Part 23 - cd3wd423.zip - Offline - A.T. for Water Supply and Sanitation: Night Soil Composting

Part 23 - cd3wd423.zip - Offline - A.T. for Water Supply and Sanitation: Night Soil Composting
MICROHCHE
REFERENCE
LIBRARY
A project of Volunteers in Asia
by: Hillel
I. Shuval,
DeAnne S. Julius
Charles
Published by.
The World Bank
1818 H Street,
N.W.
Washington, DC 20433
USA
Available
from:
The World Bank
Publications
Unit
1818 H Street,
N.W.
Washington, DC 20433
USA
Reproduced by permission
G. Gunnerson and
of the Wor!ld Bank.
Reproduction of this microfiche
document in any
form is subject to the same restrictions
as those
of the original
document.
Appropriate Technology
for Water Supply and S
Night-soil Cornposting
by Hillel I. Shuval, Charles 6. Gunnerson,
and DeAnne S. Julius.
Copyright
0
c
1981 by the International
Bank for
Development/The
World Bank
Reconstruction
and
The World Bank enjoys copyright
under Protocol
2 of the Universal
Copyright
convention.
Nevertheless,
permission
is hereby granted for reproduction
of
this nraterial,
in whole or part,
for educational,
scientific,
or developmentrelated
purposes except those involving
commercial sale provided
that (a) full
citation
of the source is given and (b) notification
in writing
is given to
tbe Director
of Information
and Public Affairs,
the World Bank, Washington,
D.C. 20433, U.S.A.
VOLUME 10
Water,
and Telecomunications
The World Bank
December 1981
Department
PREFACE
in 1916 the Uorld Bank undertook
a research project
on appropriate
technology
for water supply and waste disposal
in developing
countries.
Emphasis was directed
toward sanitation
and reclamation
technologies,
particularly
as they are affected
by water service levels and by
ability
and willingness
to pay on the part of the project
beneficiaries.
In addition
to the technical
and economic factors , assessments were made
of envSronmenta1,
public health,
institutional,
and social constraints.
The findings
of the U.rld Bank research project
and other parallel
research
activities
in the field
of low-cost
water supply and sanitation
are presented fn the series of publications
entitled
Appropriate
Technology for
Water Supply and Sanitation,
of which this report is volume 10. Other
volumes in this serie are as follows:
[vol.
l]
[vol.
la]
[vol.
21
A Planner's
Guide, by John MI Ralbermatten,
DeAnne S. Julius,
Charles G. Gunnerson, and
D. Duncan Mara [a condensation
of Appropriate
Sanitation
Alternatives:
A Planning and Design
Manual, forthcoming
from Johns Hopkins University Press]
[vol.
31
Health Aspects of Excreta and Sullage Management--A
State-of-the-Art
Review, by Richard G. Feachem,
David J. Bradley,
Hemda Garelick,
and D. Duncan
Mara [a condensation
of Sanitation
and Disease:
Health Aspects of Excreta and Wastewater Management,
forthcoming
from Johns Hopkins University
Press]
Technical
and Economic Options,
by John M.
Ralhermatten,
DeAnne S. Julius,
and Charles
G. Gunnerson [a condensation
of Appropriate
Sanitation
Alternatives:
A Technical
and
Economic Appraisal,
forthcoming
from Johns
Hopkins University
Press]
-
A Summary of Technical
and Economic Options
Low-cost Technology Options for Sanitation--A
Stateof-the-Art
Review and Annotated Bibliography,
by
Witold Rybczynski,
Chongrak Polprasert,
and Michael
McGarry [available,
as a joint
publication,
from the
International
Development Research Centre, Ottawa,
Ontario,
Canada]
Sociocultural
Aspects of Water Supply and Excreta
Disposal,
by Mary Elmendorf and Patricia
Buckles
[vol.
61
Country
Richard
Studies in Sanitation
A. Kuhlthau
(ed.)
Alternatives,
by
[vol.
71
Alternative
Sanitation
in Africa,
by Richard
and Kenneth 0. Iwugo
Technologies
for Urban Areas
G. Feachem, D. Duncan MaraT
[vol.
81
Seven Case Studies of Rural and Urban Fringe
in Latin America, by Mary Elmendorf (ed.)
[volt
91
Dasign of Low-Cost Water Distribution
Systems,
Section 1 by Donald T. Lauria,
Peter J. Kolsky, and
Richard N. Middleton;
Section 2 by Keith Demke and
Donald T. Lauria;
and Section 3 by Paul V. Herbert
[vol.
113
'*
Sanitation
Field
DeAnne S. Julius,
[vol.
121
-
Low-Cost Water Distribution--A
Charles D. Spangler
Areas
Manual, by John.M. Kalberaatten,
and Charles G. Gunnerson
Field
Manufi,
by
of volumes 1, 2 and 3 are forthcoming
-The more complete, book versions
under the series title
"World Bank Studies in Water Supply and Sanitation"
- from the Johns Hopkins University
Press (Baltimore
and London).
additional
volums and occasional
With the exception
18 completed.
firam the World Bank's Publications
DehneSJulius
Charles G. Gunnersas
Hillel
I. Shuwal
papers will be published
of volume 4, all reports
Unit.
as ongoing research
may be obtained
ABSTRACT
Among the problems facing those who depend on conservancy or other
systems disposing
separately
grey water and night soil is the lack of a safe,
inexpensive
treatment
method for night soil.
In Kyoto, for example, night
soil is collected
hygienically
to the satisfaction
of users of the system,
only to be diluted
at a central
collective
Taint for discharge
to the sewer
system and treatment
at a conventional
sewage treatment
plant.
This paper
reviews the state of the art on night-soil
cornposting.
The paper concludes
that aerobic composting of night soil represents
a method of treatment
ideally
suited for developing
countries
because of its simplicity
in operation,
limited
need for mechanical equipment,
low cost and its effectiveness
in
inactivating
pathogens,
thus assuring
that the compost can be used without
causing any public health hazar '.
TABLE OF CONTENTS
Page
Preface
Abstract
S~amary and Conclusions
.*........................*.***....%.-*..*
i - 18
. ..........................
Introduction
and Objectives
Public Health Problems Associated
with Pathogenic
Microorganisms
in Night soil and Sewage Sludge Reuse...
The Historical
Development of Composting . . . . . . . . . . . . . .
The Principals
of the Composting Process . . . . . . . . . . . l . .
Historical
Development of Composting Night soil and
Sewage Sludge . . ..I....................................
Modern Developments in Composting Sewage Sludge
and Night soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.
2.
3.
4.
5.
6.
a.
b.
C.
d.
7.
Windrow Sludge Compost Plant in
Los Angeles County Sanitation
District
.........
Ihe Beltsville
Aerated Rapid Compost (BARC)
System for Composting Waste Water Sludge . . . . . . .
Composting Night soil with the BARC System . . . . . . .
. . . . . . . . . . . . . ..*.......................
Conclusion
Economic Aspects
a.
b.
C.
a.
b.
C.
d.
e.
f.
9.
and Pilot
I
II
. ... .... .. ...
Study Needs . . . . . . . . . . . . . . . . . . . . . . . .
Characteristics
of Night Soil ....................
................................
Bulking Materials
Environmental
Parameters .........................
Engineering
and Operating Parameters .............
Evaluation
of the Final Compost from a
nicrobiological
Point of View ....................
Quality of the Compost ...........................
Bibliography
Appendix
Composting
Cost Estimates
for Composting Sludge at
Beltsville
(BAHC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Preliminary
Estimates
of Costs of Composting
10 Dry Tons of Night Soil Per Day . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . ...*...
Problems of Marketing
Research
8.
of Night-soil
. . . . ..*...................................
Technological
Aspects
to Composting Night
Utilization
of Compost,
of the BARC System as Related
Soil, Dr. E. Epstein
Dr. E. Epstein
I
4
13
15
18
24
24
29
40
41
42
42
44
45
46
46
47
47
47
47
47
50
,
LIST OF TABLES
1.
Thermal
2.
Characteristics
3.
Capital
4.
Operating
5.
Total
Costs
for
BARC System
43
6.
Total
Costs
for
LACSD System
44
Death Points
of Some Common Pathogens
of Excreta
Costs
for
and Parasites
from Mixed Populations
in the U.S.
BARC System
Requirements
for
11
19
43
BARC System
43
LIST OF FIGURES
1.
Composting/Drying
2.
Bacteria
3.
Schematic
4.
Temperatures
5.
System
Concentrations
26
Vs. Composting
Diagram of an Aerated
During
28
Pile
32
(Ray 1975)
33
Destruction
Coliforms
of Salmonellids,
Fecal Coliforms,
and Total
During Composting by the BARC System
34
6.
Destruction
of 'F'
35
7.
Mbterials
8.
Construction
Balance
Cornposting
Time
Bacterial
for
of Raw Sludge
Virus
During
Composting
38
the BARC System
of Extended
Aerated
Cells
for
BARC System
39
SUNNARYAND CONCLUSIONS
According
to the World Health Organization,
more than two-thirds
of
have improper or no facilities
for human waste disposal,
a situation
which leads to a vicious
circle
of disease and poverty detrimental
to social
welfare and economic development.
hmadty
The 1976 WAFSITATConference and the 1977 United Nations World Water
Coufereuce set global targets
for providing
water supply and waste disposal
to the whole world's
population
by 1990. Estimates show that this would
involve a cost of $60 billion
for water supply and $200 billion
for waste
disposal
based on conventional
Western engineering
practice.
If the present
rate of investments
in this sector are maintained
and population
growth
it can be estimated that the backlog
continues
more or less at current
rates,
of over 1 billion
people not now provided with water or sanitation
service
will grow, not decrease.
It has also been estimated
that most developing
economies will be unable to finance water carriage
waste disposal
systems even
if loan funds were available.
The World Bank project
to study and evaluate
appropriate
low-cost
technology
for water supply and waste disposal
is aimed
at identifying
and testing
systems capable of providing
low-cost water and
sanitation services which are both socially
and environmentally
acceptable
at
a cost developing
countries
can afford.
The objective
of this report
is to evaluate the possibility
of dehygienic
and economical means of treating
night soil by modern composting so as to allow for the continuation
or expansion of direct
night-soil
collection,
disposal
and safe reuse systems in many developing
countries
as an interim
or even long-term
measure, rather than doing nothing to improve
the health of the public while waiting
futilely
for the day that a water
carriage central
sewerage system can be afforded.
veloping
Night soil use as a fertilizer
in agriculture
has been practiced
in
China and other Asian countries
for centuries
and has been considered
by most
public health authorities
as a serious contributing
cause to the high levels
of enteric
disease and parasitic
infestations
which debilitate
the population.
Nevertheless,
night soil use as a fertilizer
has apparently
played a critical
role in laaintaining
vital
soil fertility
in areas of Asia so intensively
farmed for thousands of years.
For example, recent reports
from China
indicate
that as a reeult
of a national
campaign for night-soil
treatment
and
requirements
of agriculture
in China has
reuse, one-third
of the fertilizer
been provided by recycled
night soil.
,;
"<
The public health problems to be overcome in night-soil
treatment
and reuse are severe since research has amply demonstrated
that night soil
and sewage sludge carries
high concentrations
of the full spectrum of
pathogenic
bacteria,
virus,
protozoans
and helminths
endemic in the community.
Many of the pathogenic
micro-organisms,
helminths
in particular,
'are highly resistant
to the environmental
conditions
prevalent
in conVentiOMl
night soil and sewage sludge digestion
and storage and can survive
for weeks and even months in the soil and on fertilized
crops.
-
ii
-
From a survey of the literature
on night-soil
treatment,
it can be
clearly
concluded that the only fail-safe
night-soil
method which will assure
effective
and essentially
total
pathogen inactivation,
including
the most
resistant
helminths
such as Ascaris eggs and all other bacterial
and viral
pathogens,
is heat treatment
to a temperature
of 55' - 60°C for several hours.
Pathogen inactivation
caused by other environmental
factors
can be effective
under certain
conditions
and for certain
pathogens but cannot be considered
as reliable
as heat inactivation.
To accomplish
this direct
heating
is out of the question because of high fuel
by conventional
cost.
energy
sources
The modem day search for economical and effective
methods for
night-soil
treatment
by composting which will both assure protection
of the
public health while providing
a continued
supply of low-cost
soil conditioner
was started
by Sir Albert Howard in India in the 1930's.
Extensive modern research in composting has demonstrated
that the
very high temperatures
required
for heat inactivation
of pathogens can be
obtained during the active decomposition
of organic matter by aerobic thermophilic
microorganisms
that operate effectively
in a temperature
range of
4s" - 85°C and generate the considerable
amounts of excess heat required
for destroying
the more sensitive
pathogens.
Numerous experimental
and full-scale
composting plants have been
developed [email protected] the last 30 years in an effort
to achieve effective
aerobic
thermophilic
compostlag of municipal
refuse under controlled
conditions,
many of which could be applied to composting night soil together
with other
organic wastes.
Hovevet, most of these plants are based on very expensive
high-level
technology
whose cost has usually been greater
than could be
afforded
even in highly developed economies.
In addition,
serious operation
and maintenance problems have plagued many of the systems.
Two appropriate
processes of sewage-sludge
composting presently
practiced
in the United States were selected
for study for this report.
One
is the successful
Windrow composting plant of the Los Angeles Sanitation
Districts
which composts digested vacuum filtered
sewage sludge with 23%
solids together
with old well-composted
sludge in open windrows turned
at least once a day by huge mobile mechanical composter-shredder
machines.
Maximum temperatures
in the piles above 60°C have been reported
for most
piles while the minimum temperatures
are close to ambient.
However, all
sludge is presumed to be exposed to 60°C or more for a period of time during
the 35-day composting cycle since the piles are turned daily.
Laboratory
tests show that this process is reasonably
effective
in inactivating
pathogens
in the final
compost.
The second process reviewed in this report
is the Beltsville
Aerated
Rapid Composting (BARC) system developed at the U.S. Department of Agriculture's
Agricultural
Research Service Laboratories
at Beltsville,
Maryland.
- iii
-
This process is based on mixing either
raw or digested sewage sludge with wood
This reduces moisture content,
provides a carbon
chips as a bulking material.
source needed for more effective
composting,
and assures the open structure
required
for the free flow of air in the static
compost pile aerated by a
4" (i3 cm) perforated
pipe under the pile.
Air is sucked through the aeration
piping system by a simple l/3-hp blower.
The only other equipment required
loader and a mechanical
screenzng system for wood chip reis a front-end
cycling
whLch might not be required
for all cases.
Research on the BARC system indicates
that extremely high temperatures are achieved consistently
in all portions
of the fresh sludge mix, which
is covered by 30 cm of old compost to provide
insulation
against heat loss,
absorption
of odors and water penetration.
Maximum temperatures
reach
80°-90°C while in no case has the minimum temperature
at any point in the
pile been lower than 60°C at least for a 5-lo-day
period.
Under these
conditions
thermal inactivation
of most pathogens can be assured.
Laboratory
assays for pathogens indicate
that the system is highly effective
in destroying
pathogenic
bacteria,
viruses and helminths.
The BARC system has also been
used effectively
to compost night soil from the National
Capital
Park Service
latrines.
Sawdust is added as an additional
bulking material
to absorb the
greater
amounts of liquid
in raw night soil.
The estimated cost of sludge
or
composting with the BARC system is $38.50/dry
ton in a 50 ton/day plant,
about $8.50 per wet ton of sludge of 22% solids.
The BARC composting system appears to be ideally
a night-soil
composting system for developing
countries,
both because of its simplicity
in operation
and requirement
of only limited
simple inexpensive
mechanical
equipment and even mre so because of its highly effective
and uniform heat
inactivation
of pathogens which should assure that the final
compost is
safe from a public health point of view.
It is recommended that a series of research--pilot
studies be undertaken in several developing
countries
to test the system under varying
environmental
conditions
and night soil quality.
These studies are essential
to provide firm engineering
and economic parameters
for the development of
of
major projects
and to provide field
data on the degree of effectiveness
pathogens.
the process in controlling
The BARC night-soil
composting system if proved effective
and economical in field
trials
may well be a particularly
appropriate
low-cost
technology which can contribute
to solving the public health problems associated
with continuing
or expanding the use of the direct
night-soil
disposal
systems in developing countries
unable to afford more expensive water carriage
central sewage systems or to those interested
in developing
appropriate
alternative
systems more suitable
to local cultural
and economic conditions.
Acknowledgments
We would like to thank in particular
Dr. Eliot Epstein whose vast
experience
in composting technology
and innovative
research have provided
essential
input for this effort.
He played a major role in the preparation
Thanks are also due to Dr. Richard Feachem and Mrs. Hemda
of this report.
Garlik of the Ross Institute-London
School of Hygiene and Tropical
Medicine
for their valuable
assistance
in locating
critical
hard to obtain literature
on the health aspects of camposting.
Appreciation
is also due to the management and staff
of the composting plants visited
at Beltsville,
Maryland;
Windsor, Ontario;
and the Los Angeles County Sanitation
Districts
for their
helpful
cooperation
and for the data and reports
provided.
We would also like to thank Dr. Richard Cooper of the School of
Public Health, University
of California,
Berkeley;
Dr. Ann Prytulla
of the
Windsor Regional Public Health Laboratory;
Drs. Charles Sorber and Bernard
Sagik of the University
of Texas at San Antonio;
and Dr. Gerald Berg of the
Environmental
Protection
Agency in Cincinnati,
Ohio, for providing
their
valuable
published
and unpublished
research data concerning
the health
effects
of sevage-sludge
and night-soil
utilization.
The information
on coPrmercia1 sludge composting and marketing
supplied
by Mr. Phillip
of Windsor and Mr. H.C. Kellogg Jr. of Los Angeles
was most enlightening
and useful.
-l-
1.
Introduction
and Objectives
The World Health Organization
has estimated
that the vast majority
countries
constituting
more than two-thirds
of
of the people of the developing
humanity have improper or no facilities
for human waste disposal.
This
situation
leads to a vicious cycle of disease and poverty that is detrimental
to social welfare
and hampers development (Pine0 and Subrahmanyan, 1975).
Both the 1976 HABITAT Conference and the U.N. World Water Conference
held in March 1977 in Mar de1 Plata, Argentina,
set global targets
for providing water supply and waste disposal
to the whole world's
population
by the
year 1990.
Such a target is formidable.
Since today 60% of the population
of the developing
countries
lack access to water and nearly 70% are without
adequate sanitation,
which means that there is a current
backlog of over one
billion
persons in need of water and sanitation
service.
Moreover, if the
present levels of investment
in this sector are maintained
and population
growth continues
at close to present rates, by 1990 only about half the
population
in the developing
countries
will have access to safe water and only
40% will be provided with adequate sanitation.
It can be seen from this that,
with the present rate of investments
and the present costs for water supply
and sanitation,
it will not even be possible
to keep up with'the
needs of
the population
growth,
let alone clear up the backlog.
Estimates indicate
that the cost of providing
safe water for people in the developing
world
might reach $60 billion
while the provision
of proper waste disposal
could
cost up to $200 billion
based on current
technological
approaches.
The most common approach has been to provide the investments
required
for central
water supply systems without
providing
for adequate
waste disposal,
thus leading to serious water pollution
and public health
hazards in many countries.
It should be noted here that, based on current
conventional
Western practice,
the provision
of central
water-carried
sewer systems and treatment
facilities
costs about three times that of
providing
central
water supply.
In recognition
of this serious dilemma facing national
and international
agencies interested
in promoting better
sanitation
in developing
countries,
the World Bank has initiated
a study of appropriate
technology
for
water supply and waste disposal
in developing
countries,
the objective
of
vhich is to identify'the
appropriate
technology
for providing
the urban
poor and rural communities with socially
and environmentally
acceptable
water supply and waste disposal
services at a cost that they can afford.
In addition
to the study of the technical
and economic feasibility
of the
various options which are available
for water supply and waste disposal
in developing
countries,
special consideration
must be given to the health
constraints
associated
with low-cost
waste disposal
technology.
Social
acceptability
of such practices
is no less important,
particularly
in the
urban areas where the achievement of the Western standard of living
has
been considered
a sine qua non and where water-carried
waste disposal
has
been considered
by many as a symbol of social progress worthy of emulating.
It is the objective
of the World Bank program to collect
data on the
pu blic health,
various technical,
economic, environmental,
institutional
and behavioral
factors
that relate
to the choice of the appropriate
waste
disposal
technology.
In both the technical
and economic evaluations,
an
attempt is to be made to broaden the scope of the analysis
to include
system linkages
between the waste disposal
technology
and its effects
on
labor and product markets, as well as more complex relationships
with other
economic sectors,
such as agriculture
and energy, where reclamation
through
fertilizer
or biogas production
is practiced.
The specific
objective
of this document is to evaluate the possibility
of alternative
low-cost
technology
for the disposal
of human
body wastes, specifically
feces and urine, commonly called "night
soil,"
in urban and semi-urban areas where centralized
night-soil
collection
and
disposal
is practiced.
A precondition
for the selection
of such a technology
is to eliminate
the public health risks usually
associated
with this practice
in an economically
feasible
fashion,
which should be significantly
less
expensive than the water-carried
waste disposal
system.
In the minds of most public health authorities,
the bucket system
and other night-soil
systems practiced
in the East and in other developing
areas are associated
with severe public health problems since, in many of
these countries,
night soil has been commonly used as a direct
fertilizer
for garden vegetables
consumed raw and has thus led to the transmission
of
ntznerouz enteric
diseases to the population
at large and to the agricultural
workers directly
exposed, as well as.to their families
living
in the immediate
vicinity.
Dr. .I. W. Scharff,
former chief health officer
of Singapore,
(1946)
said in reference
to night-soil
fertilization:
"Though the vegetables
thrive,
the practice
of putting
human waste directly
on the soil is dangerous to
health.
