderly progression of work and objectives.
a Baity. H. G. (1956) The sanitary sceptics-Shall
rJnnub1ished working document WHO/Env.San./93)
-
156-
we condemn them or teach them?
EXCRETA DISPOSAL PROGRAMMES
157
In most countries of the world the disposal of human wastes should
constitute an important part of any long-range plan for sanitation develop
ment and might well be a desirable starting-point for such an undertaking.
Once a decision has been made as to the proper time and place for an
excreta disposal programme, the following elements might be considered
in planning :
(a) preparation of necessary staff;
(b) initiation of a community sanitary survey ;
(c) selection of the type, or types, of units to be built ;
(d) study of the possibility of a pilot project in the area under
consideration ;
(e) estimate of costs ;
(.f) health education of the population ;
(g) programme and schedule of construction ;
(h) maintenance of the installations ;
(i) appraisal of results and promotion of further sanitation development ; and
0’) establishment of sanitary regulations.
Preparation of Staff
The planning and execution of any programme of environmental
sanitation require the services of technically qualified professional and
non-professional staff. This is particularly true in the case of excreta
disposal programmes for rural areas and small communities. It is desirable
that in every country specialists in environmental sanitation be placed
at an appropriate level within the health administration and that they be
made responsible for the formulation and development of programmes
relating to their competence. One of their functions should be to undertake,
in co-operation with medical and other health personnel, a close study
of the status of rural sanitation and the staff required for its improvement.
Such a study would be expected to provide the facts on which a programme,
however simple, could be based, and to lead to decisions as to the means
whereby it could be implemented. 4~ The assistance of these specialists
should be made available to local health services when necessary for the
solution of difficult problems.
At the local (or district) level, there will be a need for well-trained
public health (or sanitary) inspectors, who will be directly in charge of
the execution of the programme. These officers will be assisted by a
number of health assistants and health aides posted in rural towns and
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EXCRETA
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villages. The possibility of organizing village-level workers on a voluntary
basis may also be considered as a part of a self-help movement within
each community.
In rural excreta disposal programmes, the quality and quantity of the
sanitation work performed are directly related to the quality of the supervising personnel. It is therefore important to give considerable attention,
before a programme starts, to the proper training of the sanitation staff
which will carry it out. This applies particularly to the health assistants
and health aides, who will be in closest daily contact with the population.
The training scheme should be founded on a careful analysis of the functions
to be performed by such staff. This matter will be studied further in the
next chapter.
Community Sanitary Surveys
In most rural areas, community sanitary surveys are usually necessary
to obtain first-hand information concerning local sanitary conditions and
needs. Such surveys, undertaken with the participation of local leaders
of the community, will be of immense help in programme planning and
evaluation. Depending upon the particular situation at hand, they may
cover the following factors in part or in whole.
A.
Description
of area
(1) location, topography, climate, character, communications, maps ;
(2) geology and hydrology, with particular reference to nature of
top and underground layers of the soil, its porosity, presence and abundance
of ground water (if any), direction of flow, level of ground-water table,
its appearance and potability, estimation of yields of springs, rivers, and
so on;
(3) population- number, constitution by age-groups and sex, density,
growth ;
(4) industries and agriculture, with particular reference to irrigation,
drainage, and soil fertilizing practices ;
B.
Medical
and sanitary
data
(1) general health of the population, with special emphasis on communicable diseases and on intestinal infections, helminth infestations, and
trachoma and acute conjunctivitis in infants and children ;
(2) vital statistics, mortality and morbidity data ;
(3) health and sanitary administration, with reference to organization,
personnel, budget, and activities of voluntary or other agencies in the
field of sanitation ;
EXCRETA
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(4) existing sanitary conditions in the area, with reference to description
of private and public latrines, their distribution and use ; to wells, springs,
and other systems of water supply (including such information as number
of persons served by piped water-supplies, and by wells, the consumption
and uses of water, number of dwellings with private water supply, etc) ;
to wastes collection, disposal, and composting ; to milk and food sanitation ;
to insects (flies, fleas, lice, mosquitos) ; to health aspects and standards
of housing ; and to school sanitation.
(5) sociological and cultural patterns, with particular reference to
community and family organization, leadership ; customs, beliefs, and
habits bearing on personal hygiene and community sanitation ; present
methods (if any) of health education of the public.
C.
Resources available
(1) general economic level of the population ; average income per
caput ;
(2) co-operation expected from agricultural, educational, and other
agencies or groups for training and health education of the public ;
(3) housing and vehicle transport for programme, vehicle and equipment repair and maintenance facilities ; sources of power (electricity,
fuel) ;
(4) local construction materials and their costs ;
(5) local craftsmen and wages ;
(6) potential resources for self-help.
This information has an important bearing on the project and makes
it possible to draft a reasonably accurate cost estimate. Such a survey
is a useful educational tool and also serves to acquaint the sanitation
personnel with the families and with their customs, beliefs, interests, and
attitudes. In short, it helps to prepare a “ social map ” of the community.
Health Education of the Population
In all programrnes involving the disposal of human wastes, especially
those undertaken in a rural environment, health education plays a most
important role and should be one of the earliest considerations. It is
through a well-planned and active programme of health education that
health authorities will be able to secure the understanding, support, and
participation of the rural population. This fact, which has already been
discussed, cannot be overstressed.
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Broadly speaking, the purposes of the educational programme should
be :
(a) to create a desire for the improvement of excretory habits, or more
generally, to create interest in, and awareness of, health problems which
may be solved through improvement of personal, family, and community
sanitation practices ;
(b) to help people determine what changes are needed and desirable
for improving sanitation and how they can be implemented ;
(c) to encourage people to put into practice good habits of personal
hygiene, as well as those measures which will serve to improve personal,
home, and community sanitary conditions ;
(L!) to foster those learning experiences which would feature the
people’s participation and self-help in solving sanitation and related health
problems ;
(e) to provide instruction in the designs, materials, and methods
involved in building and maintaining proper installations ;
(f> to secure sustained interest and participation in a community
programme of environmental health improvement.
In carrying out such a programme in rural areas and small communities,
it is desirable to utilize to the fullest extent the assistance of the available
local, provincial, and national personnel with skills and experience in
family and group education methods, organization of village committees
and councils, conduct of training courses for village leaders and school
groups, and production and use of simple teaching aids and visual materials.
In some countries there may be one or more persons with full or partial
training in health education of the public. There may also be experienced
leaders in adult education, rural development work, social work, rural
education, religious leadership, agricultural extension work, and others
whose collaboration should be sought and who may prove to be of
considerable heip to the sanitation personnel in planning and carrying
out educational activities with family, school, and village grcups.
Selection and Design of the Units
These subjects have already been covered in the previous sections.
