Manual 13557666

Manual 13557666
WATER PURIFICATION
AND
SEWAGE
DISPOSAL
WATER
PURIFICATION
AND
SEWAGE
DISPOSAL
DR. j/TILLMANS
DIRECTOR OF THE CHEMICAL DEPARTMENT OF THE
MUNICIPAL INSTITUTE OF HYGIENE, FRANKFORT-ON-M AINE
TRANSLATED BY
HUGH S. TAYLOR, M.Sc.
With 2 1 Illustrations in the Text
NEW YORK
D. VAN NOSTRAND CO.
TWENTY-FIVE PARK PLACE
1913
PREFACE
TO THE ENGLISH TRANSLATION
S1nce the recognition of their significance in the promotion of the
public health, methods of water purification and sewage disposal
have earned a steadily increasing importance.
Consequently,
these branches of industry have enjoyed the most zealous atten
tion of the scientist and of the engineer.
I have endeavoured in the present monograph to give a survey,
short perhaps, but as complete as possible, of the present
position in regard to Water Purification and Sewage Disposal.
Owing to the wide range of this subject particular processes
could only be treated shortly in the space at disposal.
One chapter, which is very fully treated in the present volume,
though slightly elsewhere, is the disposal of industrial sewage.
Many of the processes of purification are of quite recent date,
and fresh experience is being obtained daily and reported upon
in the most diverse publications.
I have endeavoured to collect
such information.
In the translation some small changes and additions have been
made in the chapters on sand filtration, the removal of manganese,
and Travis and Emscher wells.
The extensive literature supplied in the German original, which
served as the basis in the composition of the book, has not been
printed in the English translation, as it treats in the main of
German literature.
THE AUTHOR.
Frankfort-on-Ma1ne,
October, 1912.
263297
TRANSLATOR'S PREFACE
England, as the author points out, is the classic country for
sewage disposal. As a consequence, the translation of a book
on the subject of water purification and sewage disposal from the
German point of view, might at first sight seem unnecessary.
It is to be hoped, however, that a study of the present volume
will prove that view to be incorrect. The careful attention which
has been paid by the German authorities during the past few
decades to the provision of suitable water supplies and the
adequate disposal of sewage, renders the present critical survey
of modern methods at once interesting and useful to the English
reader. Especially should this be true of the chapter on the dis
posal of industrial sewage.
I have to express my thanks to the author, Dr. Tillmans, for
a revision of the present text, and to Messrs. Hubers and Mond.
I desire also to record my indebtedness to my friends Mr. J. W.
Yates, M.Sc, and Mr. A. Shacklady, B.Sc, for valuable guidance
and assistance in the correction of the proofs.
HUGH S. TAYLOR.
L1verpool,
October, 191 2.
TABLE
OF CONTENTS
WATER PURIFICATION.
GROUND-WATER, SPRING-WATER, SURFACE-WATER.
A. Purification of Waierfor Drinking Purposes
Bacteria and disease germs in water .......
FACE
2
2
I. Pur1f1cat1on
Large Scaleof Water for Dr1nk1ng Purposes on a
4
(i) Filtration Processes
4
(a) Slow sand filtration
.......
5
Preparation, composition, and working of the filter .
.
5
Uniformity of the sand, filtration pressure, covered and
uncovered filters
6
Washing and renewal of the sand
7
Filter film, filtration pressure, Frankel and Piefke's
fundamental investigations, double filtration according
to Gotze, and preliminary filtration, Puech-Chabal
system .
8
Cost ; control by estimation of the germ-content .
.
9
10
(6) Percolating sand filters
10
(c) Mechanical filters
Nature and control of the mechanical filler, old and new
systems .
.
.
.
.
•
.11
The Jewell Export Mechanical Filter .
.11
Experience with the Jewell Export Mechanical Filter . 13
(d) Artificial preparation of ground-water from surface-water 14
Natural bank filtration, infiltration
14
(e) Application
Importance of
ofthe
water
process
filtration
in various
in the
towns
maintenance
.
of.16
public health, and a critical examination of the value of
sand and mechanical filtration .
.
.
.16
(ii) Sterilisation Processes
.18
(/)) The Ozone Process .
.
.18
Siemens' Ozone plant at St. Petersburg .... 20
Investigations on the action of Ozone .
.
.22
(A) The Ferric Chloride Process ...... 24
ix
x
TABLE OF CONTENTS
(c) Nature
The
Investigation
Chloride
and cost
and
of of
Lime
review
the Process
process
FACE
26
25
(fi) Ultra-violet light
The investigations of Courmont and Nogier ...
The investigations of the Konigl. Prufungsanstalt fur
Water Supply) (Grimm
and Weldert)
Institute....
of Tests for
Wasserversorgung
(Imperial
27
27
Other authors on the process
Comparison of the costs of filtration and sterilisation
.
(<?) Disinfection of water-mains and wells ....
28
29
30
28
(iii) Purification of Water in other Directions than of
Health
30
(a) Removal of iron
30
Disadvantages of water containing iron ; nature of the
processes for removing iron
31
The most important methods of iron-removal .
.
. 32
Open and closed iron-removal plants
.
.
.
-33
Method of working ; cost
...... 34
(6) Removal of manganese
35
Disadvantage of water containing manganese ; the
Breslau calamity ; different methods of removing
manganese
35
(c) Corrosive
Removal ofaction
free carbon
of water
dioxide
containing carbon dioxide ; 36
removal by limestone ; description of the Frankfort
plant
Removal by
withaeration
caustic ; soda
vacuum
or sodium
processcarbonate
....
.
37
40
38
II. Pur1f1cat1on of Dr1nk1ng-Water on a Small Scale .
Basic
on a disadvantages
small scale, as of
opposed
the purification
to large-scale
of operations
drinking-water.
40
40
(i) Small or Household Filters
41
More or less uncertain action of all small filters .
41
(a) Charcoal filters
41
(6) Stone filters
42
{c) Asbestos filters ........ 42
{/t) Clay filters
42
.
.
-42
(e) Earthenware filte1b
(/") Kieselguhr filters
...... 43
(ii) Boiling the Water
45
Apparatus for boiling large quantities of water ... 45
Advantages and disadvantages of boiling the water as
compared with household filters
.
.
.
.
.46
TABLE OF CONTENTS
xi
PAGE
(iii) Small Ozone Plants and Ultra-Violet Light Apparatus 47
Stationary and transportable ozone plants, Siemens and
Halske
47
Experiments with household apparatus
.... 48
(iv) Removal of Iron from Single Wells
.... 49
Different
Bastard pump
methods
of Deseniss
of removing
and iron
Jacobi
from single wells .
. 49
50
B. Purification of Water for Technical Purposes
Requirements of a water used for industrial purposes .
.
Softening of boiler-feed water, temporary hardness, perma
nent hardness, degree of hardness
Softening by the lime-soda process : method, estimation of
the amount to be added
Advantages of
anda disadvantages
lime-soda softening
of theplant
lime-soda
(Voranprocess
system) .
Description
51
51
52
53
55
58
The Reisert Baryta Process .
.
...
.
.
.59
59
Advantages and disadvantages of the Baryta Process .
The Permutit Process : method, advantages, disadvantages 60
Importance of an intelligent supervision of softening plants,
61
so-called boiler scale preventatives
SEWAGE DISPOSAL.
The significance of river pollution and the importance of
Self-purification
Domestic
sewage disposal
and industrial
of riverssewage ......
A. Purification of Domestic Sewage
The different processes
I. Mechan1cal
(i) Screens, Rakes,
Pur1f1cat1on
and Sieves
of Sewage
Coarse and fine screens, stationary and movable rakes
Uhlfelder's revolving screen ; the Rien sieve
...
(ii) Grease Separators
Kremer apparatus
Kremer septic well's ; other grease separators
(iii) Grit Chambers ,
(iv) Sedimentation Tanks and Wells
Form of sedimentation tanks ; velocity of sedimentation .
Sludge
Clarification
disposal
effect,
: addition
sedimentation
of chemicals
wells, towers
....
...
67
63
65
67
68
68
69
69
72
72
73
73
74
74
77
76
xii
TABLE OF CONTENTS
(v) Septic Tanks
Method ; sludge and removal of sludge ; advantages and
disadvantages of septic tanks
(vi) Travis and Emscher Wells
Method ; Travis tank
Emscher wells
.........
Critical review
II. Degener's Coal-Pulp Process
PAGE
78
78
79
79
82
83
84
III. B1olog1cal Pur1f1cat1on of Sewage
84
(i) The Artificial Biological Process
85
Method
85
Sewage disposal in England, Preliminary purification,
Material of the biological beds, Contact beds, Percolat
ing filters
85
Cost
89
sewageas(Brettschneider,
to the natureTravis,
of biological
Dunbar) purification
.
. of.89
Theories
(ii) Land Treatment ; Broad Irrigation
9°
(a) Sewage Farming
Nature,
irrigation
good
of sloping
and bad
surfaces
soils for irrigation purposes,
9°
9°
Irrigation of beds
Eduardsfeld Process
Action of the irrigation
Importance of preliminary treatment
....
.
Various details on suitable methods of treatment .
Impregnation permissible, rent and cost ....
9°
91
92
92
92
93
(6) Intermittent Sand Filtration
Historical distinction
Experience
with the process
from broad
in Massachusetts,
irrigation ...
U.S.A. .
94
94
(iii) Purification of Sewage with Fish-ponds ....
96
IV. D1sposal and Prof1t from the Result1ng Res1dues
.
97
(i) Grit-Chamber
mentation Sludge
Residues, Residues from Screens, Sedi
97
(ii) Drying of the Sludge
Disposal on the land
Contents of Emscher-well sludge ......
Drying in ditches .........
Filter-presses
.........
99
99
100
100
100
TABLE OF CONTENTS
xiii
PAGE
Schafer-ter.Mer Centrifuge ....... 101
Disposal in the sea
......
102
Addition of nitrates
......
.104
Cost of the various processes
...... 104
(iii) Profit from Sludge
.104
As manure .......... 104
.
.
.
. 105
Preparation of artificial manure .
Recovery of grease
.
.
.
.
.105
Generation of electrical energy by burning .... 107
.
.107
Frankfort sludge disposal ^
Gasification of sludge
108
B. The Purification of Industrial Sewage
.
.
.
109
I. General
109
Reception into the town's sewers .
.
.109
Leakages, condenser waters, and effluents from particular
different processes
manufacturing
processes. Association of sewage . from.110
Reservoirs, filters .
.
.
.
Use of industrial sewage for laying dust on the roads .
II. The Pur1f1cat1on ok Industr1al Sewage 1n Deta1l
.111
.111
.
112
Classification of industrial sewage
112
.
.113
1. Cloth factories .
2. Cardboard works
113
3. Straw-board works .
.
.
.
.
.114
.
.
.
.
.114
4. Mines (coal-washing)
5. Sewage from works granulating slag
.
.
.114
6. Paper and cellulose mills .
.
.
.
.
115
...117
7. Breweries ......
8. Tanneries .
.
.
.
.118
9. Dairies and margarine works .
.
.
1 19
. 120
10. Slaughter-houses, knackers' yards, glue works .
11. Sugar works ........ 120
12. Starch works .
.
.122
13. Distilleries, yeast works ....... 123
14. Sour-krout works
.123
15. Dye works and print wo1ks
...... 123
.
.
.
.
.125
16. Chemical works
17. Bleach works
.
.126
18. Gas Works
.
.
.
.
.126
19. Ammonia works
....... 127
20. Potash works .
127
21. Metal works and works manufacturing mordants .
. 128
22. Manufactories of photographic material and paper .
. yi%
xiv
TABLE OF CONTENTS
23.
24.
25.
26.
27.
Sewage containing cyanides
Wool-scouring, wool-combing, and wool-finishing .
Petroleum refineries
Sewage containing soaps .
Oil works
PAGE
129
13°
13°
13 1
1 32
C. The Disinfection of Sewage
132
L1st of Authors
135
L1st of Local1t1es
137
Index ok Subjects
138
TABLE OF EQUIVALENTS IN WEIGHTS
AND MEASURES.
1 metre=1o decimetres = 100 centi metres = 1000 millimetres = 1 '093 yards =
3-28 feet = 39-37 ins.
1 cubic metre = 1000 litres = 1-308 cubic yards = 35-3 cubic feet = 220 gallons.
1 kilogram = 2 2046 lbs. 1000 kilograms = approximately 1 ton. 1 gram =
'5 -43 grains.
LIST OF ILLUSTRATIONS
r. Diagrammatic Representation of aSand Filter
2. The Jewell Export Mechanical Filter
.
...
3- Diagrammatic View of the Ozone Waterworks at St. Petersburg
Emulsifiers
Waterworks, St. Petersburg.
.
Sterilisation
.
...
Towers and
4- Ozone
PAGE
6
12
•9
20
apparatus
Waterworks, St.
. Petersburg.
.
5- Ozone
Batteries
.
for...
the Ozone
21
6. Open Iron-removal Plant, "Voran" System
7- Closed Iron-removal Plant, " Voran " System
8. Acid Neutralisation Plant in the Saxony Deep Reservoir .
.
.
...
9- Berkefeld Filter
Sons, Hamburg-Uhlenhorst
for Boiling Water of the . Firm. of Aug. Schmidt. and.
10. Apparatus
...
11. Bastard Pump of Deseniss and Jacobi .
12. Lime-Soda Softening Plant, "Voran" System
.
...
13- Uhlfelder's Revolving Screen
.
...
14. Rien Sieve .
Kremer Apparatus
.
...
16. Grease
Wiesbaden
Separators of. the " Stadtereinigung
.
Firm,"
...
Berlin-
34
34
39
44
46
5o
5°
69
70
71
72
17- Frankfort Sedimentation Tank (Cross Section)
18. Clearing Well Installation at Norwich on the Travis HydroAbwasser,"
lytic System,1909-10,
with Colloider
vol. II, p.hung
71 in. From "Wasserund
.
.
.
.
.
.
19- Emscher Wells
20. Sludge Centrifuge : Schafer-ter-Mer System
21.
11
»
11
11
XV
...
...
75
80
81
102
103
WATER
PURIFICATION
THE water present on the earth is engaged in a continuous
circulatory process.
It evaporates from the oceans, seas, rivers, etc., and passes into
the atmosphere as water-vapour. In the higher strata it condenses
to form clouds, and then returns to the earth's surface as rain,
snow, hail, and dew.
A part of this water evaporates immediately, another part
flows away to the nearest surface reservoirs. A third part, on the
contrary, penetrates into the earth's crust, and sinks deeper and
deeper until it reaches an impermeable stratum, whereupon it
collects and fills the pores and hollows of the overlying ground.
This water is called ground-water. Volger considers ground
water as a product of the condensation of ground-vapours, and
Mezger assumes that it is the vapours rising from the depths
which condense. According to Novak it mainly results from
the water of the oceans penetrating into the interior of the earth.
Although ground-water may receive considerable additions from
one or other of these sources, still it must originate in greater
part in the first-mentioned manner, through infiltration. From
the impermeable layer it passes along very slowly to the nearest
lower-lying waters.
Spring -water is a mountain ground -water which, owing
to this movement, makes its appearance in a cleft of the
mountain.
In contradistinction to ground-water, all water which remains
in contact with the outer air is designated as surface-water.
Surface - water is therefore the water of seas, rivers, ponds,
cisterns, dams, etc.
Water is obviously a necessity to man. In the first place, it
B
2
WATER PURIFICATION
is used for drinking purposes. Moreover, it is found to be an
indispensable auxiliary in almost every possible pursuit.
Frequently it must be submitted to certain treatment before
use. The application proposed serves as a method of differentia
tion. One can distinguish, therefore, two processes : purification
of water for drinking purposes, and for technical purposes.
A. Purification of Water for Drinking Purposes.
Water used for human consumption must be free from sus
pended matter. It must be colourless, odourless, agreeable to the
taste, and must not have too high a temperature. It should be
of such a nature that it may be partaken of with pleasure.
Further, and of chief importance, it must contain no disease
germs.
Surface-water and ground-water are both used for water
supply. Ground-water, taken from certain depths, is free from
bacteria ; for, during its passage through the soil, it is freed
from germs, which remain attached to the particles of sand in
the ground. Surface-water, because it is easily polluted, is
always more or less rich in bacteria.
The germs of contagious diseases, typhoid, diarrhoea, cholera,
and certain groups of the so-called ptomaines, are the most
important disease germs disseminated through water and claiming
consideration. Pus germs also are found. It is only in the rarest
cases possible to demonstrate the existence of disease germs in
infected water, since they only occasionally succeed in entering,
and also between the date of their reception by the person and the
development of the sickness a period of time always elapses (e.g.
with typhoid, one to three weeks). If, therefore, developing
diseases give rise to an investigation, it is usually too late to
trace the origin to water. Quite apart from this, also, the proof
of the existence of disease germs amidst the many other harmless
bacteria is a matter of considerable difficulty.
Proof of the absence of disease germs is not sufficient, and is
no guarantee of the harmlessness of a water to health. Sanitary
opinion is based, however, upon the assumption that the strata
of earth at slight depths are already free from any such germs,
and that therefore a discovery of bacteria in water proves that
it has come into contact with the outside world, that it has
PURIFICATION FOR DRINKING PURPOSES
3
received surface influxes. In the dissemination of typhoid and
other contagious diseases, the possibility that even secretions of
such men or animals as harbour disease germs in themselves
have been admitted to the water cannot be excluded. The more
influxes of surface-water, the greater is the probability of con
tamination in a ground-water. From these considerations it
follows that a river-water is much more dangerous than the water
from a suitably situated reservoir.
If a natural water containing bacteria be used for drinking
purposes it must first be rendered innocuous to health. This
can be done by methods of filtration or of bacteria destruction.
But the harmfulness of a surface-water to health is not its only
fault. Many surface-waters, such as river-waters, have also the
disadvantage of an unappetising odour and taste, or a dis
agreeable temperature. Then, even the sanitary improvement
of water by the destruction of bacteria or by filtration will only
remove the gravest danger—the danger to health—but will
not make of the inferior water a good one. It must furthermore
be borne in mind, that when such measures of purification are
demanded, failure must be expected either of the plant itself
or failure due to excessive demands on the available material, of
which the best-known example is the notorious water-main in
the Ruhr district.1 As regards filtration, it must be remarked
that removal of all the bacteria is not effected. Filtration
only brings about a reduction of the number of germs. Since,
however, for the origination of a contagious disease a definite
amount of disease germs is always necessary, reduction of the
germs, if it is at all considerable, signifies a considerable sani
tary improvement in the water.
Ground-water from sufficient depths is therefore superior,
for all the above-mentioned reasons, to surface-water, even if the
latter be very carefully treated. But the former also may be
doubtful for drinking purposes. There are two ways in which
disease germs may reach a ground-water and make it unsafe as a
water supply. The first manner in which it may be polluted,
and the one coming into consideration in the greatest number of
cases, is contamination from above. Through fissures in the
1 This water-main drew water from the River Ruhr. During the year 191 1 the
level of the river sank so considerably that the end of the pipe lay above the sur
face and no water could be drawn off. — Translator.
WATER PURIFICATION
4
ground, through leaking wells, and through a permeated ground
water, external streams may be incorporated without sufficient
previous filtration. The second method of pollution with disease
germs is through the so-called subterranean streams from strata
in the earth rendered contagious by human refuse. This method
of pollution has been frequently affirmed and disputed. There
come into consideration here filled-up waste sewers, drains,
depots for faeces, etc., which, owing to underground hollows, for
example, rat-runs and the like, are connected with wells, and
through which the ground-water flows into the wells. Even
without direct hollows or runs existing, a certain amount of danger
is assumed, owing to insufficiency of filtration. If the ground
water, in its passage from the suspected area to the place where
it is drawn, flows through at least 10 metres of ground free from
objectionable features, that is regarded, in general, as adequate
filtration.