The heavy toll of sickness and death from various enteric
diseases
In China is well-known.
Health officers
in this country and elsewhere
have been brought up, quite rightly,
to regard the safe disposal
of human
excrement as an essential
requisite
for safeguarding
public health.
We could
justify
our action in preventing
the use of night soil in agriculture
because
of the serious risk to health which its use involves....
We have been inclined to regard the installation
of a water-carried
system as one of the
final
aims of civilization."
A World Health Organization
Expert Committe (WHO, 1974) expressed
current
feelings
on direct
reuse of excreta as follows:
"Night soil is
sometimes used as a fertilizer,
in which case it presents great hazards by
promoting the transmission
of food-borne
enteric
disease and hookworm."
-3-
The above remarks sum up the position
of many of those veterans
in the public health profession
who have tried to grapple with the debilitating health effects
associated
with improper night-soil
fertilization
of
if
not
most,
vegetable
crops.
have
come
to
see
the
water-carriage
Many,
system as the only alternative,
while only limited
scientific
and engineering
effort
has been devoted to examine alternative
safe and hygienic
technologies
which may be more suitable
both to the economy and to the agricultural
needs
of a country.
This document will attempt to evaluate
the possibility
of composting
night soil in centralized
municipal
plants in such a manner as to assure safe
and effective
heat inactivation
of all pathogenic
microorganisms
while allowing for the reuse of the organic wastes in an economically
and socially
acceptable
manner.
It will not cover cornposting night soil for individual
homes or groups of homes. It will
also not deal with the possibility
of
bipgas production
as an intermediate
step in the composting process which
produces economically
utilizable
fuel gas, which is a mixture of methane and
carbon dioxide.
At this point it is worthy to note that the Food and Agriculture
Organization
(FAO) of the U.N. has recently
recommended that increased
emphasis be given to the conservation
and utilization
of organic manures as
nutrients
in agriculture
(Food & Agriculture
Organization,
1975).
The report
points out that mineral fertilizers
are now in short supply with a strong
increase
in price within
a very short period due to increased costs of energy.
Chemical fertilizers
are rapidly
becoming out of reach for farmers in many
developing
countries
at a time when there IS an ever-increasing
need to
step up food production.
The FAO report states,
"It is now of the utmost
importance
and urgency to increase utilization
of agricultural
and municipal
organic vastes as sources of plant nutrients.
It is imperative
that developing countries
should immediately
organize and adapt adequate and safe methods
for the collection,
processing,
and utilization
of their organic waste
materials."
The FAO report further
recommends, "In large towns, domestic
refuse should be collected
and processed,
if possible,
together w?...II sewage
sludge in composting plants."
It also points out the value of comI:osting
with sewage sludge or night soil and states
that this practice
is compatible
with crop fertilization
combined with optimum use of inorganic
fertilizer,
"
a-0 provided that adequate treatment
and monitoring
is used to ensure quality
and safeguard health.*'
It can be seen from the above position
taken by FAO as to the needs
of increasing
organic fertilizers
in developing
countries
that there can be a
close tie-in
with programs for improving sanitation
by hygienically
acceptable
processes of night-soil
composting.
Such a technology,
if it proves feasible
from a public health,
economic and social point of view, may provide an
attractive
interim
solution
for developing
countries
which cannot now afford
water-carriage
waste disposal
systems.
In some areas such programs may be
considered
as interim
measures postponing
investments
for considerable
periods,
while in other areas, depending on the success of the program and its social
and economic acceptability,
they may become adequate long-term
solutions
and
-4avoid the need for developing
central
sewer systems with all of their economic
implications
and the environmental
hazards associated
with them, particularly
in relation
to water pollution.
2.
Public Health Problems Associated
with
Night-Soil
and Sewage Sludge Reuse
Pathogenic
Microorganisms
in
An essential
prerequisite
for the hygienic
and safe utilization
of
night soil after appropriate
treatment
is the elimination
of enteric
pathogenic
microorganisms
that may be present in the original
night soil from human
sources.
Numerous studies have indicated
that the sewage and night soil of a
community contain
the complete spectrum of enteric
pathogenic
microorganims
excreted by the community, which is a function
of the endemic disease rates
prevalent
in that community.
In addition
to pathogenic
bacteria,
such as the
agents of such diseases of typhoid fever and cholera,
night soil may contain
enteric
viruses of such diseases as poliomyelitis,
infectious
hepatitis
and
numerous other diseases caused by enteric
viruses.
In warm, tropical,
and
subtropical
areas of the world, diseases caused by the pathogenic
protozoans
such as Entameoba histolytica
and Giardia lamblia are usually endemic.
Worms
or helminths
such as Ancylostoma duodenale and Ascaris lumbricoides,
and
tapevorms such as Taenia saginata are common.
Concentrations
of these pathogens in night soil may be quite high.
For example, one fertilized
female Ascaris worm living
in the human intestine
produces 200,000 eggs per day (Craig and Faust, 1970) while a female
Ancylostome (hookworm) deposits
between 25,000 and 35,000 eggs per day.
Trichuris
trichuira
female worms in the human intestine
have been estimated
to produce 6,000 eggs per day.
From the above, it can be seen that the
concentration
of parasites
in night soil or in sewage is a function
of the
type of parasite
and the number of infected
persons in the community serving
as a source.
The prevalence
of Ascariasis
may exceed 50% in moist, tropical
areas of the world.
In many other areas a 1% to 10% infection
rate is common.
Many other protozoan
and helminthic
diseases show similar
patterns
of prevalence, with the extremely high rates in moist, tropical,
areas, but with broad
distribution
in other areas at lower rates.
It' must be assumed that night*
soil or sewage sludge contains
initially
high concentrations
of the above
pathogens.
Numerous researchers
have carried
out studies to determine the
survival
of pathogens in sewage treatment
processes,
sludge digestion
and in
the soil.
Cram (1943) studied the survival
of helminth ova and protozoan
cysts in sludge.
She was able to demonstrate
that Ascaris eggs were found
to be extremely
resistant
to sludge digestion.
She reports
that for the
first
3 months of anaerobic
digestion,
the viability
of the eggs appeared to be
little
affected.
After 6 months, an average of 10% was still
viable,
and
after a year in sludge, eggs were still
found which were capable of development.
Development of hookworm eggs was more affected
by sludge digestion;
however, development and hatching
of hookworm larvae were demonstrated
after
sludge digestion
for periods up to 64 days at 20°C, and 41 days at 30°C.
By comparison,
cysts of Entameoba histolytica
appear to be much less resistant.
-5From observations
on 17 lots of sludge, cysts were still
viable after 12 days
at 20°C, 10 days at 3O'C. Ascaris eggs survived long periods of sludge drying;
they were viable for as long as 118 days of indoor greenhouse drying and 170
They were resistant
to the loss of moisture,
viable
days of outdoor drying.
eggs were found in several sludge cakes with moisture content below 10%. In
one lot of sludge, eggs were still
viable when its moisture content was 5.8%
after 81 days of drying at summer temperatures,
which frequently
reached
It was further
demonstrated
that Ascaris
llS°F (42'C) in the greenhouse.
eggs were destroyed
in 3 minutes at 103' C.
A study by Wright et al. (1942) demonstrated
that the eggs of Ascaris
be recovered from sludge at all stages of the treatment
process.
Twothirds of the samples examined from the sludge drying beds were positive.
They
concluded that the evidence obtained
indicated
that the use of sewage sludge
as fertilizer
may serve to disseminate
ova of the intestinal
parasites
studied.
could
Rudolfs et al. (1950, 1951) carried
out an extensive
study of the
literature
on the question of pathogens in sewage sludge and night soil.
They
concluded the eggs of most pathogenic
helminths
are fairly
resistant
in the
soil,
sludge and in night soil depending on external
conditions
and that the
eggs of the genus Ascaris are the most resistant
to environmental
conditions.
Their conclusion
is that vegetables
grown in soil contaminated
with infected
sewage or night soil may be a source of infection.
They suggested that although stored night soil or sewage sludge may contain viable eggs for several
months, composting for sufficient
periods of time at appropriate
high
temperatures
above 55'C can provide effective
inactivation.
Rudolfs et al
(1951) carried
out field experiments
on the survival
of Ascaris eggs on
growing tomatoes and lettuce.
Results showed that a reduction
in the number
of eggs took place with time but some eggs remained on the plants and fruits
for more than a month,
Development of eggs was greatly
retarded
and completely
developed eggs containing
motile embryos required
for infection
were
not recovered.
They concluded that it appears that the resistance
of --Ascaris
eggs on vegetable
surfaces is less than might be expected from considerations
of their resistance
in soil,
feces or night soil.
All eggs degenerated
after 27 to 35 days and were incapable of development for infection.
However, they did state that it must be kept in mind that the field conditions
under which these experiments were carried out were those of the dry, hot
sumer.
Whether or not similar
results
can be obtained under more moist
conditions
which might'prevail
in tropical
areas of the world where intestinal
helmiuth diseases are more prevalent
was open to question by the authors.
Reyes et a1..(1963)
carried
out a study of the effect of aerobic
They found that at low
and anaerobic
digestion
on &caris
eggs in night soil.
temperatures,
both aerobic and anaerobic
digestion
tend to preserve Ascaris
egg6 which subsequently
develop normally when removed to a more favorable
environment.
In the 25oC to 35'C temperature
range, both systems resulted
in egg destruction
attributable
to a factor or factors
other than heat killing.
They hypothesized
that oxygen starvation
during the period of egg development
My be a lethal
factor
in anaerobic
digestion.
In neither
system is the
-6destruction
of eggs complete at the end point of night-soil
stabilization
unless temperatures
are held at or above 38’C for anaerobic and 45’C for
Their studies
indicated
that simple heating of raw night
aerobic di estion.
(F
soil at 55 C for 20 minutes should provide a sufficient
degree of public
odors and poor dewatering
characteristics
health safety.
However, offensive
of the undigested
material
might raise practical
objections
to this heat
treatment
method.
Keller
(1951) reviewed the literature
pertaining
to the occurrence
and viability
of parasitic
ova and cysts in sewage sludge.
To emphasize the
Importance of the problem, reference
is made to an epidemic of Ascariasis
in
Darmstadt , Germany, where 80% to 90% of the population
had been found to be
infected
with Ascaris lumbricoides
and where the origin
of the infestation
bad been traced to sewage irrigation
practice.
Undigested
raw sludge and
sewage had been used to fertilize
vegetable fields.
The author notes that
the extraordinary
power of resistance
of Ascaris ova to changes in temperatures
and moisture concentrations
and to chemical influences
is due mainly to the
complicated
structure
of the eggshell.
The eggshell
consists
of 5 layers,
namely, an outer proteinacious
membrane and 3 layers of chitinous
material
membrane. The outer afbuminous coat is partially
and an inner lipoidal
coagulated
and hardened by certain
hostile
factors.
After reviewing
a long
series of studies on the thermal death point of Ascaris eggs, the author has
come to the conclusion
that although Ascaris eggs are extremely resistant
to most environmental
conditions,
including
desiccation,
there was general
agreement that heat treatment
over 55’C for a L-hour period is sufficient
to effect 100X destruction
of all parasitic
ova cysts usually encountered
in
sewage sludge.
Keller did experimental
studies with thermophilic
digestion
of
eludge between 53'C and 54’C, and he was able to achieve total inactivation
in a 24-hour period at that temperature.
Katayama (1955) carried
out experimental
heat inactivation
of night
soil in Kyoto, and succeeded in destroying
all parasitic
ova, pathogenic
bacteria
and fly maggots in night soil heated at SO’C. He carried
out a field
study in Shiga Prefecture
and was able to demonstrate
a striking
decline in
the prevalence and incidence rates of Ascaris and hookworm infections
in
the village
practicing
heat treatment
of night soil as compared with the
adjacent village where this was not done.
Hogg (1950)
studied
the destruction
of ova and cysts in digested
layers of 1” to 6” in depth (2.5 layers was found to be free of
viable Ascaris eggs, examination
of the 3” or 4” layers still
showed the
presence of viable Ascaris ova, although their numbers were very much reduced.
From these results it would appear that sun drying of sludge in relatively
thin layers for long periods is effective
in destroying
Ascaris ova.
sludge as a result of sun drying in thin
15 cm). While sun dried sludge in l-1/2"
Bhaskaran et al. (1956) studied the survival
of
site8 in sewage sludge digestion
in India.
The results
of
experiment
showed that ova survived digestion
under normal
for over 120 days.
Thermophilic
digestion
at 132’F (54’C)
intestinal
parathe sludge
air temperature
results
in
-7They
complete destruction
of the viability
of the ova within
a few hours.
demonstrated
that drying alone is not very useful because it is necessary
to dry the sludge to a very low level of moisture for complete destruction
They concluded,
however,
of viability
which is not feasible
in practice.
that thermophilic
digestion
of sludge would require
additional
heat from
external
sources and might not be economical under Indian conditions.
John S. Wiley (1962), one of the pioneers of composting municipal
vastes in the United States,
surveyed the question of pathogen survival
in
He hypothesized
that pathogen destruction
corposting
municipal
wastes.
during the cornposting process may occur primarily
as a result of two actions:
(a) Thermo kill
by sufficiently
high temperature
and time, and (b) kill
He felt that in light
of recent findings,
by some form of antibiotic
action.
the latter
might be as important
as the former.
He reports on a study
that the Taiwan Institute
of Environmental
Sanitation
conducted in 1956 in
which municipal
refuse was composted together with night soil.
In 20-day
windrow composting of ground refuse snd night soil with turning and
aeration
by means of a shredder,
temperatures
reached 70°C (158OF) persi6ting
for 24 hours and it was concluded from this that all the pathogenic
6nd parasitic
orgauisms in the pile were destroyed.
He also reports on a
nmber of studies which indicate
inactivation
of salmonella
organisms at
temperature6
below thermal inactivation
points.
He concludes that the
derrtruction
of pathogenic
organisms must also be due to antagonistic'proce66e6, possibly
caused by antibiotic
inhibitors.
He reports on the studies
of Knoll of Holland where he was able to demonstrate
effective
inactivation
of pathogens at SO°C producing a final
product which was completely
acceptThe conclusion
drawn from
able fro6 the general hygienic
point of view.
Wiley'6 analysis
was that aerobic cornposting in the thermophilic
range
acHeHog
temperatures
of 55'C for a sufficient
period of time could produce
a 66fe product from a public health pq+t of view but that even at lower
tamperatu.res many pathogens were destroyed.
Wiley and Westerberg (1969) studied the survival
of human pathogens
in corpoeted
66Wwe.
They evaluated
the effectiveness
of an aerobic composter
in de6troylng
pathogens.
Their experiments
indicated
that Salmonella newport,
pollowirue
Type I, A6CariS lumbricoides
ova, and Candida albican could not
6urvlwe the cornposting process.
The results
of the assay showed that after
43 hour6 of cornposting no viable indicator
organisms could be detected.
The
being inactivated
in the first
hour,
polioviru6
Type I was the most sensitive,
whereas Candida albican was the most resistant,
requiring
more than 28 hours
of coakpostiog for inactivation.
They concluded that the data from this
6tudy indicated
that aerobic composting of sewage sludge could destroy the
indicator
pathogens when a temperature
of 60°C to 70°C is maintained
for
a period of 3 days.
Krige (1964) carried
out a survey of pathogenic
organisms and helminthic
ova in composting sewage sludge in South Africa.
He studied various composting plants,
some of them using night soil,
others using abattoir
wastes, and
others digested
sludge.
All of the plants were windrow composting systems,
606e of which were not turned at all,
and others turned as frequently
as 5
-8Maximum temperatures
recorded ranged from
times in an interval
of 7 days.
He concluded that aerobic composting systems were much more
S3'C to 80°C.
Poliovirus
Type I was inactivated
in the
effective
than anaerobic
systems.
He concluded that composts with sewage sludge
aerobic composting plant.
and night soil under controlled
conditions
reaching
temperatures
of 65 C to
70°C were safe from a public health point of view.
He emphasized that in
static
compost heaps or those that are turned infrequently
the outside layers
never reached the optimum temperatures
required
for effective
inactivation
of
the pathogens.
Malviya (1964) studied the temperature
tolerance
of viable ova of
Ascaris in composting and concluded that 100% mortality
is obtained in a
temperature
of SO°C when exposed for 60 minutes or more.
A study carried
out by the Szechwan Research Institute
of Para6itiC Diseases in China (1964) indicates
that only partial
removal of parasitic
eggs of Ascaris and hookworms is obtained by detention
in the digestion
tanks or septic tanks.
They report that a 97% reduction
in hookworm larvae
and 94% reduction
in other parasitic
ova was achieved.
They concluded that
6uch tanks, although
they do not provide complete inactivation
of parasitic
ova, do contribute
to reducing the health risks associated
with the use of
night soil in agriculture.
McGarry (1976) in his review of the use of human excreta in
Chinese agriculture
reports
on a very successful
program of the Chinese in
the use of night soil in agriculture
which has supplied,
according
to the
one-third
of
the
nutrients
in
fertilizer
eetimatee of the Chinese government,
utilized
in that country.
They introduced
a number of relatively
simple
way6 of treating
night soil either
by detaining
it in tanks for a few weeks
prior to spreading
or by composting.
The efficacy
of some of these treatment
processes has not been fully
reported
upon. According
to McGarry, methods
of treating
night soil prior to its application
have been developed and are
in widespread use.
He reports
that at the time of the revolution
use of
excrete as fertilizer
aided the spread of disease in China.
The rural
population
of nearly 400 million
was heavily infected
with worm diseases
vith 40% to 90% of those examined harboring
Ascaris worms. Other diseases
of importance were Typhoid, Salmonellosis,
Shigellosis,
Cholera, Hookworm
and Schistosomiasis.
A massive program of hygiene and sanitation
based on health education is reported
to have reduced disease rates in the rural areas.
It is
McGarry's contention
that the combined efforts
of health education
and rural
medical schemes together
with the night-soil
treatment
introduced
led to this
improvement and that the benefits
of night-soil
reuse as fertilizer
far outweighed any d%sadvantages from the health point of view.
Ch'an et al (1959)
in their report of the achievements
in the fight against parasitic
diseases
in China state that the use of human excreta as a fertilizer
plays an important role in the spread of parasitic
diseases.
They report that the method
of storing
feces with urine in water as practiced
in some countries
was not
found as.effective
as storing
with urine alone.
They feel that this is
I,
!
-9because the ovicidal
action is mainly caused by the ammonia liberated
from
They report
that in the summer it required
2 weeks and in the
the urine.
winter 1 month to kill
most of the ova in the mixture.
Compost piles covered
by packed clay and partially
aerated by vent holes formed by bamboo poles as
practiced
in China have been reported
to achfeve inside temperatures
in the
They feel that the success
6ummer over 56'C required
to kill
parasitic
eggs.
of night-soil
control
program has been proved by the reduction
in the rates of
Undoubtedly,
the progress made in public
enteric
disease such as dysentery.
health in China is due to the combined effect of their intensive
programs
of improved medical care and personal hygiene as well as night-soil
treatment,
which have become national
programs of mass activity
with wide popular support.
Moore et al. (1977) have assessed the risk of virus survival
in
Their studies show that the level of infection
sludge disposed of on land.
of the sludge to the land
of viruses
in sludge is high and the disposal
.may become a public health problem of concern.
They report that sludge
digestion
may achieve a 3 or 4 log cycle reduction
in the virus concentration.
They have also shown that poliovirus
could survive in the ~11 for over 134
day6 of 4'C and could still
be detected at 134 days of 20°C. However, when
the soil temperature
was 30°C no virus could be detected after 49 days.
They
state that viruses applied
to the soil can move through soil systems and
lead to the pollution
of ground water or crops.
Cliver
(1976) studied the
problem of viruses
in sewage sludge and reports
that viruses have a strong
tendency to settle
with the sludge during sewage treatment,
and that some
digestion
processes do not inactivate
all of the viruses present in the
sludge.
The report of the Sandia Laboratories
(1976) indicates
that
moisture content plays an important
role on the inactivation
rates of enteric
viruses in sludge during digestion
and drying.
Gradual reduction
of recoverable infectivity
occurred with poliovirus
as the solids content of the sludge
was increased
up to about 65%. Further
reduction
in solids content to 83%
caused an additional
reduction
of virus greater than 3-log cycles.
Similar
re6dt6 were found with coxsackie virus and reovirus which suggest that
thf6 behavior may be a general property
of enteric
viruses.
Thus, dewatering
6lUdge by evaporation
may be an efficient
way of inactivating
enteric
viruses.
With and Selena (1976) report from the Los Angeles sludge composting operation in windrows that with temperatures
between SS'C and 60°C they were
able to achieve results
that yielded negative finding
for viruses,
parasitic
ova, and salmonella
in the vast majority
of final compost samples.
Total
coliform
concentrations
in the final
compost have not been uniformly
below
1HPH per gram as specified
by the California
State Health Department.
Experiments
were also carried
out in the Los Angeles area on the
application
of liquid
sludges directly
to agricultural
lands (Yank0 et al.,
1976).
In these studies
the application
of liquid
sludges to soil resulted
in extremely
high concentration
of indicator
bacteria
and salmonella.
Salmonella population
appeared to increase during the first
few weeks in the
6011. Viable Ascaris ova were also detected.
After the growing season,
all'6011
populations
appeared to stabilize.
No apparent microbial
hazard
from the organisms tested during this study was associated
with the field
,-,.,
<'.
I
crops grown in either
compost or liquid
sludge amended soils or with the
vegetables
which were grown in the compost-treated
soils.