However, it mig’?t t;.: worth while to reiterate here the fact that the choice
of installation must be made in the light of : (1) what the community
needs and is prepared to accept ; (2) what the community can afford,
giving due consideration to basic health criteria (p. 39) ; and (3) what
the community can maintain in the future. The word that should ‘describe
,.
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161
the design chosen is soundness. It does not mean luxurious or poor,
expensive or cheap. It does mean the best possible installation at a cost
which the particular community can afford.
The selection of units has a direct bearing on the success or failure
of the excreta disposal progrdmme. From the beginning, the technical
aspects of the scheme must provide for a certain degree of flexibility because,
once the programme is organized and started around a single type of
installation, it is difficult to switch to another type and to “ sell ” it to
the people.
Pilot Projects
When it is not possible, from the findings of the sanitary survey, to
arrive at a safe conclusion regarding the type or types of units, their costs,
and the construction procedure to be used, a pilot project should be carried
out first. This mettod offers the quickest and most economical way of
discovering the answers to these questions. Pilot projects are often desirable
and may be undertaken especially in conjunction with the training of the
sanitation personnel which will ultimately be employed in the programme.
The use of such projects for demonstration purposes has also proved to
be valuable in many countries in “ selling ” the programme to the people
concerned.
The Estimate of Cost and Budget
It is quite possible that rural sanitation work has often failed because
of inadequate cost estimates and budget. It is, indeed, exceedingly difficult
to prepare cost estimates for projects that are new and drawn up mostly
from unreliable information. The estimate of cost should be true, honest,
and correct. If the basic data are poor, this should be made abundantly
clear to those officials who will decide on budget matters. Health administrators throughout the world are predominantly medical people who
cannot be expected to understand in detail the engineering phases of
construction work. They are often confused when a project runs out of
funds long before completion, and this may shake their confidence in the
whole sanitation programme. To avoid this situation, it is important
that every effort be made to prepare the best possible estimates of cost,
based on complete field information and making generous allowances for
unknown factors. The total sum reqqired may appear staggering when
all the figures are added up, but it is guch better in the long run to accept
the more difficult job of promoting a rural sanitation project that seems
to be expensive beforehand than to try to justify a budget increase halfway
through.
11
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Construction
On the basis of data gathered in the course of the community sanitary
survey, a decision should first be made whether construction will be carried
out (1) by a well-organized campaign conducted by the health department,
(2) by the family with guidance only from the sanitary (public health)
inspector, or (3) by a combination of these two methods, involving the
aid of the health department and the participation of the family in the
form of labour or materials, or both. As pointed out before, the third
method yields by far the best and longest-lasting results. If method 1
or 3 is decided upon, it should be possible to draw up a fairly detailed
programme of construction of the projected facilities.
The programme of construction would indicate such things as the
rural districts which should be tackled first ; the proposed schedule of
construction ; the distribution and organization of construction gangs ;
the list and plan of utilization of available construction materials (donated
or otherwise), equipment, and transport ; and the organization and location
of field warehouses and shops, etc. The construction programme should
be flexible enough, however, to cope with unforeseen difficulties, such as
those which may be created by unstable ground formations, high groundwater level, or low permeability of soils.
Experience shows that in the early stages progress will be slow, even
though the units selected may be easy to build. Construction will then
pick up momentum and go through a period of major activity until 75x80% of the units are completed. Then it will again slow down.
Depending upon circumstances, resistance of certain groups to the
excreta disposal programme may be anticipated ; this should be taken
into account in drawing up or revising the construction schedule.
Mainten.wce of Installations
When the tempo of construction slows down following the installation
of most of the units projected, attention may be shifted to another rural
district or community. The permanent staff member (sanitary inspector
or health assistant) should pick up the work from there with whatever
help may be needed from his immediate supervisor. He should continue
his efforts to persuade the last persons still holding out to build sanitary
installations and should undertake periodic visits ta the homes where
units have been built to ensure that these are properly used and maintained.
Inspection and maintenance are necessary, since neglected installations
may lose much of their value and may even constitute potential hazards
to the community they are intended to serve. Provision should be made,
right at the planning stage, for regular follow-up by sanitation personnel
permanently stationed in the area.
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PROGRAMMES
Appraisal of Results
..
and Promotion of Further Sanitation Development
In planning a programme of rural sanitation, it is desirable to keep
in mind the need for an evaluation of results upon the completion of
construction activities or at a later date. The medical and sanitary data
collected in the course of the pre-operative sanitary survey of the area
should, if adequate and sufficiently reliable, provide a good basis for an
objective appraisal of the results of the programme. In some cases it
may be necessary to select for comparison purposes another area, similar
in character, in which comparable sanitation work is not being carried
out. This comparison area should be surveyed in the sarne manner and,
as far as possible, at the same time.
Measurements of the results may be by either direct or indirect means.
Direct measures, which are to be preferred when applicable, involve the
analysis of death-rates of specific age-groups of the population or the
study of morbidity returns and the results of special morbidity surveys.
Data on infant mortality due to specific diarrhoeal diseases are often
selected for studying the present status of sanitary conditions in an area.
However, Macdonald a states that death-rates for the ages 1 to 15 years
are a most delicate index of the amount of’infective diseases in the population and are the first to respond to sanitation programmes. He also
found that the range in death-rates for the age-group 1 to 4 is particularly
sensitive and less influenced by standards of maternal and child care and
public education. On the other hand, crude death-rates are generally
unreliable and may not reflect a successful rural sanitation programme
at all.
The study of morbidity returns may often lead to fallacious conclusions
since, depending upon local conditions, such returns may be influenced
by several factors, among which are inadequate records of notifiable
diseases, standards of diagnosis, and others. Objective measurements by
special morbidity surveys covering the faecal-borne diseases are very
desirable. Particular attention should be paid to prevalence of these
diseases in infancy and childhood.
Indirect measures involve observations of changes in the environment
which may indicate that rural health must have been improved as a result
of the sanitation programme. They do not provide direct evidence of
health improvement ; for this reason they are less desirable from a technical
standpoint. However indirect measurement is often the only way of
appraising the results of rural sanitation programmes, especially in primitive
or unorganized areas and where a complete medical team is not available
a Macdonald. G. (1953) The appraisal of the results
(Unpublished working document WHO/EN. San./371
of
rural sanitatiotl programmes
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EXCRETA
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AREAS
for making morbidity surveys. The data upon which indirect measurement
is based are those which are normally collected in the course of community
sanitary surveys.
Both pre- and post-operative community sanitary surveys will point
to the need for further sanitation work in the area and will yield valuable
information upon which future programmes may be based. These may
have to be deferred for a while because of lack of funds or the necessity
for preliminary stimulation of the interest of the local population. in the
latter case, much will depend upon the initiative, the zeal, and the ability
in public relations of the sanitation and other personnel in promoting new
health and sanitation ideas among the population.