Occasionally drinking-water must be purified for quite other
reasons than the hygienic reasons previously discussed. In such
cases it is a question of removing substances, including salts,
which give the water an unappetising appearance, or make it
unsuitable as a drinking-water or for domestic use. There may
be present substances which impart to the water a certain cor
rosive action on the walls of the pipes through which it is led
or the vessels in which it is stored.
Methods of water purification may be divided into two classes,
those on a large scale, which serve for central water supply, and
those for the purification of water on a small scale, which are
applicable on a journey, in housekeeping, and in industry.
I.
PURIFICATION OF WATER FOR DRINKING
PURPOSES ON A LARGE SCALE.
The purification of drinking-water on a large scale, in order
to obtain a healthy and unobjectionable water, is effected either
by filtration or sterilisation. In the first case the bacteria are
mechanically removed, in the second case they are killed.
(i) Filtration Processes.
The greater part of the suspended matter can be removed in
settling reservoirs, or by leading the water through clarifying
FILTRATION PROCESSES
5
basins in which the very small velocity of the water enables the
greater part of the suspensions to settle to the bottom.
Sedimentation basins for the purification of drinking-water
are constructed and managed according to the same principles
as those for the purification of effluent waters. On this account
the question may be relegated from here to the chapter on the
conduct of sewage purification.
The most finely divided suspensions, the bacteria, are not
removed from the water in this way ; for that purpose filtration
is required.
(a) Slow Sand Filtration.
For the sand filtration of drinking-water we have to thank the
Englishman James Simpson, who, in the year 1829, constructed
the first filter of this type.
In 1839 tne London Water
works introduced the first of such filters for the purification of
drinking-water. In the year 1853 Simpson sand filters were also
constructed in Berlin, and shortly afterwards in many other
towns. The inventor only had in view the removal of suspended
matter and the clarification of the water by means of sand
filtration. That it would remove the bacteria he could not have
anticipated, as at that time such micro-organisms were still un
known. We know to-day, however, that the main importance cf
sand filtration lies in the elimination of bacteria.
In case the water does not contain too large a quantity of
suspended matter, a preliminary clarification is unnecessary,
and the water flows immediately on to the filters.
The filters (see Fig. 1) consist of large, generally rectangular
surfaces, surrounded by a wall. They are filled with gravel and
sand. At the bottom there is a layer of stones 60 to 150 milli
metres in diameter. Above this rests a layer of gravel which
serves to support the superimposed sand, being coarser below
than above. The layers of gravel are generally set down with the
first about the size of nuts (30 to 60 mm.), then one about the
size of beans (20 to 30 mm.), one the size of peas (10 to 20 mm.),
and a layer about the size of millet (3 to 5 mm.). Over this there
rests the layer of sand upon which the raw water is placed to
a certain depth. The sand and gravel layers can be set down
together in varying amounts. The average height of water, sand,
and gravel is about o.6o metre (2 feet) each. The filtered water
6
WATER PURIFICATION
flows away underneath, and passes thence into the reservoirs
for purified water. To supply a town with filtered water a large
number of such sand-filters are needed.
The plans of artificial sand filters must be so arranged that each
individual filter can be separately filled, emptied and cleansed,
FIG. I. ijlAGRAMMATIC REPRESENTATION OF A SAND FILTER.
and that the purified water from each filter can be drawn upon
independently. Only in this way is complete control of each sepa
rate filter possible. The water filters the more quickly through the
sand the larger the size of the grains. Coarser sand does not yield,
however, such pure, germ-free water as does the finer sand. With
this finer sand the surface of the filter layer clogs up more
quickly than with the coarser, which latter is easier to clean.
Further, similarity of form in the sand is important. The
more dissimilar the particles of sand are, the more erratically the
filter works. In the cleaning of the filter the fine sand is in
part washed away ; sand must therefore be added from time
to time to the filter, according to the length of time it
is in use, if it is not to become continually coarser. Whilst
the form of the filter must be adapted to the disposition of the
available space, its size varies considerably. The size of a filter,
according to Konig, varies in a series of large towns from 607 to
7600 square metres, and is on the average about 2000 to 3000
square .metres. The water should be maintained in the filters
as far as possible at the same height. The. entry of the water
to the filter takes place continuously from above, and the entrance
of course lies opposite to the discharge-pipe. Frequently the
inflow of water is automatically regulated by means of valves,
to bring about as uniform an inflow as possible. A uniform
discharge of water, also, is of no less importance. In consequence
of the gradually increasing clogging of the filter the velocity of
discharge would always become less if the head of water were
FILTRATION PROCESSES
7
not increased. This head of water is the difference of water-level
in the filter and in the pure-water reservoir. To increase the
head it is best to diminish the water pressure in the pure-water
reservoir, since, as already mentioned above, it is not advan
tageous to alter the amount of water in the filter.
In the Berlin Waterworks the head amounts to 60 or 65
millimetres, in Altona to 1422 millimetres, in Kiel to 1000 milli
metres.
In order to permit the air enclosed in the filter to pass out,
so that it is not constrained to escape to the top, thus causing a
breaking-up of the filter-bed, tubes for the removal of the air
are let into the side-walls.
Filters are either covered or uncovered, both systems having
their advantages and disadvantages.
Open filters have the disadvantage that during frosty weather
cleaning is made very difficult, owing to the freezing of the moist
sand. This objection disappears with covered filters. On the
other hand, covered filters are far more costly.
A further disadvantage of the covered filter is that with it
the sediment layer is formed more slowly and more imperfectly,
and the covered filters, consequently, do not yield a sufficiently
germ-free water so quickly. This is readily explained, as the
sediment layer is composed in part of organisms containing
chlorophyll, and consequently needing light, which organisms
cannot increase, or can only do so more slowly than is the case
with open filters exposed to the full light.
In practice the filters are arranged thus. They are filled with
water from below to just above the surface of the sand ; then
the impure water is allowed to flow in from above, and to remain
at rest for a period of time during which the formation of the
sediment layer is accelerated. The filtrate is allowed to flow away
until the germ content has reached a certain limit, generally 100
or less per cubic centimetre (1600 per cubic inch). Then the pipe
to the pure-water reservoir is connected.
After a certain time, when the sediment layer has become too
strong, the filter works itself dead, and no more water passes
through. It must then be purified. For this purpose a layer
of sludge, generally about one inch thick, is first of all
scraped off. The sand lying underneath likewise contains a lot
of dirt, which is, however, of the greatest importance for the
8
WATER PURIFICATION
filter layer about to be constructed. After removal of the layer
of sludge, therefore, the sand is loosened to a depth of about
8 inches, and the filter is then allowed to remain unused
for a day, to permit the access of fresh air. The so-called
journey (running time) of a filter is likewise very varied. From
eleven different waterworks, according to Konig, it amounts on an
average to 25.5 days, during which the amount of water filtered
per square metre averaged 69.3 cubic metres.
From time to time the sand must also be replaced by fresh or
washed sand. It is removed down to the layer of gravel, new
sand filled in, and this is covered with a layer of the lower portion
of used sand, which has a sticky nature and accelerates the
formation of the sediment layer. Washed sand is only to be
recommended in place of fresh sand in cases where the fresh
material is dearer than the washed, since by washing more or less
of the fine useful portion of the sand is removed. For this
reason a sand which has been washed many times must be
replaced by fresh sand. The washing of the sand takes place
automatically in drums, or boxes, in which the sand comes many
times into contact with fresh water. There are numerous different
systems of sand washing.
The more slowly filtration takes place, the purer, as a general
rule, is the filtrate. The velocity of filtration, which varies largely
in different waterworks, amounts on an average to about 100
millimetres (4 inches) per hour.
Very soon after the introduction of sand filtration it was
recognised that the sediment layer would be difficult to control.
This layer consists for the most part of organic suspended matter,
displaying either living organisms or dead substances, while
there is also present, in smaller degree, inorganic matter like clay,
oxide of iron, etc. The most varied organisms are to be found
in the composition of a sediment layer.
C. Piefke demands a maximum filtration velocity of 100 milli
metres per hour, while other investigators could establish no
variation in the bacteriological and chemical composition of the
water with considerably greater velocities.
C. Piefke found, further, that with an increase in the pressure
of filtration the bacteria content of the pure water rises, more
so, of course, the more bacteria the raw water contains. He
also proved by investigation that a filter freed from the
FILTRATION PROCESSES
9
sediment layer yields water of small bacteria content more
quickly than fresh sand. This is explained by assuming that the
suspended matter penetrates into the sand a little, and this sand
layer, containing suspended matter, takes part in the work of
filtration. Of great importance is the answer to the question,
whether the bacteria in the pure water have passed through the
filter during the filtration of the raw water, and therefore are
derived from the raw water, or whether they are washed away
from the sediment layer or from the sand. By their investiga
tions on this question, Frankel and Piefke came to the con
clusion that the quantity of micro-organisms passing over into
the filtrate is proportional to the bacteria content of the raw
water.
For towns which have to deal with very poor raw water, like
Hamburg, Altona, Konigsberg, Warsaw, and others, double
filtration, proposed by Gotze, is to be recommended. The
most diverse hygienists express themselves very approvingly
concerning this method. By double filtration, the raw water
already passed once through a sand filter is sent again through a
filter well clogged with sludge. Gotze showed that with double
filtration a raw water with a germ content of 28,000 was purified
to one of 780 bacteria per cubic centimetre in the preliminary
filtration, and to 31 per cubic centimetre in the final filtrate.
The preliminary filtration of Puech-Chabal is largely employed.
In this system the water is purified by a series of coarse prelimin
ary filters. The fine filter then employed has only to further
diminish the already considerably reduced quantity of bacteria,
so that the water can be regarded as free, bacteriologically, from
objection.
The cost of sand filtration, exclusive of interest and repayment
gallons
of loans,(Konig).
amounts on an average to o-7d. to
per 1000
The filtered water is submitted to a continuous bacteriological
control. The constant estimation of the number of bacteria
is an excellent means of settling whether the filter is working
well. A crack arising in the sand, or any other abnormality,
reveals itself immediately in a rise of the number of bacteria.
The official rule runs that pure water should not contain above
100 germs per cubic centimetre.
10
WATER PURIFICATION
(b) Percolating or Dry Sand Filters.
In France, recently, the so-called percolating sand niters have
come into use for water purification. They are based on the
theory that oxygen plays a part in the removal of bacteria,
especially of the pathogenic kind. The ordinary filter can contain
no oxygen, since it is always covered by water. On this account
the percolating sand filter is employed similarly to the per
colating filters in bacterial sewage purification, except that it is
composed of fine material (sand).
Miquel and Mouchet, in laboratory investigations, were unable,
after using this method, to prove the presence of typhoid bacilli
added to the raw water.
This method was tested by Baudet, in Chateaudun (France),
working on a large scale. The results seem very favourable.
The number of bacteria fell from between 293 and 1498 in raw
water, to 6 bacteria per cubic centimetre in pure water. Espe
cially remarkable is the consideration that in the pure water
bacterium coli was never found.
This filter likewise requires several months to build up, and
the velocity of filtration cannot be raised indefinitely; still, the
percolating sand filters seem to be considerably more pro
ductive than the slow sand filter.
Baudet maintains that with a clear but bacteriologically impure
water, results are obtained with percolating sand filters which are
better and less troublesome than those obtained by any other
method.
The introduction of the filter for barracks has been recom
mended by the French Army administration. In Germany the
filters have not yet, to my knowledge, come into use. Further,
there has been, up to the present, no German investigation of
the method.
(c) Mechanical Filters.
The considerable cost of sand filters in relation to their pro
ductivity, and the great space necessary for a sand-filter installa
tion, shows clearly the advisability of replacing the sand filter
in technical work by other apparatus which takes up less room
and permits a greater velocity of filtration. From these considera
tions the mechanical filter originated. Since the natural, workable
layer is first formed after a long interval of filtration, chemicals
FILTRATION PROCESSES
11
are generally added to the water, especially with the newer filters
of this type, in order to produce an artificial plankton and an
artificial filter layer. With the mechanical filters of newer
pattern, aluminium sulphate is almost always used for this
purpose, as it reacts with the alkaline earths present in the water
according to the following equation :
Al2(SO4)3+3 Ca(HCO3)2 = Al2(OH)6+3 CaSO4+6CO2.
Most of the flocculent, gelatinous aluminium hydroxide sinks
to the bottom, and the suspended matter travels along with it.
The flakes still remaining in the water form a sediment layer on
the filter. The velocity of filtration exceeds that of the sand
filter, generally being 60 or 70 times more rapid.
There is a large number of different systems of the mechanicalfilter type.
Older patterns are, for example, the Anderson revolving
purifier, the Warren Filter, the Krohnke Filter.
Filters of newer construction are, amongst others, the Jewell
Export Mechanical Filter, the Halvor Breda Filter, the Bell
Filter, Reeves Filter, Candy Filter, Puech Filter, Sucro Filter.
These filters are not only employed for removing bacteria from
drinking-water, they frequently find application in technical work.
As a type of this filter the Jewell Export Filter, which has been
studied closely from different points of view, may be described
more carefully.
The Jewell Export Mechanical Filter.—The Jewell Filter, repre
sented in Figure 2, consists of the steel cylinder containing the
filter-bed, which is encased in a second cylinder of somewhat
larger diameter, so that between the two there is an annular space
which is closed underneath. In this annular space, through the
valve situated on the left-hand side, the raw water, which has
been previously treated in sedimentation tanks, and also with
aluminium sulphate, passes into the filter, in order to flow over
the edge of the inner cylinder on to the filter-bed. After it has
streamed through the filter-bed, composed of sand, it passes at
the bottom through sieve heads in a system of outlet tubes which,
in their turn, fit into a diametrically placed collector, and to
which they are all rectangularly placed. From the collector
the water passes through the regulator (Weston Controller),
shown in the front of the diagram on the right side, into the
12
WATER PURIFICATION
pure-water basin to be found underneath. This regulator serves
to keep filtration constant. The importance of a constant
velocity of filtration has already been brought into prominence
in the case of sand filters. With mechanical filters this importance
is increased owing to the employment of chemical coagulants
associated with it, and which can only be added in these cases
in precisely estimated amounts. By means of a float working on
a throttle-valve (shown on the left in the diagram) the inflow is
F1g. 2. The Jewell Export Mechan1cal F1lter.
also regulated, and the water in the filter kept at a constant
height.
To clean the filter the water takes the reverse direction. It
is allowed to stream in under the pressure of a pump or a high
reservoir, through the cleaning-valve situated at the extreme
right in the diagram. It is then allowed to flow through the
collector, exit tubes, and filter-bed in the reverse direction from
bottom to top, to pass over the rim of the inner cylinder into the
annular space, out of which it streams into the effluent tube,
through a valve not visible in the diagram. At the same time the
stirring arrangement shown in the diagram is set in motion, which
thereby gets the whole of the filter-bed into a floating condition,
so that each separate particle of sand is washed by the water
FILTRATION PROCESSES
13
and is consequently thoroughly purified. In the cleaning process
it is necessary, of course, that the cleansing water be distributed
uniformly over the whole surface of the filter-bed, so that no
stagnant corners or angles result. This important need is met
in the Jewell Filter by keeping the throats of the strainers in the
outlet tubes very narrow, so that the pressure and velocity of the
cleansing water at these points are very large.
After the first cleaning there comes a further cleansing process,
in which the first water filtered is allowed to flow through the
third of the three valves shown on the right of the diagram, in
order to remove the muddy water still present in the filter. The
cleaning and the subsequent operation take up about ten minutes,
and are effected as a rule once daily. The starting of the filter
is always performed mechanically without any manual labour
on the filter-bed.
Jewell Filters have come into use largely for the water supply
of municipalities. I mention the towns of Alexandria, Trieste,
Helsingfors (Finland), Annecy (France). Critical examinations
on the basis of the tests previously put forward generally prove
favourable.
Bitter and Gottschlich have obtained very favourable results
with the Jewell Export Filter in Alexandria.
Hilgermann has likewise made investigations with the Jewell
Export Filter, and come to fewer favourable results. He holds,
according to his experiments, that the Jewell Export Filter, like
every other mechanical filter, is, in bacteriological respects,
absolutely inferior to the sand filter.
K. Schreiber has searchingly investigated the Jewell Filter,
in a series of experiments with an experimental plant at the
Berlin Waterworks, and comes to the conclusion that it is quite
as good as the sand filter in bacteriological respects, in the
removal of the turbidity and colour of the raw water, as well
as in the method of washing, which takes place quite mechani
cally, without danger of contamination from the hands and
clothes of the workmen.
According to Schreiber, the method
may, however, be far superior to the sand-filtration method.
The amount of aluminium sulphate added is of great import
ance. Schreiber comes to the conclusion that with an addition
of 33.6 g. of aluminium sulphate per cubic metre (5 oz. per 1000
gallons), with a time of sedimentation lasting 1 hour 28 minutes,
14
WATER PURIFICATION
and at a velocity of nitration of 4 metres (13 feet) per hour,
94.3 per cent of the bacteria in the raw water are removed by the
Jewell Export Filter.
The increase of sulphates occasioned by the addition of the
chemicals is confined within such narrow limits that a deteriora
tion of the water for drinking and domestic purposes does not
come into the question in practice.
The increase of aluminium salts, apart from the consideration
that this disappears completely with well-ordered management,
is so small that hygienically it may be neglected. At all times in
those places where in the water-supply plant there is no horizontal
space at disposal for expansion, the Jewell Export Filter can be
applied with advantage, as, for example, in cases of water supply
in besieged strongholds in time of war.
Further, Friedberger has also carried out searching investiga
tions with the Jewell Filter, with the water of the town of Konigsberg. He comes to fewer favourable conclusions than Schreiber.
With water rich in bacteria, mechanical filtration does not
guarantee so complete a reduction of the bacteria that one could
be satisfied with mechanical filtration alone.
A quite new work of Gottschlich and Bitter gives an account
of over four years' practical experience of Jewell Filter man
agement for the town of Alexandria.
The plant worked
excellently during this time as regards removal of bacteria and
turbidity, as well as the trustworthiness of the method.
(d) Artificial recovery of Ground-water from Surface-water
(Intermittent filtration) .
For the reasons discussed on page 2 ground-water is to be pre
ferred to purified surface-water. As a consequence, municipalities
which are in a position to do so are always attempting to supply
themselves more and more with ground-water for drinking
purposes. In order to obtain such water in sufficient quantity,
many towns find it necessary to go a considerable distance from
the town. Considerable expense thereby results in conveying,
and also in superintending the water conduits, etc. Owing to the
expense of bringing water from a distance, it has been attempted
many times to increase artificially the ground-water in the
neighbourhood of towns.
FILTRATION PROCESSES
15
The recovery of artificial ground-water was originated scienti
fically by Thiem.
So-called natural sand or bank filtration comes into considera
tion here. It consists in the sinking of wells on the banks of a
lake or river. The water in these wells is then pumped away, and
its level thereby considerably lowered. As a consequence water
enters the wells from the lake or the river through the sand or
gravel strata, which act as the filtering medium.
In its progress through the ground the water is freed from
bacteria in a manner similar to ground-water. Bank filtration
results in the suspended matter being gradually drawn through
the sand. As opposed to artificial sand filtration in which fil
tration is vertical, bank filtration is horizontal, and this is really
the cause of the observed passage of suspended matter through
the filtering layer.
The investigations of Scheelhaase with Maine River water
showed that with wells at a distance of 25 metres from the riverbank, while the bacteria were of course removed, the water had
become like ground-water in no other respects, since the tempera
ture was not sufficiently adjusted, nor was its odour nor taste
improved.
Intermittent filtration in a vertical direction has later been
investigated in various ways. According to Richert there are
the following methods : The surface-water is conducted to an
irrigation field, where it is allowed to drain away. This method
ought to have been tested on an experimental scale. It has proved
of little use, as it is untrustworthy and difficult to control.
It is better to lead the surface-water to an intermittent filtra
tion basin or well, which has been sunk to the ground-water level,
or to a basin which lies over the ground-water.