This study
indicates
that even pathogens remaining in sewage sludge or compost seem
to disappear
rapidly
in the soil.
Microbial
hazards to crops grown appear
to be limited,
according
to the authors.
Epstein et al. (1977) show effective
inactivation
of F bacteriophage
during RARC cornposting at Beltsville
with minimum temperatures
a %ove 60°C
at all times for a 5-10 day period.
Total coliforms,
fecal coliforms
and
salmonella
are undetectable
after 10 days of composting while less effective
inactivation
of pathogens was found in windrow composting (Burge et al., 1973,
1974).
Studies have indicated
that elevated temperatures
in sanitary
landfills
between SS"-60°C are effective
in inactivating
poliovirus.
Studies by
Dr. Robert Cooper at the University
of California
at Berkeley (unpublished)
indicate
that composting of sewage sludge together
with refuse led to the
inactivation
of poliovirus
in a 3-day period.
Bacteriophage
concentrations
in the same compost heap dropped 6-log cycles in a 35-day period.
The
temperature
in the hottest
part af the compost pile reached 60°C for a 4-day
period during the first
25 days, then dropped of 45'C at 30 days, and 20°C
at 35 days.
The pile was turned 9 times in a 2S-day period.
This can be
coneidered
quasi-aerobic
windrow composting and, undoubtedly,
the surface
of the pile remained at close to ambient temperature.
inactivation
Cotaas (1953) summarized the available
of pathogens (see Table 1).
information
on the thermal
- 11 Table
1
THERMAL DEATH POINTS OF SOME COMMONPATHOGENSAND PARASITES
(From Gotaas, 1953)
Organism
Salmonella
typhosa:
Salmonella
spp.:
Shigella
spp.:
Escherichia
No growth beyond 46'C;
55'C to 60°C.
Death within one hour at 55'C;
to 20 minutes at 60°C.
'Death within
saganita:
Trichinella
Necaeur
americanus:
Micrococcus
five
larvae:
or -suis:
var.
Streptococcus
pyogenes:
Mycobacterium
tuberculosis
diptheriae:
death
minutes
Infectivity
exposure
62-72OC.
death within
pyogenes
Corynebacterium
Thermal
Death within
abartus
-
death within
minutes
at
15 minutes
one hour at 55'C.
cysts:
spiralis
Brucella
thirty
Most die within
one hour at 55oC, and within
20 mintues at 60°C.
~011.:
Endamoeba histolytica
Taenia
death within
SO minutes
var.
at 71'C.
at 45OC.
three
mintues
Death within
Death within
is 68'C.
reduced as a result of one hour
at SO'C; thermal death point is
Death within
aureus:
point
15 days to
10 minutes
hominis:
Death within
at 61°C.
10 mintues
at 5O'C.
at S4'C.
Death within
15 to 20 mintues at
66'C, or momentary heating at 67 C.
45 mintues
at 55'C.
- 12 Conclusions
From the above studies carried
out over the last 35 years, it is
quite apparent that night soil and sewage sludge can carry very high concentrations
of pathogenic
bacteria,
viruses and parasites,
depending on the
endemic disease rates in the commurity.
Most of these pathogens are not
effectively
inactivated
by conventional
sewage treatment
process and most of
them are highly concentrated
in the sludge.
Neither are these pathogens
inactivated
entirely
during conventional
sludge digestion
and drying processes
although
their numbers may be reduced.
The concentration
of such pathogens in
fresh night soil is even greater
than that found in sewage sludge.
It has
been amply demonstrated
that viruses,
bacteria,
and helminth ova can persist
for extended periods of weeks and months, and sometimes years, in the soil,
particularly
in moist climates.
There appears to be presumptive
epidemiological
evidence from many tropical
and subtropical
areas that indiscriminate
use of fresh night soil in fertilizing
vegetables
and salad crops usually
eaten raw has led to extensive
disease transmission
both to the consumers of
such crops and to the farmers themselves.
Some researchers
have suggested,
however, that environmental
factors
are often effective
in inactivating
the
pathogens in night soil so used, thus reducing the risk significantly.
Although a number of factors
are active in inactivating
pathogens
of various types in the environment
including
biological
activity,
desiccation, and other antagonistic
environmental
factors,
it is abundantly
apparent
from all the reports
presented that the only fail-safe
method of inactiving
pathogens in night soil or sewage sludge is heat treatment
55’C for an
extended period of time.
In those processes where only part of the compost
pile reaches this temperature,
it is apparent that there appears to be a
regrowth of enteric
bacteria,
including
salmonella
organisms,
in the cooler
exterior
portions
of the pile after it is turned, so that a population
of
pathogenic
salmonella
organisms can continue to survive in a windrow type
of operation
which is turned infrequently.
Daily turnings
and thorough mixing
may bs able to overcome this problem.
The most effective
method to assume total destruction
of the pathogens of public health concern in night soil and sewage sludge is a method of
digect heating or of composting which assures a uniform temperature
above
60 C in all portions
of the compost pile at the same time over an extended
period of days. Direct heating of night soil to destroy all pathogens has been
used in Japan and Singapore but the final product is still
not suitable
for
direct
reuse and would require
further
treatment
while, with current
costs of
energy, direct
heating
is not feasible
from an economic point of view.
Since the reuse of night soil would require
some form of treatment
to reduce its moisture content and to improve its soil conditioning
characteristics,
the remainder of this document will be devoted to an evaluation
of night-soil
composting.
The aim is to determine whether techniques
and
systems are now available
to meet the strictest
public health goals of
assuring
an essentially
pathogen-free
material
which will also provide a
- 13 useful,
organic
fertility.
3.
socially
materials
The Historical
acceptable
and economically
to the soil to improve its
Development
feasible
structure
procedure for
and increase
returning
its
of Composting
Cornposting in its simple and traditional
form has been practiced
by
farmers and gardeners
throughout
the world for many centuries.
Vegetable
matter and animal manures are placed in piles in some available
open space
or thrown into pits and allowed to ferment through natural
microbial
action
This process usually
requires
until
ready for application
to the soil.
sir months to a peat and traditionally
involves no control
except perhaps
coveting
the mass with soil or turning
it once or twice during the year
Composting of night soil together
with other vegetable
and
(Comas, 1953).
animal manure wastes has been practiced
in China through the centuries
and has
been considered
a vital
aspect of maintaining
the soil fertility
of that
country.
It has been reported
that the Chinese practice
of composting with
crop residues and human wastes has been the key in supporting
high population
over some 4,000
densities
and in maintaining
soil fertility
and structure
yesrs (HcGarry,
1976b).
The arousal of interest
in composting in the West probably stemmed
from an extended visit
to China, Japan and Korea in 1909 by Professor
F. H.
King of the U.S. Department of Agriculture
(King, 1927).
It has been reported
that his text was read by Sit Albert Howard, a British
economic botanist
employed by the Indian goverument, who was able to put King's observations
After
several years of experimentaon composting in China to test in India.
tion,
Howard established
that h&s fndote method of camposting gave optimal
and animal waste, supply of labor and
results
In terms of the vegetable
the cliurte
conditions
available
in his dfsttiet
(Howard, 1935).
Howard's
system was essentially
based on building
piles of vegetable material
and
animal manure and wood ashes which were heaped and turned after 16, 30 and
60 days with intermittent
watering.
The finished
compost was removed to the
fields
after 90 days.
His experiments
showed very favorable
results
from
an agricultural
point of view and was rapidly
taken up by plantations
and
farm8 in many parts of the world.
The system was based on the use of hand
labor which watt particularly
suited to the economic situation
existing
in
India at time.
Hadifications
of the original
system used closed or open cells.
Various attempts were made to fntroduce
air into the piles so as to avoid
the escape of foul odors associated
with the breakdown of organic matter
under anaerobic
conditions.
In 1931 Jean Bordas (Gotaas, 1953) is reported
to have made one of the first
attempts to completely
eliminate
the anaerobic
stage by Introducing
forced air into a fermentation
silo.
The silo was
divided by a grate into an upper and lower section and air was introduced
along the walls and through a central
pipe.
With the growing interest
in composting of municipal
urban areas, various mechanical devices for materials
handling,
refuse for
grinding
.
- 14 of refuse and aeration
of the refuse were developed.
Among them the Dana
developed in Denmark, and the VAM practiced
in Holland.
In the
pacess.
refuse is fed into a large, slowly rotating
horizontal
cylinder
Dana process,
where it is homogenized, aerated and broken down to some extent during a 3After removal of ferrous metals by a magnetic
to 5-day storage period.
separator,
it then passes to a grinding
and homogenizing machine where
granulation
is accomplished.
The ground material
is then composted in
open piles S- or 6-feet high which often become anaerobic.
The VAM process,
practiced
in Holland since 1932, is essentially
an adaptation
of the Indore
process to the cornposting of municipal
waste on a large scale.
In some
such installations,
the refuse is first
ground in a special mill which is a
device like a rimless wheel with spokes at the hub rotating
above a roughened hotitontal
plate.
The ground refuse is then placed in open piles and
sprinkled
and turned from time to time during the cornposting period.
During
most of the composting period the piles are anaerobic
and have been known
to be a source of nuisances.
Since those early developments in mechanical cornposting,
numerous
proprietary
camposting systems have been developed including
multi-staged
silos and various systems which attempted to achieve aerobic conditions
through forced aeration
with a static
pile.
In addition,
in recent years,
special
devices have been developed for turning
and shredding compost
wbdrows.
Especially
designed mechanical equipment passes along the windrow
'as it processes the refuse.
It is beyond the scope of this report to review
all such systems developed in the last 30 years.
During
the 1950's, basic studies and research on composting for
munkipal
waste treatment
were conducted at the University
of California
under the direction
of Professor
Harold (Gotaas, 1953).
He later published
a widely known and comprehensive monograph entitled
"Composting and Sanitary
Disposal and Reclamatton of Organic Wastes," under the sponsorship
of the
World Health Organization
(Gotaas, 1956).
Composting of municipal
refuse developed rapidly
in Europe with
8ome 200 plants reported
to be in operation
at the present time.
A number
of mechanical cornposting projects
wet a initiated
in the U.S. using high
technology
equipment (Office
of Solid Waste Management, 1971) (Stone et al.
1975).
Some of these plants have been plagued with technological
problems,
and odor nuisances and have come under severe criticisms
equipment failures
due to high costs and poor operational
records.
Another key factor fn limiting
the success of cornposting processes
in the U.S., as well as to a certain
extent in Europe, has been the limited
market for the sale of municipal
composts due to the low price and easy
application
of inorganic
fertilizer
which has been heavily promoted.by agricultural
authorities
as the quickest
and most certain
way of producing high
yields
in agriculture.
Another problem that plagued the sale of municipal
compost was poor quality
since it often contained
many splinters
of broken
glass, metals and plastics
which could not be successfully
removed and led
to serious problems in its agricultural
useD Another problem has arisen
/
‘.
- 15 when municipalities
onto the product
attempted to charge the total
cost thus outpricing
the market.
refuse- or sludge
disposal
The EPA summarized its position
on the composting of municipal
"Economically
composting does
refuse in the U.S. in the following
statement:
not compete on a net cost-per-ton-processed
basis with either
landfilling
Evidence gathered from many sources
or incineration
of municipal
refuse.
indicates
that the rather high cost of producing compost is not sufficiently
offset
by income from its sale to permit the process to compete economically
The most optimistic
estimate of an incomewith other acceptable
systems.
producing market for compost suggests that only a small fraction
of the waste
generated by a unit of population
could be marketed as compost.
Many feel
that if the techniques
of landfilling
and incineration,
however, fail to keep
pace with increasingly
stringent
environmental
protection
criteria
or manage
to do so but become more and more expensive reflecting
all the costs associated with their
process, composting may become a relatively
more important
tool in resource systems management that could accommodate various proportions
industrial
and agricultural
waste."
of municipal,
4.
The Principles
of the Composting
Process
The principles
of composting have been well described
by a number
of authors (Gotaas, 1953, 1956; Gray et al., 1971; and others).
It shall be
summat:ized here briefly
for purposes of completeness,
based mainly on the
works of Gotaas (1956).
Composting can be defined as the biochemical
degradation
of organic
materials
to a humus-like
substance by natural microbiological
processes
constantly
carried
out in nature.
Simple forms of composting long practiced
by fanners throughout
the world involves ataerobic
decomposition
over a long
period of time.
Anaerobic decomposition
of organic matter is, however, often
associated
with the formation
of foul-smelling
gases such as indol,
skatol,
and metcaptans and usually
proceeds at a relatively
low temperature
close
to ambient, with microorganisms
operating
in the mesophilic
range between
the temperatures
of 8O and 45OC. Aerobic composting requires
sufficient
amounts of atmospheric
oxygen and produces none of the objectionable
features
associated with anaerobic decomposition.
Both mesophilic
and thermophilic
organisms involved
in compostfng are widely distributed
in nature and are to
Research
a great degree indigenous in all types of refuse and sewage sludge.
studies have shown that no supplemental
inoculants
are required
for normal
composting (Gotaas, 1956).
Because it is a biological
process, environmental
factors
influencing
the activities
of the organisms determine the speed and the course
of the composting cycles.
Most important
are particle
size of the material,
moisture content,
aeration,
hydrogen ion concentration,
temperature
and
initial
carbon-nitrogen
ratio.
The particle
size is important
since the
more minute the particle
the more susceptible
it is to bacterial
or fungal
attack because of the greater
surface area exposed (Gotaas, 1956).
- 16 An optimum moisture
content
of the mixed refuse
is essential
to good
csmposting since all living organisms require moisture for their existence.
Water is an important
constituent
of cell protoplasm
and, in addition,
it
dissolves nutrients
rendering
them available
for utilizatian
by the organisms.
the moisture
content drops below 20% the microbial
processes are severely
inhibited
and slowed down while if the moisture content increases
above 60%,
passage of air becomes difficult
and anaerobic
processes set in.
For aerobic
-sting,
a freely
available
supply of oxygen is essential
in order for
the aerobic bacteria
to carry on their activities.
An aerobic process is
mre efficient
than an anaerobic
one in the decomposition
of organic matter.
In fact, organic material
cannot be stabilized
completely
under anaerobic
conditions
because further
oxidation
is always possible
by aerobic organisms
Therefore,
the control
of moisture
oxygen.
in the presence of atmospheric
is a critical
factor
in the operation
of composting processes.
If
Microorganisms
are sensitive
to the temperature
changes in the
Mesophilic
forms exist in temperatures
of 8' to 4S°C, activity
compost heap.
diminishing
at either
extre:e.
Thermophilic
organisms grow and thrive
in
taperatutes
higher than045 C although
only a few groups carry on any activity
at tsmperatures above 65 C. However, significant
biolo#cal
activity
in compost heaps can continue in the range between 65’ and 90 C. Obtaining higher
tsmperatures in the thermophilic
range is very desirable
from the hygienic
pint of view since as noted earlier
most pathogenic
microorganisms
are inactivated abowe temperatures
of 55OC with most others inactivated
at tempera-
ture above 60°C.
The activities
of living
organisms are enhanced by proper nutrition.
is the supply of available
carbon to serve
for the building
of protoplasm.
Energy
than nitrogen
is needed; however, there
ti a limit
in the excess of carbon over nitrogen
beyond which organic activity
didnishes.
The proportion
of carbon to nitrogen
is termed the C/N ratio.
It
ir felt that an optimal C/N ratio for efficient
and effective
composting is
about 25 to 30, while stabilized
compost or humus are characterized
by a C/N
ratio tanging from 10 to 20, depending on the original
material
from which the
-8
was formed and the degree of decomposition.
lrportant
in the matter of nutrition
a8 an energy source, and of nitrogen
rsquitements being high, mote carbon
An optimsl combination
of all the above factors
including
particle
pH, aeration and temperature
is essential
for effective
caposting.
Numerous researchers
have demonstrated
that with proper combinstion of these factors
under aerobic conditions,
compost hea s can reach the
8
tbcrmophilic
range and continue at high temperatures
above 60 C for S- to
l+day periods which would be adequate to inactivate
all forms of pathogens.
Therefore, aerobic,
thermophilic
composting can provide a high degree of
ssfety from the health point of view as far as the destruction
of pathogens
is concerned,
and produces a stable well-composted
material
which has been
S~OWII to he a useful and effective
soil conditioner.
site,
C/N ratio,
- 17 Since the maintenance of aerobic conditions
is an essential
condition
for effective
thermophilic
composting,
considerable
efforts
been devoted to developing
technologies
to assure adequate air supply.
is beyond the scope of this report to describe all the equipment and
that have been developed but they can all essentially
be divided into
following
groups:
prehave
It
processes
the
(a) Windtows.
In the original
Indote process and similar
processes,
the windtow form of composting was essentially
anaerobic
during most of the
period except the period immediately
after turning
the pile.
In the course of
years, equipment has been developed to turn the pile mechanically
so that the
windrows could be turned daily or even mote frequently.
As currently
practiced by the County Sanitation
Districts
of Los Angeles (1975), mechanical
equipment is used to turn the piles daily and, on occasion,
two or three times
a day, maintaining
aerobic conditions
and thermophilic
cornposting during the
total
composting period of 20 to 35 days.
Another way of assuring aeration
in the windtow system is through forced aeration
from the bottom of the
compost pile.
Most of the early attempts in aerating
compost piles in this
manner were only partially
successful.
Recently Epstein et al. (1976) developed a forced aeration
system for composting wastewater
sludge with wood chips
at the Agricultural
Environmental
Quality
Institute
of the U.S. Department of
Agriculture
in Beltsville,
Maryland.
The system, called the Beltsville
in detail
later in
Aerated Rapid Composting (BARC) System, will be described
this report and is based on placing 4-inch (10 cm) plastic
perforated
drainage
pipes in a loop under a static
pile of sludge mixed with wood chips and other
bulking materials,
covered with a layer of well-composted
material.
Air is
drawn through the piping system with a small l/3-hp
blower.
This system has
heen shown to effectively
aerate the pile in such a manner as to assure
aerobic thermophilic
camposting during a 220day period=
(b)
Closed Composting Systems.
Various manufacturers
have marketed
enclosed cornposting systems which involve either
a rotating
drm or multistage tower klos
or &her complicated
mechanical devices which are designed
to assure thorough mixing and aeration
of the compost.
Some of these systems
have demonstrated
effective
aeration
and thermophilic
composting but they
ate usually associated
with extremely high-cost
and complex operation
and
maintenance problems.
Although composting in windtows occasionally
turned as proposed by
Sir Albert Howard does not assure aerobic conditions
for extended periods,
several reports
indicate
that aerobic thermophilic
fermentation
doe: take
place for part of the period achieving
temperatures
in excess of 55 C for
sufficient
per$ods of time to provide effective
inactivation
to that portion
of the pathogenic
microorganisms
near the center of the pile exposed to the
high thermophilic
temperatures.
If such piles are turned a number of times
in the course of the camposting period,
there is a reasonable
chance that a
significant
portion
of the pathogens will be inactivated
although it is difficult
to assure total
destruction
of them all since the outer layers of the
Compost heap are maintained
close to the ambient temperature.
This does not
assure thermal ina<rtivation.
There is some evidence,
however, that other
- 18 -
biological
factors
may contribute
to the inactivation
of some of the pathogenic
even if thermal inmicroorganisms, thus reducing the risk of their survival
activation
temperatures
are not achieved in all portions
of the compost pile.
It
is the purpose
of this
report
to determine whether effective
is obtainable
under conditions
of
operation,
and maintenance that
aerobic thermophilic
composting of night soil
lov capital
investment
and minimal equipment,
are essential for developing countries.
5.
Historical
Development
of Composting
of Night
The Chinese have composted night soil
agricultural
vaate in anaerobic
piles but little
in antiquity.
on the process as practiced
Night
soil
Soil
and Sewage Sludge
for centuries
together with
scientific
data are available
is a term frequently
used to describe human excreta with
collected
in buckets from the home daily or at
stored in vaults.
This form of excreta collection
in large areas of Africa and Asia including
indus-
or without urine vhich is
larger intervals
if it is
and disposal is practiced
trialized
countries such
as Japan.
Little
scientific
data Is available on the composition and quantities
of night roll produced in various parts of the world but the quantities
and
composition vary according to local customs and culture as well as based on
the dietary bablts.
Mann (1976) reports on the average daily output of waste
per person based on his experience in Africa.
He estimates
400 grams wet
tight
per day of feces and 1,200 grams of urine per day, giving a total of
variation
between communi1,600 grams. He states that there is considerable
ties based on diet, water consumption, general health and the amount and
nature of the personal cleaning materials used. Moslem countries,
for example,
we water for anal cleaning purposes. McGarry (1976) reports that a volume of
about 2 liters
ie estimated
for China since this includes
a certain
amount of
water wed for flwhing
purposes. He also reports that the nitrogen content
of feces is 5% to 7% and that of urine is 18%. Kubo and Sigiki (1977) report
tb8 following
analytical
results
for crude night soil in Japan:
BOD
COD
volatile
12,000
3,000
acid
(as acetic acid)
m4 (as N)
PO (as P)
Chforides (as C -)
Albumenofd
(as N)
PD
nitrigen
6,000
ppm
ppm
ppm
4,500
1,000
5,230
780
Ppm
PPm
ppm
ppm
7 to 9
- 19 -
population
Snell (1943) evaluated
of the United States
the daily production
in 1930 as follows:
Table
of excreta
2
CHARACTgRISTICS OF EXCRETA FROM MIXED POPULATIONS IN THE U.S.A.,
Weight
per day
Matter
86
x
x
(g-s)
Feces
Organic
Matter
Total
Residue
by the mixed
Nitrogen
x
Phosphoric
Acid
--
1930 (SNRLL, 1943)
Potassium
%
%
22.8
19.8
1.00
1.10
.25
Urine
1,055
3.7
2.4
.60
.17
.20
Total
Excreta
1,141
5.15
3.7
.63
.24
.20
In comparison, the author cites China which is believed to produce about 80%
of the above veights vith a nitrogen content of about 0.4% owing to a lower
body vcight and food with .less protein.