Sanitary Regulations
Basic legislation is necessary in order to enable a public health agency
to initiate and develop activities in the field of public health and sanitation.
Such legislation is normally passed by a legislature, a parliament, or a
similar official legislative body of a country or state. The collection in
an orderly manner of legislative acts in the form of public health or sanitary
codes is done from time to time by the public health agency. Basic, or
enabling, legislation is confined to statements of broad principles, responsibilities, and penalties. On the basis of such legislation, the public health
agency concerned is in a position to formulate and issue more detailed
rules, regulations, and standards relating to the organization and operation
of local health work and to procedures for carrying it out. Also, ordinances
dealing with such matters as the source of food and milk, the health and
sanitation practices of persons who come in contact with them, the sanitary
nature of processing equipment, the sanitary quality of water, and so on,
may be issued by the public health agency in order to explain or qualify
in detail the basic legislation enacted.
An existing sanitary code in a country may exert a strong influence
upon the nature and content of a rural excreta disposal programme under
planning. If the sanitary regulations are outdated or too elaborate or
exacting, they may have too much of a restricting influence upon both
the technical and administrative aspects of the programme. Such regulations
defeat their own purpose and are usually ignored by the population. When
suitably drafted, regulations are useful in helping to ensure a basic minimum
of sanitary safeguards and the ehmination of potential health hazards,
especially in densely inhabited communities or industrialized rural areas.
They usually deal with, and prescribe standards for, such matters as the
prevention of soil and water pollution ; the disposal of human and animal
wastes ; the hygienic aspects of housing ; the protection of milk and other
food supplies ; the control of arthropod, rodent, and mollusc hosts of
disease ; and the use of surface waters.
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When elaborating sanitary regulations, it is important to keep in mind
the following principles ,28 which have been set forth for milk, but which
apply as well to all sanitary legislation :
1. No regulation should be made which cannot be enforced.
2. No law can be enforced without the co-operation of most of the
persons concerned.
Rules and regulations applying to excreta disposal in rural areas should
be reasonable and no more drastic than is necessary ; above all, they
should adhere to basic principles of sanitation. Only in this way can they
be applicable at the same time to several (or all) rural areas within a given
country. It is important to consider every contingency which may occur
within the foreseeable future, and the best way to do so is to consult the
people for whose benefit the regulations are formulated. While the
experience of others may be useful in drafting new regulations, it is always
a mistake to adopt the regulations of another country without making
some necessary modifications.
On the need for the co-operation of the people in the enforcement of
legislation, Lethem 28 has written :
“ No form of c%rtrol can be effective without the support of most of the people
concerned, backed &y an enlightened public opinion. Hence, education must precede
legislation ; in fact, it might be described as the father of legislation. The lower the
standard of education, the greater the need for careful preparation before new regulations
can be introduced and enforced. It is better to start in a small way and work up, than
to introduce a multiplicity of rules and raise a wall of opposition, which makes enforcement difficult. Legislation alone cannot improve hygiene. To launch regulations without
first preparing the way, is like sowing seed without first ploughing the ground. Old
traditions die hard, and bad habits are not easy to change.”
This statement applies particularly well to excreta disposal programmes,
which are designed to effect desirable changes in people’s attitudes and
practices. In this field public health instruction is more important than
compulsion, and sanitary inspection should not aim at the enforcement
of regulations by means of sanctions. Instead, it should be directed away
from that concept.
TRAINING
AND FUNCTION
OF THE SANITATION
STAFF
Categories of Personnel Required
Sanitation programmes in general, and rural excreta disposal schemes
in particular, require for successful planning and execution a number of
competent sanitary staff at various levels of responsibility. This staff
includes public health (or sanitary) engineers, health (or sanitary) inspectors, health assistants, health aides, and village workers.
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It is quite probable that rural sanitation work has been carried out
in many parts of the world without sanitary engineers, but not without
sanitary engineering.” Often medical officers of health, assisted by health
inspectors, are responsible for all phases of sanitation. However, experience
has repeatedly shown that, because of the multiple engineering aspects
involved, engineers trained in the sanitary sciences are needed at the
highest possible level of the health services for the formulation, administration, and development of sanitation programmcs, including rural
schemes. On this subject, the WHO Expert Committee on Environmental
Sanitation 43 stated :
” The assumption, perhaps too widely made, that underdeveloped regions are not
prepared for the services of the best-trained specialists in environmental sanitation can
readily be contested. Countries of minimum resources arc most in need of the highest
expert service available, both for diagnosis of need and tbr planning of solutions. The
relegation of these functions to less-adequately prepared persons results from a great
misunderstanding of the complexity of the problems in environmental sanitation encountered in areas of low economic level. These problems require for their solution the
impact of high intelligence, training, and experience, even when the number of persons
possessing such qualifications is necessarily a minimum. It is unsound practice literally
to send a boy to do a man’s job.”
Apart from a few public health (or sanitary) engineers, the numbers
and types of the other officers to be trained will be governed, according
to circumstances in countries, by : (a) the background education of the
potential recruits, (b) the ability and capacity of the training establishment
to train different grades simultaneously, and (c) the pattern of the health
services, if any, into which the new staff will be integrated.
Whether a new training programme is aimed at producing sanitarians
(health inspectors, assistants, and aides, as listed above) for general
sanitation wbrk, or for a specific rural sanitation scheme, it is perhaps
preferable not, to dissipate teaching resources, but to concentrate all efforts
on producing a single type of sanitarian. In the case of rural sanitation
programmes, the greatest need is usually for sanitarians of the “ health
assistant ” or “ health aide ” levels. Such personnel are assigned to rural
towns and villagesi and work under the supervision of health inspectors
who are posted in district headquarters.
Village workers are trained within the rural areas concerned, not
necessarily in the sarn? training school as the sanitarians. The training
of such workers is directed towards the stimulation of the self-help
movement, of which sanitation is only one of several elements. Village
workers are usually trainu;d to do spe’cific jobs, such as latrine or well
construction, or maintenance of hand pumps or other equipment.
a The term ” sanitary ensineerins ” includes the public health aspects of aII environmental conditions and situations the control of which is based upon engineering princiDles
and the application
of scientific knowledge.
The terms “ sanitary
health engineer “, as used in this monograph.
are interchangeable.
engineer ” and “ public
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In addition to sanitation staff, foremen and workers must be trained
in the construction practices and procedures adopted for field application
in the excreta disposal scheme.