Success in producing a workable ground-water depends on the
possibility of leading the stream sufficiently far in a horizontal
direction, and on the water having time, apart from the removal
of bacteria, to become a useful ground-water in respect of the
temperature, colour, taste, and smell. In this direction, Scheel
haase, in Frankfort-on-Maine, has lately published important and
interesting researches.
River Maine water purified by means of a sand filter was allowed
to flow to a double-branch irrigation bed laid out 3 metres deep,
50 metres long, and constructed of gravel and drans. The
16
WATER PURIFICATION
infiltrate, finely distributed by this treatment, had to trickle
in a vertical direction, to the natural ground-water level, through
a layer of ground 13 to 14 metres deep, consisting of fine sand
and gravel. Then it joined with the natural ground-water, and
flowed along with it to the nearest pumping-station following
the incline of the ground. The result of the investigation was that
at 100 metres from the place irrigated, a distance which the in
filtrate flowed through in 190 days, Maine water, which is very
dirty river-water, had been transformed as regards its bacterio
logical nature, its temperature, smell, taste, and colour, into a
water equally as good as ground-water.
J. Braikowitz reports on the nature of artificial ground-water
in different towns : "In Offenbach-on-Maine the water of the old
waterworks is brought to the neighbourhood of the new works,
which draws upon a well of water free from any objection. In
Brunswick the condenser water from steam engines in the water
works is made to percolate through the ground, whereby the
ground-water obtained only experiences a rise in temperature
of 0.4° C. In the Ruhr Waterworks the river-water is led through
ditches, or through a broken-up portion of the choked-up river-bed,
to the layer of rubble-stone underneath. The Ruhrtalsperren Co.
seeks to increase the lower waters of the Ruhr, and also to
augment the ground-water, by constructing dams."
According to Richert the ground-waterworks of the town of
Schweinfurt is a beautiful example of natural filtration.
Since the year 1875 the town of Chemnitz has employed inter
mittent filtration with the best results, in which, above a series
of wells sunk in a ground-water area, an irrigation field for
intermittent filtration was dug out to the ground-water level.
The water introduced into the open ditches of the irrigation field
unites directly with the ground-water, and flows along with it to
the wells.
. In a similar manner the town of Gothenburg produces artificial
ground-water.
(e) The Importance of Water Filtration in Public Health Ad
ministration, and Critical Opinions on the value of Sand
and Mechanical Filtration.
The purification of surface-water for drinking purposes by
means of filtration has become a question of great importance
FILTRATION PROCESSES
17
as affecting the health of towns and their economic improve
ment.
According to Hilgermann, cholera and typhoid diseases
especially have decreased in those places where sand filtration
has been introduced and properly conducted. In those places
where epidemics have appeared in spite of filtration, they have
been caused by faulty arrangement of the sand filter or faulty
management of the undertaking. During the cholera epidemic
in Hamburg, in the year 1892, sand filtration worked splendidly,
since, for example, the town of Altona, which used filtered Elbe
water, was quite free from the epidemic although the filters
received for their work Elbe water, rendered contagious by all
the Hamburg discharges.
According to Vincey, as recently as 1905 a number of town
ships around Paris employed raw Seine water. After the intro
duction of sand filters mortality in typhoid cases fell about
42 per cent, cases of typhoid about 48 per cent.
Hilgermann, in his work already mentioned, critically com
pared the newer American mechanical filters with the sand
filter.
European workers who have experimented in recent years
with American mechanical filters have in general come to favour
able conclusions. American professional men who have had the
opportunity of studying the mechanical filter on the spot for
ten years are not especially favourable.
According to Hilgermann, the main difficulty with the American
mechanical filters which work by addition of aluminium sulphate,
is that it is not possible, with the varying composition of the raw
water, to add the right amount of chemicals. This causes faulty
sedimentation and faulty formation of the filter layer.
On the basis of his researches with the Jewell Filter, Hilger
mann comes to the following conclusions on the working of the
mechanical filter :—
1. With raw water containing a small number of bacteria
the American mechanical filter yields good results.
2. The efficiency of the whole method of filtration depends
upon the sedimentation.
3. The addition of aluminium sulphate at any time is dependent
upon the amount of the substances suspended in the raw water.
4. With poor raw water the mechanical filter fails if the addition
c
18
WATER PURIFICATION
of chemicals cannot be immediately increased with the increase
of suspended matter in the raw water.
5. There is no principle for such a regulation. The increase
must be settled by experiment.
6. As regards the removal of turbidity due to clay and also
the removal of colour, and in respect of the hygienic method of
cleaning, the mechanical filter is superior to the sand filter.
Closer examination shows that as regards cost, sand and
mechanical filtration are approximately alike. Of course, the
cost of setting up the mechanical filter a second time is far smaller
than with the sand filter, owing to its small dimensions and to
the small space it requires. Still, the wear and tear of these
machines is much greater than is the case with sand filters ;
hence one has to allow for a greater depreciation. Further, the
constant consumption of chemicals raises the cost of manage
ment considerably.
(ii) Methods of Water Sterilisation.
The removal of bacteria from water can take place by filtration
and by sterilisation, i.e. the destruction of the bacteria. For
this purpose a number of chemicals have been employed, e.g.
ferric chloride, chrome iron alum, lime, hydrogen peroxide,
calcium permanganate, chloride of lime, bromine, copper
chloride, organic acids, ozone, etc. Of these very many must be
rejected, since they either do not work with certainty in general,
or they need a long time for the development of their sterilising
action, or they alter the appearance, smell, and taste of the water
too much. The only methods of any practical value are those in
which ozone and chlorine (as chloride of lime or sodium hypo
chlorite) are used.
(a) The Ozone Method.
Ozone, the so-called active oxygen, which is formed from the
oxygen of the air by the silent discharge of high-tension electric
current, has proved to be a good medium for sterilising water.
When dissolved in water it kills the greater part of the bacteria
and then escapes again from the water, without influencing
taste or smell in the slightest degree, since it decomposes to
ordinary oxygen. For the sterilisation of drinking-water a number
of ozone plants of varying design have been proposed ; for example
u•
on...
•aiux•vanj.joJ-vamMkavhaovdAiaVqyj
oij-t
20
WATER PURIFICATION
the system of Siemens and Halske,1 Trindall, Abraham Marmier,
Otto and Vosmaer. Quite a number of towns now purify their
water by means of ozone, e.g. Paderborn-i.-W., St. Petersburg,
Hermannstadt, Nizza, St. Mans, near Paris, and others.
As an example of an ozone plant, that of the metropolis, St.
Petersburg, may be more closely described here as one of the
newest according to the system of Siemens and Halske. As
can be seen from Figure 3, the raw water is taken direct from the
F1g. 4. Ozone Waterworks of St. Petersburg.
Neva by means of a pump, and pumped to the sedimentation
reservoirs for purification. Before entering the purification
reservoir the water is treated with aluminium sulphate. It is
then filtered through thirty-eight mechanical filters. These filters
% are on the Howatson system, which is similar in many respects
to the previously described Jewell Filter. To the filtration plant
1 Recently the Berlin Ozone Company has incorporated the firms of Siemens
and Halske and the General Electric Co., and has taken over all the patents
of Siemens and Halske.
STERILISATION PROCESSES
21
there is attached the actual ozone plant, which consists of two
parts, the ozone batteries and the steriliser.
In Figure 4, on the left, the ozone batteries, consisting of 128
pieces of apparatus, are shown, and on the right the five sterilisers
can be seen, one of which serves as a reserve. The individual
apparatus are Siemens and Halske ozone cylinder elements, as
shown in Figure 5. In this apparatus the oxygen of the air is
converted into ozone by means of high-tension discharges. The
F1g. 5. Ozone Waterworks, St. Petersburg. Ozone Batter1es.
concentration of ozone amounts to 2.5 grams in 1 cubic metre
(1 grain per cubic foot) of ozonised air. The air, before entering
the apparatus, is dried in a cooling machine. The movement of
the air through the ozone batteries and pipes takes place by the
aid of the so-called emulsifiers (Otto's system). These emulsifiers
are injectors or water-jet air-pumps, which, by means of a water
pressure of about 4 metres (160 in.), sucks the ozonised air out
of the ozone batteries, and brings it mixed with water into the
steriliser. The absorption of the ozone and the consequent steri
lisation of the water takes place partly in the emulsifiers placed
WATER PURIFICATION
near the sterilisers, and partly in the agitators, from the bottom of
which the ozonised air rises to the top in a very fine state of divi
sion, and therefore in very intimate contact with the water. From
the emulsifiers and sterilisers the water passes over a cascade for
removing the air to a pipe which leads it to the pure-water reser
voir. From there it is pumped away into the town's mains.
It is a necessary preliminary for the satisfactory working of an
ozone plant that the water to be sterilised contain no suspended
matter, and not too large an amount of organic matter, or ferrous
oxide. In such cases the ozone is in great part consumed in the
oxidation of the dissolved substances, or of the iron. The
unsatisfactory working of a plant in Schierstein was attributed
to the presence of a considerable amount of iron in the drinkingwater.
The researches undertaken by Erlwein, Ohlmiiller, and Prall on
the "Auftrage des Kaiserlichen Gesundheitsamtes" (Commission
of the Imperial Sanitary Board) , and by Proskauer and Schuder, of
the "Konigl. Institut fur Infektionskrankheiten " (Royal Institute
for Infectious Diseases), with the water of the Spree, and with
water to which large quantities of pathogenic bacteria (typhoid,
diarrhoea, cholera) had been added, are in agreement in proving
that the bacteria are almost entirely destroyed, and that the
pathogenic variety were in all cases destroyed without exception.
The Pasteur Institute also obtained favourable results in its
investigations on ozone processes.
Halbertsma and Dolezalek prove that the opinion that no daily
control is necessary in ozone processes as contrasted with sand
filtration is wrong.
Karl Schreiber, in the " Auftrage der Konigl. Prufungsanstalt
fur Wasserversorgung und Abwasserbeseitigung " (Commission
of the Royal Test-Institution for Water supply and Sewage
disposal), as a consequence of the unfavourable observations of
Halbertsma and Dolezalek, undertook a searching examination
of the ozone works in Paderborn, in which he established that the
ozone process satisfied all demands.
G. W. Chlopin and K. E. Dobrowolski report that in St. Peters
burg the bacteria are not completely killed off, but are decreased
on an average about 98-8 per cent. Intestinal bacteria should
be absolutely destroyed. The water should also undergo an
improvement in taste and colour. The chemical- composition
STERILISATION PROCESSES
23
does not alter essentially, and the ozone dissolved in the water
disappears after ten minutes.
S. Rideal reports on his experience in the works at Paris.
After ozonisation all bacteria, except the more resistible spores,
were destroyed. The temperature of the water was not raised.
According to Gartner the bacteriological action is as good with
ozonisation as with sand filtration, and it is also more certain.
Sauna made experiments in which ozone was used in quantities
averaging about 4 milligrams per litre (1.75 grains per cubic
foot. It gave the following results : Nitric acid is completely
destroyed ; 15 to 43 per cent of organic matter is oxidised.
The efficiency of ozone on the organic matter increases accord
ing as the water is more oxidisable.
Ozone also oxidises
ammonia present in water. Sulphates, carbonates, and chlorides
are not altered. Nitrates and free oxygen show an increase.
Within a few minutes the last traces of ozone disappear.
Hydrogen peroxide is not formed By using suitable amounts of
ozone, complete sterilisation of the water takes place. Ozone
acts most effectively on pathogenic bacteria.
The sterilising effect of ozone depends, according to Schreiber,
on four1.factors,
On theviz.
nature
— of the water.
2. On the amount of water passing through the plant.
3. On the concentration of the ozonised air.
4. On the amount of the ozonised air used.
For the right working and control of ozone plants, Schreiber
recommends that a hygienist and an official experienced in
electrical management should undertake a test of the four factors
mentioned, and that they should then work out regulations for
running the process in accordance with the test. The finished
plan should be tested, as regards its sterilising action, with water
in which bacterium coli and similar bacteria have been dis
seminated. The maintenance of the working regulations must
be controlled from time to time by an electrical engineer.
The cost of sterilising water in Paderborn ranges, according
to Schreiber, from 0.43d. to 1.5d. per 1000 gallons without pre
liminary filtration, and with filtration from o.66d. to 1.o^d. per
1000 gallons.
At the Parisian works, according to Rideal, 1.31 kilowatts
24
WATER PURIFICATION
current were necessary to sterilise 100 cubic metres of water. The
total cost, exclusive of the repayment of loans and payment
of interest, amounted to o.33d. per 1ooo gallons.
In the St. Petersburg undertaking the cost of working is
o.87d. to 1.od., of which only half is due to ozonisation.
The cost of sand filtration, according to Schreiber, amounts in
comparable cases from 1.05d. to 1.87d. per 1ooo gallons.
(b) The Disinfection of Drinking-Water with free Chlorine.
In the year 1894 it was shown by Traube that, by treatment
with very small amounts of free chlorine, the bacteria in water
could be destroyed. Later investigations by other authors
showed that for certain destruction of the bacteria the amounts
of chloride of lime must be greater. The process remained thus
for a long time, but was eventually taken up again in practice
several years ago. Recently, however, the method has been
extensively applied, especially in America.
The Duyk Ferric Chloride Process, Howatson System
(Thumm and Schiele) .
In this process the raw water, either during or immediately
after the sedimentation of the undissolved particles, is treated
with a solution containing chloride of lime, and then with one
of ferric chloride. The mixture is led on to a mechanical filter
(Howatson system) without further sedimentation, or with an
intermediate disposition of sedimentation arrangements ; the
filtered water is then ready for use.
By the addition of the chemicals the following reactions take
place :
6 CaOCl2+Fe2Cl6=6 CaCl2+Fe203+3 C1,O.
3 0,0=301, +3 O.
The resulting chlorine and oxygen act as disinfectants, whilst
the voluminous ferric hydroxide and the calcium carbonate,
resulting from the decomposition of the calcium chloride, draw
the suspended matter along with them to the bottom on settling.
In Middelkerke, in Belgium, the method is in practical applica
tion ; there, and later in Paris, it has been tested. The con
clusions are favourable. The destruction of the bacteria must
have been extensive.
STERILISATION PROCESSES
Thumm and Schiele, who inspected the Middelkerke under
taking, and base their view on the impressions obtained and the
accounts received, express themselves as generally favourable.
In the ferric chloride process it may be important to consider
that the chlorine disappears of itself after some time, and that
the water treated does not then contain any harmful chlorine
compounds.
(c) Sterilisation with Chloride of Lime or Sodium Hypochlorite.
This method, according to Imhoff and Saville, has been intro
duced in considerably more than one hundred American towns.
The method is especially suitable in those places where the water
is physically good, but has the disadvantage of containing either
permanent or transitory disease germs.
The chloride of lime is generally added to the water in the
proportion of 1 part to 350,000 parts of water (which means 1 part
of active chlorine per 1,000,000 parts of water).
The free chlorine acts upon the bacteria, more especially on
those which communicate disease.
The cost of the process is very moderate, being only o-027d.
per 1000 gallons, therefore only a twentieth the cost of other
purification processes.
The method is not applicable where much suspended matter,
or even organic matter, or iron, is present in the water, for then
the free chlorine is consumed in the oxidation of these substances.
On account of the small amount of bleach added, it should not
be necessary to displace the chloride of lime from the water
subsequently ; the water, also, should not possess any appreciable
taste or smell.
Quite recently a series of reports upon the method have come
from English and American towns.
G. A. Johnson, who has taken up the process again in America,
declares that sodium hypochlorite can be used as well as bleach.
The following are mentioned as advantages of the process :
the rapidity with which the bacteria, especially pathogenic
bacteria, are quickly destroyed ; the ease with which the addition
of chemicals can be adapted to any change in the water ; the
absence of any harmful reaction product in the water ; the
rapidity of the reaction.
26
WATER PURIFICATION
The bleach treatment is useless in the following points : bac
teria spores are not destroyed ; the bacteria embedded in the
suspended solid particles remain unaffected.
C. Walker reports on the chloride of lime water-purification
process called the De Chlor process, which was tested for six
months on an experimental scale. The De Chlor system removes
the excess of chlorine by means of a preparation (charcoal)
insoluble in water, added to the filter in granular form. The
number of bacteria fell, after passing through the filter, to
between 234 and 421 per cubic centimetre ; the purified water
contains on an average 32 germs per cubic centimetre. Bac
terium coli was found in 1 cubic centimetre of raw water, in
10 cubic centimetres of the first filtrate, and in the pure water
was no longer found in 100 cubic centimetres.
According to Craven, 0.3 to 0.4 milligram of chloride of lime
is added to every litre (20 to 25 grains per 1000 gallons) of
Ohama water, which is previously treated in clarifying basins.
The number of bacteria is thereby reduced by about 97 per cent.
Bacterium coli could only be found in isolated cases. In
Minneapolis from 1.54 to 3.04 milligrams is added to a litre
of water. The number of bacteria in the raw water sank from
between 250 and 8000 to between 7 and 1200. Bacterium coli
was not found in the water so treated.
In the opinion of the author it is of advantage to use the
method for a time with a certain amount of scepticism, as sus
picion almost prescribes that to be certain of the destruction
of all the bacteria such an excess of bleach is necessary, that it
is noticeable in smell and taste, or vice versa, that if there is
no smell and taste in the purified water the bacteria are not
destroyed with certainty.
Add to this also that it is not yet established that the con
tinued use of small quantities of bleach, even should they be
imperceptible by the senses, is not a matter for serious mis
givings.
For this reason this method cannot be recommended for general
imitation. It might possibly be of service in certain circum
stances, if there were temporary dangers with the drinkingwater, as in times of epidemic, or it might perhaps be used with
success in time of war.
STERILISATION PROCESSES
27
(d) Sterilisation of Drinking-Water by means of Ultra-Violet
Light.
It is well known that if white light be analysed into its com
ponents by means of a prism, beyond the extreme violet end of
the spectrum there can be indicated certain rays which cannot
be perceived as light rays, and are therefore invisible, but to
which there belong powerful chemical activities, e.g. towards a
photographic plate.
That these ultra-violet rays also possessed the power of killing
bacteria has long been known. Downes and Blunt, two English
investigators, observed this in the year 1877, and the power of
sunlight to kill bacteria is* attributed to these ultra-violet rays.
Ultra-violet rays are to-day generated by means of the quartz
mercury-vapour lamp. An electric current is sent through
mercury vapour which is enclosed in an evacuated quartz-tube ;
the mercury vapour thereby glows and sends out ultra-violet
rays which have the property of passing through quartz though
they are retained by glass.
The real discoverers of the sterilisation of drinking-water
by means of ultra-violet rays are the French workers, Courmont
and Nogier. In their experiments a lamp was fastened in the
axis of a cylinder of 60 centimetres diameter, so that the walls
were not more than 30 centimetres distant from the source of
the light. Only clear water, without turbidity or colour, is
sterilisable in this manner. The lamp is purposely immersed in
the water. In the first place the sterilising action is better when
the lamp is immersed, as the water is in closer contact with the
source of the rays, and all the rays are used up on every side.
It seems, however, to be also necessary to immerse the lamp
in order to cool it, and to prevent it varying on account of heat
changes. It was formerly thought that the action of the ultra
violet rays rested on the formation of hydrogen peroxide or ozone.
That is not the case ; such compounds could never be shown
to be present. The taste, smell, temperature, and chemical
properties of the water are in no way altered by the rays, and
protracted experiments on animals have further demonstrated
the complete harmlessness of the water so treated.
The sterilising action, as communicated by Courmont and
Nogier, is good, and not inferior to that in the water-purification
28
WATER PURIFICATION
methods previously mentioned. Also as regards economy, the
process, according to the accounts of Courmont and Nogier, can
bear comparison with the above purification methods.
From experiments conducted by two members of the Konigl.