Snell experimented
with the composting
of feces and urine.
He reports
that feces seeded with proper material
digest
normally with the speed equal to that of sewage solids.
Unseeded feces takes
mixtures of feces and urine
more than 10 times as long.
In his experiments,
do not digest quickly even if seeded.
Snell succeeded in the digestion
of
urine
by adding
cellulose,
straw,
starch,
sucrose
and garbage.
Hovard (1935) experimente‘&with
the composting of night soil by
adding it to other agricultural
re 'dues and municipal
rubbish.
He was
able to demonstrate that the temperatures
reached in the compost pile were
Further modifications
of
effective
in inactivating
most of the pathogens.
tbir
process resulted in the creation
of the Calcutta
method of composting
pits instead of mounds or trenches.
in vhlch the compost Is made in bricklined
In the later part of the 19,30's, Dr. Scharff (1940), inspired by
the work of Howard, introduced
the composting of night soil into Malaya.
He
reports successful
night-soil
composting operations
in three large centers
draviog supplies from about 10,000 inhabitants
yielding
approximattiy
3 tons
of crude compost daily.
Scharff wed two methods of cornposting night soil.
With the Calcutta method, a battery of bricklined
trenches,
12' long, 4' wide
and 2' deep, is constructed.
Appropriate
amounts of refuse are dumped daily
into the trenches,
then crude night soil undiluted
with water is poured directly
from the night-soil
pails onto the layer of refuse.
About 1 gallon of night
so&l Is required
for each cubic foot of refuse.
Immediately
after adding
the night soil the refuse is thoroughly
mixed using a long rake.
The pile is
formed and left undisturbed
for a week. No watering
is done.
In very wet
veather, a loose layer of leaves or grass is used to protect the heap from
- 20 At the end of a week, the rubbish is turned and is
excessive moisture.
drawn over to the side and another pile is formed and left to mature for
It is then removed and stacked in a heap on a concrete floor
two weeks.
for another two weeks, by which time it is ready for use.
Scharff regorts
that the average temperature
recorded during the first
2 weeks is 145 F
(59OC).
The Indore method of camposting was also used in Singapore.
Welldrained land, free from flooding,
is suitable
for this method of camposting.
The area required
is leveled and drained with shallow earth drains.
Village
A trench in the refuse is filled
with
refuse is packed loosely
in heaps.
vell-stirred
crude night soil.
The top of the trench is then covered over
loosely vith refuse drawn from the side of the heap.
The quantity
of night
soil filling
the trench should be equal to about l/6 of the volume of the
heap.
The heap is left undisturbed
for one week, except for daily moistening
No watering
is done during wet weather.
At the
with vater in dry weather.
end of the first
week, the heap is turned so the outer portion
of the heap
becomes the inner and the rubbish inside the heap forms the outer covering.
An additional
volume of crude night soil is added, equal to about l/10 of the
The top of this trench is then covered over with parvolume of the heap.
At the end of the second week, the operation
is
tially
composted refuse.
repeated with the same quantity
of night soil again added.
At the end of the
third or fourth week the heap Is again turned but no more night soil Is added.
Daily vatering
fs discontinued.
The heaps are now left to mature for one
month.
In the event of heavy rain a loose covering of grass or coconut fronds
is laid over the heaps.
Two months after the commencement of composting,
the
heap will have reduced to almost l/3 its original
size.
The compost is then
fully matured and according
to Scharff,
can be used on the land.
Temperatures
recorded in the Indore method are relatively
higher and more prolonged than
The temperatures
reached in the first
week average
in the Calcutta
system.
l6OoF (65OC) and this heat is maintained
at a high level (average (150'F)
during the first
three weeks.
Fly maggots may'be seen on the surface of the
heap during the first
week but disappear
after the first
turning of the heap.
Scharff reports
that by the end of the third week the compost is free from
intestinal
worm eggs.
In h%s paper, Dr. Scharff also reports
that the sludge
from the municipal
works in Singapore was heat treated
from the gas evolved
It reached a temperature
of 140'F
in the Imhoff tanks, starting
in 1932.
(57OC).
Tests carried
out by Dr. Gilmore, the municipal
bacteriologist
of
Singapore,
indicated
that at that temperature
all pathogenic
organisms which
may be present in the sludge, including
the eggs of intestinal
worms, were
effectively
destroyed.
It is interesting
to note that on the conclusion
of Dr. Scharff's
successful
camposting experiments
with night soil and on seeing the good
agricultural
returns
from the fertilized
fields,
he stated that he was
I .*a
prepared to prophecy that composting of night soil in the villages
of
maya
will cawe a revolution
in the sanitary
organization
of the rural
areas, ” and affirmed
"...
that it is clearly
the duty of health officers
to
- 21 encourage the composting of night soil together
with municipal
refuse or
agricultural
wastes so as to provide a satisfactory
hygienic
solution
to a
severe sanitary
problem as well as to provide fertilizer
to improve the
nutrition
of the population.'*
Stone (1949) provides one of the early reports of camposting in
He reports
that in the rice-growing
areas, fecal matter is mixed in
china.
pits or clay containers
with ricestraw,
ashes and garbage.
The mixture contains about 90% water and digests anaerobically
with a great loss of nitrogen, the nitrogen
content being 0.62% in fresh mixtures of feces and urine
Stone succeeded in Shaoyang, China,
and only 0,26X in the digested mixture.
in controlling
the digestion
in such a way as to lower the loss of ammonia
nitrogen to such au extent that the higher fertilizing
quality
obtained
He claims that he was able to establish
aerobic digestion
covered expenses.
at between 60° ant 65OC in a warm, moist climate of 22'C by laying alter2 parts of night soil,
and 1 part
nste layers of 4 parts of ground ricestraw,
of povdered bone with enough lime to keep the pH at 7.1.
Stone reports
that
The first
batches digested in
the carbon nitrogen
ratio was kept at 2O:l.
50 to 60 days and gave a semi-solid
humus-like
mass, which after 7 days of
drying in a layer about U-cm thick had the following
chemical composition:
Total nitrogen
Phosphates (as P 05)
Potasium (as K203
Moisture
3.94%
1.50%
2.27%
42%
Similar
results
were achieved in Hong Kong. Stone reports
that
ov&ng to the high temperatures
of digestion
between 60°-65’C
in the first
days and 49OC or less in the next 15 days the product was practically
free
from pathogenic
germs and Ascaris eggs.
Studies on the composting of human excreta with other kinds of
organic refuse were carried
out in northern
China by Scott and his collaborators at Cheeloo and Yen Chin Universities
prior to World War II in order
to find methods capable of producing
a better
final
product from the agricultural
point of view and to eliminate
the dissemination
of pathogenic
organisms and intestinal
parasites
(Scott,
1952).
Both aerobic and anaerobic
methods were studied.
Scott was able to demonstrate
with aerobic composting,
in which fecal matter vae composted with vegetable matter in mixtures of
varying proportions
and vith the addition
of some soil and small quantities
of vegetable
ash or horse and cow manure in varying proportions,
that he was
able to obtain temperatures
of 55'-60°C,
at which level,, they would remain for
3 weeks, except immediatley
after the subsequent turnings.
Practically
all
Scott reports
the Ascaris eggs were dead and protozoan cysts were eliminated.
that the optimal micro-biological
action was obtained with a moisture content
of betveen 50% and 60%. Fly breeding was insignificant.
Anaerobic composting
took a little
longer than 3 months and showed a better
nitrogen
conservancy
but a somewhat less effective
destruction
of Ascaris eggs.
Scott devoted considerable efforts to obtaining
optimal nitrogen
conservation
using various
combinations
of night soil and vegetable matter.
- 22 -
population
composted
different
Eamlin (1949) found in South Africa that excreta of the non-European
which lives on carbohydrates
were almost indigestible
but could be
when mixed with excreta of the European population
which lives on a
diet.
Night-soil
composting methods pioneered by Howard were introduced
into various parts of Africa.
Van Vooren (1949) in South Africa and Wilson
(1948) in East Africa have both reported
consistent
success using variations
of
Howard's original
methods.
The process was introduced
into Nigeria by Gillis
(1946) in 1941.
The first
composting plant was near Kano. After a trial
period the system was extended to other larger townships in northern
Nigeria.
During the period 1950 to 1960 there were 5 large composting depots in Kano
which were working continuously.
Night soil from some 3,000 bucket latrines
was treated
daily together
with most of the city's
garbage and litter.
The
mainal
contents
of all cattle,
sheep and goats slaughtered
in Kano's two
abbatoirs
was also disposed of in the same manner.
The average weekly kill
was of the order of 700 cattle
and 2,000 small animals.
The techniques
used
were based on the Indore system.
Appropriate
quantities
of night soil were
thoroughly
mixed with carefully
sorted refuse.
The mixture was loaded into
concrete chambers and the whole mass was thoroughly
turned on three consecutive
occasions after 5, 15 and 30 days.
At the end of 30 days, the process was
complete and the resulting
compost was a dark material
resembling
soil with
an earthy,
inoffensive
odor which did not attract
flies.
According to Peel
(1973), under uormal operation,
temperatures
over 68'C in the center of the
compost mass were regularly
reached in the dry season although these were
slightly
lower during the rainy season.
No temperature
measurements of the
outside layers of the pile were reported
but they were presumably lower than
those reported
for the center.
Peel reports
that when cornposting was first
introduced
into Nigeria
in 1951, Gillis
encountered
a certain
amount of prejudic~? among the indigenous
farmers who were reluctant
to handle a product in
which innuan excrement was a constituent,
but by painstaking
educational
work
and demonstrations
he and his staff were able to overcome this and eventually
the agricultural
community developed considerable
faith in the manurial value
of the compost and frequently
traveled
long distances
to the nearest depot
to them for a nominal charge; demand frequently
exceeded
where it was supplied
supply at certain
depots.
It was Peel's opinion
that manual composting must always be a primitive operation
which is difficult
to control,
with a highly variable
quality
of the end product.
He reports
that it was decided to initiate
a pilot
project in the city of Kane for the establishment
of a mechanized night-soil
compost
operation.
An engineering
firm from the United Kingdom prepared a provisional
design and a large area of land on the outskirts
of the city was selected for
a central
depot.
All of the existing
depots were to be closed down. The project was not carried
out following
the administrative
reorganization
in the
1960's.
Peel, in concluding
his review of the cornposting of night soil in
Africa,
states "Health standards of the vast peasant farming communities,
although slowly improving,
are still
low and two of the principal
contributing
factors
to this low standard are the continuing
high incidence
of fecal-borne
- 23 Thus, measures to secure improved nutridisease and widespread malnutrition.
tion and to control
these infections
are of paramount importance
in each
Peel
feels
that
the
effective
composting
of
country's
public health program."
night soil together
with other organic wastes under controlled
hygienic
conditions can contribute
to the solution
of these two problems.
He states that
although it has been thought that the local climate in some parts of Africa
is unsuitable
for the introduction
of composting it is possible
to overcome
these conditions
by proper composting arrangements.
He further
states that in some areas there may well be local prejudices against the use of the compost which contains
human excrement.
He
feels that in these circumstances
a vigorous campaign of education
and practical demonstration
by both the health and agricultural
authorities
may be
necessary.
"It is not claimed that composting will
In conclusion,
he states,
provide a complete solution
to the mass of problems of ill health and malnutrition
which face governments in tropical
Africa
today, but experience
has
shown that a properly
designed and supervised
system will secure a substantial
reduction
in fecal-borne
disease and will provide a valuable
end product which
enables plant nutrients
present in organic waste to be returned
to the soil.
Thus the benefits
to be obtained from the adoption of this method of waste
disposal
are such that they merit the most careful
consideration
by administrative,
public health and agricultural
authorities
throughout
the Continent."
Mr. Peel, who was formerly
chief health superintendent
in Sierra Leone and
northern
Nigeria,
is of the opinion
that in the present financial
climate in
Africa
simple manual composting schemes should be the most attractive
since
little
capital
outlay is required
and the end product has a cash value which
During the discan substantially
reduce the operating
costs of the project.
cussion of Mr. Peel's paper, it was brought out that the composting plant at
Kane, which apparently
is still
in operation,
is not popular because of odor
nuisances.
Pell admitted that it was not a completely
hygienic
system.
He
stated that there were no outbreaks
of disease which could be contributed
to
the failure
of the composting system.
However, he did feel that despite the
economic advantages of simple manual cornposting there would be a need for more
mechanized foolproof
cornposting municipal,systems
in the future.
Petrik
(1954) in his excellent
survey on the
soil,
sewage and sewage sludge in agriculture,
points
agricultural
advantages of cornposting night soil.
He
fact that there is not much sympathy among sanitarians
utilization
of human excreta and night soil,
it seems
many agricultural
countries
not only highly important
good method of ultimate
disposal.
Therefore,
both the
tary aspects of such disposal
deserve further
study."
A similar
view was taken by
Committee on Environmental
Sanitation
it stated:
"The Committee recognizes
world, of human excreta as fertilizer
utilization
of night
out the hygienic
and
states,
"In spite of the
for the agricultural
that such a use is in
economically
but also a
agricultural
and sani-
the World Health Organization
Expert
at its third session (WHO, 1954) when
the widespread
use, in many parts of the
. . . with the growing world population
- 24 and the limited
extent of world resources all efforts
to utilize
sanitary
byproducts
and return them to the soil should be encouraged.
The necessity
of controlling
these activities
in such a way as to reduce to an absolute
minimum their inherent
public hazards cannot be too strongly
emphasized."
6.
Modern Developments
in Composting
Sewage Sludge and Night
Soil
In those countries
of the world where central
water-borne
!
sewage systems are almost universal
for urban areas, the problem of the
treatment
and disposal
of sewage sludge has become a major issue in wastewater management and pollution
control
due to the heavy expenses involved
and the large areas of land required
for drying sludge.
Rudolfs (1942)
studied various aspects of the use of sludge as a fertilizer.
He considers
sewage sludge a good soil-builder
with some fertilizing
value and containing
relatively
small amounts of the main fertilizer
elements and minor elements
and materials
advancing the growth of plants which may be used to advantage
in some soils.
However, he recognized
the unfavorable
attitude
toward sludge
utilization
by sanitary
engineers
in general by the fact that they have
looked upon the sludge problem '*... as a question of the destruction
of
noxious matter rather than conservation."
The Agricultural
Research Council
of Great Britain
(1948) concluded from 80 experiments with sewage sludge that
the sludge is of moderate but positive
agricultural
value as a slow source
of nitrogen
and phosphate.
Various studies on sludge utilization
have been
carried out in the United States, South Africa,
Canada, and Germany and have
been fully reported upon by Petrik (1954).
a.
Windrow Sludge Compost Plant
District
in Los Angeles
County Sanitation
Current interest
in sludge composting and utilization
is exemplified by the studies
carried
out by the Los Angeles County Sanitation
District
(1974).
They evaluated
six methods of sludge disposal:
1.
2.
3.
4.
5.
6.
Incineration
Compost-air drying
Xechanlcal drying
Direct hauling of sludge to a landfill
Pyrolytic
processes
Pipeline disposal to a remote location
In evaluating
the proposed
alternatives,
the main criterfa
were reliabilitv,
and environmental
impacts and resource recovery.
Pyrolysis
and pipeline disposal were eliminated
in the initial
screening
process because
of the high initial
cost and limited
data on the feasibility
of a large-scale
system. They concluded that the ultimate
disposal
of sludge to any of the
three natural sinks, air, land, and water, is strictly
controlled
by a number
of regulatory
agencies and environmental
constraints.
However, they felt
that all of the disposal alternatives
are capable of meeting these constraints
provided adequate precautions
are taken during the design, construction
and
annual
cost,
social
- 25 Compost-air
drying was found to be superior
in the
operation
of the system.
cost analysis
due to its relatively
low capital,
operation
and maintenance
It also involved
the lowest use of scarce resources.
It was detercosts.
Based on the foregoing
mined to have the least negative environmental
impact.
analysis
the Los Angeles County Sanitation
District
selected compost-air
It established
a large-scale
drying as the recounnended disposal
method.
windrow sludge composting system at the Joint Water Pollution
Control Plant
(County Sanitation
Districts
of Los Angeles County, 1975).
in 1974, composting of dewatered-digested
sludge
At that plant,
was initiated
on a routine
basis on a 40-acre plot of land using the windrow
process with mechanical
equipment for turning
the piles.
They used the Cobey
the sludge and old compost added to
Rotoshredder
composting machine, turning
it several times a day for the first
days of processing
both to achieve comEach windrow must be
plete mixing and aeration
of wet and dry material.
turned initially
2 or 3 times a day to minimize odors and to insure sufficient
The sludge is then turned daily for a period of about 30
oxygen transfer.
The plant is presently
handling
up to 1,200 tons per day of sludge (23%
days.
solids)
(see Figure 1).
Major items of heavy materials
handling equipment are required
for
the operation:
4 Cobey Rotoshredders,
9 large "Flowboy" trailer
units,
2
forced-feed
loaders,
2 dry-sludge
transfer
trucks.
Composted dried sludge is
presently
transferred
by the Kellogg Supply Company, with earthmovers, to a
neighboring
site.
Distribution
and sale of the composted sludge as an organic
soil conditioner
shows a highly successful
marketing
record in the area.
The windrow compost piles have a base of 15', a height of 4#3”, a
This conwidth across the top of 6’, and a distance
of 3.75' between piles.
figuration
allows for a sludge volume of 3,900 cubic yards per acre.
M$ximum
veratures
in the central
portion
of the windrsw reagh as high as 160 F
The operating
temperatures
of about 150 F (61 C) in the central
(65 C).
portion of the windrow apparently
are maintained
for as much as a IO-day
period.
Data for the temperature
of the outside layers of the windrow are
not available,
but it is apparently
lower tha?r the center.
According
to the compoeter specification,
the unit which cost about
$130,000 is capable of processing
3,400 tons per hour at a density of 70 lbs.
per cum ft.
This translates
into a volume capacity
of 3,600 cubic yards per
bout.
Based on an assumed residence
time of 40 days in the windrows,
assuming
that the windrows must be turned twice a day for the first
5 days and once
per day for the remaining
period,
it has been calculated
that 3 machines opersting continuously during two shifts a day would be required.
A fourth
machine is required
for standby in the case of failure
which might result
in
the affected machine being out of service for up to 10 days. In the case of
rainfall
the processing
time would require
4 machines operating
in two shifts,
or 3 machines operating
continuously.
Therefore,
the minimum number of
Problems with cornposting
machines required
for assured operation
is four.
- 26 -
Fipra 1. Design Assumptions for Cumposting/Drying System
County Sdtation Districts - Los Angeles
T1600 Tons/day
23 percent solids
368 drytons
70 LSSIFTJ
1690 YD=
S6 percent volatile solids
drying area
N2.5 tons/
1 acre/d, W
I
‘1820 Tons
60 percent solids
lOQ2 drytons
46 LBSlPT=
3000 Yd
46 prrcent volatile solids
I
I
Landfill
- 27 A visit
to the Los Angeles
machine maintenance service have been reported.
County Sanitation
Districts
Joint Water Pollution
Control Plant was made on
No odor nuisances were detected and the plant was operating
July 20, 1977.
at full capacity under satisfactory
conditions.
Intensive
studies have been carried
out by the Los Angeles County
Sanitation
Districts
to determine the pathogen inactivation
during the windrow
Sludge samples
sludge composting process (Smith and Selna, 1976 and 1977).
have been analyzed for human parasites,
bacteria
and viruses.
The proposed
California
State Health Department standard for sludge that is to be sold as
agricultural
fertilizer
is a total
coliform
count of less than or equal to
Additionally,
the absence of human parasitic
ova
1MPN per gram of sludge.
Ascaris ova have been detected consistently
and in
and viruses
is required.
However, embryoabundance at the beginning
of each of the compost cycles.
nated ova have been detected only through the first
10 days of cornposting.
Embryonated viable ova have been detected near the end of the compost cycle
infrequently.
Ova of Trichuris
trichuria
and hookworm have been less
frequently
isolated
throughout
the compost cycles.
As with Ascaris,
viable
representatives
of these two parasites
have not been consistently
detected
after the first
week of composting.
The coliform
standard of less than 1 MPN
per gram was met only in the interior
samples during warm climate periods
Regrowth of coliforms
in
when the camposter was in continuous
operation.
the exterior
of the composting windrows has been detected.
This regrowth is
believed
to be due to lower temperatures
in the pile exterior.
In general,
fecal coliform
concentrations
match the total coliform
concentration.
The
majority
of the coliform
concentration
typically
detected in composts at the
Los Angeles plant can be accounted for as fecal coliforms.
Salmonella
assays were performed less frequently
than the coliform
assays, but also indicate
rapid kill
within
the first
10 days of composting.
In most cases, during warm climate composting cycles the detection
limits
of less than 0.2 MPN per gram Salmonella was observed although salmonella
Since this
organisms were detected in a few samples of final compost.
organism is not an obligate
pathogen it can regrow outside the human host
but in general the limit
of detection
of Salmonella was much shorter than
the period of time to reach the minimum concentration
of coliforms.
This
indicates
that the rate.of
inactivation
of Salmonella during composting
was greater
than the rate of inactivation
of coliforms
(see Figure 2, showing
typical bacterial
concentrations
versus time during composting operation).
Considerable
effort
has been made by the Los Angeles group to
methods to effectively
assay compost for viruses.