Function of Sanitation Personnel
The nature and scope of the training of the rural sanitation worker
engaged in the excreta disposal programme depend primarily upon the
function which he will be expected to discharge. Sometimes training
schemes are initiated without a clear understanding of what sort of health
worker is wanted and what jobs the sanitarians are expected to perform.
As a result, the sanitarian produced under such training is likely to be
disoriented and dissatisfied when confronted with rural problems and
situations for which he finds himself unfit, and he may decide to quit the
job, thus creating an undesirable turnover of laboriously trained staff.
In order to determine the functions of the future sanitarians, it is
necessary to study such matters as the national sanitation plan (if one
exists) of the country concerned, the present organization and responsibilities of health services and municipal administrations, and the country’s
general health and sanitary conditions to which attention will have to
be paid in the future. The duties of the various categories of sanitarians
may be described in general terms as :
(1) making preliminary surveys of a district, recording its sanitary
conditions, and participating in the formulation of a plan of action for
their improvement ;
(2) carrying out programmes of practical sanitation based on 1 above;
(3) establishing good relations with the public, and educating the
public in health matters ;
(4) maintaining active collaboration in all of the duties mentioned
above with other services whose activities have a bearing on environmental
sanitation.
The health (or sanitary) inspector must be able to perform all these
duties. The work of the health assistant will be concerned mainly with
item 2, and he should perform duties 1, 3, and 4 under direct supervision. The health aide should be limited to duties under 2. This distribution of functions among the sanitation staff will, in most cases, be
well suited to the execution of programmes of excreta disposal in rural
areas.
Conditions of Service
In planning a training scheme for sanitarians, it is necessary to consider
the future conditions of service, including such matters as the possibility
of personnel rotation from urban to rural areas and vice versa, the scales
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of pay and allowances which will be granted to this sanitation personnel,
and their chances for promotion. Since the duties of sanitarians range
over a broad field of actiyities, their status and emoluments should compare
favourably with the pay in similar professions. These should preferably
include periodic within-grade increases for satisfactory performance and
promotions to higher grades, eventually to supervisory positions. In rural
sanitation programmes, the need for supervisors will arise at a relatively
early date and will be more and more pressing as the activities expand.
The supervisory positions should be filled from the ranks of the inspectors.
While at the beginning these promotions may be made on a somewhat
informal basis, they should eventually become a part of the personnel
policy of the health departments concerned. In some countries a system
of rewards for good work has been found to be desirable to help maintain
a high morale among the staff and to reduce turnover.
Selection of Trainees
A discussion of this subject raises several questions of an economic,
educational, and social character. Men of high calibre and education
will almost always perform the best work in sanitation ; but, of course,
they are usually the most difficult to recruit, and demand higher salaries
than those which may be offered to them. On the other hand, people
willing to accept very low pay are often incapable of sustaining the effort
and interest necessary for the long-range successof rural sanitation undertakings. It is therefore necessary to study the local scene and to offer
scales of pay and allowances sufficient to attract “ trainable ” persons.
The level of general education of the potential recruits may be another
stumbling-block. It is desirable to investigate the curricula of local schools
as well as the teaching methods used in these schools. The information
obtained will point to certain gaps. in general education which need to
be filled before technical subjects can be taught. It has been suggested
that : 43
(a) the educational background of health inspectors should be the
equivalent of some twelve years of education from the beginning, and
should be suticient to permit them to matriculate at a university ;
(b) the educational standard for health assistants should be the equivalent of at least seven to eight years of education from the beginning,
or in some countries to that of the highest class in the elementary school ;
(c) in the case of health aides, the standard of education may be
elementary, comprising reasonable competence in reading, writing, and
simple arithmetic,
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169
It is always wise to choose men from the small towns and villages where
the rural sanitation work is to be done. These men are accustomed to
rural life and are not apt to get discouraged too quickly when facing the
challenges of the job. Staff turnover is always greater among persons
recruited from cities, even though the cities may be within the same general
area or province concerned. Family status of recruits is also an important
factor to consider. A good rule is to start training single men (for they
are much more mobile), or at least to keep married sanitarians in the
towns from which they were recruited. The suggestion has been made
that women might be trained as sanitarians who could perform duties
in places inaccessible to men. In addition to the above-mentioned qualifications, sanitarians should be selected among persons exhibiting good
character, personality, and integrity.
Training
It is desirable that sanitarians should be trained within the country
concerned and, preferably, at a centre located within a region possessing
the same general characteristics as the rural area where the sanitation
programme will be developed. Facilities such as health centres and laboratories, hospitals, water and sewage works, and refuse disposal and other
sanitary installations should be available for the practical demonstration
and training of the students. In fact, most of the duties of sanitarians
are of a practical nature, and their training should therefore be essentially
operational. Much of the teaching should take place outside the classroom
during field visits and inspections, and the theoretical lectures should
relate as much as possible to field applications. Such training will aim
at developing the trainees’ abilities in observation, criticism, and constructive suggestions. Particular care should be taken to stress the future
advisory and teaching role of the sanitarian and to combat the idea of
police-power inspection.
In reviewing the literature on the subject of training of sanitarians, it
is noted that the duration and contents of courses differ widely throughout
the world : training courses vary from five weeks to three years, and the
course material from application of simple sanitary measures through
class work and closely supervised field exercises to academic work of
university calibre with field training in health departments. This might
well be expected, for each training course has been developed in the light
of the customs, history, needs, and health programmes of the country
concerned. The WHO Expert Committee on Environmental Sanitation 43
has suggested courses which might be included in the training programmes
for various categories of sanitarians (see Annex 1, p. 175).
i
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AREAS
Unless one has had iong teaching experience, the first training course
and the beginning work in community sanitation in rural underdeveloped
areas are likely to be more enlightening to the teacher and administrator
than to the students. With a large class and a long course, the investment
of resources-e.g., for school buildings, transportation facilities for students,
demonstration and library materials, and equipment-is apt to be considerable ; yet it is difficult to foresee all the personnel needs of the sanitation
programme, as well as the reaction of the students to the courses presented.
For these reasons a pilot type of training school may be desirable in the
first instance under such a situation. After the sanitation work has been
going on for a while, the needs for personnel and for a particular type
of training will be better defined, the less capable students and staff will
have been weeded out, and it will then be possible to readjust the training
programme accordingly.
Another advantage in starting the training scheme on a small scale
is the aid this gives to good supervision and leadership of the trainees,
particularly from the standpoint of the supervisor. It is fallacious to
believe that the sanitarians, upon the completion of a short training course,
are capable of solving all kinds of problems. The majority of them will
be going into the field with considerable uncertainty and, if left by themselves too long a time at the beginning of their career, may either fail or
get off on the wrong track. To avoid this, it is necessary for the supervisor
to visit them frequently.