Prufungsanstalt fur Wasserversorgung und Abwasserbeseitigung
(Royal Institute for the Testing of Water Supply and Sewage
Disposal) the results are not so favourable as those of Courmont
and Nogier in all points. Grimm and Weldert carried out their
researches with the mercury-vapour lamp of the Quartz Lamp Co.,
Ltd., Hanau-on-Maine. They collect the results of their work as
follows
" (1) With
: — the apparatus tested clear water, containing few bac
teria, can be sterilised at the rate of 0.55 cubic metres (120 gallons)
per hour under the conditions described above. Clear water, very
rich in bacteria, can, on the other hand, only be rendered sterile
at the rate of 0.45 cubic metre per hour, in which case it
does not make any difference whether the bacteria are water
bacteria or, with pathogenic bacteria, coli bacteria. (2) Turbidity
of the water, even to a small extent, makes disinfection uncertain.
With a high degree of turbidity the destruction of bacteria by
the lamp is impossible, at all events within the limits which come
into practical consideration. (3) Likewise the yellow colour of
water due to colloids, such as bog-water shows, acts as a very
great hindrance. Indeed, with only a slight amount of coloration,
the hindrance is so great that it is practically impossible to
accomplish disinfection by this method. (4) The water is not
altered in any physico-chemical respects by its passage through
the experimental apparatus, with the exception of an increase
in temperature of a few tenths of a degree. With prolonged action
of the rays, further increases of temperature result, as well as
symptoms of chemical decomposition.
(5) The expenses of
water purification by means of ultra-violet light, reckoned on the
basis of the researches, are, comparatively speaking, very high,
and cannot bear comparison with the cost of the methods of water
purification employed at the present time on a large scale."
Erlwein reports on the experience of the firm of Siemens and
Halske in this respect. The energy required is greater than in
sterilisation with ozone. With regard to the other factors, a com
parative estimate of the cost of working, under the conditions
operative in a central waterworks undertaking, is wanting in the
STERILISATION PROCESSES
29
case of the ultra-violet light method, and especially the most
important, viz. a more exact knowledge of the deterioration
and cost of repairs of the still very expensive quartz lamps.
Buywid is of the opinion that the ultra-violet light method is
more promising than the ozone method.
To the knowledge of the author the method has not been to
the present applied on a large scale. Mercury-vapour quartz
lamps are supplied by different firms, e.g. The Ultra-Violet Firm,
22 Rue Chanchat, Paris ; Westinghouse, Cooper, Hewitt and
Co., 131 Wilhelmstrasse, Berlin, the Quartz Lamp Co., Ltd.,
Hanau-on-Maine.
Taking into consideration the fact that the water is not in any
way changed as regards its nature, and that extended researches
with animals have shown that water acted upon by the rays even
for a long time is not harmful, the method should have a future
if the cost can be reduced.
In addition to their researches on the ultra-violet light method,
Grimm and Weldert collected together the costs of the principal
water-purification methods. Nos. 1 to 4 of the following table
are the averages of estimates of various undertakings on a large
scale. No. 5 is reckoned on the basis of the experiments of
Grimm and Weldert.
Cost per 1000 gallons
List of tile various Processes.
of purified water.
(1) Slow Sand Filters.
Cost of working
....
o.61d.
Total cost
. , .
.
. .
5 .2d.
(2) Mechanical Filters.
Cost of working
....
2.8d.
Total cost
.....
5'8d.
(3) Ozone Plants.
Cost of working
....
2.8d.
Total cost
.....
8. 2d.
(4) Chloride of Lime Plants.
Cost of working (Johnson) .
.
.
o.o7d.
Total Cost (Johnson, Imhoff, and Saville)
o.34d.
(5) Ultra-violet
Cost
100%ofBacteriological
working
light plant.
:
Effect
.
.
14s. 6d.
99 to 99.9%
„
,,
.
5s. to 7s. 3d.
30
WATER PURIFICATION
(e) Disinfection of Water-Mains and Wells.
If an epidemic reigns in a town, and there are grounds for
believing that the contagion is to be attributed to drinkingwater, the disinfection of the water-mains is to be recommended,
especially in those cases in which a fresh drinking-water, free
from any objection, must be led into the infected main. Fliigge
and Bischoff, during a typhoid epidemic in • Beuthen (Upper
Schleswig), employed for this purpose a 0.2 per cent solution of
sulphuric acid. The acidified water remained standing in the
main many hours. The strength of the sulphuric acid in the water
is controlled at the stop-cocks. In an epidemic of typhoid fever
in Gelsenkirchen, in the year 1901, the mains were likewise dis
infected with sulphuric acid.
With wells which in general are suitably situated and lie in
surroundings free from objection, but which seem to be infected
from above, it is possible, according to a proposal of M. Neiszer,
to introduce compressed steam (5 atmospheres) ; the whole
contents of the well are thereby brought to the boiling-point.
The same method, or disinfection with •" Carbolic-Sulphuric
acid " (Frankel), which is subsequently pumped away, can be
applied in the preliminary works of a central water supply for
disinfecting borings, so as to be able to take away samples
bacteriologically free from objection.
(iii) Purification of Water in directions other than that of Health.
As already mentioned, substances occasionally appear in water
which, without being detrimental to health, still cause great
trouble, since, as with iron and manganese, they may discolour
the water, or, as with free carbonic acid, may attack the walls
of pipes and reservoirs.
(a) Removal of Iron.
Ground-waters of the diluvial and alluvial strata of the North
German Lowland often contain iron in greater or lesser quantities,
as ferrous carbonate or the ferrous salt of humic acid. When
freshly drawn the water is generally clear, but becomes turbid
after some time owing to the separation of a brown precipitate,
OTHER PROCESSES
31
since the oxygen of the air converts the ferrous salt into in
soluble ferric hydroxide with evolution of carbon dioxide.
Although this turbidity due to iron is objectionable not so
much from the point of view of health as from that of appearance,
still it frequently causes trouble. The flocculent hydroxide,
settling in the pipes and reservoirs, renders their frequent cleans
ing necessary. Further, the presence of iron in water favours the
appearance of numerous micro-organisms which store up iron,
especially the iron bacteria, which decompose and evolve odours
of sulphuretted hydrogen and other decomposition products,
and gives to the water a specific metallic taste.
Such water is not suitable for most technical purposes.
A few tenths of a milligram of iron in a litre of water may make
an iron-removal plant necessary, since iron bacteria thrive best
in waters weak in iron.
The methods of removing the iron are based on three physicochemical actions.
First, by contact of dissolved ferrous iron with air, oxygen
converts the ferrous compound into insoluble ferric compounds.
Consequently the water may be aerated, and subsequently filtered.
Secondly, since carbonic acid keeps the iron in solution, the
precipitation of the iron may be effected by neutralisation of the
carbonic acid with lime.
Finally, if the iron is present in the water in colloidal form
(organically combined), a coagulant, such as aluminium sulphate
or ferric chloride, is employed.
The last method is often used in America, whilst in Germany all
processes for the removal of iron are based upon aeration and
filtration.
The method of effecting this aeration and filtration varies
considerably with different systems.
Aeration is effected by allowing water to fall through the air,
cascades (Elbing), by means of raining devices using perforated
troughs (Wismar), in coke-towers (Piefke), over wood (Berlin),
over clinkers (Delitzsch), over glazed brick (Sternberg), and in
other ways.
Similarly, the method of filtration varies. In general, sand and
gravel have proved the best media for filtration. The size of the
grains of sand is an important factor in the formation of the filter
layer, and in the complete retention of the ferric hydrate particles.
32
WATER PURIFICATION
The method of cleaning the filter and aerator is also different
in the various systems.
In the following review of the most important methods for
removing iron are also included those which are used mainly
for industrial purposes, since they are based on the same principles
and are conducted in precisely the same way as are the larger
undertakings for central water supply. The removal of iron
from single wells, on the other hand, will be specially treated on
page 49.
The most important systems for the removal of iron are
characterised as follows (Schwers) : —
1. Piefke system : One of the oldest and best systems. The
water containing iron is brought to the coke-tower, a cylindrical
upright vessel, filled with pieces of coke the size of a man's fist.
The water flows slowly over the coke and passes into a settlingtank situated underneath, whence it flows on to a sand filter,
which is arranged on the usual lines. The coke-tower is cleaned
by flushing in the reverse direction. It should only be necessary
to refill the tower once or twice each year. These Piefke towers
are largely used, and have proved excellent.
2. Oesten system : A raining arrangement (2 m. rainfall),
with roses, and filtration through gravel the size of wheat-grains.
3. Kurth system : Violent rainfall and gravel filtration, worked
by the stroke of a piston ; for small plants.
4. Bieske system : Analogous to the previous one.
5. Thiem system : Raining arrangement with perforated trays.
6. Reichling system : Raining arrangement with centrifuge
or sieve, closed filtration upwards, under pressure, through layers
of sand, gravel, and wood-wool ; used in industry.
7. Koerting system : Similar to the previous one.
8. Pfeiffer system : Simple aeration and sand filtration.
9. Wingen system : Waterfalls, sand filtration.
10. Taacks system : Waterfalls, sand filtration.
11. Krohnke system : Coke-tower, rotating cylindrical filter
that is alternately filled with sand and water.
12. Lanz system : Filtration through natural sandstone.
13. Fischer system : Filtration through porous artificial stone
(Wormser Kunststein).
14. Agga system : Filtration through pipes of artificial stone
in the sand filter, purification by a reverse stream of water.
OTHER PROCESSES
33
15. Reisert system : Filtration in the open air through gravel,
with or without previous aeration over coke ; cleansing by a
reverse stream of water.
16. Bollmann system : Gravel filtration under pressure without
previous aeration, purification by a stream of water in the
reverse direction.
17. Breda system : Filtration under pressure through " Tonkoks " (clay-coke) and gravel of various sizes, after preliminary
aeration in a mixer ; purification by a reverse stream of water.
18. Helm system : Filtration through brown iron-ore slag
in which aeration takes place by means of occluded oxygen ;
purification by reversing the water current.
19. Buhring system : Filtration, as in the previous case,
through bone charcoal ; purification with dilute hydrochloric
acid ; for domestic purposes.
20. Buttner system (von der Linde and Hesz) : Filtration under
pressure through wood shavings, impregnated with tin oxide
without any special aeration ; purification by reversal of stream.
21. Bock system : Filtration analogous to the previous one,
through wood-wool.
22. Sellenscheidt system : Raining arrangement, filtration
through plant-fibre ; used especially in breweries.
23. Dehne system : Aeration by raining with an injector,
addition of milk of lime, filtration under pressure through felt
discs ; used in industrial concerns.
24. Jewell system : Rapid sand filtration with or without
addition of milk of lime and sulphate of alumina, unaccompanied
by any aeration. This system was introduced in Posen, in 1909,
producing 30,000 cubic metres per day. No chemicals are added ;
the water is freed from iron by simple filtration.
25. " Voran " system : Frankfort-on-Maine.
Aeration in
the closed system by compression through nozzles, in the open
system by sprinkling over a cataract-like erection of coke, bricks,
etc. An open and a closed " Voran " plant are pictured in
Figures 6 and 7. The figures are intelligible without further
explanation.
Plants for the removal of iron are built both open and closed.
Closed systems offer greater protection, naturally, against
infection of the water by bacteria ; still, according to Schwers,
plants with open apparatus have proved as good as the closed
1t
34
WATER PURIFICATION
from the bacteriological point of view. In recent years a vehe
ment dispute has been in progress with reference to the greater
or lesser suitability of the open and closed systems. Both systems
have been equally praised and criticised. On the whole they may
be regarded as of equal value.
The efficiency of iron-removal plants depends upon the height
of the aerator and filter, the velocity during aeration and filtra
tion, and other technical points.
F1g. 6. Open Plant for
the removal of iron.
" Voran " System.
F1g. 7. Closed Plant for the removal of
iron. " voran " system.
The height of the aerator is generally about 3 to 7 metres ;
the velocity of filtration in open systems seldom amounts to more
than 1 metre, in closed systems it is often 10 metres (per hour).
The pressure is generally produced by the difference in level
between the surface of water in the filter and in the pure-water
reservoir.
Good iron-removal plants yield a water which at most still
contains o.1 milligram iron per litre.
The cost of removing iron from water amounts in a series of
German towns from 0.04 to o.4d. per 1000 gallons.
OTHER PROCESSES
35
(b) Removal of Manganese.
As a result of the water calamity in Breslau in the year 1906,
general attention has been turned to the occurrence of manganese
salts in water. Although only present in small amounts, they
deposit a weak scum which makes the water insipid, stains linen
and paper, pollutes the reservoirs in breweries, injures the com
plete action of yeast, etc. Certain micro-organisms absorb it
to a still greater degree than iron. Manganese almost always
accompanies iron, but the amount is generally so small that its
presence in the majority of cases does not approach practical
importance at all.
Proskauer was the first to point out the occurrence of man
ganese salts in water.
Manganese is removed by aeration, like iron, but it separates
out with greater difficulty, since, during aeration, manganimanganous compounds result, which are soluble to a considerable
extent in water.
The calamity in Breslau originated in consequence of the
existing geological conditions. Iron and manganese sulphides,
in the humous layers situated over the ground-water, were
converted to sulphates by oxidation and then passed into the
ground-water owing to a flood which inundated the whole tract
of country.
For the removal of manganese, and also of iron, Permutit has
recently been recommended. Permutit is an artificially prepared
product (aluminium silicates), principally employed in the
softening of water (see page 60) .
Permutits have the property of withdrawing from water,
lime, magnesia, iron, and manganese, in exchange for sodium,
if the water be allowed to flow over them. Luhrig and Becker,
Gaus and Noll, have carried out experiments on the removal of
manganese by means of calcium permutit. The manganese is
thereby exchanged for calcium. Whilst Luhrig and Becker
obtained good results in laboratory experiments, a trial on a large
scale proved a failure. The water took from the permutit sub
stances which imparted to it an alkaline reaction, causing a
precipitation of manganese as oxyhydrate. This precipitate
choked up the filter. Noll found on an experimental scale that
manganese was quantitatively removed from water by calcium
36
WATER PURIFICATION
permutit, so long as the content of the permutit in manganese
was less than 2 per cent. The cost of removing manganese with
calcium permutit is estimated by Noll to be o.ogd. per 1000
gallons.
Quite recently the Permutit Filter Company, Berlin, have recom
mended a new method for removing manganese and iron by means
of permutit. According to Kriegsheim, the method is as follows :
From a suitable permutit, e.g. sodium permutit, a manganese
permutit is prepared by treatment with a solution of manganese
chloride. This manganese permutit is then treated with potassium
permanganate. The permanganic acid is thereby easily combined
with the manganese oxide of the permutit to form highly oxidised
manganese compounds. If a water containing manganese be now
filtered through a permutit filter so treated, these higher oxides
of manganese can very rapidly effect complete removal of the
manganese, even with rapid velocity of filtration. The action
is based upon the fact that the oxygen necessary for the oxidation
process is presented to the manganese separating out during the
filtration of the water in the solid condition and easily split off
from the highly oxidised manganese oxides. The oxidation
causes the precipitation of the manganese in the water in an
insoluble form. Should the action diminish, the filter can be
regenerated by means of a 2 to 3 per cent solution of perman
ganate. The cost of this process should be very small.
As already mentioned, the process is not only recommended for
removal of manganese, but also for the removal of iron. The
principle is the same in the latter case also.
(c) Removal of free Carbon Dioxide.
If water contains much free carbon dioxide, it exercises a very
deleterious action on the various materials required in water
works. Thus it was observed, for example, at Frankfort-onMaine, that a newly constructed deep reservoir made of reinforced
concrete was strongly corroded by the water. Similarly the iron
pipes were vigorously attacked.
Whilst the action of the water on these materials is more a
matter of economy than of hygiene, the corrosion of lead pipes,
which are used in most cases for the conveyance of water inside
houses, is in the highest degree serious from the point of view of
OTHER PROCESSES
37
health, since lead passes into the drinking-water as a result and
is, even in the smallest quantities, inimical to health.
In practice three methods are used for the removal of free
carbonic acid.
1. The water is allowed to flow through limestone (HeyerScheelhaase) . The free carbonic acid is thereby converted into
calcium bicarbonate according to the following equation :
CaCO3+H2O+CO2=Ca(HCO3)2.
By this method, therefore, hardness due to carbonates is in
creased. Where the water is of itself very soft this increase in
hardness is not harmful, and may even be desirable. If, however,
the water is already fairly hard, the increase in hardness might
be a disadvantage. Besides, the removal of carbon dioxide by
means of limestone is not accomplished in such cases, or only
incompletely. The method is in use on a large scale in Frankforton-Maine for the removal of the free carbonic acid from Stadtwald water of 1-5° hardness, and containing 30 milligrams CO2
per litre. It had caused great trouble in the new deep reservoirs
of Sachsenhaus, and also in the mains. The hardness of the water,
when freed from acid, amounts to about 50.
As the Frankfort plant for removing carbonic acid has proved
excellent, it may be shortly described as follows (see Fig. 8) :—
In the years 1906-7 the plant for removing carbon dioxide
was erected at a cost of 78,000 marks (about £3900) in the
Chamber A of the deep reservoirs of the Sachsenhaus plant.
Seven of the ten passages of the chamber were employed for
the neutralising process. The first serves as an inlet chamber,
the second and third as sand filters, and the four following as
limestone scrubbers.
From the inlet chamber the water is distributed through per
forations in the partition-wall on to the sand filter, which only
serves to retain the particles of ferric oxide carried along out of
the pressure tubes. The velocity of filtration amounts to 80 m.
in 24 hours. The filtered water passes through openings to the
base of dividing-wall, and with the help of distributors passes
under the limestone scrubber. The limestone scrubber is com
posed of a layer of flints at the bottom, over which rests a layer
of gravel, and then four layers of limestone in different states of
division, namely, about the size of walnuts, beans, peas, and
38
WATER PURIFICATION
coarse sand. Each of the first three layers is 3 inches high, the
height of the fourth being 2 feet. The velocity of water in the
scrubber reaches 40 metres (130 feet) in 24 hours. The water,
when neutralised, flows partly through an opening in the partitionwall between sections 7 and 8 to the last three sections of Chamber
A, and partly through a special pipe to Chambers B, C, and D
of the reservoir. About every three months the sand filter has to
be cleaned, by being washed through with water in the reverse
direction from the bottom upwards.
With about 5,000,000 gallons of water neutralised daily,
approximately i\ tons of limestone are dissolved by the water
and carried away.
2. Caustic soda, or sodium carbonate, is added to the water
in calculated amount, according to the estimation of carbonic acid
(Heyer). The free carbonic acid is converted to the bi-carbonate.
CO2 + H2O + Na2CO3^2 NaHCO3.
This method was introduced by Heyer to neutralise the drinkingwater in Dessau. In the eighth decade of last century a large
number of persons became ill through lead poisoning. Heyer
perceived that the capacity to dissolve lead was due to the
amount of free carbonic acid present. After various other
experiments he finally proposed the neutralisation of the water
with caustic soda and sodium carbonate.
There are many types of apparatus for measuring the amount
of chemicals to be added. It is stated and agreed concerning
this method that it makes the carbonic acid quite harmless. The
general public, however, has generally an instinctive aversion
towards a drinking-water treated with chemicals. This fact is,
doubtless, the main objection to this otherwise good system.
3. If a water containing carbon dioxide is allowed to rain
down in a fine state of division, or allowed to trickle slowly over
coke, glass, gravel, etc., it is freed from carbon dioxide.
With larger amounts of carbon dioxide present, the raining
process has to be repeated many times to remove the carbonic
acid. Further, the height of the fall has an influence. The
removal of carbon dioxide in this way is disadvantageous for the
reason that the water is greatly enriched with oxygen. A water
rich in oxygen is also not good as, in its turn, it causes severe
rusting of the iron pipes.
40
WATER PURIFICATION
H. Wehner has now advanced the idea of effecting the trickling
process in a vacuum. According to the accounts of the inventor,
not only ought the carbon dioxide to be removed more rapidly,
and with less height of fall necessary, but also, simultaneously,
the amount of oxygen should be considerably diminished.
Wehner's vacuum process is to be used in some English and
German towns.
II. PURIFICATION OF DRINKING-WATER ON A
SMALL SCALE.