Although the
methods still
are not considered completely reproducible,
viruses were not
detected
towards the end of the compost cycle.
develop
In conclusion,
the Los Angeles group has found that temperatures
as high as 60-6S°C have been produced at the center of the compost heap
during composting cycles when rain did not occur and when the composting
Low ambient
apparatus was consistently
available
throughout
the cycle.
temperature, rainfall,
and composter malfunctions
cause temperature
in the
interior
of the compost windrows to reach a maximum of 55-60°C during the
-
FII~
28 -
2 Bsteria Concentmtions vs. Cornposting Time (LCGAngeld
I
-*
0
1U
I
I
^cJ
20
Timr. dew
Note: 1. Opuatii
Smra:
Smii
modr - 1 arm/d~
md WirU. (1977).
2 date:
4-12-76 to 524-76
I
40
60
- 29 -
winter months.
Viable
cooler.
The outside
-1ortions of the pile are of course considerably
Ascaris ova have been isolated
in only three of the final
during their study, while only six of the 116
compost samples collected
samples collected
after more than 10 days of composting contain embryonated
Ascaris.
Total coliform
and Salmonella concentrations
are rapidly
reduced
Final compost coliform
concen10 days of the composting period.
trations
of less than 1 MPN per gram have been achieved during warm weather
conposting
in samples collected
in the interior
of the compost windrows.
Exterior
windrow samples have not been below 1 MPN per gram with consistency.
Final compost Salmonella
concentrations
of less than 0.2 MPN/g have been
achieved in both interior
and exterior
samples collected
from warm
Regrowth of Salmonella during winter compost cycles
climate compost cycles.
has been observed but it has not been determined whether poor winter performance was due mainly to climate or failure
of the cornposter.
Assays of
virus,
parasitic
ova and Salmonella have yielded negative
results
in the vast
concentrations
in
majority
of final
compost samples, whereas total coliform
compost samples have not been uniformly
below 1 MPN per gram.
final
in the first
Generally
satisfactory
results
as far as bacterial
and pathogen inProbably better results
with
are concerned have been obtained.
higher temperatures
could be achieved in higher compost piles,
but this is
not presently
feasible
due to the configuration
of the existing
composting
machines. There also have been operational
problems with the composting
machines which have led to failures
in the process at times.
activation
In conclusion
it
can be:said
that the composting air-drying
operDistric.ts
of Los Angeles County provides a
good demonstration
of the feasibility
of sewage sludge composting on a large
The heavy capital
investscale with relatively
good pathogen inactivation.
mentin their complex composting equipment and other materials-handling
equipment makes this process relatively
expensive and subject to serious
operational and maintenance problems, limiting
its suitability
for developing
ation of the County Sanitation
countries.
b.
The Beltsville
Aerated Rapid Compost (BARC) System for Cornposting
Waste Water Sludge
Dr. Eliot
Epstein
and his
group at the Agricultural
Environmental
Quality Institute
of the U.S. Department of Agriculture
Research Station at
Reltsvllle,
Maryland, have been experimenting
with sewage sludge composting
for a number of years.
Their first efforts
were in the direction
which the digested sewage sludge was mixed together
of windrow composting,
in
with bulking materials
such as wood chips and composted in open windrows using various compostingturning machines, including
the Cobey Rotoshredder
currently
used in Los
Angeles.
Temperatures reached at the hottest point in the compost piles were
as high as 60 C on a number of occasions,
while the temperatures
of the outThe piles were turned daily.
side layers of the piles were considerably
lower.
Results of their studies on the destruction
of pathogens in the
composting of sewage sludge were reported by Burge, et al. (1974).
In the
first studies, total and fecal coliforms were greatly reduced during 2 weeks
of windrow
cornposting
in the surface
(0 to 20 cm), subsurface
(20 to 40 cm)
and interior
(80 to 100 cm) of the windrows.
During the 4 weeks of the
stockpile phase these organisms survived in the surface and subsurface but were
destroyed at depth. Salmonella numbers increased during the early part but
were essentially
destroyed by the end of the windrow phase. Enteric viruses
were detected during the windrow phase but were not detected during the stockprepile phase. The above results apply to both digested and raw chemically
cipitated
sludge.
Total and fecal coliforms increased in numbers in composting
of chemically precipitated
raw sludge during the winter months, Salmonella
numbers increased only sporadically.
During
the winter
months F2 bacteriophage
was incorporated
into
the
sludge. During the winter months F2 was destroyed despite the low ambient
temperatures affecting
the efficiency
of cornposting.
The authors report that
weather conditions greatly influence the ability
of the windrow composting
process to control pathogens. In the fall,
during the composting of the
digested and chemically-precipitated
raw sludge, coliforms,
and Salmonella
were considerably reduced in the windrows and essentially
wiped out in the
interior
of the stockpiles.
however, continued
The total and fecal coliforms,
to survive in the stockpile surface (O-20 cm) and subsurface (20-40 cm).
During winter cornposting of chemically-precipitated
raw sludge, the total and
fecsl coliforms increased in numbers with cornposting indicating
they were
growing in the portion of the compost windrows and stockpiles
in which killing
temperatures were not reached. The initial
were low
salmonella concentrations
and for the most part remained at low levels.
Viruses were present in the
d&eated and chemically-precipitated
raw sludge samples composted in the fall.
Tests for their presence were positive during much of the windrow phase including that last tests made, but they were not detectible
in the stockpiles
indicating
that they were eventually destroyed.
The results of these windrow cornposting studies led Epstein and
hi8 group to investigate more efficient
ways of composting so as to assure
temperatures
in the upper theraophilic
range during the entire composting
period and to guarantee the inactivation
of pathogens in all portions
of the
pile.
The system developed, celled the Beltsville
Aerated Rapid Compoeting
(B4RC) method, wau based on the building of static piles of mixed sludge and
mod chips used as a bulking
material
(Epstein
et al., 1976).
The wood chips
which were added to $he sludge in a ratio of 1 part sludge to 2 parts wood
chips reduced the moisture content from 78% in the initial
sludge to 60% in
thenixture.
Wood chips also provided for a lighter
structure
of the mixed
pile to enable the free passage of air through the pile.
The wood chips provided for an increased carbon source. The C/N ratio of the sludge was about
10, uhich is too low for rapid cornposting. Perforated
plastic
drainpipe,
lbcr disoeter, was laid out in a loop on the ground and covered with 15 to
2Orr of wood chips or previously manufactured unscreened compost.
This
- 31 -
layer
absorbed liquids
and prevented
sealing of the pipeholes
by fine parThe mixture of sludge and wood chips was then placed over the comticles.
post and wood chip base and piping system with a front-end-loader.
Each pile
contained
approximately
40 metric tona of filter-cake
sludge mixed with wood
chips and had the dimensions of 12m x 6m with a height of 2.5m. The entire
pile was then covered by a 30-cm layer of finished
compost that had been
This layer was designed to prevent odors
passed through a l-cm mesh screen.
from escaping from the pile surface into the atmosphere as well as to provide
insulation
for better heat maintenance and reduce the penetration
of rain.
The pipe system was connected to a 0.33 hp centrifugal
blower which was used
to draw air through the pile according to a predetermined
schedule controlled
by a timer.
The gases drawn into the pipe were deodorized
by passing them
into a pile of previously-screened
compost (see Figure 3).
Temperatures
in the pile
increased
rapidly
into
the thermophilic
rising
over 80°C.
Temperarange during the first
3 to 5 days, ultimately
tures started to decrease after about 3 weeks indicating
that the more decomposable organic constituents
had been utilized
by the microflora
and that the
Temperature measurements were
sludge had been stabilized
(see Figure 4).
made at 14 points
within
the pile
daily
during
the experimental
composting
These points were at various depths within the pile including
those
at the interface between the sludge and wood chip mixture and the compost
cover which should be the coolest area.
According to Dr. Epstein's
data from
over 100 experimental piles, minimum temperature
of at least 60°C have been
recorded for a minimum of 5-10 days in each composting cycle, while temperatures of 80°C were achieved in the hottest areas. This 60°C temperature
is
uell above the thermal inactivation
point of all of the pathogens considered
to
This is truly an impressive
be of importance in sewage sludge and night soil.
NllS*
accomplishment
considering
the simplicity
of the operation
which uses a minimal
anouat of mechanical equipment.
It apparently
assures failsafe
thermal inactivation of all pathogens of importance in the pile.
Extensive
studies
on the destruction
of pathogens
in the compost
pile have been made. Although Salmonella,
fecal coliforms
and total colifolrae increased initially
in numbers, they were reduced to essentially
undetectable levels by the tenth day. Studiea using F bacteriophage
or virue
es an indicator showed that the virus was essentlall$
destroyed
by the
thirteenth
day. Survival of the virus did occur for some time, however, in
the blanket-compost mixture interface
where lower temperatures
prevailed.
Storage in a curing pile for 30 days, in accord with the present process
technology, should complete the destruction
of viruses
or at least reduce
the numbers to an extremely low level (see Figures 5 and 6 on bacterial
and
virus inactivation).
The authors state that the numbers of coliforms
and
salmonella may increase in the outer layer of the curing piles where the conStudies are in progress to assess
ditions for regrowth are more favorable.
this possibility.
Epstein and his colleagues
feel that their studies demonstrate that composting with forced aeration
is essentially
unaffected
by low
ambient temperatures and/or rainfall,
which makes this system particularly
The BABC system
attractive
for operations under various climatic
conditions.
i
- 32 -
F&n, 3. Schematic [email protected] of an Aemted Pile Indicating Location of
Aeration Pipe. Loop is Perforated for Air Distribution
(millimeters)
c
Aeration Pip is -tad
awn air distribution
,
for
SectionDC
- 33 -
Figure 4. Temperatures During Cornposting of Raw Sludge (May 1975)
BQ
Max.
70
60
Mean
50
00
30
Min.
Rainfall
(cm)
5.0
10
10
1
3
5
7’9
11
13
15
Days
Sourea: Emrain El Al, 1975).
17
19
21
23
25
27
/
_I,
- 34 -
Figure 5 Destruction of Salmonellids,
Fecal Coliforms, and Total Coliforms
During Composting by the BARC System
Total coliforms
colifarms
I
~UKC
Epstein Et Al, (1977).
1
--
-, s-j, = ,- -,
- 35 -
Figure 6. Destruction of F2 Bacterial Virus During Cornposting
by the BARC System
8
Sampling
piper
0
0
5
10
-ifs
!Zource:
Epnein
Et Al. 11977).
15
20
base
- 36 -
is currently in operation since 1975 in Bangor, Maine, serving a population
of 50,ooO persons and handling 50 tons filtered
primary and secondary undigested sludge at 22% solids per week. The thermophilic
bacteria
apparently
continue operating to heat the pile to above 55'C in the aerated compost pile
even during periods of sub-zero weather common in that area.
The external
layer of well-composted material
insulates
the pile and effectively
prevents
the cooling of the compost pile during heavy rains.
The BARC system is no longer
in the experimental
stage
and at
Beltsville
is operating on a full-scale
composting basis using filter-cake
from the Blue Plains Sewage Treatment Plant in Washington.
The plant has been
operating routinely
since early 1975 receiving
60 wet tons of sludge per day
for processing; this is equivalent
to the sludge produced from a plant serving
a population of l25,COO. They have been able to demonstrate the feasibility
of a large-scale routine operation of the plant.
In a site visit
to the plant
operation on July 12-15, 1977, no nuisances were detected,
fly breeding was
uot present, nor were odors typical
of many composting operations.
It
has been reported
that
there are very few mechanical problems
with the simple airblowers used in the system.
The unit is relatively
inexpeusive, costing about $100 and can be easily replaced in case of failure.
Tbere is small amount of liquid extracted through the blower system, which
se-es
as a drainage system for the compost pile.
This liquid
has a BOD
of about 3,ooO; it is drained away to a stabilization
pond adjacent
to the
compost site which also receives the general site drainage.
In a very rainy
&irate,
the leachate rate may prove to be a greater problem and special
facilities
should be designed to deal with this.
The Beltsville
plant is now
on an asphalt surface although earlier it was operated on gravel-covered
soil
surface.
A well drained soil base may be satisfactory
under the conditions
of lirited
rainfall.
soil and rainfall
However, with plants with different
conditions it might be necessary to operate the plant on a hard surface area
covered ui,th asphalt or concrete.
The wood chips and sludge mixture is made
with a front-end loader which is standard earth-moving
equipment.
The mixing
process is carried out on a paved area.
The area requited
for the BARCsystem has been estimated
to be
per 10-12 dry tons per day of sewage sludge.
This area estimate
includes (1) area8 for mixing the sludge or night soil with bulking materials,
~2) the area required for compoeting, (3) the area required for storage and
curing piles and long-term storage before marketing,
(4) the area required
for screening of the final compost and separation
and recycling
of wood chips,
(5) area required for lagooning or oxidation ponds of leachate and drainage
from the composting area, and (6) area required for administration,
workshops, parking of vehicles,
and storage of spare parts.
1 hectare
As more experience
is gained using the BARC system of composting,
to refine the design criteria
concerning
area requirements
10 that design estimates can be made. Without knowing soil conditions
in
adva=e,
one should assume that 50% of the area should be paved.
However,
it
will
be possible
- 37 with proper firm,
simple conposting
mechanical mixing
area.
vell drained soil it might be possible
to carry out the
except
for
the
mixing
surface.
A
on unpaved areas,
could replace the open mixing
device such as a **pug-mill"
According
to the calculations
of Dr. Epstein,
the materials
balance
of the BARC system is as shown in Figure 7. As can.be seen from this figure,
for 1 ton of dry veight of sludge, 2 tons of vood chips are added to make up
the mix vhile 0.69 tons of vood chips are used to make up the base of the pile,
and 1.42 tons of screened compost is used to cover the pile,
adding up to
5.11 tons dry weight in the pile for every ton of sludge entering
the plant.
However, according to the Beltsville
procedure,
the wood chips are recycled
and only 0.64 tons of vood chips must be added for each incoming ton of sludge
Screened compost is also recycled as a cover for the piles and
as makeup.
calculations
for every ton of dry sludge solids
according to Dr. Epstein's
entering the plant, 1.13 tons of marketable screened compost is produced.
In addition
there are a n-bet
including Windsor,
to the BABC system in operation
at Beltsville,
Maryland,
of other full-scale
BARC composting plants with operation,
Ontario,
and Bangor, Maine and Durham, New Hampshire.
A site visit
was made to the BARC sludge composting plant in Windsor,
The West Windsor Pollution
Control Plant has been
Ontario oxi July 18, 1977.
composting filter-dried
primary sludge cake from a 21 mgd plant since 1976.
15 q/liter
of ferric
chloride
is added to the raw sludge, then 0.3 mg/liter
The sludge is concentrated
partially
by
of an anionic
polymer is added.
vacuum filtration
and partially
by centrifuge
giving a solids content between
20X; to 24X. The pH of the filtered
sludge is about 11. In Windsor part of
the sludge is hauled 24 miles to a landfill
site at a cost of $6.50 per ton
for hauling and landfill.
It is estimated
that this may go up to $9 per ton,
and there is a possibility
that in the future there may be no landfill
area
available.
Therefore,
there is a great interest
in the possibility
of composting the sludge and marketing
the final
product through commercial chan-
nels.
No operational
problems have been encountered
at the plant and no
A wood
nulmnces
were apparent at the site which appeared to be well-run.
chip screening and recycling
installation
is presently
under construction
The piles at the West Windsor
using a vibrating
screen separating
system.
plant are arranged in the piggyback system, that is, each day's pile is laid
contiguous to the previous day's pile and covered at the end of the day in
such a manner that there is no free space between the piles,
which form a
singlemound.
Each pile,
however, has its own aeration
system (see Figure 8).
This configuration
reduces the area requirements
considerably
and has been
shown to be highly
effective.
Apparently
no problems have been encountered
composting the sludge
which bas been treated
to a high pH of 11. The pH of the mixed pile with
the bulking materials
has not been determined.
Dr. Ann Prytulla,
Director
of
out microthe Regional Public Health Laboratory,
Windsor, has been carrying
biologial
tests of the raw sludge and completed compost since April 1977.
Figure 7. Materials Bd#~ce for the BARC System
)
fw0aoc”IP’
STaclc
PILE
INPUT
/
b”“S”
M
SLUDGE
1.001s
MIX
ä
3.ooTs
0.48VS
MIX
+
-
2.28VS
\
/
<
BASE
A
I
--&
UNSCREENED
FINISHED
COMPOST
4
--&
SCREENING I
4.7OTS
s.txvs
I
T.S., Total dry solids {tons); V.S., volatile
Assumptions:
Volatile
Solids
%
New Woodchips
Used Woodchips
Sludge
Compost
*Data irom:
E. Epstein
90
48
40
Water
%
35
50
78
olids (tons).
1
, COMPOST
2.56TS
l.OlVS
OUTPUT
1 COMPOST
-
To MA dK ET
1.13TS
0.44vs
1
Figure 8. Constnation
(millimeters)
Skt*
or ni*t
mixed
with
wood
&I*
of Extended Aerated Cells for SARC System
tail
stnvu.
at
omw
~wacer
comoon
n
’
Fai
I1 ‘3
WWI
norsdno
Pi00
be0
, Filter ~IIO 01
’
finIShed
comctost
Comporting extended piles with forced aeration
c0tnQan
mmd
wm
wood
chm.
straw.
or attw
Porforrree
comoosr
CompostinQ with forerd
rrration
She ha6 tested
fecal streptococci,
Salmonella
particularly
Ascaris and Giardia.
Temperature measurements are taken at regular
intervals
from a number of
sites within the pile including
points at the center of the pile and at
the periphery
next to the cover and next to the bedding.
The site nearest
the outside cover next to the bedding usual18 is the coolest
spot in the
pile.
Even at that spot, temperatures
of 60 C have been recorded for several days during the al-day composting period.
and viruses,
for
coliforms,
fecal
coli,
as well as for parasites,
bacterial
counts f?r coliforms
are of the order of 108/100
coliforms,
abow 10 IlOO grams; and of Streptococcus
fecalis
about 10 /lOO grams. 3After 21 days of composting,
the total coliform
count
drops to less than 10 /lOO grams.
Thirty determinations
for salmonella
bacteria were made in the fini hed compost with no positive
findings.
Bacterial
counts of slightly
above 10 J /lOO grams were, however, found at the coolest
spot in the pile close to the base and at the periphery.
It is felt that this
can be overcome by avoiding excess aeration
which may lead to the cooling of
the pile.
While parasite
eggs have been found in the raw sludge, none have
been detected
in the final compost.
In the West Windsor plant,
6 acres have
been allocated
to treat 120 wet tons of sludge per day with 20% solids.
The
area is gravel cowered and has 10 cm drains at S-meter intervals.
The cost
of vood chips is $4 per ton.
grars;
fgr
C.
Initial
fecal
Coapoeting Night
Soil
with
the EMRC System
Hr. James C. Patterson,
research agronomist
with the National
Cepltal
Park Service,
Ecology Laboratory,
in Washington,
D.C., has initiated
a project for conposting night soil from sanitary latrines
in the Dargon and
C60 Cans1 Parks of the National
Capital
Park System.
This project
has been
carried
out under the supervision
of Dr. Eliot Epstein,
and is based on the
NABC 6ystem.
The tight
soil is accumulated in the vault of the standard
6anitary
latrine
of the Park Service,
which contains
SO-75 gal.
This vault
is emptied by a vacuum truck as frequently
as twice a week during the peak
6e66on and 66 infrequently
a6 once every other week during the winter season.
A mixtun
Of weed Chip6, COPlpO6t, and sawdust is made and formed into a
b6rin onto which the liquid
night soil is spread by being pumped from a
1,000 g6l holding
tank at th6 compost site, which is used to receive the
liquid tight roil pumped fram the vacuum trucks which extract the night soil
from the latrines
spread throughout
the park.
The compost pile is made up
about every 3 weeks during the summer season.
The raw night soil is estimated
to have 95% liquid
concentration.
According
to estimates
provided by the Park
bcpartment
for every volume of night soil,
1.6 volumes of wood chips are added,
and 1.0 volume of compost and 1.5 volumes of sawdust.
These provide bulking
material
which absorbs most of the liquid
and largely
avoids the problem of
runoff Mch
was initially
encountered
(Patterson,
1977).
Temperatures up
to 80 C have been recorded in the compost pile.
The main problems encountered
have keen using adequate amounts of sawdust to absorb the moisture.
About
1x of the liquid
night soil applied
to the pile runs off as drainage and is
disposed of into a lagoon.
Analysis
of the final
compost indicates
that
- 41 the total
organic nitrogen
(TN ) concentration
is 1.3 to 1.6X, phosphorus is
0.6 to 0.7X, carbon is 46% to 50%. No loss has been detected in the nitrogen
The night soil has also been
content in the year of storage of the compost.
tested for heavy metals and the following
concentrations
have been found:
Lead (Pb)
Zinc (Zn)
Nickel (Ni)
Cadmium (Cd)
128-138
400-790
61-101
3-7
ppm
ppm
ppm
ppm
The pH of the final
compost varied between 6.6 and 6.9 and the
soluble salts concentration
between 960 and 7,000 ppm. It is interesting
to
contains
540 ppm lead,
note that municipal
sludge, as reported
by Dr. Epstein,
in the com2,000 ppm zinc, and 19 ppm cadmium. The high zinc concentration
posted night soil for the Park Department is apparently
due to the use of a
chemical disinfectant
containing
zinc, called ZEP, in their latrines.
Nevertheless,
the concentrations
of the other heavy metals apparently
indicate
the
amount of heavy metals excreted by humans as a result
of heavy metal intake
sources.
f ram dietary
Approximately
27,000 gallons
(lOO,OCO liters)
of night soil is produced each year by the visitors
at the C&O Canal Park, a historical
park which
run6 parallel
to the Potomac River in Washington and neighboring
Maryland.