This feeling of uncertainty on the part of the sanitarians can also be
considerably reduced if their training has prepared them to do a limited
number of jobs very well-a point which cannot be emphasized too much.
It is not wise to give the trainees a great deal of vague, theoretical notions
and to expect them to go out into the field and be successful. Such training
is bound to lead to failures ; and, what is worse, the sanitation programme
itself may fail or receive an irreparable setback. The training should be
highly objective and should be designed to make the men confident and
aware of where to start, how to start, and where to go.
A compendium of the lectures and field notes should be given to the
new sanitarians at the end of the course. This will serve them as a reference on problems which often arise and for which there is no clear-cut
solution.
In most instances, training courses are initiated under the conduct of
teachers selected from among existing health department personnel.
However, it is acknowledged that the training of sanitarians is an exacting
task which requires at least a nucleus of full-time and experienced teachers,
preferably possessing previous kncwledge of teaching principles. Such
teachers should be able to develop training manuals written in the local
language and adapted to local problems and to the educational level of
trainees, Foreign books should be used only as references.
EXCRETA
DISPOSAL
171
PROGRAMMES
In planning the training programme, provision should also be made
for various extension activities designed to widen the influence of the school,
to establish a link between the teaching staff and the health activities in
the territory, and to encourage and follow up the work of the former
students.a The following types of activity are suggested :
(a) Team-work in varied regions, possibly under the supervision of
the teaching staff. This may be a very desirable activity immediately after
the course, where the qualifying students are young and inexperienced,
or where the governments have insufficient health staff to provide the
necessary supervision.
(b) Refresher courses. Such courses give everyone a chance to develop,
and offer encouragement to the sanitarians, who feel that the health
department is paying attention to their welfa,re. The sanitarians do not
have to absorb much new material at any one sitting, and the engineer
can develop the sanitation programme more objectively in the light of
what his whole staff can learn and contribute in such courses.
(c) Conferences, seminars, dealing with one or two special topics.
(d) Health weeks, with the participation of schools and the public.
(e) Promotion courses, preparing lower-level sanitarians for upgrading.
Utilization of Sanitarians
Proper utilization of sanitation personnel is as important as their
training, and should be based on the principle that each sanitarian should
fill a position fitted to his grade and training. To sanitarians who are
beginning rural or community sanitation work there is nothing so important
as success; and success will come much more easily and quickly if the
scheme provides for concentration on objectives limited in number and
scope to what the sanitarian can achieve at any one time. Such a technique
is the surest and quickest way to get to a broader programme. A latrine
project is excellent as an initial objective, provided the health department
is prepared to contribute leadership and its proper share of funds, materials,
and supervision, the last by means of sanitarians assigned to each
community.
It is important that the sanitarian be assured at all times of the full
material and moral support of the health authorities. This is especially
true in the initial stages of his work in a new area. He will need encouragement and recognition from his superiors. Above all, his talents should
not be misused by making him a “ Jack of all trades “.
a Slater. A. R. F. (1956) The planning of training progrommes
(Unpublished working document WHO/EnvSan./98)
for
sanitation personne
ANNEXES
Annex 1
EDUCATION
AND
TRAINING
OF SANITARIANS
*
Snnitarians
Health inspector
A large part of the training of the health inspector should consist of
practical demonstrations with a period of experience in a health department.
The course should be so designed that the subjects may be expanded to
higher stages to enable the health inspector, with further study, to advance,
if he is suitable and so desires, to the academic course. He should be
imbued with a spirit of inquiry and enthusiasm for public health ideals.
The basic idea is to educate and train a good general practitioner of
environmental sanitation.
The courses of study should include the elements of the following subjects :
mathematics, physics, chemistry, bacterioiogy, parasitology, epidemiology,
anatomy, and physiology, * the control of communicable diseases; disinfection and disinfestation ; water-supply and treatment ; sewerage and
sewage treatment ; the collection and disposal of refuse and excreta ; insect
and rodent control ; factory inspection ; building construction, including
drainage, septic tanks, soakage pits, and the like ; and the drawing and
examination of simple plans. The health inspector should be instructed
in the inspection of meat and food-stuffs and the procuring of samples
for analysis, and be able to deal with special sanitary problems in places
such as hospitals, schools, airports, mines, etc. He should also receive
instruction in public health administration, statistics, legislation, and legal
procedure.
Health assistant
The education and training of the health assistant should be designed
so that he may play an important part in environmental sanitation in
urban and rural areas under suitable direction. The course of study should
provide ample time for practical demonstrations. The subjects taught
should include : very elementary anatomy and physiology ; mensuration,
simple geometry, simple arithmetic, and sketching ; general hygiene,
causes of disease, and sanitation, including air, water, and food. The
course should provide some instruction in communicable diseases,
disinfection and disinfestation, case investigation and control methods,
* Reproduced from the second report of the WHO Expert Committee on Environmental
Sanitation.4a
175 -
176
EXCRETA
DISPOSAL
FOR RURAL
AREAS
elementary medical entomology and elementary helminthology, collection
and disposal of refuse and night-soil, with some information on the more
complex sewerage, sewage disposal, and water-supply systems. The health
assistant should also be instructed in food inspection, with visits to food
production establishments ; in nutrition ; in rodent and insect control ; in
the use of artisan’s tools and the construction of latrines and privies ;
and in personal hygiene. He should be encouraged to promote health
education in rural communities.
Health aide
Under suitable direction the health aide would be a valuable person
in the promotion of rural sanitation. His instruction, therefore, should
include a knowledge of sanitary work as applied to rural areds, such as
the raising of the standard of housing, the improvement of rural watersupplies, and refuse and excreta collection and disposal. The course
should include elementary understanding of the factors concerned in the
spread of the common communicable diseases in relation to sanitation,
It should also include the preparation of simple hygiene reports and the
keeping of a diary. The health aide should be able to recognize local
insect pests and rodents and be instructed in disinfection and disinfestation.
He should be able to construct simple sanitary works.
Voluntary Leaders for Mobilization
of Self-Help
The people in this category cannot spare the time for long and forma .1
education far away from their homes. Short but intensive training for
about two weeks has been tried and found sufficient.
The curriculum should be simple and practical. Besides explaining
the causes and mode of communication of the most important diseases
prevailing in the area, the curriculum should emphasize the need for
personal hygiene,’ sanitation of the environment, and maternal and child
care. It should also provide data on, and point out sources of, materials
and skilled service that may be available to the local people for improving
the environment, and for constructing sanitary facilities such as wells for
safe water-supplies, or sa.nitary latrines.
The trainee will have to be ?utght in the language of the locality. In
the case of volunteers and village schoolmasters, the period of training
should be so chosen as to interfere least with their normal business.