The greatest advantage of a central water supply is this, that,
owing to the size of the project, there are more extensive pre
liminaries for securing a water free from any objection, greater
certainty for carrying out the process according to conditions,
and greater possibility of expert supervision of the process,
so that disturbances are easily recognised and prevented.
Over and above this there exists in all small-scale purification
processes the main weakness that the points of preference named
above with regard to large-scale operations are either non
existent or are not sufficiently assured.
Isolated houses, estates, establishments, etc., would do well,
therefore, to choose for their water supply, water free as far as
possible from any objection, and not needing any purification.
Should unforeseen circumstances intervene, making the water
of a central water supply, or even a single supply, seem doubtful,
then methods of purification on a small scale can find application.
Of first importance is boiling of the water before use.
Moreover, the employment of purification apparatus on a small
scale is to be regarded as a makeshift, since it should be con
stantly controlled to determine whether it works well and
continuously. This, naturally, in the majority of cases, cannot
be accomplished.
Circumstances like epidemics, war, journeys in unknown or
quite uncivilised lands, constitute an exception. In such cases
it is often impossible to procure water free from objection. The
small amount of water necessary, comparatively speaking, on
such occasions can be purified with sufficient certainty by the
aid of purification methods on a small scale. This is all the more
SMALL OR HOUSEHOLD FILTERS
41
true when, as, for example, in wars, or in times of epidemic,
the necessary personnel is at one's disposal. The observance of
the regulations can then be supervised.
This review of apparatus for water purification on a small
scale naturally refers only to methods which aim at the removal of
bacteria. Of apparatus for removing substances prejudicial to
the appearance of the water, such as iron, etc., there are also
many on a small scale, as already set forth above, and it appears
that the small apparatus has the same action as the corresponding
apparatus on the large scale.
(i) Purification by means of Small or Household Filters.
The household filter serves a double purpose : firstly, it removes
suspended matter and makes the water clear ; secondly, it is
used for retaining bacteria also. Household filters are much
less germ-tight than sand filters. The bacteria are washed
through the filter if it is not very frequently cleaned, and not
infrequently does it happen that the filtered water is richer in
bacteria than the raw water. Small filters, therefore, are to be
used with great caution.
The number of different forms of domestic filters is legion.
They are all based on the filtration of the water through some
porous material with or without the employment of increased
pressure. Von Esmarch divides them into the following groups : —
(a) Charcoal Filters.
These are the oldest form of apparatus of this kind. They are
composed of plastic retort carbon or finely sieved charcoal,
powdered coke, and compounds of the most varied preparations.
They generally cost between 30 and 70 shillings each.
Charcoal filters are scarcely used nowadays, since their bacterio
logical effect is practically nil. Indeed, if a charcoal filter is in use
for some time, the filtrate is often worse than the raw water, since
the bacteria which have remained behind in the charcoal have
increased considerably, and are then carried along with the
stream of water passing through. Also, as regards the removal
of turbidity these filters are of little use.
42
WATER PURIFICATION
(b) Stone Filters of Sandstone, Pumice, and the like.
The stone is burnt from coarse or fine sand, quartz, lime, and
magnesium silicates. For nlters that work without pressure
coarse material is used, whilst for pressure filters extremely fine
material is employed.
The clarification of the water may be rather good with such
apparatus. The bacteria, on the other hand, go through the
filter fairly readily, at the latest after two or three days. The
productivity of the filters is generally small, usually about 1 litre
per hour. Frequently the yield falls off quickly also, and cleaning
then becomes necessary.
(c) Asbestos Filters.
Asbestos of very fine fibre is used as the filtering medium, and
is employed as a pulp, or compressed or mixed with other
materials. Asbestos filters are also used in technical work for the
filtration and clarification of turbid liquids (beer, oil, wine, etc.),
and for the retention of ferric oxide in iron-removal plants.
The filter of C. Piefke and the micro-membrane filter of Friedrich Breyer are capital asbestos filters. Asbestos filters retain
bacteria fairly well ; but in general they choke up very quickly ;
this necessitates frequent cleaning and sterilisation of the appara
tus, which takes up much time.
According to Gartner, Breyer's micro-membrane filter ought
to be germ-tight.
Good asbestos filters are supplied by the firm of Arnold and
Schirmer, 123 Grosze Frankfurter Strasze, Berlin, N.O., or by
H. Jensen and Co., 20 Reichenstrasze, Hamburg.
(d) Clay Filters.
Of these filters there are likewise a number of different speci
mens as, for example, those of Olschewski and Hesse. They only
filter free from bacteria for a short time. The greater the yield
of water the shorter time are they germ-tight.
(e) Porcelain Filters.
The principal example of this type of filter is the Chamberland
;T\ilter.. : Ii consists of a metal cylinder, which can be screwed on
SMALL OR HOUSEHOLD FILTERS
43
to the water-tap. Inside the cylinder there is fastened an inner
hollow mould, made of fine porous kaolin and attached to the
cylinder so as to be water-tight. The water enters between the
outer shell and the porous mould, penetrates inwards through
the porous cylinder, and flows away through the opening situated
underneath.
The filtrate is bacteria-free and so the yield of the filter is
small, amounting after a few days to but a few litres per day.
The apparatus is cleaned by boiling and thoroughly heating
the dried apparatus. The purified filter then regains its original
productivity.
The Chamberland Filter can be obtained from the firm of
Lautenschlager, Dramenburger Strasze, Berlin.
(/) Kieselguhr Filters.
The chief representative of these filters is the Berkefeld Filter,
which is constructed on the same principles as the Chamberland
Filter, but is composed of baked infusorial earth (see Fig. 9).
They filter free from bacteria for various lengths of time, as a rule
several days. They generally yield from £ to 2 litres per minute
at a pressure of 1 to z\ atmospheres. Gradually the yield
diminishes, but it can be raised again to just the original amount
by brushing the cylinders clean. They can be sterilised by simply
warming slowly on the water-bath.
The filters are, as far as freedom from bacteria and yield are
concerned, certainly the best small filters. With daily sterilisa
tion one can rely with tolerable certainty on a filtrate continuously
free from bacteria.
The price of a filter for attaching to the water-tap in houses
is from 30 to 35 shillings ; smaller types from 13 to 16 shillings,
and as pump filters from 46 to 200 shillings. The price of a repair
cylindrical mould is 4s. 6d., of an army filter (yielding \ litre
per minute) 30 shillings, and a transportable pump £8. The
filters can be obtained from the Berkefeld Filter Co., Celle
(Hanover).
P. Schmidt has studied the mechanism of bacterial filtration
with Berkefeld Filters. He finds that the effective size of the
pores in Berkefeld Filters (with Liliput moulds) is probably about
0.5 /j.. By finely grinding Berkefeld Filters choked :up with
44
WATER PURIFICATION
bacteria, it was shown that the choking only takes place on the
surface of the filter, so that complete cleaning is possible in the
mechanical way by reversal of the water-current.
Staphylococcus and organisms of about that size never pass
through the filter, but, on the other hand, a number of small
bacteria pass through in measurable amount if they are washed
F1g. 9. Berkefeld K1lter.
along in the water in very large quantities. Schmidt is of the
opinion that for the passage of bacteria through a filter their size
is of
In primary
general, importance,
according to
andKonig,
their mobility
the capacity
next in
of importance.
a domestic
filter to retain bacteria depends : (1) on the nature of the filtering
medium ; it must be uniform, with the pores not too big ; (2) on
the water-pressure ; this should not be more than 1 to 2 atmo
spheres; And should not act jerkily, since such pressure assists
BOILING THE WATER
45
the passage of bacteria through the filter ; (3) on the amount of
pollution in the water ; the more suspended matter a water
contains, the more quickly does the filtrate cease to be free
from bacteria ; high temperature also assists the passage of
bacteria.
Generally speaking, the more germ-tight a filter is, the less
productive it is also.
(ii) Boiling the Water.
All vegetative forms of bacteria are killed by long-continued
heating of water at the boiling-point. Those bacteria which form
endogenous spores withstand, of course, for the most part, the
process of boiling, but even they are considerably weakened.
The pathogenic varieties coming mainly into consideration—
cholera and typhoid—form no endogenous spores. For this
reason boiling has been employed with advantage for the sterilisa
tion of drinking-waters on a small scale.
If larger quantities of water have to be boiled—for families,
hospitals, schools, factories, ships, etc.—and if this sterilisation,
as for example in times of epidemic, has to be undertaken for
a long time, then the following apparatus, according to von
Esmarch, are to be recommended : —
(a) The apparatus of the German Continental Co. (Deutschen
Continentalgesellschaft), of Dessau, for gas-heating, yields
61 gallons per hour, using 10-5 cubic feet of gas (price £3 15s. od.).
(b) An apparatus by Grove, Friedrichstrasze, Berlin, also for
heating by gas an attachment to the water-pipe. This apparatus
yields 15 to 22 gallons per hour with 14 cubic feet consumption
of gas (price £15). The water flowing out is about 50 warmer than
that flowing in.
(c) Apparatus by Siemens and Co., Berlin, yields about 8 gallons
of water hourly ; 100 gallons require 80 cubic feet of gas. The
price is £2 5s. od., or, with a control apparatus which is to be
recommended, £3 15s. od. The effluent water is from 5 to 1o°
warmer than the inflow.
(d) Apparatus by Schaffer and Walcker, Berlin, for gas-heating,
yielding 6 to 8 gallons per hour.
(e) Apparatus of Pape and Henneberg, Hamburg, for burning
gas, petroleum, or coal with automatic self-regulation of the
inflow. The smaller apparatus yields 55 gallons hourly, and costs
46
WATER PURIFICATION
£38; 220 gallons of water require about 300 cubic feet of gas, or
28 lb. of coal.
(/) Apparatus by C. Aug. Schmidt and Sons, Hamburg-Uhlenhorst. The firm supplies apparatus for houses, hospitals, etc.,
also with automatic self-regulation of the inflow. For a yield
of 20 to 30 gallons per hour the apparatus costs £37 to £60
(see Fig. 10).
F1g. 10. Apparatus for Bo1l1ng Water of the F1rm of
Aug. Schm1dt and Sons, Hamburg-Uhlenhorst.
(g) Transportable apparatus of Rietschel and Henneberg,
Berlin, for the use of armies and in case of epidemics. The plant
yields about 66 gallons per hour ; smaller portable apparatus
can be had, yielding 20 gallons per hour.
As against filtration, purification of drinking-water by boiling
has the following disadvantages :—
(1) It only kills the bacteria, and does not remove the suspended
matter.
SMALL OZONE PLANTS
47
(2) The upkeep of the apparatus is expensive.
(3) As a result of loss of gases and salts, and as a consequence
of the rise in temperature, boiled water is generally much less
palatable than filtered water.
As opposed to these disadvantages there are the following
points of preference : —
(1) The productivity remains continuously the same, whilst
with filters it falls away.
(2) Boiling the water renders the destruction of disease germs
absolutely certain. It is, on this account, the best of waterpurification methods in this direction.
(iii) Small Ozone Plants and Ultra-Violet Light Apparatus.
The ozone method of sterilising drinking-water, as set forth
previously, has proved itself good in central water supplies.
Lately, various firms, especially the firm of Siemens and Halske,
have constructed small ozone plants for sterilising smaller
quantities of water for communal and private industrial concerns,
as well as for the purpose of supplying drinking-water to troops
in the field.
Both stationary and transportable small ozone plants have
been designed.
They are used in the Munich Brewery, for the purification of
the water used for cleansing vessels and for similar purposes.
Transportable ozone plants are employed for the supply of water
to troops in the field. Such plants were used by the Russian
authorities in the Russo-Japanese war, and their use for military
purposes is said to be under consideration by various other
Governments. The whole apparatus is lodged on two waggons,
the machine-waggon and the sterilisation-waggon.
In practice the raw water is brought, by means of a water-pump
on the machine-waggon, through a thick suction and pressure pipe
to a filter, and from there to the sterilising-tower. The filter and
tower are on the sterilising-waggon. Through a thinner airsuction and pressure pipe the air passes from bellows on the
machine-waggon into the ozone apparatus on the sterilisingwaggon, and from here passes to the base of the sterilising-tower.
By means of a cable the primary current of an alternating-current
machine on the machine-waggon is conducted to the transformer
48
WATER PURIFICATION
on the sterilising-waggon, which is set up directly underneath the
ozone apparatus to generate the requisite working-tension.
Each waggon requires one horse, and weighs about 1 ton.
The plant yields 400 to 600 gallons per hour, and requires for
the process about 2 horse-power.
For safety the ozone is generated in such excess that with
very dirty water only one-third to one-half is consumed.
The apparatus was tested by Proskauer, the Russian hygienist
and bacteriologist, K. Kressling, and a Russian military com
mission prior to its despatch to the seat of war in Manchuria. The
results of these tests were very satisfactory.
M. Neiszer made a report on experiments with two ozone
plants for work on a small scale, which were placed at his disposal
by the firm of Felten and Guilleaume-Lahermeyer-werken A.G.
of Frankfort-on-Maine.
In both apparatus the ozone was generated by current
from the supply for lighting purposes. The mixing of the ozone
with the water was effected by means of an aspirator attached
to the water-tap.
Opening the water-tap started both the generation of ozone
and its mixing with the water. The ozone generator consists
of a 120 to 5000 volt high-tension transformer enclosed in a
protecting box, with plate condensers. The ozone generator
is attached to the town supply (120 volts, 45 periods) and con
sumes 0-55 ampere. The amount of ozone generated is about
5 to 6 milligrams per litre of air, with about 2 litres per minute.
The experiments were conducted with staphylococcus (Staph,
pyog. Aur.) and with bacterium coli. They showed that with
suitable water (no suspended matter, no iron, and little organic
matter), thousands of bacteria per cubic centimetre can be killed
with certainty, provided they have a resistibility intermediate
to that of staphylococcus and bacterium coli. It is important to
observe that when mixing was intimate, and when sufficient
quantity of ozone was used, momentary contact was sufficient
to kill the germs.
Further, the firm of Siemens and Halske have designed, as a
result of their previous experience, a sterilising apparatus, making
use of ultra-violet light rays, for affixing to the domestic supply
and also for single water-supplies. Their contrivance is character
ised essentially by a mechanism whereby, on turning a single
REMOVAL OF IRON FROM WELLS
49
handle, the lamp is set working through being tilted, and at the
same time the water-tap is opened. An electro-magnet is further
provided which only allows a flow of water through the apparatus
when the lamp is properly alight. Also, if the lamp goes out
during the process the water-inflow tap immediately closes, so
that water which has not been sterilised cannot be drawn from
the apparatus.
(iv) The Removal of lion from Single Wells.
The methods of iron removal, using small plants, whether it
be for the purposes of a central water supply or for industrial
application, have already been discussed on page 32 and
the following pages.
There remain still to be mentioned
those methods which serve especially to remove iron from
single wells.
The oldest and simplest method of removing iron from wellwater is to pour into the well iron-free water which has taken up
oxygen (generally by standing in the air). The oxygen precipi
tates the iron as hydroxide, which then settles to the bottom.
Water can in this way be freed for many days from the iron it
contains. The chief disadvantage lies in the fact that the
precipitated iron remains in the well. In addition to this the
water poured into the well should, of course, be hygienically
free from any objection, which it never is.
For this purpose the Dunbar Filters are very suitable. Of such
filters the simplest and cheapest construction consists of a tub
filled with sand, having a tap in the side at the bottom. The
water is allowed to flow out of the pump on to the sand. The ironfree water is removed through the tap underneath. About every
three months the sand must be freed from the precipitated
oxide of iron by washing. Such an arrangement is not suitable
to wells situated in the open, since they are liable to freeze.
Still, this objection can be overcome, as the whole plant can
be housed against the frost in a special small hut.
The Deseniss and Jacobi system of so-called bastard pumps
(see Fig. 11) differs from all other systems in this, that by means
of a pump the water is taken from the well already freed from
iron. All intermediate apparatus, such as scrubbers, clarifying
reservoirs, etc., are therefore not required.
E
50
WATER PURIFICATION
The following is the arrangement and method of working such
pumps : To the pump employed for raising the water there is
attached a second cylinder of double the circumference of the
cylinder of the water-pump. In both cylinders there move
F1g. 11. The Bastard Pump
of Desen1ss and Jacob1.
tightly closing pistons, provided with valves and fastened to
a piston-rod. The water streaming in from the lower cylinder
to the one above, since the latter has double the capacity of the
former, is thus mixed with an equal volume of air, sucked in
through a valve laterally placed in the higher cylinder. After
being mixed with air the water is forced on to a forged-iron filter,
carrying sand of 0.5 millimetre grain as filtering material. It is
thereby freed from the hydroxide of iron that has been formed.
The filter can be set up in a small shaft standing in close proximity
to the pump, or it may even be placed in the pump uprights
itself.
It is not necessary to renew the filter layer at all ; the purifica
PURIFICATION FOR TECHNICAL PURPOSES
51
tion of the filter is effected by temporary automatic flooding
in the reverse direction, and is attained by simply reversing the
stop-cocks.
Schreiber has tested this method in an experimental plant, set
up in the chief pumping-station of the Charlottenburg ground
water works. He finds that the pump removes even the last
traces of iron, or at most leaves an inconsiderable amount behind.
It further fulfils all the demands made upon a hand-pump as
regards simplicity in construction, slight supervision, and pro
tection against pollution.
Moreover, the bastard pump is not only supplied for hand
work, but also for working by machinery.
According to the declarations of the firm, the removal of the
iron should be alike complete with a hand-pump of usual size,
or with a large-scale plant yielding many thousands of litres per
hour.
B. Purification of Water for Technical Purposes.
Besides the use of natural water for drinking purposes, water
is needed for almost all human occupations. In most cases with
a natural water purification is not necessary for technical pur
poses, since the demands made upon the quality of such a water
are naturally less than with a drinking-water.
For cleansing public urinals and lavatories, for fountains, and
for watering the streets and gardens, untreated river-water is
frequently used. Where the river-water is very dirty, at most
a coarse gravel filter is employed, and this simply serves to retain
suspended matter, but not, as is the case with drinking-water,
the bacteria. Many towns, like Frankfort-on-Maine, have along
side the drinking-water pipe, one for river-water, which serves
the purposes mentioned.
For many industrial purposes the water, however, must undergo
treatment. For example, in paper manufacture, the presence of
iron is troublesome, since iron forms a compound with cellulose
and makes the paper spotty. The removal of iron in such cases
is effected in small iron-removal plants, which have already been
described on page 32 and the following pages. In many industries
—for example, with laundries, dye works, and others—hard water
is a great disadvantage, as a part of the working material is
52
WATER PURIFICATION
precipitated by the constituents causing hardness, and is thereby
rendered useless. Hence, for such purposes the water must be
softened. Quite generally, however, the softening of water
plays a large part in industry, owing to the use of water in boilers.
The Softening of Boiler-Feed Waters.
The hardness of a water is due to the calcium and magnesium
salts dissolved in it. A distinction is drawn between temporary
hardness, or hardness due to carbonates, and permanent hardness,
or hardness due to mineral acid salts. Carbonate hardness is
caused by the bicarbonates of calcium and magnesium which,
unlike the normal salts, are soluble in water. On boiling the water
these bicarbonates give up half their carbon dioxide in the free
state, change to the normal salt, and therefore become insoluble.
The observation that a part of the hardness of water disappears
on boiling has earned for such hardness the title of temporary
hardness.
Permanent hardness is due to the presence of the salts of cal
cium and magnesium with sulphuric, hydrochloric, and nitric
acids, and therefore to calcium and magnesium sulphates,
chlorides, and nitrates.
Hardness is measured in German or French degrees of hardness.
10 on the German scale is equivalent to 1 mg. CaO or 074 mg.