The incentive
for camposting was the overloading
of the local sewage treatment
plant6 which were unable to accept the night soil from the vacuum truck transport vehicles.
Hicrobiological
testing
of the finished
compost has been carried
Maryland.
The results
indicate
effective
inactivation
of enteric
bacteria
including
pathogens in the composting process.
Compoeting of night soil by the National
Capital
Park Service at the site in
Dargon using the BARC sytem is in fact the first
test operation
using this
system for composting of real night soil,
and can serve as a model for the
6tudy of this method.
At the moment the project
is being carried
out with
rinim61 scientific
surveillance.
ln order to gain the maximum amount of
Information
from this operation,
it would be deeirable
to carry out an intenparameters and the effective61~6 l-year
study to verify
both the engineering
m666 of pathogen inactivation
in the system.
out by the USDA in Beltsville,
d.
Conclusion
Based on the extensive
review of the literature
on public health
problems associated
with pathogenic
microorganisms
in night-soil
and sewage
sludge reuse covered in Section 2 of this document and on the review of available composting technology,
past and present,
it would appear that the best
method most likely
to be capable of meeting all the objectives
for safe and
econodcally
feasible
night-soil
treatment
and reuse for developing
countries
would be the Beltsville
Aerated Rapid Composting (BARC) System.
- 42 Temperature data from over 100 piles that have been composted by the
B&C system indicate
that every portion
of the pile has reached a temperature
of at least 60°C for approximately
a 5- to lo-day period during the course of
that this can provide effective
All available
evidence indicates
composting.
thermal inactivation
of the pathogens of major public health significance
including bacteria,
protozoans,
helminths
and viruses,
producing a final compost
which will be free of public health risks.
The advantage of the BAN system
is not only the very effective
and uniform thermal inactivation
of pathogens
in an assured manner, but the fact that it is a relatively
inexpensive
method
using simple equipment which is particularly
suited to developing
countries.
The final
compost produced is of good quality.
It is a stable,
nuisance-free
granular material which in no way resembles the raw materials
from which it is
made and which may well be socially
acceptable
even in areas where the direct
handling of human excreta is not looked upon with favor.
Such compost has a
demonstrated agricultural
value as an effective
soil conditioner.
Based on these conclusions,
it is recommended that a major effort
be
areas of developing
made to develop a nmber of pilot
projects
in appropriate
countries where night soil of varying characteristics
can be composted with
BARC system with local bulking materials
and under the specific
local enviranMIktal conditions.
This is an essential
step in providing
for a more complete
ev6lu6tion of effectiveness
of the system from a public health point of view
under field conditions and to obtain the required engineering
parameters
required for the rational design of full-scale
systems.
7.
Economic Aspect6 of Night-Soil
The following
Composting
is based on an analysis
prepared
by Dr. Epstein:
Colacicco
et al. (1977) estimated the cost of composting raw (priby the BARC method in the U.S. to range between $38.5 and $55
per dry metric ton of sludge.
The $38.5 figure relates
to a SO dry ton per
day operation and the $55 to a 10 dry ton per day operation.
mary)
sludge
In the U.S., it is assumed that each person produces 55 grams of
per day (primary sludge).
Thus a 10 dry ton facility
would serve
180,ooO perron6.
fwai, Honda, and Chang (1962) estimate that the total
6Olidr in night soil is 30 grams per liter
and aseuming 1 to 2 liters
of night
roil p6r person per day, then a IO dry ton facility
for composting night soil
would serve a.-ppulation
of 150,000 to 300,000 persons.
Accurate data of
night-eoif
quantity per capita is not available at this time.
rolidr
a.
Cost Estimates
The capital
for Composting
Sludge at Beltsville
(BABC)
costs are estimated
to be between $3O,COO and $38,000
per dry ton per day capacity,
for facilities
with an output of 50 and 10 dry
tons capacity per day, respectively.
Table 3 shows details
of the capital
CO6t6 in 1976 dollars:
- 43Table
3
CAPITAL COSTS FOR BARC SYSTEM
Dollars
Item
50 dry tons
10 dry tons
Land
16,000
10,000
4,000
20,000
14,000
4,000
TOTAL
30,000
38,000
include
Equipment costs
Land costs were estimated at $10,000 per acre.
tractor,
mechanical
screen and blowers.
front-end
loaders,
trucks,
Site development
ma=-t
Table 4 identifies
the operating
inputs
for
a lo-
and SO-ton
facility:
Table
4
OPERATING REQUIREMENTSFOR BARC SYSTEM
Item
Quantities
50 tons
Idot
1.5 h sa
2.1 m4
2.85
rs.
2.1 m5
4.2 liters
10
liters
7.5 kWh
4.2 liters
13
liters
17.3 kWh
uoodcbips
Ga6oline
Diesel
Electricity
Labor
Cost6
labor time for light
Tb6 total
6hown in T6ble 5.
Consumed per Dry Ton
10 tons
include management overhead, vacation,
maintenance of equipment and site.
cost
e6timates
for
Beltsville
Table
Aerated
sick
Pile
leave
Method are
5
TOTAL COSTS FOR BARC SYSTEM
Percent
50 tons
of Annual Costs
10 tons
Item
Dollars
per Dry Ton
10 tons
50 tons
Operating Cost6
Site Development
28.36
3.23
3.75
0.63
41.37
4.00
5.26
0.63
79
9
10
2
81
8
10
1
35.97
51.26
100
100
Equm-t
Land, excl6ding
, facilitie6
TOT&
and
- 44 -
Labor is the greatest
operating
the operating expenses. Labor costs
5 weeks of sick and vacation
time and 6%
secutiry plus $400 per worker for health
all
expense and represents
half of
were based on $6 per hour with
for the employer's
share of social
care.
The estimates
for the costs of the BARC composting system by Epstein
and his group (Colacicco
et al., 1977) are higher than the 1974 estimated
costs of the equipment and energy intensive
composting operation
of the Los
Angeles County Sanitation
Districts
(TACSD). It is estimated
that the BARC
eystem costs per dry ton of sludge for a 50 tons/day p].ant is $38.50.
The
Districts'
estimate was $2.02 per wet ton or $8.80 per dry ton (assuming 23%
moisture) for operating, maintenance,
and capital
recovery for equipment and
structures;
land costs were not included.
Current estimates
by Gunnerson
(personal
communication)
are as follows:
Table
6
TOTAL COSTS FOR LACSD SYSTEM
170 Tons/day
.
Capital (including
land)
Operation and Maintenance
Total
$13.20
14.30
$27.50
Composting is more economical than incineration,
wet oxidation,
pyrolysis or other advanced technologies.
Since the BARC method is more
and more economical in developlabor-intensive,
it is considered more suitable
ing countries than the highly mechanized windrow-turning
operating
as practiced
in Los Angeles.
b.
Preliminary
Soil per Day
Estimates of Costs of Composting
L
10 Dry Tons of Night
1. Site size:
0.8 to 1.2 hs. The lower figure
is for a site which
do66 not need runoff coll6ction
or adminietrative
areas. Site cost will
depend on land valuee. For example, at $25,00O/ha the costs would range
from $19,200 to $30,000 for 8 compost site.
2.
Site development: This will depend on climate,
existing
soil
condition6 and facilities
present.
The availability
of power and water would
reduce site development costs. Where electricity
is not available,
a small
portable generator would be required to supply electricity
to the air blowers.
A concrete pad would be most expensive followed by asphalt and crushed rock.
Approximately half the site should have a hard surface unless local conditions
allow for operation6 on an unpaved area.
It is estimated
that equipment and
6ite development costs would vary beruatz $1~0,000 and $2OO,OGO.
- 45 3.
(excluding
Bstimated
annual
operating
costs
per 10 dry tons per day capacity
labor):
a.
metal pipe recoverable
or (plastic
pipe, non-recoverable)
power - fuel, electricity
equipment maintenance
miscellaneous
supplies,
etc.
b.
C.
d.
Total:
s 5,000
to
12,000
10,000
10,000
5,000
$30,000 - $37,000
4.
Labor. Labor cost Will depend on the remuneration
in each country.
The folloving
is an estimate of the minimum labor force required
to compost
10 dry tons of night soil per day.
1 foreman
2 equipment
operators
for front-end
loaders
1 tractor
operator for mixing
2 general hands for laying out pipe and general
1 screen operator
if screening
is to be done
work
it will be possible
to develop preBased on these tough estimates,
limiuary designs for demonstration night-soil
composting plants in several
Houever, real cost figures can be developed only after
developing countries.
demonstration-pilot
Studies have been carried
out in several appropriate
developing
C.
countries.
Problems
of Marketing
Julius
(1977) has studied the economic aspects of low-cost
waste
disposal and reuSe in developing countries
and suggests that urban wastes
8uch 8 night-soil
compost may behave according
to the economic theory of "inferior goods." This theory states that contrary to normal demand curves which
goods" decreaee.
tend to go up with increasing income, the demand for "inferior
As an example, she cites the historical
data from Ireland which shows that
potato demand decrcaees when consumer income wa6 high since other higherpriced carbohydrate8 were purchased instead.
She 8hOWS that for selected
cases in Taiwan, Japan, and Korea night8021 demand by farmers decreased as farm income increased and alternative
higher costing chemical fertilizer
could be purchased.
This situation
may have certain far-reaching
policy implications
as
to the suitability
of "appropriate
low-cost
technology"
for waste disposal
Even if **appropriate"
technology
is develand reuse in developing
countries.
oped, the problem of a decreasing demand or even difficulties
in ultimate
disposal 8t no charge may plague the economics of the system as living
standards
increase.
.
- 46 Julius
suggests that no less important
than developing
and testing
new low-cost
waste disposal
and reuse technology
is the need to develop
educational
programs stressing
the long-term
economic and ecological
benefits
Such an effort,
if successful,
may lead to
of safe and hygienic
waste reuse.
organic waste reuse being perceived
as a socially
desirable
objective,
the
demand for which could actually
"increase
as their price goes up."
The success of such a program would depend on successful
demonstration of the agricultural
benefits
derived from night-soil
co;llpost reuse.
Such
agricultural
research and extention
work should be seen as an essential
part
of the pilot
study program of night-soil
composting since demand for the product may provide the key to its long-term
social acceptability
and economic
8UCCe88.
In any eveat, night-soil
treatment
and reuse systems should not be
seen as a profit-making
venture but rather as a way of solving a serious
sanitary
problem in the least expensive manner consistent
with good hygienic
and environmental
practices
and norms.
8.
[email protected] and Pilot
Study Needs
A8 stated previously,
it is concluded that the BARC night-soil
compo8ting system is suitable
for developing
countries.
Further research and
pilot
studies are required
to establish
the suitability
of the process.
At
the moment there is only one night-soil
composting plant operating
according to
the RARC system from which direct
information
can be gained as to the efficacy
of the process from a public health point of view and from which the engineering
parameters and design criteria
for the development of full-scale
plants in developing
countries
can be derived.
That night-soil
composting
plant is operated by the National
Capital
Parks Service at Dargon in
WaShingtOn, D.C. To date, only limited
scientific
monitoring
of the above
plant has been carried
out although from the data available
to date there is
a good indication
that the system works, is nuisance free, and effectively
inactivstee
pathogens in the final composted night-soil,
sawdust, wood chip
mixture.
It
to obtain the following
InformatZon
before proceedof full-scale
night-soil
composting plants using the BARC
I8 e8eent,ial
ing with the design
System in developing
a.
Characteristics
countries.
of Night
Soil
Representative
data should be collected
on the chemical and physical
of night soil in different
countries
of the world following
different
practices
of nutrition
and personal hygiene.
Chemical tests which
should be carried
out include total and volatile
solids,
carbon, pH, Kjeldahl
nitrogen, amonia, zinc, cadmium, nickel,
Physical
characteristics
and lead.
that should be determined
include moisture content,
total volume per capita,
density and seasonal variations.
In addition,
information
could be obtained
Op the concentration
of several key pathogens,
such as salmonella,
Ascaris
eggs,hookwormeggs,
and enteric viruses might be assayed as well.
characteristics
- 47 -
b.
Bulking
Materials
In each site selected
for study a survey has to be made of the availability
of appropriate
bulking materials
since the BABC process required
the
addition
of bulking materials
both to absorb the moisture of the night soil,
to
provide additional
carbon, and to provide the pile with an open structure
enable effective
aeration
of the static
compost pile.
The availability
of
such materials
as rice husks, straw, wood chips, sawdust, peanut hulls,
tin
trash,
coconut shells,
and any other organic waste materials
which might be
appropriate
for the composting process should be studied.
The C/N ratio of
the m&a:rials
should be determined
as well as their water-holding
capacity
and compostability.
C.
Environmental
The effect
should be determined
ture range, relative
d.
Parameters
of environmental
parameters on composting operations
including
such factors
as daily precipitation,
temperahumidity,
and soil conditions.
Engineering
and Operating
Parameters
Key engineering
and operating
parameters to be determined
include
of night soil and other wastes to be composted, land
cost of materials,
labor and other
are88 utilized,
drainage requirements,
operating
expenses, temperature
profiles
within
the pile,
oxygen levels
within
the pile under various operating
conditions,
volatile
solids destruction and percent moisture during composting,
and the availability
of infrastructure
for technical
operation
and maintenance of equipment.
sources and quantities
e.
Evaluation
A series
of the Final
Compost from a Microbiological
Point
of View
samples from every composted batch should be analyzed
and parasites,
as well as for a number of key indiAssays for
such as coliforms and fecal call bacteria.
cator organisms,
enteroviruses
should be carried
out if facilities
are available.
of
for pathogenic bacteria
f.
Quality
of the Compost
Standard assays for the chemical composition
of the final
compost
should include C/N ratio,
and the percent nitrogen,
phosphorous and potassium.
Where possible
agricultural
tests and demonstrations
with the final
compost
should be carried
out to determine
its suitability
as a soil conditioner
and
fertilizer.
Market surveys should be carried
out to determine the possibility
for the sale and distribution
of the final
product in the local economy.
The pilot
studies should be carried
out in developing
countries
tith varying climatic
conditions
so as to include
the full spectra of possible
conditions
to be faced by night-soil
composting operations,
including
cold
wet climates,
cold dry climates,
and hot tropical
climates.
The cities
selected
for night-soil
composting pilot
plant demonstrations
should be
selected
based on the availability
of an existing
night-soil
collection
and
di8pOSal system which is Oper8ting in a fairly
effective
manner so as to
assure the supply of fresh night soil for the composting operation.
Another
criterion
in the selection
of the city is the availability
of a principal
investigator
who has the appropriate
technological
and scientific
background
to organiee and coordinate
a project
of this type.
Availability
of chemical
or a governmental
and microbiological
laboratories,
either
at a university
department, is essential.
The analytical
tests, both chemical and microbiological,
listed above are the optimum desirable
tests that should be carried
out where facilities
are available.
However, it will be possible to carry
out studies with a somewhat reduced schedule of testing if it is possible to
obtain the other required services.
In order to fully develop design criteria
for a variety
of environmental parameters, a number of pilot projects
should be developed in such
countries as India, Korea, Taiwan, Indonesia,
Singapore and Nigeria.
It might
be particularly
feasible to conduct such studies in United Nations supervised
refugee camps, such as those in India, Cyprus, Israel and Jordan.
Supervisory,
scientific
and technical personnel at such camps may be available.
The
cooperation of the local camp and government authorities
could be assured
through United NatiOnS channels. Another possible site would be at one of the
Oxfam sanitation
unit locations operating successfully in Bangladesh.
The above mentioned
research
and demonstration
pilot
projects
carried out in the developing countries can provide essential
information
required for furthering
the goals of the appropriate technology research
project.
However, it will take considerable time to organize the scientific
and technical infrastructure
required in any of the above countries.
In order
to gain vital information concerning the BA?K composting system of night soil
in the shortest possible time, serious consideration
may be given to the
possibility
of finding ways of supporting a more detailed scientific
monitoring and evaluation
of the night soil composting plant carried
out by the
W8tfOIIal Park Service in Washington.
D.C., using night soil obtained from the
park latrine system. The advantages of this project are that it is already
operating with the total norms1 operating expenditure
covered by the Park
Depsrtment itself.
and technical
personnel in
The availability
of scientific
the vicinity
m&e8 it possible to initiate
the scientific
studiee required
in
the ShOEteSt pO88ible time. Preliminary discussions with Mr. J. Patterson,
tcre8rch sgronoakiet of the National Capital Park System in Washington, indicate
that he and Ns organization would be pleased to cooperate in such a study if
the addition81 funds required to carry out the microbiological
and chemical
tests were made available.
Another possible site for a research-pilot
study that could be
quickly organized would be at the University of Texas at San Antonio where
Dr. Bernard P. Sagik and Ns group have developed considerable
expertise
- 49 in the health aspects of land disposal of sewage sludge and are interested
in
the po88ibility
of initiating
a BARC compostlug study with night soil from
portable latrines used extensively at construction
sites in the area.
The
workers are mainly low-income groups of Mexican origin with known high endemic
A study at that location
would provide
infestations
of intestinal
parasites.
valuable information on the inactivation
of such parasites
by the BARC system
They
by a high-level. scientific
team uniquely qualified
for such a study.
could also do virus work which might nt% be possible in most developing
countries.
studies
In conclusion, an extensive program of research-pilot
is needed to determine the full range of technological,
public health,
and
economic effectiveness‘of
the BARC night-soil
composting system in several
developing countries before long-term municipal-scale
programs are initiated.
,.”
,.:
I
- 50 -
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- 5s APPENDIX I
Page 1 of 20
.
TECHNOLOGICALASPECTS OF
THE BARC COHPOSTING SYSTEM AS RELATED TO COMPOSTINGNIGHT SOIL:
Eliot
I.
Epstein,
Ph D.
INTRODUCTION
The Beltsville
Aerated Pile Composting System was developed as a
sewage sludge processing
system.
The major advantages
low-cost, low-energy,
to this eytem are:
1.
Compoeting raw sludge, i.e. primary or secondary
eliminates the need for further
processing,
e.g.
oxidation,
heat treatment,
or other technology.
2.
?%e microbial decomposition
posting alleviates
malodore
organic material.
3.
Heat produced during compoeting effectively
human pathogens.
4.
The eyeten
is not capital
or night
digestion,
soil,
wet
of sludge or night soil during comand produces a stable,
humus-like,
intensive
destroys
many known
and does not require
for such
the
technical and engineering expertise required
systems es incineration
or heat drying.
5.
Energy inputs
6.
The product can be utilized
for
operation
The major dieadwantagee or limitations
1.
It generally
2.
More labor intensive
requires
are extremely
as a fertilizer
to composting
more land
than other
than many of the other
low.
and soil
conditioner.
are:
treatment
systems.
systems;
and,
- 56 APPENDIX I
Page 2 of 20
PrOCeSS
I.
Collection
Design
and Transportation
The present Belteville
Aerated Pile method utilizes
dewatered raw
(primary coebined with some secondary) sewage sludge for cornposting.
This
sludge eontaine 78% water and 48% volatile
solids.
The sludge is transExperimentS
with liquid
ported to the compost site in 10 ton sealed trucks.
sludge (98% water, 66% volatile
solids) have been carried out at Beltsville.
Liquid sludge was transported in tandem cement vehicles.
Table 1 provides
data on the compoeition of the raw sludge from the Blue Plains waste water
treatment plant in Washington D. C.
Data from A. SinghL/
(1975)
indicate
that
a moisture content of 85% to 90% and volatile
night
soil
from India
has
solids of 80 to 88%. The U.S.
Depert.ment Of Interior,
National Capital Park Service has been compoating
aieht e0i1 (pumping from portable sanitary outhouses) using the BARC
system. The night soil is pumpad out of the outhouses (sanitary john),
capecity SO to 75 gal (190 to 280 liters),
up to twice a week in the summer
and once every two weeks in the winter.
The tank which pumps out the night
roil, has a 500 gal. (1450 liter)
capacity.
that
Pradt (1971) 2/ indicates
there are eubetantial differences between night soil and f;eeh sewage
sludge. Night soil has a pH of 8.5 and high concentration
of a-onia,
chloride and volatile
solids.
It is not believed that these should Cause
~ypreblemeincompoeting.
Data from Belteville
show that cornposting
can take place OVCTa large pl? range of 5.5 to 12. Neither the amania
nor chloride
are known to present problems.
II.
The BeltevilIe
4
Aerated Pile Method (BARC)
The process consists
1.
Mixing
- sludge (liquid
of the following
steps:
or devatered)
is mixed with
meteriel.
'2.
1/
The Belteville
Aerated Pile construction
3.
Screening - recovery
(optional).
4.
Curing and storage.
5.
Metribution.
Singh. A- Soils Bull.
Pradt.
of bulking material
a bulking
and maintenance.
for
recycling
27, p. 19-30, FAO, Rome (1975).
L. (1971) Some recent developments
Water Ike, 5: 50-21.
in night
soil
treatment
- 57 APPENDIX I
Page 3 of 20
Chemical Analysis of Raw Dewatered Sewage Sludge from the Blue
Plains Wastewater Treatment Plant, Washington, D. C., and the
Raw Sludge Compost Produced at the U. S. Department of Agriculture's
Conposting Research Facility
at Beltsville,
Maryland.
Table 1.
cOrganic
-
nent
Raw Sludge
31%
Carbon
Water
78%
Raw Sludge Compost
23%
35-58X
Potaeeirn
0.19%
0.16%
Phoephorue
1.46%
1.0%
C8lCitr
1*39x
1.42%
B&ypeeium
0.41%
0.40%
Total llitrogen
3.8%
1.6%
1,540
lOitnte
end !?itrite
PPB
1 PP
235 PP~
3 Ppm
zinc
980 PP=
770 Ppm
mw=
420 PP~
300 Ppm
NiCkSl
67 PF
cednim
10 PPm
420 PP~
L/
6.