After receiving training, the volunteers and trained teachers should
be the chosen repositories of confidence of the local health-authorities
in those matters which come reasonably within their competence, for
example, the issue of insecticides.
Annex 2
LIST OF REVIEWERS
Mr A. Amramy, Professor of Public Health Engineering, Madras University, Madras,
India
Dr N. Ansari, Endemo-Epidemic Diseases Section, WHO, Geneva, Switzerland
Mr J. de Araoz, WHO Public Health Engineer, Iraq
Mr J. Arbuthnot, WHO Public Health Engineer, Ceylon
Mr C. H. Atkins, United States Public Health Service, Charlottesville, Va., USA
Mr M. Aziz, Assistant Professor of Sanitation, American University, Beirut, Lebanon
Dr H. G. Baity, Director, Division of Environmental Sanitation, WHO, Geneva,
Switzerland
Mr F. E. Benjafield, Chief Health Inspector, Peri-Urban Areas Health Board, Pretoria,
Union of South Africa
Dr W. Bonne, Director, Division of Communicable Disease Services, WHO, Geneva,
Switzerland
Mr J. Bwell, Regional Adviser in Environmental Sanitation, WHO Regional Office
for the Eastern Mediterranean, Alexandria, Egypt
Mr R. Casanueva, WHO/PASB Public Health Engineer, Mexico
Mr F. Chellapah, formerly Deputy Director, WHO Regional Office for South-East
Asia, New Delhi, India
Mr R. N. Clark, Chief Adviser in Public Health Engineering, WHO, Geneva, Switzerland
Mr P. Echavez, formerly WHO Sanitary Engineer, Taiwan
Mr T. Femarrdez, WHO/PASB Public Health Engineer, Dominican Republic
Professor John C. Geyer, Professor of Sanitary Engineering, The Johns Hopkins University, Baltimore, Md., USA
Mr A. Goor, WHO Public Health Engineer, Philippines
Professor Harold B. Gotaas, Professor of Sanitary Engineering, University of California,
Berkeley, Calif., USA
Mr C. Hilburg, WHO/PASB Public Health Engineer, Paraguay
Dr W. M. Howells, Medical Officer of Health, Kaduna, Northern Nigeria
Dr J. L. Hydrick, Rockefeller Foundation, New York, N.Y., USA
Professor C. W. Kruse, Associate Professor of Sanitary Engineering, The Johns Hopkins
University, Baltimore, Md., USA
Mr S. A. C. Lord, WHO Sanitarian, Afghanistan
Dr K. Martin, WHO Public Health Officer, Nairobi, Kenya
Mr C. Morse, WHO Public Health Engineer, UNRWA, Beirut, Lebanon
Mr L. Orihuela, WHO Public Health Engineer, Ethiopia
Dr E. J. Pampana, Director, Division of Malaria Eradication, WHO, Geneva,
Switzerland
12
-
177 -
178
EXCRETA
DISPOSAL
FOR RURAL
AREAS
Mr G. Ponghis, Regional Adviser in Environmental Sanitation, WHO Regional Office
for South-East Asia, New Delhi, India
Mr M. Roy, formerly WHO Public Health Engineer, Afghanistan
Mr P. Ruiz, WHO/PASB Public Health Engineer, Uruguay
Mr J. C. Scott, formerly Professor of Agronomy, Cheeloo University, China
Mr H. Shipman, WHO Public Health Engineer, Calioub, Egypt
Mr Purtej Singh, Public Health Engineer, Nagpur, India
Mr A. D. Smythe, WHO Public Health Engineer, North Borneo
Mr D. Souter, WHO Sanitarian, Thailand
Mr 0. Sperandio, Service Especial de Salide de Araraquara, %-lo Paulo, Brazil
Dr A. J. W. Spitz, formerly WHO Team Leader, Seychelles
Mr P. Stevens, formerly WHO Public Health Engineer, Iran
Mr G. Tapia-Murillo, WHO Public Health Engineer, Syria
Mr V. W. Vickers, Senior Health Inspector, Public Health Department, Kampala,
Uganda
REFERENCES
REFERENCES
1. Anderson, G. W. & Arnstein, M. G. (1953) Communicable disease control, 3rd ed.,
New York, p. 17
2. Baars, J. K, (1957) BuII. Wld Hlth Org., 16, 727
3. Bendixen, T. W. et al. (1950) Studies on household sewage disposal systems. Second
in a series of research reports on individual sewage disposal systems, Cincinnati,
Ohio (Federal Security Agency, Public Health Service)
4. Caldwell, E. L. & Parr, L. W. (1937) J. infect. Dis., 61, 145
5. Caldwell, E. L. & Parr, L. W. (1938) J. infect. Dis., 62, 225, 272
6. California State Water Pollution Control Board (1954) Report on the investigation
Sacramento, Calif. (Publication No. 11)
of travel of pollution,
7. Carter, J. C. (1938) Bull. Hyg. (Lond.), 13. 591
8. Derryberry, M. (1954) Bull. Wld Hlth Org., 10, 145
9. Derryberry, M. (1955) Bull. int. Un. Hlth Educ. Publ., 3, 3
10. Dyer, B. R. & Bhaskaran, T. R. (1945) Indian J. med. Res., 33, 17
11. Dyer, B. R., Bhaskaran, T. R. & Sekar, C. C. (1945) Indian J. med. Res., 33, 23
12. Ehlers, V. M. & Steel, E. W. (1950) Municipal and rural sanitation, 4th ed., New
York, p. 28
13. Fair, G. M. & Geyer, J. C. (1954) Water ~cpply and waste-water disposal, New
York, p. 26
14. Foster, G. (1951) A cross-cultural anthropological analysis of a technical aid program,
Washington, D .C .
15. Fournelle, H. J., Day, E. K. & Page, W. B. (1957) Pub/. Hlth Rep. ( Wash.), 72,203
16. France, Bureau Central d’Etudes pour les Equipements d’outre-Mer (1955) Le
p&i1 f&al et Ie traitement des de’chets en milieu tropical, Paris
17. Glenn, H. E. (1950) Bamboo reinforcement in Portland Cement concrete, Clemson,
S.C. (The Clemson Agricultural College of South Carolina, Bulletin No. 4)
18. Gotaas, H. B. (1956) Composting: sanitary disposal and reclamation of organic
wastes, Geneva (World Health Organization : Monograph Series, No. 31)