MgO per 100 c.cs. of water. 1° on the French scale is equivalent
to 1 mg. CaCO3 or 0-84 mg. MgCO3 per 100 c.cs. water.1
If hard water is used for feeding boilers, in process of time there
settles on the boiler plates a scale, consisting of precipitated
calcium and magnesium salts. With a large amount of tem
porary hardness, there further results in the boiler a big sludge of
loose, precipitated normal calcium carbonate. The troublesome
effects of this boiler scale are well known. In the first place, once
a boiler scale has reached a certain thickness, the conductance of
heat to the water is greatly hindered, and so coal is consumed
very uneconomically. Boiler scale can also lead, however, to
the direct deterioration of the boiler plates, since the scale
possesses a different coefficient of expansion from that of the
boiler plates. In this way fissures and cracks result. The
chlorides of lime and magnesium, when present in water in fairly
1 1° on the English scale is equivalent to 1 grain CaC03 per gallon. — Trans.
PURIFICATION FOR TECHNICAL PURPOSES
53
large amounts, are very troublesome as they are hydrolysed
with formation of free hydrochloric acid, which passes away with
the steam and attacks the equipment.
At the present time three methods are principally employed
for softening water, namely, the Lime-soda method, the Reisert
Baryta process, and the Permutit process.
The lime-soda method, as the name implies, consists in adding
to the water lime and sodium carbonate. The temporary hard
ness is removed, by the addition of lime, in the form of calcium
carbonate and magnesium hydroxide, according to the following
equations :—
1.
Ca(HCO3) , + Ca(OH) 2 = 2 CaCO3 + 2 H2O.
2. (a) Mg(HCO3)2+Ca(OH)2=CaCO3+MgCO3+2H2O.
(b) MgCO3+Ca(OH)2=Mg(OH)2+CaC03.
Permanent hardness is removed by means of sodium carbonate
according to the following equations : —
2.
1. (a) MgCl2
CaSO4 +Na2CO3 =MgCO3+2
=CaCO3 +Na2SO4.
NaCl.
{b) MgCO3+Ca(OH)2 =CaCO3 +Mg(OH)2 (Pfeiffer).
All calcium salts in the water are therefore precipitated in the
form of the normal carbonate ; all magnesium salts, no matter
in what form they are present (whether as temporary or per
manent hardness), are finally precipitated as the completely
insoluble hydroxide. Hardness due to carbonates is therefore
entirely removed from water by this method, but in place of the
precipitated salts causing permanent hardness, an amount of
sodium equivalent to the calcium and magnesium originally
present passes into the water as sulphate, chloride, or nitrate.
From the equations given it can easily be calculated that, for
each degree of temporary hardness, 10 g. of lime (100% CaO) are
needed to soften 1 cubic metre of water. Also it is obvious from
the equation that for each milligramme of magnesia present
in a litre of water, no matter what the form, 1-4 g. of lime (100%
CaO) must be added to a cubic metre of the water. For each
degree of permanent hardness 19 g. of sodium carbonate (100%
Na2CO3) are needed per cubic metre. In the measurement of the
quantity added, it is to be borne in mind that natural waters
generally contain some free carbon dioxide. Since carbonic acid
54
WATER PURIFICATION
combines with lime to form bicarbonate, which then, of course,
combines with more lime to form the normal carbonate, for every
milligram of free carbon dioxide per litre an addition of 1.27 g.
of 100% CaO must be made per cubic metre, in order to neutralise
this free carbonic acid. The addition of lime, therefore, must be
increased by such an amount for every milligram of free carbon
dioxide present.
From various investigations, however, the amount of lime to
be added, thus theoretically reckoned, proves to be too high in
practice. It must be cut down by about 20 to 25 per cent. Vari
ous reasons for this have been put forward.
Instead of calcium hydrate, caustic soda can be used. From
the bicarbonate there results sodium carbonate which, in its
turn, serves to remove permanent hardness.
Ca(HCO3)2+2 NaOH= CaCO3+Na2CO3+2 H2O.
Mg(HCO3)2+4 NaOH=Mg(OH)2+2 Na2CO3+2 H2O.
If precisely so much temporary hardness is present that the
sodium carbonate resulting according to the above equations
is just sufficient to remove the permanent hardness, then the
water can be completely softened with sodium hydrate. If
more permanent hardness is present, then the sodium carbonate
still required has to be added. If, on the other hand, there is too
little permanent hardness, only so much sodium hydrate should
be added as can form the amount of sodium carbonate requisite
for the removal of the permanent hardness. The remainder of
the unprecipitated carbonates must then be removed by means
of lime.
Formulae for reckoning the necessary addition of caustic soda,
sodium carbonate, and lime have frequently been given. If a
is the combined carbonic acid, b the total lime, and c the total
hardness expressed in equivalents of hardness, then the following
formulae of Kalmann give the necessary additions of caustic
soda, lime, and sodium carbonate :—
m=2a—b ;
n=c—a.
If m and n are positive, the water contains more temporary
than permanent hardness ; m is then the lime to be added, n the
caustic soda.
If 2a — b=o, there is present in the water as much temporary
PURIFICATION FOR TECHNICAL PURPOSES
55
as permanent hardness. No lime is then needed, but only n units
of caustic soda.
If 2a— b is negative, the water contains more permanent than
temporary hardness. There must then be added m parts of
sodium carbonate and c—a=n parts of caustic soda (Wehrenpfennig). .
The caustic soda is generally prepared by mixing sodium
carbonate solution with lime and allowing the precipitated
calcium carbonate to settle.
In ascertaining the necessary addition, if lime and sodium
carbonate be reckoned, and not caustic soda, precisely the same
amounts require to be added as were given above, on page 53,
for lime and sodium carbonate. Therefore, with caustic soda
as the softening agent, the numbers given with respect to lime
and sodium carbonate can be adhered to.
The lime-soda process is the oldest, and doubtless, also, has
the widest practical application at the present time. Softening
with lime and sodium carbonate never attains o0 hardness, but
generally only about 30 to 40, which, however, is quite sufficient
for general requirements. There are numerous firms who construct
softening plants of the lime-soda type, which are used with the
greatest success in practice. Among others are the firm of
Humboldt in Kalk, Dehne in Halle a. S., Reisert in Cologne, and
the " Voran " firm of Frankfort-on-Maine. Figure 12 represents
a lime-soda softening plant, " Voran " system.
This plant may be briefly described as an example of a lime-soda
softener.
The automatic water-purification apparatus of the " Voran "
System (Model BI) consists essentially of reservoir A, divided into
three parts by means of partition-walls, the clarifying tank B,
the lime saturator C, the sodium carbonate regulator D, and the
filter of wood shavings and wood-wool arranged under the
clarifying tank B.
The raw water which is led into the apparatus through the
pipe E next flows through the discharge pipe F into the part of
the tank A set aside for the raw water.
In this section, at equal heights, are placed two stop-cocks
G and H, through which the raw water can flow away. The
larger portion goes, through the stop-cock G and the pipe Gx,
directly to the funnel-shaped central portion I, in which it
56
WATER PURIFICATION
takes up a violent whirling motion owing to its tangential
entry.
The smaller quantity of raw water, arranged exactly according
to the amount of lime-water required, flows through the stop
cock H and the discharge tube H: to the lime saturator C, to the
bottom of which it is led through the central funnel-pipe H2 in
order that it may pass into the saturator equally distributed on
all sides.
From here on its way to the overflow K the raw water is com
pelled to percolate through the milk of lime which, since it is
specifically heavier than water, has settled to the bottom. The
PURIFICATION FOR TECHNICAL PURPOSES
57
water is thereby itself completely saturated with caustic lime
and flows away at the top completely saturated and clear limewater, through the overflow-pipe K to the mixing-trough.
If the ratio of clear saturated lime-water to raw water is once
fixed, then it will always remain the same, whether much or little
raw water is flowing in, for the amounts of raw water flowing
through the two stop-cocks G and H should always be pro
portional.
The soda solution necessary flows from its particular part of
the reservoir A through a hair-sieve M and the attached pipe Mx
to the sodium carbonate regulator D, in which the inflow is
regulated by the float N. From the regulator D the sodium
carbonate solution passes to the mixing-trough through the
exit pipe Q, so arranged that it can be revolved, and which is
attached in its turn to the float R in the raw-water reservoir.
When the float R sinks the discharge-pipe Q is raised and the
discharge reversed.
If the raw-water section of the reservoir becomes empty at
any time, the float R will sink to the bottom, thereby raising the
discharge-pipe so high that no more sodium carbonate can flow
out.
On the other hand, the three streams of raw water, lime-water,
and sodium carbonate solution commence to flow simultaneously,
as soon as raw water flows into its particular section of the
reservoir.
By this means the amount of chemicals added always bears a
fixed ratio to the amount of raw water consumed, that is to say,
the apparatus is automatically self-regulating.
If too much raw water be led into the raw-water reservoir it is
run off by means of an overflow-pipe.
The lime-water and sodium carbonate solution, after mixing,
flow from the mixing-trough to the central funnel-shaped pipe
I, and of course meet the circular motion of the raw water there.
In this way an intimate mixing with the water is ensured, and
the commencement of the reaction is hastened. It is especially
advantageous for the rapid progress of the reaction to have the
cross section of the pipe I wide at the top and decreasing down
wards, since with a constantly increasing velocity of water a
stronger whirling motion is produced and a more intimate mixing
ensues.
:
58
WATER PURIFICATION
After leaving I the water is reversed in direction and then
distributed uniformly in the reaction space and clarifying portion
B. Owing to the comparatively large cross section of the chamber
the water rises to the top with very slow velocity, and on this
account is freed as far as possible from fine suspended matter.
The greater part of the sludge does not alter its- direction with
the water, but in consequence of its higher specific gravity sinks
to the bottom. It settles there in the sludge tank T, from which
it can be withdrawn as required through the stop-cock T.
The water rising to the top of the clarifying space B, by the
time it has reached the discharge-pipe U, has allowed the greater
part of the insoluble precipitated components to settle out.
Consequently through the discharge-pipe M, water carrying
only floating particles passes to the underneath side of the filter.
These remaining particles are retained during the passage of the
water through the filter, with the result that the water leaves
the apparatus at Uj softened and filtered, to be led away to the
place of consumption.
The wood-shaving or wood-wool filter will only need cleaning
or renewing at long intervals of time, perhaps after six to twelve
months, since it is only very slightly used. Renewal should
easily be effected at a cost of a few shillings.
The disadvantage of the lime-soda process is simply this, that
in place of permanent hardness, as has been already mentioned,
an equivalent amount of sodium salts passes into solution.
These sodium salts are, of course, quite neutral and readily
soluble in water, but in course of time attain to such a strong
concentration in the boiler that they cause inconvenience. The
salts crystallise at the valves, irregular boiling of the water
occurs, and so on. The lye must then be blown off. A further
disadvantage of the process is this, that with the addition of too
much lime and sodium carbonate the boiler plates may be
attacked. Generally, however, with frequent checking of the
pure water produced, the process can be worked in such a way
that just the right amount of substances is added. Blacher
rightly calls attention to the fact that it is not sufficient to control
only the softened water, but that the control must extend also
to the water in the boiler. For, even if only a slight excess of
the reagents be present, these excesses are concentrated in the
boiler in such a way that the boiler plates will be attacked.
PURIFICATION FOR TECHNICAL PURPOSES
59
According to Blacher it is considered permissible for the water
to contain up to 30 of permanent hardness and excess of sodium
carbonate up to 57 milligrams Na2CO3 per litre.
The Reisert Baryta process for softening water removes
temporary hardness by means of lime exactly as in the first
named process. The most troublesome permanent hardness in
boiler-water is due to gypsum, as this yields hard boiler scale,
which adheres very tenaciously to the boiler plates. The Reisert
method is therefore confined to the removal of that permanent
hardness due to gypsum, and this is effected, of course, by the
addition of barium carbonate. Barium carbonate is practically
insoluble in water. It is deposited in the water, care being taken
that it remains in contact with the water for a period of time,
during which the following decomposition with the calcium
sulphate takes place :—
CaSO4 + BaCO3 = BaSO4 + CaCO3.
Gypsum and barium carbonate are therefore converted into
insoluble calcium carbonate and completely insoluble barium
sulphate. The lime necessary is naturally the same as in the
lime-soda process, no matter what the amount of barium car
bonate is. Also, the whole of the magnesia is finally precipitated
as hydroxide, so that it holds in this case also that each milli
gramme of MgO present in the water requires double the amount
of lime. Therefore, for each milligramme of MgO per litre the
amount of lime to be added per cubic metre must be raised to
1 .4 grammes of 100 per cent CaO, according to the methods of
estimation on the basis of hardness discussed previously.
The chief point of preference in the baryta process lies in the
fact that the sodium carbonate, which when present in con
siderable excess in the softened water acts very corrosively on
the equipment, is done away with. Since barium carbonate as
mentioned is practically insoluble in water, the baryta process
possesses the further advantage that the addition of carbonate
may be liberal. An excess of barium carbonate is thrown into the
water, which is then allowed after a certain time to settle free
from the undissolved matter, whereupon it can be employed
immediately. An excess of barium carbonate is impossible in
the water softened. Further, in the baryta process, another
inconvenience mentioned in the lime-soda process disappears.
60
WATER PURIFICATION
In that process in place of the permanent hardness sodium
salts enter the water. By the baryta method the temporary
hardness and that due to calcium sulphate is removed practically
quantitatively. It can therefore be said of this process that there
is less risk of corrosion in the boiler than is the case with the
lime-soda process.
Against these advantages of the baryta process there stand a
number of disadvantages. Only sulphate hardness and not that
of chlorides or nitrates is removed with barium carbonate. It
is consequently only applicable to water which does not contain
these salts in appreciable amounts. Waters containing alkali
sulphates cannot be softened by the baryta process, since in this
case sodium carbonate would be formed by the interaction of the
barium carbonate with the alkali sulphates, according to the
following equation :
Na2SO4 + BaCO3 = Na2CO3 + BaSO4.
Sodium carbonate would therefore be present in the softened
water, would get into the boiler and ruin it.
The most recent method used in practice is the Permutit
method. Permutit is a complex compound of sodium, aluminium,
and silicic acid. Such compounds occur in nature as zeoliths.
Permutit is the name for the artificial product obtained by
melting aluminium silicate with sodium carbonate, and has
the peculiar property of removing lime, magnesia, manganese,
or iron from water when such water is slowly filtered over it.
At the same time equivalent amounts of sodium are given up to
the water. The process would scarcely have come into practical
consideration at all if it had not been discovered simultaneously
that permutit or zeolith, through which water has been filtered
for a long time, and which has quite lost its softening capacity,
can be easily regenerated by washing it with a solution of common
salt. Thus the process can be reversed. The bases removed
pass back into solution, and in their stead sodium from the
common salt passes into the compound. The product so washed
is precisely of the same utility as the original, and after working
itself out again can be regenerated anew.
The advantages of the process are manifest. Above all, the
process is extraordinarily simple to manage. It is simply a
question of filtering the water to be softened through a layer of
PURIFICATION FOR TECHNICAL PURPOSES
61
permutit of a certain depth at a velocity determined by tests.
Unlike the two softening processes previously mentioned, which
both reduce the hardness only to about 3 to 40, with methodical
control the softening in this process readily reaches o0. A further
advantage is naturally that the necessity for the addition of
definite amounts of reagent is obviated. The main disadvantage
of the process lies in the fact that with water rich in carbonates
(and most hard waters are rich in these salts), in place of the
substances removed an equivalent amount of sodium bicarbonate
enters. In the boiler the sodium bicarbonate gives up half its
carbon dioxide and is converted to the normal salt. There will
therefore be constantly present in the boiler water containing
sodium carbonate which may cause corrosion as already men
tioned.
The method is employed, as previously noted, not only for
softening, but also, especially of late years, for removing iron
and manganese from waters.
Softening plants of the Permutit type are supplied by the
Permutit Filter Co., Berlin.
For the correct working of a softening plant, expert super
vision, by examination of both the softened and the boiler water,
is of the utmost importance. Blacher a short time ago suggested
a very subtle method, by the aid of which exact insight can be
obtained into the existing conditions in boiler management.
The method consists in finding out the acid required to neutralise
the boiler water by titration with
acid, first using phenol
phthalein and then methyl-orange as indicator. In addition the
total hardness is estimated with potassium stearate and phenol
phthalein. From these three values, which can be obtained in
quite a short time, one is in a position to suggest how the water
is constituted. Professor Blacher has constructed a box for
testing raw water, softened water, and boiler-water, which with
the accompanying instructions can be obtained at a cost of
25 shillings from the Vereinigten Chemischen Fabriken fur
Laboratoriumsbedarf of Berlin.
Every boiler user is warmly
recommended to provide himself with one. The necessary experi
mental work can be learned by an intelligent foreman.
In conclusion it may further be pointed out that the so-called
boiler-scale preventatives which are often recommended are
very much advertised and overrated. In the majority of cases
62
WATER PURIFICATION
they are crude swindles, for it is self-evident that substances like
sugar, starch, and others are not such as would prevent boiler
scale. Of late, remedies have come into the market whose action
depends on simultaneous deposition of the medium along with
the boiler scale, whereby the scale is of a softer nature and more
easily removed. It is not impossible that such a remedy might
actually be successful, but a certain amount of scepticism exists
in regard to them. The most rational method of protecting
oneself against damage due to the formation of boiler scale is
always a properly managed softening plant.
SEWAGE
DISPOSAL
THE SIGNIFICANCE OF RIVER POLLUTION AND THE
IMPORTANCE OF SEWAGE DISPOSAL.
A LL water, whether for drinking or domestic purposes generally,
lx or whether employed in cleansing, washing, and industrial
processes, when not consumed through leakage, evaporation, or in
some such manner, eventually becomes sewage. Unlike purified
water, or even a natural unpurified surface-water, sewage varies
considerably in composition. It contains suspended and dis
solved organic and inorganic matter in more or less large quanti
ties, and on this account is characterised by a muddy appearance
and frequently also by a foul odour.
The purification of sewage is quite recent in its origin. Even
up to a few decades ago short work was made of effluents.
Generally speaking, the water used in dwelling-houses wasv
conducted in ordinary open sewers to the nearest river.
The vast increase of large towns and the unexpected progress
of industry led to the most serious nuisances in this disposal of
sewage into rivers. The evil, which is every day becoming more
apparent, is both hygienic and economic.
Many large towns are dependent on river-water for their
water supply. As was explained in the previous section, the
bacteria are generally removed by means of a sand filter. Apart
from the consideration that the filter naturally cannot remove
dissolved filth, substances which owing to their origin may be
harmless seem to leave a water unappetising as a drinking-water.
Also a greater pollution of surface-water with sewage produces a
larger number of bacteria in the filtered water, since no filters
are completely germ-tight. This is all the more serious, as,
naturally, in sewage waters which contain all human excreta,
disease germs may very easily be present.
In those places where surface-waters are not used for the
63
64
SEWAGE DISPOSAL
water supply, river-water is nevertheless often used for baths,
washing, watering the streets, and similar purposes. All these
processes ought to be carried out without any danger to health.
It was shown by the Director of the Pasteur Institute in
Constantinople that cases of cholera that occurred in the year
1908 could be attributed to infection of the hands with the water
of the Bosphorus and the Golden Horn. Similarly it was medi
cally established with absolute certainty that a number of typhoid
cases in the French army had resulted through bathing in
polluted waters.
These examples show that river pollution may be very serious
both as regards washing and bathing. Apart, however, from
these direct dangers it is greatly to be regretted if river baths,
which in the view of experts are decidedly superior from the
standpoint of health to baths in closed rooms, are avoided as a
result of the foul and unattractive nature of the water.
Besides, a river polluted with sewage, choked with mud, or
even smelling badly, will excite in every normal man feelings of
repugnance and displeasure which may have economic results,
for the banks of such a river are avoided as places of residence.
Where a polluted river flows through or by a town, there is
always a danger of the river-banks depreciating in value.