Honitoringandmanagement~/
7.
Health aspects of sludge compoeting A/
5s Ppaa
8 ppm
290 Ppa!
control
are based on procedures
in
Operational and research quality
Methods of Soil Anelyeie, Agronomy Monograph No. 9, American Society
of
Agronomy, wadison, WI. (1963) and in Standard Methods for the Examination
Of Water and UaeteYater, 14th Ed. American Public Health~Aseociation,
Waebington, D.C. (1976).
- 58 APPENDIX I
Page 4 of 20
Figure
1 is a flow diagram illustrating
the process for dewatered
(22% solids)
sewage sludge.
Modification
of the process has been used for
liquid
sludge or night soil as illustrated
in figure 2.
Two volumes of woodchips maximum dimensions of 4 to 5 cm, are mixed
1.
Other bulking materials
which will be discussed
with one volume of sludge.
later may require different
ratios.
The final mix should not contain lumps of
sludge larger then 7.5 cm in diameter.
Mixing can be achieved by using a
front-end loader, farm tractor
and rototiller,
commercial mixers, pug mills or
of equipment will depend on the size of operation,
rotary drume. The selection
location of coGposting site, climatic
conditions
and availability
of labor.
It ie essential that the bulking material
be kept as dry as possible
so that
the final mix is at approximately
60% moisture without
using excessive amounts
of bulking materials.
During mixing odors can be produced causing excesWhere large volumes of materials
are to be mixed, it would be
sive nuisance.
perferable to mix in an enclosed stationary
mixing facility.
In the case of
night soil, mixing in a closed system may also be hygienically
preferable.
.
PROPOSEDSYSTEM FOR COMPOSTINCNIGHT SOIL
The following
night
eoil
1.
(Figure
Delivery
sequence
of night
Tranefering
A concrete
study.
and operations
is recommended for
by tank trucks
to a camposting
composting
2).
soil
the night
soil
into
mixer (tandem type)
,
a mixing
is ideally
site.
drum or storage tank.
suited for a pilot
Bullring matbriale are then added. A fine, absorbent bulking
material such as sawdust can be used initially
to absorb
Finished
compost itself
can also be used.
excess moisture.
The mix (concrete
consistency)
can then be applied onto a
bed of coarse material
such as woodchips,
or the woodchips
added to the previous mix in the mixer.
4.
If the mixer is needed for incoming night soil, then the
first mix can be applied to a bed of woodchips and mixed with
Mixing can also be
a rototiller
attached to a farm tractor.
accomplished with a front-end
loader.
The final
described
nix
can then be used to build the aerated
Aerated Pile Method.
in the Beltsville
pile
as
Figure 1. Flow Diagram for Comporting Operation
waolJclllPs
4
RECYCLED
’
OPTION A
SLUDGE
(1 VOLUME)
+
SCREENING +
CURING
I30 DAYS)
4
w
v
MIXING
ORYING . q
-b
AERATED
PILE
STORAGE
m
I21 DAYS1
.
COMPOST
MARKETlNG
- 60 APPENDIX I
Page 6 of 20
Figure 2 Flow Diagram for Camposting Night Soil or Liquid Sludge
r
I I
BULKING
MATERIAL
A
(COMPOST1
NlGHT SOIL
STOW%
SOLIDS
\
L
/
BULKING
MATER IAL
B
~WOODCHIPS~
SLUDGE
b&lY *
MIX B
.
1
AERATED
PILE
=
\
I
SCREEN
P
t36TRt~UtkON
CURING
COMPOST
-
- 61 -
APPENDIXI
Page 7 of 20
The purpose
Bulking
Materials
of the bulking
materials
is as follows:
a.
Reduce the moisture
to 50 to 60 percent.
b.
Prowide structure
or poros'lty
for air movement through the mixture.
The Beltsville
Aerated Pile system is an aerobic process requiring
content
of the sewage sludge
or night
soil
Oxpgen.
c.
Provide carbon to raise the Carbon to Nitrogen (C/N) ratio to
approximately 20-30 to 1. The C/N ratio of sewage sludge is
in the range of 9-15 to 1. Raising the C/N ratio reduces the
loss of nitrogen
as ansaonia. The addition
of carbon as a
bulking
material ensures the conversion of nitrogen
into organic
constituents
of the biomass.
Various materials can be used as bulking materials
e.g.-- wood chips,
aavdurt, wood ahawlnge, peanut hulls, corn cobs, straw, rice hulls,
cotton
fracgin trash, leaves, shredded bark, shredded paper and air-classified
Mona (mainly paper) obtained from solid waste recovery plants, etc.
2.
The Belteville
Aerated Pile
A.
The Aerated Pile
schematic diagram of the Beltsville
Aerated
A three-dincnaional
Pile Method for compoeting sewage sludge is shown in Figure 3. In their
aimpleat form the individual,
stationary,
aerated piles are constructed
as
follollm:
8*
A loop of b-inch
diameter
(10 cm) perforated
plastic
pipe
is
placed on the compoeting pad, oriented lengthwise, and eymetrically
under what till
become the ridge of the pile.
Perforated
steel
pipe can also be used and later removed for reuse.
The perforated
pipe
should not extend under the end slopes of the pile because excessive
amounts of air may be pulled through the sides, causing localized
2onaa (i.e.
"coldspots")
that do not reach the thermophilic
range.
The pipe should be placed at least 8-10 ft (2.5 to 3 m) from the ends
of the pile.
b.
A 6 to 8 inch (15 to 20 cm) layer of wood chips or other bulking
material is placed over the pipe and the area to be occupied
by the pile.
This layer comprises the pile base and facilitates
The
the movement and distribution
of air during composting.
base material also absorbs excess moisture that may condense
and leach from the pile.
-
62 -
APPENDlX I
Page 8 of 2"
FIGURE 3
ELEMENTS OF THE BELTSVILLE AERATED
RAPID COMPOSTING SYSTEM
(EPSTEIN ET AL. 1976)
COIIIIPOsllNG
WITH FORCED AERAnON
WOODCHIPS
AN0 SLUDGE
PIPE
/
WATER TUAP
FOR CONDENSATES
dTER
PILE
SCREENED COMPOST
World Bank - 18059
’
- 63 APPENDlX I
Page 9 of 20
C&
The mixture of sludge and wood chips is then placed loosely
upon the prepared base (with a front-end
loader or conveyor
with a triangular
cross-section,
35
system) to form a pile,
feet wide (5 m) and 7.5 feet high (2.5 m).
d.
The pile is completely
covered with a 120inch (30 cm) layer
of cured, screened com(often referred
to as the "blanket")
The blanket
layer provides insulation
and prevents
post*
the escape of malodorous gases during composting.
If finished
compost is not available,
as would be the case for the first
the bulking material
itself
can be
piles of a new operation,
used for this purpose. However, the blanket thickness may have
to be increased
to achieve the same degree of insulation
and
odor control
as obtained with cured compost.
e.
During construction
of the pile base, the perforated
pipe is
connected to a section of solid plastic
pipe which extends
beyond the pile base. The solid pipe is connected to a 1/3=hp
Aerobic composting conditions
blower controlled by a timer.
are maintained by drawing air through the pile intermittently.
The exact aeration schedule will depend on pile geometry and
the amount of sludge to be composted.
For a pile containing
up to 80 tons of sludge (20 m x 5 m x 2.5 m), the timing sequence
for the blower is 5 minutes on and 15 minutes off.
The blower
is then turned on and the composting period begins.
f.
The effluent
air stream from the compost pile is conducted into
a small cone-shaped pile of cured, screened compost approximately 4 feet high (1.3 m) and 8 feet in diameter (2.7 m), where
malodorous gases are effectively
absorbed.
These are co=only
refvred
to as odor filter
piles.
The moisture content of
compost used for this purpose should not exceed 50% because the
capacity tends to decrease at higher moisture
odor retention
lewels.
A Q-inch (10 cm) base layer of wood chips or other bulking
material under the odor filter
pile is necessary to minimize back
pressures which could cause leakage of malodorous gases around the
blower shaft and to absorb excess moisture.
Research has shown
that
the odor filter
pile should contain about one cubic yard of
screened compost for each 10 wet tons (4 dry tons) of sludge
being composted. In the case of new operations,
where screened
some bulking materials
or soil (or
compost is not yet available,
a mixture thereof)
could be used in the filter
piles.
Variations
in pile shape aud size can adapt the process to differences in the rate of sludge production
by most treatment
plants.
The
individual
pile method described
here is suitable
for operations
ranging
from as little
as 5 tons of sludge (20% solids)
from a single weekly
deuattring operation to more than 100 tons per week.
- 64 APPENDIX I
Page 10 of 20
B.
The Extended Aerated Pile
Another version of the aerated pile is the aerated extended pile.
Each day's sludge production is mixed with a bulking material
and a pile
is constructed which utilizes
the slope (lengthwise
dimension)
of the
previous day's pile, thus forming a continuous or extended pile.
The
extended pile offers certain advantages for larger municipalities
on a
daily sludge production schedule. For example, the area of the composting
pad can be reduced by about 50% as compared with that required to accomodate an equal amount of material in individual
piles.
Moreover, the amount
of blanket material (i.e. screened compost) needed for insulation
and odor
control, and the amount of bulking material
for the pile base are both
decreased by 502.
In constructing an extended pile, the first
day's sludge production
is placed in an individual
pile with triangular
cross-section
as described
earlier.
The exception is that only one side and the ends are blanketed.
The remaining side is dusted with about an inch (2.5 cm) of screened compost for overnight odor control.
On the next day, additional
aeration
pipe is placed on the pad surface parallel
to the dusted side, the pile
base is extended, and the sludge-wood&tips mixture is placed in such a
manner as to form an extended pile.
On the second day, the flat top and
ends are blanketed with screened compost and the remaining side receives a
thin layer of compost as before.
The pile is extended each day for 28 days.
However, after 21 days the first day's section is removed for either drying
and screening or placing in a curing pile.
After the removal of seven
sections in chronological
sequence, there is sufficient
space for operating
the equipneat so that a new extended pile can be started where the old
one has been.
Thereafter, a section is removed each day from the old pile
and a section is added to the.uew one.
c.
Temperatures Attained
During Cornposting
of sludge into compost is essentially
complete
The transformation
after 3 weeks in the aerated piJe. Microbial decomposition
of the volatile
organ&c fraction of the sludge In an aerobic atmos here soon raises the
temperature throughout the pile to above 60°C (140 gF), which effectively
destroys pathogenic organisms that might cause diseases in human beings.
Typical temperatures recorded during the composting of raw sludge by the
Reltsville
Aerated Pile Method are shown in Figure 4. As can be seen from
this figure, temperatures in the pile increase rapidly into the thermophilic range of 80°G (176’F) or higher.
Temperatures begin to decrease
after about 16 to 18 days, indicating
that the more decomposable
organic constituents
have been utilized
by the microflora and that the
ltcsidual sludge has been stabilized
and transformed into compost.
Figure 4 also indicates that if piles are constructed properly, neither
excessive rainfall
nor low ambient temperatures affect the composting process . Studies at Bangor, Maine, Durham, New Hampshire, and Windsor, Canada
showed that neither cold weather nor snow affected
compoating.
- 65 -
APPENDIX I
Page 11 of 20
FIGURE 4
TEMPERATURES DURING COMPOSTING OF LAW SLUDGE
(MAY 1975)
BARE AT BOTTOM iNDiCATED RAINFALL EVENTS
(EPSTEIN EL AL, 1976)
MAX
70
-
c
Eo-
fu,
MEAN
z
z
s
k!
B
40-
r
30-
RAINFALL
(CM)
MIN.
20-
10
-
I
I
I
1
3
b
II
7
I
I
m
III
9
11
13
15
17
I
I
I
I
I
19
21
23
25
27
DAYS
World Bank - 18060
5.0
- 66 APPENDIX I
Page 12 of 20
D.
Aeration
and Oxygen Supply
Centrifugal
fans with axial blades are usually
the most efficient
for developing the necessary suction to move air through the compost piles
and into the odor filter
piles.
A pressure differential
of about 5 inches
(12.5 cm) (water gauge) across the fan has been adequate when woodchips are
used as the bulking material.
However, when finer textured materials
such as
emdust
are used for composting sludge, an increase
in pressure differential
w%ll be required.
The aeration rate should maintain the oxygen level in the pile
between 5 and lSX for rapid decomposition
of the sludge and extended
themophilic
activity.
This
eve1 can be achieved with &IL aeration
rate
of about 500 cubic feet (14 m3 ) per hour per dry ton of sludge.
Research has
shown that continuous aeration results
in rather large temperature
gradients
within the pile.
A more uniform temperature
distribution
is obtained by the
use of intermittent
aeration.
Cycles of 20 to 30 minutes, with the fan
operating l/l0 to l/2 of the cycle, have been satisfactory.
Four-inch (10 cm) flexible
perforated
plastic
drain pipe has
been used to collect the air under the piles and to deliver it to the odor
filter
piles.
The pipe is damaged beyond reuse when the piles are taken down
inexpensive it is regarded as an expendable item.
but since it is relatively
Rigid steel pipe has also been used and can be pulled lengthwise
out of the
pile without damage zu-& irem&.
The uipe spacing for the extended piles should
not exceed the pile height.
The pipe-should
be large enough so that friction
lo6ses will not cause a pressure differential
of more than 15% along the
length of the perforated section.
Manifolding
the outer ends of the pipe will
equalize
B.
pressure
in the event of accidental
damage to the pipe.
Condensate and Leachate Control
As air moves down through the comporting sludge, it is warmed and
picks up molrture.
Temperatures near the base of the pile are slightly
cooler ao a result of heat loss to the ground.
As the air reaches this
area, it is cooled slightly,
causing moisture to condense.
When enough
condensate collects,
<it will drain from the pile,
leaching material
from the
8ludge.
Condensatioq will also collect
in the aeration
pipes and, if not
vented, can accumulate and block the air flow.
The combined leachates
and
condensate may amount to as much as 5 gallons per day per ton of dry sludge.
If the bulking material is sufficiently
dry to begin with, there will be no
leacbste drainage fr6m the pile.
Since the leachate
contains
sludge fractions,
it cm be a source of odor if allowed to acrcmulnt~ in puddles, so it should
be collected and handled in the same manner as runoff water from the site.
The purpose
of screening
reuse and/or to provide for a better
is to recover
product.
the bulking
material
for
- 67 APPENDIXI
Page 13 of 20
Bulking materials
are not always available
and may represent
a
At Beltsville
the cost of wood chips represents
substantial
operating
cost.
Wood chip recovery is therefore
essential
19% of the annual operating
cost.
This
cost
figure
is
based
on
$3.5
per
cubic
yard.Screento reduce costs.
ing is expensive requiring
labor and capital
investment.
The use of bulking
material such as rice hulls or peanut hulls would eliminate
screening.
The physical
and chemical characteristics
of the final
product
Particle
th& agronomic or utilization
value of the compost.
c8u affect
Fine particles
of material
can be
size can affect
application
systems.
applied with standard fertilizer
spreaders,
whereas coarse particles
The chemical characteristics
will affect
ray require
special
equipment.
The C/N ratio of the
the quantity
and the way the material
can be used.
compost should not exceed 3O:l as this will require
additional
supplemental
nitrogen.
Wood chips and other high C/N ratio material
therefore
need to
be 8creened out if the product is to be used as a low-analysis
fertilizer
If refuse is used as a bulking
(S8e 8ection on product utilization).
material,
rrcreening is needed to remove undesirable
material.
Prior
to screening
it
may be necessary
to dry the material.
Drying require8 both additional
land, site development,
and labor.
At
Belt8ville
for a 10 dry ton per day operation
it is estimated
that drying
Two screens have
co8t8 account for less than 5% of the operational
co8ts.
been used at Beltsville,
a rotary
(trotmel)
and an oscillating
axema
50th 8ereens can handle material
having a moisture
to 502.
The moisture
content of the material
should not be
8ince this will lead to dust production.
If the material
is
8creen, drying c8n be accomplished by spreading the compost
tumiqg
or harrowing
or vibratory
content of up
much below 30%
too wet to
and periodically
it.
Curing and Storage
4.
the compost ha8 been cured for about 30 days (screened
or
may be placed In a storage pile for an indefinite
period.
Wing further etabilices
the compost. Use of the compost is ordinarily
the bulk of it applied either in the spring or fall.
Thus, a
8888ou8l, tith
Cmhg 8nd storage area is needed to accoannodate 3 to 6 months production.
After
unscreened),
it
to decompose at a slow
During storage, the compost will continue
rate.
Usually thie doe8 not present any problem because by this time the
comporrt is well etabilized.
DeCOmpO8itiOn in storage can be largely
curtailed
by drying the compost to a moisture content of about 15%. If
it i8 stored in large pile8 at a moisture content of, say 45x, temperatures will increase to the thermophilic
range, and additional
composting
will occur. This may actually
improve the quality
of the compost for some
Me8 I
The compost can be stored
with the equipment
th8 top8 Of the storage piles
88 i8 convenient
fatmd
without
cover and may be piled as high
available.
Care should be taken to
so that wet pockets do not develop.
- 68 APPENDIX I
Page 14 of 20
Distribution
Di8tributiOn
of the compost will depend on the location
and type
of market.
If the market is located near the composting site then direct
Distribution
centers may be utilized
if the market
haulage is preferable.
The city of Chicago maintains
several distribution
areas
area 18 wide.
Citizens
may pick up the material
without
charge
for their "Nu Earth" sludge.
for their u8e.
may dictate
the
The type of market, i.e. agronomic or horticultural,
packaging aspect of the product (bagged or bulk) and distribution
system.
Product8 used for horticultural
purposes (nurseries,
greenhouses,
home use)
Agrocan co-d
a higher value for the product and may need to be bagged.
nomic use, for example revegatation
of strip mines, will deal with large
quantities
so that bulk handling
is preferable.
Bquipment may be needed for loading and packaging
and the market strategy,
which might be:
market
depending
a.
Compoclting and marketing
8ewage authority.
to be done by the municipality
b.
CoPposting
and marketing
to be done by private
C:
i%=6huhm+ims
"'---w-..~
+n
m-
-..mZri8~atZi-aaYu.Lb&p*LLJ
&
&pa=
==jr
ant
-
-rrr2.rc&rr
mo.abs~zr‘~
or
enterprise.
*s
"L
dfStri=
(Los Angeles County has this
bution by private
enterprise.
in conjunction
with the Kellogg Supply Company).
6.
Honftoring
on the
system
and Management
Monitoring is essential
to ensure proper operating
conditions,
high
temperatures for pathogen reduction,
and odor control.
Operational
monitoring
can be kept at a minimum with low cost, uneophisticated
equipment.
a.
Temperature
Temperature8 will reveal more about the process than any other
8ingle par8meter.
Most of the pile should reach 55'C within 2 to 4 days,
indicating
satisfactory
condition8
with respect to moisture content,
bulking
material ratio, nixing,
and PK.
Low average temperature8
below 60°C can result
from excessive
The former can be corrected
by
88ration or too high 8 moisture content.
reducing the blower cycle or placing a baffle in the pipe just in front of
the blower.
If the moisture content is too high it indicates
an improper
The pile can then be torn down and
sludge to bulking material mix ratio.
mbuilt with additional
bulking material
and future piles built with the
correct ratio.
Cold spots in the pile may also result from improper pipe
Temperature monitoring
should
ming
or an inadequate insul8tion
cover.
- 69 APPENDIX I
Page 15 of 20
be done daily for the first
week. Once temperatures
level only periodic
spot checks are needed.
Several
thermistors
b.
simple
and bimetallic
temperature
probes.
probes
peak at the desired
are available
and include
Oxygen
Oxygen analysis of gas samples drawn from the center of the piles
for locating
problems and optimizing
the aeration
system.
The
oxygen level should be in the range of 5 to 15%. Scattered
readings
below 5% indicate
poor distribution
or movement of air, and are probably
the result of an excessively
high moisture content or incomplete mixing.
there are no voids for oxygen movement and
If a gas sample cannot be obtained,
If all readings are low, the
the sampling location
is probably anaerobic.
aeration rate should be increased.
The type of equipment recommended for
monitoring oxygen levels during composting is listed
on page 20.
is useful
C.
odors
Site
operator8
should
pay particular
attention
to odors.
Whenever
unplea8ant odor8 are noted, the source should be located and corrective
action taken. X&nosed eludge, ponding around compost piles, and partially
Improperly
constructed
odor
odor sources.
tomposted 81udge are potential
filter
piles or leaky pipes between the blower and the filter
pile can
al8o contribute odors. Over a period of time the odor-filter
pile can also
contribute odors. The odor-filter
pile can also collect
condensate which
lowers the capacity to absorb and retain odors.
When the moisture content of
the odor-filter
pile8 reaches 75-80X, they should be removed and rebuilt
with
dry (50% moieture content or less) materials.
While rewage 8ludge can emit a strong unpleasant odor, it gradually
di8appear8 a8 the 8ludge 18 stabilized
by compoeting.
Each of the unit
operations
can be a potential
source of odors.
Some of the odors emitted
are intermittent
while other8 are continuous.
Odor potential
increases
conrriderably during and immediately following
periods of excessive precipitation.
To minimize
it
18 essential
the odor potential
to manage each operation
throughout
as follows:
the composting
process
(a)
The mixing operation - Prompt mixing of sludge and bulking material
8nd plrrcement of the mixture in the aerated pile reduces the time for odor
generation.
An enclosed mechanical mixer could eliminate
the release of
odor8 from this operation.