19. Hanlon, J. J. (1950) Principles of public health administration, St. Louis, MO.
20. Hardenbergh, W. A. (1950) Sewerage and sewage treatment, Scranton, Pa.
21. Hill, F. G. & Ackers, G. L. (1953) Principles of design for small domestic-sewagetreatment plants. In : The design and operation of septic tanks, Geneva, p. 31
(World Health Organization : Monograph Series, No. 18)
22. Hyde, H. van Zile (1951) Amer. J. publ. Hlth, 41, 1
23. Imhoff, K., Muller, W. J. & Thistlethwayte, D. K. B. (1956) Disposal of sewage
and other water-borne wastes, London
24. India, Ministry of Health (1949) Report of the Environmental Hygiene Committee,
New Delhi
25. India (1954) Manual of hygiene for the armed forces, 1953, Simla, pp. 359-60
26. Kilpatrick, J. W. & Schoof, H. F. (1956) Pub). Hlth Rep. (Wash.), 71, 787
-
181 -
182
EXCRETA
DISPOSAL
FOR RURAL
AREAS
27. Kligler, I. J. (1921) Monogr. Rockefeller Inst. med. Res., No. 15
28. Lethem, W. A. (1956) The principles of milk legislation and control, Rome (FAO
agricultural development paper No. 59)
29. Macdonald, 0. J. S. (1952) Small sewage disposal systems, London
30. Minnesota Department of Health, Division of Environmental Sanitation (1953)
Small sewerage systems, Minneapolis
31. Sanner, L. (1956) Elements d’hygiene rnrole tropicale, Paris (Section de Documentation Militaire de I’Outre-Mer, Centre Militaire dInformation et de Specialisation pour I’Outre-Mer)
32. Scott, J. A. (1953) Health considerations involved in the treatment and disposal of
sewage from isolated dwellings. In : The design and operation of septic tanks,
Geneva, p. 9 (World Health Organization : Monograph Series No. 18)
33. Scott, J. C. (1952) Health and agriculture in China, London
34. Simmons, J. S. et al. (1944-51) Global epidemiology. A geography of disease and
sanitation, Philadelphia, Pa., 2 vols
35. Tisdale, E. S. & Atkins, C. H. (1943) Amer. J. publ. H&h, 33, 1319
36. United Nations, Administrative Committee on Coordination (1956) Twentieth report
TOthe United Nations Economic and Social Council, Annex III, New York (Document E/293 1)
37. United States Department of Health, Education, and Welfare, Public Health Service
(1957) Manual of septic-tank practice ; developed in cooperation wit!! the Joint
Washington, D.C. (Public Health Service PublicaCommittee on RuralSanitation,
tion No. 526)
38. United States Federal Security Agency, Public Health Service (1943) Individual
sewage disposal systems. Recommendations of Joint Committee on Rural Sanitation, Washington, DC. (Reprint No. 2461 from the Public Health Reports
[Revised 19471)
39. Weibel, S. R., Bendixen, T. W. & Coulter, J. B. (1954) Studies on householdsewage
disposal systems. Third in a series of research reports on individual sewage disposal
systems, Cincinnati, Ohio (Federal Security Agency, Public Health Service ;
Public Health Service Publication No. 397)
40. Weibel, S. R., Straub, C. P. & Thoman, J. R. (1949) Studies on household sewage
disposal systems. First in a series of research reports on individual sewage disposal
systems, Cincinnati, Ohio (Federal Security Agency, Public Health Service)
41. World Health Organization (1957) Annual Epidemiological and Vital Statistics, 1954,
Geneva
42. World Health Organization, Division of Environmental Sanitation (1956) Bull.
Wld Hlth Org., 14, 816
43. World Health Organization, Expert Committee on Erivironmental Sanitation (1952)
Wld Hith Org. techn. Rep. Ser., 47, 5, 11-12, lb-17
44. World Health Organization, Expert Committee on Environmental Sanitation (1954)
Wld Hlth Org. techn. Rep. Ser., 77, 9, 8, 17
45. World Health Organization, Expert Committee on School Health Services (1951)
Wld Hlth Org. techn. Rep. Ser., 30, 9
46. Yeager, C. H. (1931) Philipp.
J. Sri., 46, 681
INDEX
INDEX
Amoebiasis, 13
Antipole system, 65
Aqua privies, 40, 76-87
advantages and disadvantages, 85
bowl, 79, 80, 81
construction, 86, 87
cost, 84-85
effluent disposal, 82
floor, 79-81
location, 82
operation and maintenance, 84
superstructure, 8 1
tank, 79, 83
ventilation, 81-82
Ascaris, 9, 13, 16, 27
Augers, 100-103, 104
Bilharziasis, 9, 123
Bored-hole latrines, 41, 95-103
advantages and disadvantages, 98-99
construction, 99-102
equipment, 100-102, 103, 104
door, 97-98
hole, 95-96
location, 98
materials, 99-100
mound, 98
superstructure, 98
Box-and-can privy, see Bucket latrines
Bucket latrines, 41, 103-l 11
collection chamber, 106
collection of buckets, 106-107
cost, 110-111
disadvantages, 1; 3
night-soil disposal, 107-l 10
receptacle, 105
superstructure, 106
Building sewer, 131-132
,
Campaigns, see Sanitation programmes
Caustic soda, 119
Cesspools, 34, 122, 123-124
Chemical toilet, 42, 119-120
-
Chiengmai bowl, see Water-seal latrines,
bowl
Chlorine, 138
Cholera, 9, 14, 16
Cleanliness of latrines, 38, 65
Community responsibility for public
latrines, 23
Compost privies, 42, 11I, 115-l 19
advantages and disadvantages, 119
“ double-vault ” latrine, 118-l 19
night-soil as fertilizer, 11S-I 16
operating procedure, 116-l 17
parts, 116
volume, 117
Contracts between families and health
departments, 20
Cost estimation for sanitation work, 161
Covers, privy holes, 34-35
septic tanks, 137
Criteria for selection of type of unit, 38-39
Decomposition of excreta, 25-27
Demonstration projects, see Pilot projects
Design of privies, 25-38, 160-161
cost factors, 38
engineering factors, 35-36
human factors, 36-38
Diarrhoea, 9, 10, 14, 15, 16
Digestion of night-soil, 108, 109-110
Dilution of wastes for disposal, 122-l 23,
138
Distribution boxes, 141-143
Dosing siphons, 146-147, 149, 153
Dysentery, 9, 14, 16
Earth closet, see Bucket latrines
Economic aspects of insanitation,
Effluent, aqua privies, 82
septic tanks, 136, 138-155
Enteritis, 9, 10, 14, 15, 16
15-16
Faeces, quantities, 27-28, 46-48, 117
Fertilizer, night-soil as, 27, 115-l 16
185 -
186
EXCRETA
DISPOSAL
FOR RURAL
AREAS
Percolating filters, see Trickling filters
advantages and disadvantages, 113-114 Percolation tests, 139-l 4 1
Pilot projects, 21, 161
Filter trenches, see Sand-filter trenches
Flies, 9, 33-34, 35, 40, 41, 79, 80, 84, Pipes, aqua privies, 146
septic-tank effluent, 143-144
87, 96, 110, 113, 121, 124, 155, 1.59
Foot-rests, 52, 53, 57, 60, 61, 80-81, 87, Pit privies, 40, 42-76, 183
advantages and disadvantages, 40, 69
92
base, 44, 45, 46, 50-52
construction, 69-76
Grease interceptors, 124, 129-131
jigs and forms, 71-73, 74, 7,?