In addition to the great economic disadvantages of the pollu
tion of rivers, harm also results in the destruction of fish. Often
the fish are ruined in large quantities by the introduction of
sewage into the river. The delicate and precious varieties
especially are very sensitive to pollution of the water, and very
soon disappear entirely with continued pollution. With certain
kinds of sewage containing substances of specific taste or smell,
the fish assume similar taste and smell. An embarrassing point
of social significance relative to this is, that lower middle-class
people, like fishermen and proprietors of baths, the protection
and maintenance of whom in these days of the capitalist on the
one hand and the proletariat on the other seems to be demanded,
are either annihilated or grievously injured economically. A
disadvantage too of river pollution, by no means insignificant
economically, is demonstrated also in this, that as a result of the
deposition of mud on the river-bed, expenditure has to be in
curred in dredging operations to remove the mud and in similar
processes of purification.
RIVER POLLUTION
65
Consequently the most diverse and weighty reasons have
constrained authorities in most civilised lands to face the problem
of excessive river pollution, and to require of towns and factories
adequate purification of sewage before disposal.
Self-purification of Rivers.
Up to a certain point, of course, rivers are able to purify
themselves from the filth that becomes incorporated. It is by
no means seldom that just beyond a town a river-course is seen
to be very dirty, but that a few miles further on the water has
already reassumed a good condition. This so-called self-puri
fication of rivers is explained as being due to a wonderful co
operation of physical, chemical, and, above all, biological forces.
The suspended matter deposited in a river by the sewage gradu
ally settles to the bottom as mud. Here it is disposed of by
snails, mussels, insect-larvae, beetles, worms, and other organisms,
which consume it, or by continually loosening it prepare it for
a gradual washing away. Since the organisms mentioned
represent the chief source of nourishment for the fish feeding on
the river-bed, it follows that they can never get the upper hand.
The dissolved organic matter which an effluent water carries to
a river, especially the more molecularly complex portions, and
therefore above all the albumens and their decomposition
products, are mainly decomposed by bacteria. There then
appear Ciliata, Rotatoria, and Infusoria, which in their turn
live on these bacteria. Green Algae also join in. These and the
previously mentioned groups are able to absorb dissolved
organic matter directly from the water. In the main, however,
the green algae provide for their own nourishment by assimilating
carbonic acid, nitrates and nitrites which again originate from
the activities of the bacteria, and from them with the help of
their green colouring matter, chlorophyll, they build up the
necessary albumens. During these processes of assimilation
oxygen is liberated, and this produces powerful aeration of the
water. This aeration accounts for the existence of the inhabitants
of the water already mentioned, and also for that of the more
highly organised parts. The green algae, rotatoria, ciliata, and
infusoria, etc., serve in their turn as food for the small watercrabs or water-fleas, and these again play quite a considerable
F
66
SEWAGE DISPOSAL
part as food for fish. So, finally, the sewage deposited in the
water is converted into useful fish.
Industrial sewage containing heavy metals deposits these as
insoluble sulphides or basic carbonates on the river-bed. Owing
to the bi-carbonates present in river-water many river-waters have
a considerable capacity for neutralising acid. The Maine, for
example, at Frankfort, shows an average alkalinity of about
3 cubic centimetres of normal acid per litre of water. Since with
the Maine at average height, 80 cubic metres of water pass
through its cross section per second, it follows that the amount
of water passing one point in twenty-four hours would be able
to take up in round numbers 830,000 litres or 500 tons of
concentrated 100 per cent sulphuric acid without the water
giving an acid reaction. For this it is, of course, presumed that
these amounts of sulphuric acid could mix thoroughly with the
amount of water under consideration, which naturally is not
possible. It always happens in the introduction of acids into
river-water that only a small portion of the river-water at dis
posal will mix with the acid effluent, and the consequence is that
the river-water becomes acid over a certain stretch.
The same limitation operates as regards what was said above
with respect to the biological self-regulating process. The
wonderful co-operation of all these forces and the accompanying
correct self-purification, are only attained in a satisfactory
manner when the amount of sewage bears a certain relation to
the purifying forces. If this relation is unsuitable the river-bed
becomes covered with mud and with foul suspended matter.
In the water, large amounts of putrefying bacteria appear, the
above-mentioned organisms do not get their requirements of
life and disappear. When this occurs important links in the
chain are wanting and the orderly co-operation of the whole is
destroyed. The water at these stages will assume a foul nature
and cannot sufficiently purify itself.
As a rule, good limiting values cannot be given as regards the
amount of sewage that a river can absorb. The amount of
effluent with which a river may be burdened without being
harmed is a question which cannot be decided generally, but only
from case to case with tests of all the factors coming into con
sideration. In the first place, for example, the composition of
the sewage varies greatly. Also, every river possesses its own
PURIFICATION OF DOMESTIC SEWAGE
67
specific biological activity, and with that its own specific
capacity for self-purification which varies from river to river.
Quite generally it may be said that a river can absorb more
sewage the more water there is present, and the greater the
velocity of that water. Demands as to purification of sewage
must be correspondingly stricter the smaller the flow of the river
into which it is to be conducted. On the contrary, large rivers,
containing much water affected by the tide, and having a swift
current, can fully absorb sewage that is only quite superficially
purified.
Sewage can be divided into domestic and industrial sewage.
Domestic sewage comprises, in the main, waters from dwellinghouses, containing therefore faeces, cleansing and washing waters,
kitchen refuse, and similar substances. It is therefore rich in
easily decomposable organic substances which very soon become
foul. Many towns, however, now receive large amounts of
industrial effluents into their sewage, and consequently in many
industrial towns the domestic sewage is often mixed with very
considerable quantities of industrial sewage.
The sewage from many industrial concerns is characterised,
as with domestic sewage, by a large content of dissolved organic
matter which causes it to putrefy readily. Many industrial
effluents have, however, quite a different composition. Definite
information on this point cannot be given, since it is dependent
wholly on the nature of the manufacturing process.
Although the particular methods of purification are capable
of equal application in their main features to both classes of
sewage, the, kind of purification necessary for normal domestic
sewage is always the same, while for industrial effluents, quite
frequently, variations in the processes occur, adapted to the
individuality of the sewage coming at the moment into question.
A distinction between the methods of purification for domestic
and industrial sewage is therefore to be recommended.
A. Purification of Domestic Sewage.
The different methods for the purification of domestic sewage
may be thus distinguished : —
Mechanical purification (rakes, screens, sieves, grease extractors,
grit chambers, settling-tanks, settling-wells, septic tanks, Travis
and Emscher wells).
68
SEWAGE DISPOSAL
Coal-pulp processes.
Artificial biological purification (contact beds and percolating
filters).
Land treatment (broad irrigation or sewage farming and
intermittent filtration) .
And lately also fish-ponds.
Mechanical methods of purification aim solely at the separation
of suspended matter. They have no action on dissolved sub
stances.
The coal-pulp method, on the contrary, has a small influence
on the dissolved matter, whilst the artificial biological processes
and land treatment remove dissolved substances so largely that
the water loses its capacity to putrefy. There is consequently
this distinction between sewage purified mechanically and that
purified biologically, that the former becomes foul on standing,
whilst the latter is incapable of so doing. Mechanical methods
of purification are therefore applied in those cases where, owing
to the nature of the river into which it is run, the sewage need only
be partially purified. Dilution with large quantities of riverwater prevents a mechanically purified sewage from becoming
foul. Where the ratio of river-water to sewage is small and the
dilution does not guarantee that the purified sewage will not
putrefy, biological treatment must be adopted, in which case land
treatment is generally superior to artificial biological processes.
I. MECHANICAL PURIFICATION OF SEWAGE,
(i) Rakes, Screens, and Sieves.
Apparatus of this nature serves to separate the undissolved
substances over a certain size. Of first importance are the
coarser floating substances such as paper, vegetable leaves,
orange-peel, match-boxes, corks, etc., which are removed from
sewage by this treatment. According to Fruhling, one under
stands by screens all the particular varieties of such devices for
removing coarse suspended matter, such as bear the particular
names of bar-screens, sieve-screens, grating-screens, etc. Barscreens consist of bars set parallel to one another, grating-screens
of wires crossing each other, and sieve-screens of a network of
wires or of perforated metal plates.
RAKES, SCREENS, AND SIEVES
69
There are both coarse and fine screens. Coarse screens are
mostly iron rods about 10 to 20 centimetres apart, obliquely
placed at an obtuse angle to the surface of the water. These
only serve to keep back the coarsest suspensions, such as tin
boxes, the larger pieces of wood, large pieces of entrails, large
rags, and the like.
Fine screens are generally stationary, or automatically moving
apparatus. Stationary screens are mostly bar-screens, also
consisting of bars laid alongside one another, and placed at an
obtuse angle to the surface of the water. The distance of the
bars apart is, however, considerably less than with coarse screens,
usually between 10 and 25 millimetres. The water flows against
these bars and leaves there substances of larger size. Movable
screens differ from the stationary type in that they are driven
through the water and fish out the floating material. Of the best
constructed and most frequently used movable bar-screens in
municipal clarifying plants (Frankfort, Elberfeld) is the Uhlfelder
Revolving Screen (Fig. 13). It is a circular revolving screen,
70
SEWAGE DISPOSAL
composed of five single screens, which rotate uniformly against
the current of water. The coarser matter floating upon or
suspended in the water is removed by the screens while in motion
and is raised out of the water. An automatic brush follows
which, pressing through the screen, brushes it outwards and casts
the material on to a platform underneath. This is then tipped
up by the motion of the screens and empties the contents on to
a travelling platform which carries the material away. With such
F1g. 14. R1en S1eve.
screens the work is purely automatic and the purification me
chanical. Other kinds of screens may be cleaned by hand.
Among automatically working sieve-screens the Rien has
frequently been employed. It is used to screen Dresden sewage,
which is then run into the Elbe without further treatment.
The Rien apparatus, as is shown in Figure 14, consists of a
metal disc set obliquely in the water and composed of sheetmetal sieving or sieve plates. In the centre of the disc there is
placed a truncated cone of the same material. The water flows
against the disc, which is continually turning. As a consequence
the suspended filth remains on the disc, whilst the water passes
RAKES, SCREENS, AND SIEVES
71
through the openings. Owing to the motion of the disc, the
sludge is removed from the water, and then scraped away from
the screens, and from the truncated cone also, by means of
brushes.
F1g. 15. Kremer Apparatus.
a, Inlet channel, b, Lateral inflow pipes, c, Space for
attaining an upward thrust in the water, d, Grease ex
tractor, e, Floating layer rich in fat. f. Clarifying space.
g. Reversal of the direction of the water at the edge of the
circular partition.
Circular overflow channel, an outlet
for the clarified water. i, Sludge cylinder. k, Sludge
drain. /, Cleansing pipe.
72
SEWAGE DISPOSAL
(ii) Grease Extractors.
Many effluents, such as those from slaughter-houses, kitchens,
and other similar places, contain a large amount of grease.
Since the fats are lighter than water they cannot be separated
in grit-chambers, settling-basins, and other contrivances. They
can, however, be removed from sewage in grease extractors, and
in certain circumstances these allow of a recovery of the grease.
There is a whole series of plants for the recovery of grease.
The best known of these is the Kremer apparatus. This apparatus
F1g. 16. Grease Extractors of the " Stadtere1n1gung
F1rm " of Berl1n-W1esbaden.
can also be used independently as a clarifying plant, since it also
separates from the sewage any suspended matter that is heavier
than water. The apparatus (Fig. 15) separates the undissolved
substances by means of a peculiar motion of the stream working
in such a way that the substances are divided into two layers of
sludge, according to their specific gravity. Grease particles
adhering to light organic matter form the upper floating layer,
whilst the lower layer is composed of the heavy particles of
suspended matter. According to Vogelsang, the Kremer ap
GRIT CHAMBERS
73
paratus is to be recommended strongly for preliminary purifi
cation with the biological processes, since it separates much of
the light suspended matter, such as grease, paper, straw, and the
like, which cannot be removed by sedimentation processes, and
which consequently choke up the contact beds and percolating
filters with mud. The " Gesellschaft fur Abwasserklarung " (Sew
age Clarifying Co.), of Berlin-Schoneberg, supply this apparatus.
The firm also employ them in combination with Emscher wells
(see page 82 in this book) . They call the combination the KremerFaulbrunnen (Kremer septic well), and warmly commend its
great utility.
A grease extractor of another type is that of the " Stadtereinigung und Ingenierbau A.-G." firm of Berlin-Wiesbaden.
As shown in Figure 16, the greasy water enters through the
funnel c into the space d, where by means of a deflector e it is
uniformly divided and diverted in direction upwards. The
particles of grease have time to separate out in the upper
parts of d, whilst a quantity of water in the space d, corresponding
to the inflow from above, passes out below through the circular
opening F. The sludge sinks lower and falls eventually into the
sludge-pail g, whilst the water, freed from grease and mud, rises
to the brim of the reservoir and, overflowing at i, passes into the
outlet pipe at z.
Of other systems the grease extractors of Kaibel, Darmstadt,
of Kremer-Schilling, and of Heyd, Darmstadt, may also be named.
(iii) Grit Chambers.
Many plants for preliminary purification also make use of
grit chambers. Whilst screening removes the coarser floating
matter, grit chambers are intended to separate the heavier and
coarser sinking suspensions. This is attained by allowing the
pipe conveying the water to the clarifying plant to suddenly
discharge its contents into a larger space known as the grit
chamber. As a result, the velocity of the sewage, owing to the
increase in cross section of the chamber, is quite considerably
reduced. Consequently the coarse suspensions, like rags, bones,
sand, and such-like, settle to the bottom. The cross section of grit
chambers varies greatly. They may be funnel-shaped or rect
angular, or they may have arched bottoms, etc. The mud which
74
SEWAGE DISPOSAL
settles is removed either by hand or mechanically, and the
removal may take place either after emptying or during the
process. The mechanical sludge-remover generally consists of
a dredging-machine, which dredges the sludge and casts it on to
a travelling platform. With grit chambers built funnel-shaped,
the dredger can remain standing in the one place. With other
forms the dredger can often be moved from one end of the
chamber to the other, as at Frankfort-on-Maine. According
to the investigations of the author in Frankfort, with a good grit
chamber and a system of fine screens, about one-fifth of the
total suspension in a sewage is removed.
(iv) Sedimentation Tanks, Wells, and Towers.
These contrivances serve for the deposition of the finer sus
pended matter. The sewage is simultaneously introduced into
a number of such tanks or wells, so that, owing to the increased
cross section, the velocity of water is very considerably di
minished, and consequently the finer particles of suspended
matter can settle to the bottom.
Sedimentation tanks are generally elongated rectangular
chambers, constructed either open or covered, though they are
most frequently open. They are generally about 40 metres long,
but there are, however, sedimentation tanks considerably shorter
and longer. The inflow generally occurs through openings
situated below the surface of the water, in order that the already
precipitated sludge shall not be disturbed by the motion of the
water. The beds of the tanks are built both rising and falling
towards the outlet. According to the researches of Steuernagel
and Grosze-Bohle, the rising bed has proved satisfactory for
sedimentation work. Generally at either inlet or outlet, or even
at both places, sump-pumps are placed to pump away the
deposit which collects there. The Frankfort sedimentation tanks
are 40.6 metres long and have pumps at 7.5 metres distance from
the inlet and outlet. The chamber bottom is so constructed
that in the middle it is raised and falls away with a fall of 1 in 10
to the sumps. There is the same fall from both inlet and outlet.
This arrangement of the chamber bottom serves to lead the mud
of itself to the pumps, through which it is removed. This renders
superfluous the cleaning of the tank bottoms with shovels or
SEDIMENTATION TANKS, ETC.
75
similar contrivances. In Figure 17 the form of the Frankfort
sedimentation tank is shown in cross section.
It was formerly thought that to effect good sedimentation the
chambers must be built so large that the velocity of the water
1
101 OS 0
11
21
31
4-1
Sm
F1g. 17. Frankfort Sed1mentat1on Tank (Cross Sect1on).
would be extraordinarily small (2 to 4 mm. per second). Ex
periments of Grosze-Bohle in Cologne have shown, however, that
with a velocity of 20 to 40 millimetres the same sedimentation
is attained. Also in Frankfort it could be demonstrated that
76
SEWAGE DISPOSAL
the abnormally small velocity of 2 to 4 millimetres per second
gave no better results than one of 12 millimetres per second.
With higher velocities than 12 millimetres per second considerable
diminution of the sedimentation was obtained, so that one
cannot generalise on the results from Cologne without further
details. According to Schiele, in England they still keep quite
generally to the small velocity of 2 to 4 millimetres.
In the settling tanks there also separate out a number of floating
substances which are composed firstly of the fatty matter in the
sewage, and secondly, especially when the tanks have been in
use for a long period, of particles of sludge rising up on account
of fermentation. In order to avoid admitting these floating
particles into the outlet, a board is generally partially immersed
in the water and set obliquely a short distance in front of the
outlet. The particles collect in front of this.
The mud is generally disposed of first by running off all the
water. The sludge is then pumped away from the slime deposit.
In some sedimentation plants sludge-pumps working under
water might be tried ; these naturally would be advantageous
in that the sludge could then be removed during the sedimenta
tion process without the chamber that is to be purified being
emptied. In general, however, sludge-pumps do not appear to
have worked well. The main difficulty lies in this, that the
sludge does not slip along sufficiently towards the pumps ; on
the contrary, a crater is often formed in the sludge and the
sewage is suddenly sucked over instead of the sludge.
The settling process is frequently assisted by the addition of
chemicals. Alum and lime, or ferrous sulphate and lime, and
other substances are used. The principle upon which the use
of these substances is based is as follows : The chemicals form
gelatinous and voluminous precipitates (alum+ lime=gypsum
and aluminium hydroxide) , which on sinking to the bottom carry
the suspended matter along with them. The chemicals have
also a slight action on the dissolved organic matter. This action,
according to some, will be insignificant in itself, the main action
being the assistance which the chemicals render towards settling
out the suspensions. With domestic sewage the action of
chemicals is frequently denied. Thus, parallel experiments have
been carried out by Lepsius and later by Freund in Frankfort on-Maine with chemical precipitation and with purely mechanical
SEDIMENTATION TANKS, ETC.
77
sedimentation, by which it was established that the influence of
chemicals on sedimentation was practically insignificant. Accord
ing to Schiele, however, in opposition to this view, the addition
of chemicals to domestic sewage is still practised in England.
In the author's opinion chemicals certainly have an effect on
the dissolved substances, and also act in the case of domestic
sewage on the pseudo-dissolved substances, the colloids, to no
inconsiderable extent. Aluminium hydroxide and ferric hy
droxide are, as is well known, also colloids, and have an adsorbent
action on the colloids in the sewage. Frequently, addition of
chemicals to industrial effluents must be made. The main
drawbacks to the addition of chemicals are the considerable
increase in cost of the sedimentation process, and the difficulty
of disposing of the sludge. The sludge obtained when chemicals
are used is, in the first place, far more aqueous, and so takes up
much more room, while secondly, on account of the sludge
containing chemical substances, which at least are indifferent from
the manurial point of view, it is considerably depreciated in value
as a manure. The amount of chemicals added varies greatly
according to the composition of the sewage to be purified. It
varies between about 43 and 950 grammes per cubic metre (7 to
150 oz. per 1000 gallons) of sewage. The chemicals are added
either in the liquid or solid state. In the liquid form it is allowed
to flow into the sewage in a thin stream. When applied in solid
form the chemicals are added to the water in wire baskets, so
that the water flowing through dissolves out the chemicals. For
these to work properly it is of great importance that care be taken
to get good mixing between chemicals and sewage. If there be
sufficient space between the place of addition and the settling
tanks, the water itself ensures adequate mixing. Now and again,
however, various devices are employed to attain good mixture.
Thus, tongues are placed in the sewage-pipe, by which means the
water is broken up.
The amount of suspended matter separated out, expressed as
a percentage of the total content of suspended matter in the
crude sewage, amounts, with good sedimentation tanks and not
too high a velocity (12 mm.) in the basins, to 60 or 70 per cent.
Sedimentation wells and towers are generally cylindrical in
form and are distinguished essentially from tanks in that the
water flows through them upwards and in a vertical direction,.