(b)
Aerated pile surface - This will not be a source of strong odors
if the blantret of compost is adequate for insulation.
Thin spots or holes
- 70 APPENDIX I
Page 16 of 20
in the blanket
of the blanket
60%.
will be a potential
source
for odor control
decreases
of odors.
The effectiveness
when its moisture content exceeds
(c)
Air leakage between the blower and odor filter
file
leakage can occur at this point, all joints
should be sealed.
- Since air
Back pressure from the odor-filter
pile should be minimieed to prevent gaseous
losse8 around the blower shaft.
Back pressure can be virtually
eliminated
by placing a 4- to 6-inch layer of bulking material
under the filter
pile.
Odor-filter
piles - As mentioned earlier,
the odor-filter
piles
(d)
are a potential
source of odors.
They should be cone-shaped,
and symmetrical and contain about 1 cubic yard of dry (50% moisture or less)
screened compost per IO wet tons of sludge being composted.
(e)
Condensate and leachate - These are potential
sources of odors.
A8 these liquids drain from the compost pile, they should be collected
into a sump and conveyed in a pipe to the sewer system or stabilization
pod*
(f)
Removal of compost from the aerated
pile
to the curing
pile
- If
the sludge has not been adequately stabilized
prior to this operation,
odors
will be released.
Excesrrive odor during this operation
can probably be
attributed
to too high a moisture content in the composting mixture and
can be avoided by lowering the moisture content of the mix with additional
bulking material.
(g)
Curing piles - These can be a source of odors when the material
removed from the aerated pile has not been completely stabilized.
The use
of drier materials in the initial
mixing operation
will prevent this problem.
BlaaLcting the curing pile with dry cured compost will also help to contain
8ny adore. Where sludges are incompletely
composted after 21 days because
Of c1LCe88moieture, low temperatures, improperly
constructed
piles,
or
improperly treated rludge, th8 odor potential
will be high.
In these
curing pile,
but mixed
C88e8, th8 sludge 8hould not be put on a regular
with additional
bulking material and composted another 21 days, or put
into a separate isolated
pile,
heavily blanketed
with screened compost,
and 8llowed
(h)
8tructed
to compost for several
months.
Storage piles - Odors could arise
tith excessively
wet compost.
in storage
if
the piles
were con-
(0 Aggregates or clumps of sludge - When aggregates of sludge are
allowed to remain on the compost pad after mixing and processing,
even though
small in size, they can 8oon-emit-unpleasant
odors.
Workers should be made
amre of this so that all aggregates of sludge are carefully
removed from
the mixing We8 as soon 8s possible.
(3)
Ponding of rainwater - When rainwater
is allowed to pond on
site, 8naerobic decomposition
can occur and cause unpleasant
odor.
Threfore,
the site must be graded and compost piles located so that
pOnaiag will not occur.
th
'
- 71 APPENDIX I
Page 17 of 20
Studlee to define the risk of infection
by pathogens for people
tmrking with sewage wastes are not as extensive as might be desired, but
the available data indicate that the risk is probably low. The preddmitent route of infection
is from the waste material
through the mouth.
Prevention of iqfection
involves such precautions as thorough washing
of the hand8 before eating to prevent ingestion
of the pathogens with
contaminated food.
The following recommendations and provisions
en8ure the health and safety of personnel at facilities
are being composted:
(1)
vorkers.
(2)
appropriate
Inoculations
for
typhoid,
tetanus
are advisable
to
where sewage sludges
and polio
should
be given
to
Rules pertaining
to personal cleaniness
should be posted in
items should be emphasized.
areas. For example, the following
a*
Wash haads before
eating,
b.
Wash hand8 before
returning
C*
Never store food in close proximity
samples taken for analysis.
d.
If accidentally
change clothes,
(3)
Shower8 and locker8
(4)
The municipality
drinking,
and smoking.
home after
work.
to sludge
or compost
contaminated with sewage sludge or effluent,
take a hot shower, and put on clean clothing.
ehould
be provided
at the composting
ehould provide protective
clothing
for
facility.
all
worker8.
(5)
Worker8
8hould chnge from protective
at the end of each day.
Protective
clothing
clothing
to street clothes
should not be
uomhoac.
(45)
A8 necemary,
8terilizt&
(7)
During periods of dry weather, the area should be sprinkled
periodically
to ensure that workers do not inhale the dust.
workers should be encouraged to wear
Duriug 8uch conditions,
f8ce ma8k8 or respirators.
III.
clothing
should
be cleaned
and/or
Site Design
The compost
wa8teu8ter
protective
treatment
site
should
facilities.
be located
as close
The advantages are:
as possible
to the
- 72 I
Page 18 of 26
APPENDIX
a.
Low hauling
b.
Effective
facif.itie8
C*
Bliuination
and transportation
costs.
utilization
of space and elimination
of duplicating
such as administrative,
general storage,
and parking.
of sludge
transportation
through
residential
areas.
Since uight soil is collected
in tank trucks, the compost site
can be located in non-reeidential
areas. The site should be located so as
to provide easy access for transportation
and removal of the product.
This
may be adjacent to a rail line or barging facility
on a river if the product
need8 to be transported to remote agricultural
areas.
climate
Fscilities
design need to take into consideration
c%aUy precipitation
and wind) and soil conditions.
In areas where
cipitation
18 high or distributed
over the entire year, some cover
These areas may also require a
needed for the various operations.
In addition
runoff facilities
8itc underlaid by concrete or asphalt.
dmiuage ey8tems m8y be needed.
(espepremay be
stable
and
fn dry climate8 cover is not essential.
The Belteville
operation
in existence
for eeveral years without cover.
Bangor, Maine, Durham,
N.K., aud Wind8or, Ontario, Canada have been composting in the open without
any prOblCr8.
Kowever, because of the uniformly distributed
precipitation
in the8e area8 (approximately 100 cm per year, 8 to 10 cm per month) a stable
b88e ha8 been recommended for several of the operations.
Muddy conditions
m8ke it difficult
to operate equipment and provide a potential
for odors.
h88 ken
A 8ludge compostlag facility
should comprise the following
areas:
(a) receiving 8nd mixing, (b) composting pad, (c) drying and screening,
(d) COmpO8tcuring and 8torage, (e) storage of bulking material,
(f) admini8trative paling
and maintenance building,
(g) runoff collection
and disposal.
Aa indicated earlier several of these areas may not be needed.
adm%nirtrative,
p8rking and maintenance area may already be part of an
cri8tiag
facility.
A runoff collection
system may not be needed if the
runoff can be channeled into a sewage system.
The
Th8 areas which need to have a stable base are the mixing,
compo8ting pad and crcreening. Materials which can be used for the base are
cru8hed rock, asphalt, concrete or fly ash. Concrete is the prefered
materi8L.
The City of Windsor, Ontario, Canada, 'tomposts on a tile-drained
mvel
aud fly=ash bed. Bangor, Maine, composts on a part of an unused
asphalted airport runway. At Beltsville
the mixing and composting areas
have been asphalted and the screened'area is underlain with crushed rock.
8t6lltuY
Mixing in a stationary mixer
reduce the area required for
(drum
the
mixer
mixing
or pug mill)
operation.
will
sub-
- 73 APPENDIXI
Page 19 of 20
If runoff collection
system is necessary,
a collection
pond fed
runoff is discharged
to adjoining
by waterways can be used. The collected
woods or pasture.
In arid areas where high winds exist precautions need to be taken
to avoid excessiwe dust. A shelter belt can greatly reduce the wind veloUnpawed areas may require watering to reduce dust.
city within the site.
Land area requirements are estimated at 1 acre per 3 to 5
dry tons (total solids) of sludge produced. The lower figure (1 acre/
administration,
parking,
and
3 dry tons) includes space for runoff collection,
The actual composting area (mixing, piles, screening, drying
general storage.
and storage) is estimated at 1 acre per 5.0 dry tons of sludge.
Source of Supply and Types of Equipment
for
Composting
Est.
Type of Equipment
Specifications
I.
1. Ront-End
Loader
or Model
cost
Dollars
Compostive Equipment
Rubber wheeled, 3.59~~. yd.
bucket or larger.
Approximately 150 hp.
$60,000
2. Hixing Equipment
a. Tractor
Tiller
&
Standard Farm
Equipment
Tractor
Tiller
$10,000
$5,000
b. Easy-Over Compost Mounted on Tractor
Turner and Tractor
$5,000
(not inc.
tractor)
c* Pug Hill
$20,000
Stationary mixing:
material
needs to be fed into mill.
Conveyors' hoppers, etc.,
may cost an additional
$30,000 or more.
- 74 APPENDIXI
Page 20 of 20
Type of Bquipment
Specifications
or Model
Est. Cost
Dollars
3. Screens
a. Trowel
b. Shaker
4. Blowers-fans
Specifications
to depend
on capacity
needed;
7-9 nun opening.
113 hp; 115 v
4 hr,
115 v with
2 min.
interwals
If.
1. Oxygen Meter
(including
hoppers,
conveyers)
Specifications
to depend
on capacity
needed;
7-9 mm opening.
22-23 cm (9")
Axial vane, centrifugal
fan; 3450 rpm
335 CFM at 10 cm (4”)
static pressure
5. Tlmers
$60-80,000
Monitoring
$80
$20
Equipment
0-25X gaseous oxygen
portable, D.C., rugged
$600
for field
use.
180-200 cm rteel probe
needed for gar sampling
2. a- Temperature
indicator
Thetristor
I Portable, rugged for
i field use, D.C. Range . 20 Cot0 100°C 1.5 + meter
probe
b. Dial
Bimetal
C. Thermocouple
Potentiometer
thermocouple
$600
$50
and
wire
II
,,
“
- 75 APPENDIX II
Page 1 of 7
UTILIEATION OF COMPOST
by
Eliot
The potential
till
depend on several
headings.
Ph. D.
for utili8ation
of compost in Developing Countries
These factor8 are discussed under three
factors.
I.
11.
III.
I.
Epstein,
Socio-economic
factors
Edaphic factors
Marketing
factors
Socio-Kconomic Factor8
Population - Population density will affect the availability
of
A.
raw materials for cornposting. Sparsely populated areas will increase the
cost of collection
and transportation
resulting
in projected
increase costs
of tha final product.
Tht availability
of a centralized
collection
system may
rt8ult in reduced costs and facilitate
handling and composting.
wastes contribute
to the sludge
8.
Industrialization
- If industrial
king composted, pollution
from heavy metals and organics can result
in a low
The heavy metals of greatest concern are zinc,
value or undesirable product.
coppar, nickel and cadprim. Zinc, copper and nickel in large amounts can
result in soil enrichment and cause phytotoxic effects resulting
in decreased
crop growth and yield.
Beavy*metala may also accumulate in plant tissue8
ingestion
by humans or indirectly
and eater the food chain through direct
through aaimah.
The tlament of greatest concern to human health where sewage
8hd8tn
and 6hd8t
coaportr are applied to land 18 cadmium (Cd), since it
is raadily absorbed by most crops and is not generally
phytotoxic
at the
concentrations nonmally encountered.
Therefore,
Cd can accumulate in
plants and enter the food chain more readily
than, for example, lead (Pb)
Or mercury (Bg), which are not absorbed by crops to any great extent.
Host W
expoenrte to Cd comes from food (principally
grain products,
vegetables, and fruits)
and results in an accumulation
of the element in
the liver and kidneys.
Approximately 3 to 5 percent of dietary Cd is
absorbed by these organs. Absorbed Cd is excreted very slowly and can
accmulate to levels which might be expected to cause kidney damage and
ftllart.
Among the sources that contribute
to the level of Cd in food
are (a) soils and surface waters contaminated by disposal of wates, (b)
80lh~ inherently high in Cd because of geochemical factors,
(c) food proand (e) phosphatic
fertilizers
containing
cewing, (d) industrial
fallout,
Cd.
- 76 -
APPENDIX II
Page 2 of 7
The World
maximum permissible
person per day. The
citizens
now ingest
Health Organization
(WUO) has established
that the
level of dietary
Cd should not exceed 70 micrograms per
U.S. Food and Drug Administration
(FDA) calculates
that U.S.
from 70 to 90 percent of this amount, and that any further
increase in dietary intake of this element should be limited wherever possible.
Thus, the level of the Cd in food chain crops may ultimately
impose constraints
on land utilization
of organic wastes as rertilizers
and soil conditioners.
differ
markedly in their
Plant species, as well as varieties,
ability
to absorb and translocate heavy metals and to accumulate them within
edible organs of the plant.
Leafy vegetables
are usually
sensitive
to the
toxic
effects
of metals:
cereal
grains,
corn,
and soybeans are less
sensitive;
and grasses are relatively
tolerant.
Uptake studies with corn, soybeans, and
cereal grains have shown that heavy metals accumulate to a lesser extent in
the edible grain than in the leaves.
The availability
and uptake of heavy metals by plants are influenced
by certain chemical and physical properties
of soil,
especially
pH, organic
matter, cation exchange capacity (CEC), and texture (i.e.,
the proportions
of
sand, silt,
and clay).
Phytotoxicity
and plant availability
of sludge-borne
metals are increased in acid soils.
Haintaining
soil pH in the range of 6.0 to
6.5 by iSming is recommended to suppress the availability
of heavy metals to
plants.
Appliration
of organic amendment8 such a8 manures and crop residues
can also dtcrtast
the availability
of heavy metals through chelation
and
complex formation.
The CEC is an expression
of the soil's
capacity
to retain
sets1 cations and is usually associated with higher clay and organic matter
contants.
Heavy metals are relatively
lees available to plants in high CEC
soils (e.g., clay loams) compared with low CEC soils (e.g.,
sandy loams).
Recent research at lteltsville
suggests that on a total metal basis heavy
metals are less available to plants in composted sewage sludges than in
mmmposted rav and digested sludges. The reason for this is not known and
the Patter is the subject of continuing research.
IndUStriSl organic compounds such a8 peStiCide8,
PCBs or PBB8
CM rtanalt in contaminated compost. This could restrict
its use and limit
-markst availability.
its
If industrial
contamination is suspected, i.e. if plating,
pigment
and dying, pesticide formulations,
and insulation
industries
are present,
it
vould be best to analyze the compost product.
Whenever possible,
night
soil should be kept separate from heavy industrial
wastes.
C. Health - Night soil and sewage sludge contain pathogenic
parasites and viruses.
If composting is done properly,
it destroys
reduces to insignificant
levels all pathogens present in night soil.
one of the lain purposes in compostlug night soil is to reduce the
hosard to the local population,
then the cost of composting should
bacteria,
or
Thus, if
potential
be partially
- 77 APPENDIXII
Page 3 of 7
borne by the sanitation
authorities
and not considered
in the cost to the
In various countries different
agencies or ministries
have responfarmer.
The composting operation
could be a
sibility
for night soil coilection.
shared venture between agricultural
authorities,
municipalities
or other
A
study
by
Papa
and
Peyron
(1970),
showed
that
the
use
of nignt
sgencies.
soil in agriculture
resulted in numerous cases of salmonellosis f/.
Composting of night soil would have destroyed these and other organisms resulting
in an economic benefit to the community. This type of socio-economic
benefit
needs to be considered in the overall
cost of composting.
11.
Edaphic Factors
The important
edaphic factors
are soils,
crops
and climates.
A.
Soils - The application
rate of compost will depend on soil
texture, slope and depth to water table.
Since composted materials
are
soil conditioner8 containing small amounts of plant nutrients,
they can
be used to improve soil physical properties as well as provide fertilizer
for piaN growth.
addition of sludge composts to soils is known to impGove
soil physical proparties as evidenced by (a) increased water content,
(b)
increased water retention,
(c) enhanced aggregation, (d) increased soil
8sration, (e) increased permeability,
(f) increased water infiltration,
snd (8) decreased surface crusting.
Addition
of sludge compost to sandy
soils will increase the moisture available to the plant and reduce need for
irrigation.
In heavy textured clay soils, the added organic matter will
itcrease permeability
to utter and air, and increase water infiltration
The
thereby
runoff.
In turn, these soils will have a greater
water storage capacity to be utilized
for plant growth. Addition
of sludge
compost to clay soils has also been shown to reduce compaction
(i.e.,
lower
tba bulk daasity)
and increase the rooting depth.
ninimiting
surface
One of the greatest
benefits from the use of compost is to reducethe wster requirements
for plant growth.
In arid and irrigated
areas
this may mean water conservation and reduced irrigation
frequency.
Table 1 gives recomended compost application
rates for various
soil conditions.
These application
rates are designed to provide necessary
material for soil improvement as well as plant nutrients.
Crops - Compost can be used to provide the total amount of
needed for crop growth,
For developing
countries,
this would
me8n the u8e of compost on crops which will provide the greatest
return.
This muld be particularly
advantageous to those countries
which do not
B.
ftrtiliser
II
Papa, PI and Peyron,
mw
&:Wl.
g ris,
R. (1970).
A contribution
to the study of salThe Salmonella of Souf. ARCH Inst. Pasteur Alger
APPENDIX II
Page 4 of 7
produce chemical fertilizers
purchase of fertilizers.
or need foreign
currency
exchange
for
the
The application
rates of compost as a fertilizer
will depend
primarily on the nitrogen and phosphorus analysis of the compost and the
crop aitrogen requirement.
Most of the nitrogen
form and must be "nineraliaed"
is available for crops.
in sewage-sludge
compost is in the organic
to inorganic
ammonium or nitrate
before it
Research by USUAat Beltsville
of the organic
nitrogen
(El) will
period following application.
slow-release N fertili8er.
indicates
that from 15 to 20 percent
become available
during the first
cropping
Thus sludge compost can be considered
as a
The fertilizer
benefit to the crop from nitrogen
depend on the following
factors:
contained
in
tha compost till
1.
The crop requirement for nitrogen.
This will depend on the
potential
yield, crop variety and species, and edaphic conditions.
2.
The percent
estimated
availablt
% available
3.
nitrogen
in the compost.
This can be
a8 follow8:
N - % inorganic
The amount of nitrogen
previous practices
application
etc.)
The folloving
supplied
(ftrtilization,
ebation
N + 6.2 x 2 organic
N
from the soil as a result
of
compost application,
manure
can then be used to calculste
the compost
application:
Rtquirtd
N application
is kg/ha x
1
-
Required
Rg available
.
compost la ton/ha.
by crop - available
Where required
soil N).
N application
- (N required
Table 2 provide8 the recoamended compost applkation
if the material
iS to be used as a fertilizer.
As pointed out earlier,
the amount needed for
agronomic crops will depend on the N requirement
of the crop as well as the N
level in tbe soil.
C. --Climste - Organic matter such as compost applied to soils does not
break down as readily under moist, cool clinmtic
conditions
as under hot,
-d
climates.
These factors should be considered
in terms of repeated
amxusl applications.
Another aspect of climate is the availability
__
-
- 79 -
APPENDIXII
Page 5 of 7
The application
of compost of
of rainfall
or water for crop irrigatiok
It may be possible
msnures can influence the available water to plants.
to reduce irrigation
frequency as a result of organic matter application.
Table 1
Recomended Compost Application Rates
For Various Soil Condition8
SO11
Sand or Gravel
Ssnd or Gravel
Surface or Ground
Conditions
Plants
or Crops
Shallov to groundutter (less than 4 ft.)
vith no intervening soil
Grass or
Deep to groundwater
(over 6 ft.)
Heavier
material intervening
GrtS8,
Rates
Tons/hectare/year
50 - 100
shrubs
shrubs,
cereals,
cotton,
crops
50 - 100
50 - 100
Amount depend8
on crop
requirement
Clays, clay
losms,sllty
clay loams
Shallov to
groundvater
Deep
to ground
water
Disturbsd
soils
DStp
water
Grass
50 ': 100
Grt8S ,
50 - 200
turf
t0
8rOUnd
Parks,
highways
construction
sites
100 - 300
tilled
into
upper
100 mm layer
- 80 -
Table 2
Rates
Recomended Compost Application
For Different
Plants or Crops
Plsnt or
Compost Rate
crop
Method of
Application
in TOnS/ha/yr
Sod, Turf,
New Lawns
Sod, Turf,
Lawns
Bstablished
Otber Cereals,
100 - 200
so-
Cotton,
and Agrosomiccrops
75
required by
the crop e.g.
corn 50
As
Till into surface
layer prior to
seeding
Apply onto surface
as required
Till
prior
into
soil
Tree Nurseries
50 - 100
Till into soil
prior to planting
Pastures
50 - 100,
depending OF
species
Till into
prior to
planting
Pssmrts
50
_
to planting
8011
Apply onto surface
periodically
,
- 81 APPENDIX II
Page 7 of 7
III.
The Effect
of Market
Conditions
on Compost Utilization
Market Location
- Transportation
is expensiwe.
Since night
A.
is produced in urban areas the transportation
of composted night soil
soil
can
be expensive in comparison to concentrated
chemical fertilizers.
Compost
or night soil is lover in nutrients and therefore larger quantities
are needed
to provide couparable levels of nitrogen
or phosphorus found in chemical
fertilizers.
Inexpensiwe transportation
means such as water barging or
rail to agricultural
regions can enhance compost utilization.
Distribution
and transportation
costs uould need to be assessed.
Market Value of Produce or Crops - Compost in developing countries
B.
will probably be best used on those crops providing
the greatest
cost return.
Its value to the farmer will depend on the increased yield which would be
obtained or on a reduction in production costs.
It may be necessary to
demonstrate the benefit of the compost through existing
agricultural
experiment rotations or pilot studies.
c. Product Quality - Compost product quality can affect its market
valueauddemamd.
If the night soil is contaminated
by industrial
wastes
or malts and the product is restricted
to lower cash crops such as pastures,
the demand for its utilisation
may be reduced.
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