Ground-water pollution, 28-33, 44, 79,
labour, 73
98, 113, 119, 121, 123, 125, 139,
mass production, 70-7 1
164
materials, 69-70
procedures, 73, 75, 76
Health aides, 157, 158, 165-168, 176
cost, 68-69
Health aspects of rural sanitation, 9-16
floor, 48, 52-62
Health assistants, 157, 158, 165-168, 175location, 68
176
mound, 62, 65
Health education of the public, 18, 22pit,
42-50
23, 159-160
dry,
43-49
Health and excreta disposal, direct relation,
life,
43-49
9-10
lining, 49-50
indirect relation, 11
sludge
accumulation, 44, 46, 47
Health inspectors, 16, 19, 157, 165, 167,
ventilation, 66, 67
168, 175
wet, 43-49
Hookworm, 9, 13, 16, 27, 31, 50, 53,
superstructure, 63-67
108, 113
Pollution, see Ground-water pollution,
Soil pollution, Surface-water pollution
Incineration of night-soil, 107
Pour-flush
latrine, see Water-seal latrine
Insanitation, effect on disease, 9-11
Privacy,
36-37
Insecticides, 34, 49, 113
Programmes for excreta disposal, 17-24,
Installations, desirable types, 39-40
156-171
less desirable types, 41-42
Public
health engineers, see Sanitary
special types, 42
engineers
Irrigation with septic-tank effluent, see
Public health inspectors, see Health
Subsurface irrigation
inspectors
Public
latrines, 23-24
Latrines, location, general conclusions,
Psychological
implications of rural sanita32-33
tion,
17-24
See also individual types
Ferrillcfes, 41, 11 l-l 14
Measurement of
163-164
Morbidity due to
Mortality due to
Mosquito control,
health and sanitation,
insanitation,
insanitation,
49
10, 11
10, 11
Nitrogen cycle, 26
Overhung latrines, 42, 114-l 15
Paratyphoid fever, 9, 10, 14
Pathogenic organisms, survival,
115, 128
27, 3 1,
Sand filters, 138, 144-153
open, 149, 151-153
subsurface 149, 150
Sand-filter trenches, 138, 147-148
Sanitarians, education and training, 169171, 175-176
See also Health aides, Health assistants,
Health inspectors, Sanitary engineers
Sanitary engineering, definition, 166
Sanitary engineers, 16, 165-l 66
Sanitary regulations, 164-165
Sanitary surveys, 158-I 59
INDEX
Sanitation, state in various countries, 13
Sanitation programmes, 17-24, 156-l 71
campaigns for privy construction, 22-23
community participation, 17-I 8
construction, 162
cost estimation, 161
evaluation of results, 163-l 64
family participation, 1B-20
health education, 159-160
maintenance of installations, 162
pilot projects, 161
role of health department, 20-22
sanitary regulations, 164-l 65
staff, 157-158, 165-171, 175-176
surveys, 158-l 59
Selection of unit, 38-39, 160-161
Septic tanks, 122, 125-138
building sewer, 131-132
capacities, 132-l 34
construction, 136-I 37
efluent, 136, 138-155
grease interceptors, 129-131
inlets, 135
location, 136
multi-compartment tanks, 134-l 35
operation and maintenance, 137-l 38
outlets, 135
primary treatment, 127-I 29
secondary treatment, 129
shape, 135-l 36
size, 132-134
Sewage, see Dilution of wastes for disposal,
Effluent, Water-carried systems
Sewers, night-soil disposal, 108, 109
See also Building sewer
Siting of latrines, see Latrines, location
Sludge, 44, 46, 47, 79, 84, 109, 127, 128,
132-134, 137-138
Social aspects of rural sanitation, 17-24,
158-159
Soil pollution, 28, 30-32, 41, 79, 121, 164
Squatting plate, bucket latrine, 106
pit privy, 42, 52, 56, 57, 68, 69
water-seal latrine, 87, 89, 91, 92, 93
187
Staff for excreta disposal programmes,
categories, 165, 167
conditions of service, 167-I 68
functions, 167
selection, 168-169
training, 157-l 58, 169-l 71, 175-l 76
utilization, 171
Subsurface irrigation
with septic-tank
effluent, 138, 139-146
disposal field, 141-146
percolation tests, 139-141
Surface-water pollution, 41, 113, 114-115,
122-123
Tinettes, see Bucket latrines
Training of sanitarians, 157-158, 169-171,
175-176
Transmission of disease through excreta,
11-13
Trench latrine, see Fed&es
Trenches, aqua privies, 146
night-soil disposal, 107, 108-109
sand-filter, 138, 147-148
septic-tank eRuent disposal, 144-145
Trickling filters, 138, 153-l 55
Typhoid fever, 9, 10, 11, 14 15, 16
Ventilation, aqua privy, 81-82
bored-hole latrine, 98
bucket latrine, 106
pit privy, 65, 66, 67
Water-carried systems, 39, 103, 121-135
Water-seal latrines, 40, 87-95
advantages and disadvantages, 93-95
bowl, 87, 88-92
disposal system, 92-93
location, 93
squatting plate, 87, 89, 91, 92, 93
Water supplies, 9, 11, 15, 121, 123, 136
See also Ground-water pollution,
Surface-water pollution
WORLD HEALTH ORGANIZATION
MONOGRAPH SERXES
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ASPECTS OF JUVENILE
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HOSTS OF SCHISTONo. 37 INTERMEDIATE
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METHODS IN MALARIA
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Sir
IN THE SWBTROPNo. 29 INFANT NUTRJTION
ICS AND TROPICS - D. B. Jelliffe (2nd
edition, 1968)
a.70 $9.00 SW.ft. 27.- (clothbound)
a.50
:
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HYGIENE
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-
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No. 27 CHEMOTHERAPY
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FEVER
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a
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-
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No. 26 PoLIoMYELITIs
AP-
H. A.
No. 42 WATER SUPPLY FOR RURAL
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R. Pollitzer ( 354)
No. 23 LABORATORY
No. 33 MEAT
No. 41 PRINCIPLES OF ADMINISTRATION
PLIED TO NURSING SERVICE Goddard (1958)
No. 45 DIFERENTIAL
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