78
SEWAGE DISPOSAL
whereby the suspended matter settles out underneath. In such
sedimentation reservoirs the velocity of the sewage is generally
considerably less than in sedimentation tanks. With towers and
wells the sludge can be removed more easily while the process is
in operation than is possible with tanks, since it is in such cases
more conveniently concentrated into a certain space. To guard
against the water breaking through (see page 76), various con
structions have been proposed, based on the closing of the water
space whilst the sludge is being pumped off.
(v) Septic Tanks.
Septic tanks are only employed as preliminary purifiers in
biological purification plants ; they do not come into considera
tion as separate clarifying plants. They are employed in a
manner similar to the usual sedimentation tanks, but with the
difference that the sludge which separates out is allowed to lie
for a long period. It is thereby converted into a foul state of
fermentation, which is then communicated to the sewage. The
sewage is coloured black, owing to the presence of ferric sulphide,
and assumes a very foul odour. As a result of the activity of
the fungi setting up putrefaction a portion of the organic matter
is decomposed. There forms on the septic tank after a short
time a scum consisting of grease mixed with particles of sludge
raised by the fermentation. This scum shuts off the air from the
sewage, and is of great importance in the putrefactive action
which is caused by anaerobic bacteria. In some English septictank installations the floating layer, according to Schiele, now
and then becomes so strong that one can actually walk upon it.
Moreover, these septic tanks act like sedimentation tanks as
regards removal of suspended matter. With the slow passage of
the water through the septic tanks the suspensions settle out.
A certain amount of time always elapses before a septic tank is
in good working order, that is, until it yields a thoroughly
putrefied effluent. Septic tanks are built both open and covered.
The open tanks have the drawback that they cause annoyance
from their smell. Septic tanks, according to Schiele, must be
capable of holding at least half a day's dry-weather drainage.
Smaller plants are generally built large enough to hold from
three to six times the dry-weather discharge.
TRAVIS AND EMSCHER WELLS
79
Naturally the removal of sludge takes place less frequently in
this case than with the usual settling tanks. It is useful never
to remove the whole of the sludge, but always to leave some still
lying ; the tank then gets into working order afresh more quickly,
because the putrefactive fungi from the thoroughly putrefied
sludge can more easily communicate themselves to the sewage.
The main advantages of septic tanks may be thus noted. In
the first place, the sludge need not be removed so often, which
naturally means cheaper working ; and secondly, the sludge from
septic tanks, especially according to the results of recent work,
is by no means so disagreeable as the sludge from the usual
sedimentation tanks. It is more easily freed from water and
contains a considerably larger bulk of dry substances. These
relations will be more carefully dealt with in the chapter on
sludge. As a further advantage of septic tanks, there has to be
considered the decomposition of a portion of the organic sub
stances which, from the observations of Dunbar and his pupils,
takes place both in the sewage and the sludge.
With septic tanks there is the disadvantage that the effluent
is not so completely freed from suspended matter as with sedi
mentation tanks. Owing to the fermentation set up in the sludge,
fine particles are propagated upwards and so pass into the dis
charge. Since suspended matter vitiates bacterial action in
contact beds and percolating filters to a considerable degree, and
also causes their more rapid pollution, sieves are often placed in
the discharge-pipe to check this annoying feature.
(vi) Travis and Emscher Wells.
These apparatus are distinguished from sedimentation and
septic tanks by the separation of the sludge from the actual
sedimentation space.
According to Collins (" Surveyor," 1909), the Travis plant in
Norwich consists of rectangular tanks, whose lower parts are
wedge-shaped in cross section (see Fig. 19). Lengthways in each
tank a roof is built, which is cut open at the coping in the long
axis of the tank and is carried upwards above such axis. Where
the roof is joined to the tank-walls and to the coping, gaps are
left. Through these gaps the three compartments of the tank,
arising out of the mode of construction, are in communication
80
SEWAGE DISPOSAL
with one another. Both the outer compartments serve as sedi
mentation compartments. The sludge on settling out slides
down the sloping surface formed by the roof and falls through
the gaps into the middle section of the tank, the reduction or
sludge chamber. In the central portion of the settling tank there
are placed grating-like frames (colloiders) about 10 inches from
each other. These devices should serve to retain and to exert a
certain coagulating influence on the colloids ; 80 per cent of the
sewage enters through the two outer settling tanks, whilst 20 per
cent enters the reduction chamber or sludge area through the
openings at the coping of the roof. The water passes out over
F1g. 18. Clear1ng Well Installat1on at Norw1ch on the Trav1s
Hydrolyt1c System, w1th Collo1der hung 1n.
(From " Wasser und Abwasser," 1909-10, II, 71.)
a weir which occupies the whole breadth of the tank, and which,
corresponding to the three tanks, is three-sided. The effluent
from the liquefying chamber is subsequently purified in a special
tank provided with " colloiders " like the sedimentation tank.
The removal of sludge, necessary from time to time, is con
veniently attained by having the bed of the sludge chamber
composed of a number of funnels. The walls of these funnels are
so inclined that, on opening the outlet situated at the lowest
point of the shoulder, the sludge is pressed out by means of the
pressure of water above.
Travis tanks have come into use considerably, especially in
England, and presumably have proved excellent. The main
difference between the Travis tank and Emscher wells consists
F1g. 19. Emscher Wells.
Arrangement of several wells with settling channel in common. Re
moval of sludge by excess water pressure to the lower lying sludge
storage grounds.
A, Inlet. B, Screening chamber, e, Channel for screenings 11, Cir
culating channel. P, Outlet. D, Fume Chamber. G, Partitions.
11, Waste-weir. F, and F2, Liquefying chambers. R, Sludge pipe.
S, Cleansing pipe. .
G
SEWAGE DISPOSAL
in this, that with the former from time to time fresh water is
purposely led through the liquefying chamber in order to remove
the liquid constituents of the sludge generated by the putre
faction. With Emscher wells the principle is to avoid any
flushing of the liquefying chamber.
Emscher wells (Fig. 19) consist in the main, according to
Middledorf, of deep wells which are intended for the reception of
the sludge. In the upper part of these wells by means of a partitionwall a settling tank or well is apportioned off, and through this the
water flows. As soon as it touches the sloping bottom the sludge,
settling out in the tank, flows of itself through gaps at the lowest
parts of the sedimentation space into the sludge wells. The
water flows only through the sedimentation area and, in agree
ment with the principle, not through the putrefactive area. The
putrefaction is thereby confined to the sludge alone, and the
water flowing away is obtained as fresh as possible, unmixed with
any of the polluted water. The amount of water from the
sludge which gains access to the sewage should amount to about
one part in a thousand. With variation of temperature also there
should be little tendency for water from the sludge to rise into
the sedimentation tank, since it is specifically heavier than fresh
sewage. As the sludge from the settling tanks is withdrawn
uninterruptedly and automatically, there is absolute certainty
that it is always removed at the right time and does not remain
lying in the settling tanks, injuring the clarifying process by its
foulness. The particles of mud propagated upwards by fer
mentation cannot pass through the clefts in the partition-wall,
but are forced against the wall underneath the sewage and sink
again from there to the bottom. The sedimentation in Emscher
wells should be equally as good as with other good-settling plants
with the same period of sedimentation. The sludge putrefies in
the liquefying chamber, and thereby becomes more suitable for
disposal (see under Sludge). The fact that water is not allowed
to flow through the chamber has not proved a hindrance to the
putrefaction of the sludge. It is because of this that the freshness
of the water to be purified is maintained, and it may be reckoned
an advantage in the process. With Emscher wells, in contra
distinction to other liquefying chambers through which the water
is allowed to flow, scarcely any trace of sulphuretted hydrogen is
evolved. According to the investigations of Spillner, the gases
TRAVIS AND EMSCHER WELLS
83
which escape from the liquefying chamber and pass both through
the sewage and around the sedimentation tanks consist mainly
of methane and carbon dioxide. Odourlessness of the sludge
should be attained equally well with purely domestic sewage
purifiers, and with plants receiving industrial effluents. The
sludge is led through pipes from the liquefying chamber to the
sludge drying-place. The end of the pipe reaches to the lowest
point of the funnel-shaped bed of the well. Only the under
neath portion of the most thoroughly putrefied sludge is led away.
If the area for drying the sludge can be situated from 1.5 to 2
metres lower than the water-level in the wells the sludge can
then be removed by the natural fall, since for this purpose a head
of 1 metre is generally sufficient. If this head cannot be obtained
the sludge is removed either by a Wagner suction apparatus,
with a hand or air-pressure pump, or with a vacuum plant
driven by an air-pressure pump. In all plants of the Emscher
Co. the sludge should be displaced through the sludge-pipes
without any difficulty. The reason for this is largely because the
sludge during the septic action loses its felt-like nature and
forms a black, pulpy, fluid mass, in spite of its low per
centage of about 70 to 80 per cent water. The removal of the
sludge takes place perhaps once every two or three months. The
liquefying chamber should be so large that it can hold the sludge
falling in during this length of time.
Meanwhile, the question of Emscher wells has been vigorously
debated in the literature. In the main the following points have
been contested : Whether the plant is practically odourless ;
whether the sedimentation is as good in Emscher wells as in
other good sedimentation plants ; whether liquefaction actually
occurs in the sludge ; whether the water remains at rest in the
liquefying chamber, or whether rather, just so much of the
polluted water from the liquefying chamber enters the sedi
mentation tank as sludge separates out.
It must be pointed out, however, that Emscher wells are com
ing more than ever into application, both as separate sedimenta
tion plants and also as plants for the preliminary purification of
sewage about to be bacterially treated.
The main advantage of Travis and Emscher wells over the
usual sedimentation tanks is therefore the simplicity with which
the sludge problem is solved.
84
SEWAGE DISPOSAL
" There is this great advantage in a joint plant working with
automatic separation of sludge. A small velocity of sedimenta
tion can be chosen without the process becoming more difficult
as regards the handling and disposal of large amounts of thin
sludge containing high percentages of water, such as generally
settle out under such conditions " (Schmidtmann, Thumm, and
Reichle).
II.
DEGENER'S COAL-PULP PROCESS.
As regards the nature of its action, this method stands midway
between the mechanical and the bacterial methods, for like the
former its main action depends on the removal of the suspended
matter, and like the latter it has an undoubted action on the
dissolved substances.
I to 2 kilograms of ground-peat or 2.5 to 4 kilograms of turf
are added to a cubic metre of the sewage to be purified. Chemicals,
such as aluminium or ferric sulphates, are simultaneously added.
Generally, the sewage is then allowed to settle in sedimentation
towers. The sludge is fairly aqueous, but is usually freed from
water in filter-presses, and in this case is then no longer capable
of putrefaction. The air-dried sludge, on account of its high
carbon content, is a valuable burning material. Lately it has been
rendered more valuable by gasification (see under Sludge).
The whole process should work without smell, and on this
account, and because the troublesome sludge question with its
dangers is obviated, it is a method of great importance. The
further advantage of a reduction in the dissolved organic sub
stances has been referred to previously. Against these advan
tages there is the main disadvantage of cost, which is very
considerable. It is because of this that the number of plants
working the process on a large scale remains so limited, in spite
of the method being so superior.
III.
BACTERIAL PURIFICATION OF SEWAGE.
As already mentioned, the dissolved organic matter is un
changed in a mechanically purified sewage. If such an effluent
be allowed to stand for some time it very soon begins to putrefy
and, from the plentiful development of putrefactive bacteria,
assumes a stinking condition.
ARTIFICIAL BIOLOGICAL METHOD
85
The task of bacterial sewage purification is so far to remove
the dissolved organic matter from the sewage that putrefaction,
with its accompanying disagreeable phenomena, is avoided. As
the name indicates, in bacterial purification processes bacterial
agencies come into play.
In particular two processes are distinguishable, viz. artificial
biological sewage treatment, and broad irrigation or sewage
farming.
(i) The Artificial Biological Method.
Artificial biological sewage purification is the designation
applied to that treatment whereby, after suitable preliminary
purification by mechanical methods as detailed in Part I, the
sewage is led over large pieces of slag, coke, or similar materials.
The organic matter is by this means so far removed from the
sewage as to prevent subsequent putrefaction in the effluent.
Biological processes for the treatment of sewage arose in
England, where they were first used and tested on a large scale.
That this method was first improved in England is quite reason
able, since England is the classic country for sewage disposal.
In consequence of the peculiar circumstances operating there,
its position as the premier country in the world, England was
compelled to work out good methods of sewage purification.
The largest English rivers have not the capacity and velocity
even of our Spree or Havel (tributaries of the Elbe, Trans.). With
industry flourishing in the middle of the last century there went
hand in hand alarming pollution of the whole river system of
England.
Thorough preliminary purification is of vital importance for
the continued good working of biological processes. Grit cham
bers, screening, and the mechanical purification involved in
sedimentation and septic tanks, all come into consideration.
For domestic effluents the sewage is generally first purified in
sedimentation or septic tanks. If much industrial effluent be
admixed with the household sewage, chemical treatment is
generally indispensable. Moreover, it is advisable to find out in
each case, by special experiments, the most suitable preliminary
treatment for the sewage.
Many substances are used as material for the beds employed
in these biological processes. Clinkers from refuse destructors,
86
SEWAGE DISPOSAL
slag, earthenware, bricks, coke, pieces of slate, and such-like
materials have all been tried. According to Schiele, the main
requirements in such a material are great hardness, capacity to
withstand the action of sewage, roughness, and firmness.
Large beds are laid down composed of lumps of these materials
loosely collected together. Distinction must be made between
contact beds and percolating filters. The distinction between
the two lies in the manner of their impregnation with sewage.
Contact beds are filled with sewage ; the sewage remains for a
period of time lying in the beds and is then led away again, by
which means air is sucked into the beds. With percolating
filters the sewage is continually percolating through the beds.
The size of the pieces of material used should be about 3 to 8
millimetres (x\yth to Jrd in.) in the case of contact beds, whilst
with percolating filters it is considerably larger, amounting to 15
to 75 millimetres
to 3 in.), and there are even larger in use
(Schiele). With contact beds there are two processes, known
as single-contact and double-contact treatment. In the singlecontact process treatment is complete after leaving the bed.
In the double-contact process the sewage from the primary bed
is delivered to a secondary bed. The material of a primary bed
is coarser in grain than that of the secondary bed. Percolating
filters are generally worked with single contact.
As with septic tanks, so here the beds have to be prepared for
the work in order that in course of time they cease to yield
effluents capable of putrefaction. The time for this process to
take place may amount to some months. It is generally shorter
with percolating filters than with contact beds, and depends on
the gradual formation of a slimy layer on each piece in the bed, a
discussion on the nature of which layer will be detailed below (see
page 89). Contact beds are so worked that they are filled with
sewage, which is then allowed to stand some time in contact
with the beds, and then to drain away. The sewage is generally
led on to the contact beds from above, and is drawn off from under
neath. After each impregnation contact beds must be allowed
to stand some time, in order to work up the substances taken
from the sewage. In England good results have been obtained
with the beds full for two hours and standing empty four hours
(Schiele). In practice single-contact beds can be impregnated
twice per day, double-contact beds three times daily. According
ARTIFICIAL BIOLOGICAL METHOD
87
to this, I cubic metre of single-contact bed can be treated with,
at most, o.66 cubic metre of sewage, double contact with 0.5
cubic metre per day.
Percolating filters can be continuously impregnated with
sewage without the purifying action falling off.
The beds are either built in the ground or on the ground. It is
important for good working that they should be maintained at
uniform temperature. They should therefore be protected under
certain circumstances against cold in winter.
Contact beds are generally rectangular ; percolating filters are
either rectangular, octagonal, or circular in shape.
In the case of contact beds the water is distributed on to the
beds in a very simple manner. It takes place through feed
channels, perforated clay, or stoneware pipes, open, perforated
drains, perforated gutters, and other devices. With contact beds
good uniform distribution is not by any means so important as
with percolating filters. In the case of contact beds the main
concern is the quickest possible filling. They are generally filled
and emptied by sluices and valves worked by hand. Frequently
there are also automatic devices for filling and emptying. Uni
form distribution is, however, a matter of very special importance
in the case of percolating filters. The number of devices invented
to attain this is almost legion. There are sprinklers, movable
revolving sprinklers, stationary perforated pipes, portable
sprinklers, etc.
In general, according to Schiele, with regard to distributors
for percolating filters, the following can be said : The system
employed must always be adapted to local circumstances. It is
most suitable to carry out experiments beforehand. In Birming
ham the following requirements were demanded of a good
distributor :—
(1) Uniform distribution, so that each portion of the surface
of the bed contains precisely the same quantity of water.
(2) Distribution in the form of drops.
(3) Absolute control over the distributor.
(4) Limited cost of plant.
(5) Small working expenses.
(6) As few movable parts as possible.
(7) Small consumption of power in distribution.
With regard to the water-pressure necessary for working,
88
SEWAGE DISPOSAL
fixed sprinklers are at a disadvantage when compared with
the automatic revolving sprinklers. The revolving sprinklers
are found in English experience to be limited to a bed of
30 metres diameter, or at the most 35 metres. When they
are to be worked mechanically, large rectangular beds with
movable or fixed sprinklers prove more useful and advan
tageous than circular beds with revolving sprinklers.
In
Germany automatic revolving pipe sprinklers, with a bed 20
metres diameter and perforations every 10 millimetres, have
proved the best for withstanding strong cold in winter. In
England at the present time stationary sprinklers, especially
the Fiddian type, are being increasingly employed.
Contact beds and percolating filters are on the whole to be
regarded as. of equal value. Both have their advantages and
disadvantages. The advantages of contact beds are : Simple
distribution of the sewage on to the beds, small trouble due to
smell, no plague of flies, little suspended matter in the discharge ;
small need for a head of sewage on account of the small depth of
the bed, greater certainty of working in the cold weather. As
opposed to these the main advantages of percolating filters are :
Greater mechanical power than with contact beds ; since the
beds can be built higher smaller space is necessary ; coarse
grained, cheap material ; little attention. Whilst contact beds
are always gradually getting choked with sludge, and on this
account need purifying more frequently, percolating filters do
not get choked with sludge, or at most with very little. Per
colating filters also withstand an overload of sewage in rainy
weather, since the admittance of air is never quite cut off. On
the contrary, percolating filters always contain a great deal of sus
pended matter, and the discharge must be subsequently freed from
this. In percolating filters small flies establish themselves in
extraordinary numbers. Especially is the Psychoda (the butterfly
gnat) to be noted. Further, smells are never quite avoided in the
treatment of sewage with percolating filters. After the invention
of percolating filters one often heard the opinion expressed that
contact beds would soon disappear. This view has not proved
correct. For the purification of sewage in large towns it is true
that percolating filters have proved themselves superior to con
tact beds, since all the above-named advantages of percolating
filters mean cheaper cost of construction and of upkeep. For
ARTIFICIAL BIOLOGICAL METHOD
89
the centralised clarification plants of towns, therefore, percolating
filters are nowadays generally erected. Still, even in the most
recent years in England, in large towns like Manchester, contact
beds have been put down and have proved excellent. They are
especially suitable where the proximity of places of residence, as,
for example, with small domestic or manufacturing plants,
compels one to avoid smell or flies.
As has been already mentioned, the percolating filter effluents
always contain large amounts of suspended matter which are
washed out of the beds. These substances differ greatly from
those in the raw sewage, in that they are not capable of putre
faction. They impart to the purified water an objectionable
appearance, and would lead to the deposition of sludge in the
river ; consequently percolating filter effluents are always sub
sequently clarified. In England this is frequently effected by
land irrigation (1 acre to 1ooo inhabitants).
Generally,
however, the discharges are subsequently treated in simple
sedimentation tanks or wells. Since the sludge is no longer
capable of putrefaction, it is easily freed from water and its
disposal
The cost
causes
of sewage
no difficulty.
treatment by the biological process varies
greatly. The price of material for the beds varies, accord
ing to Schiele, from 3 to 12 marks per cubic metre (2s. 6d. to
10s. per cubic yard), whilst 1 cubic yard of ready - prepared
material costs from 5 to 35 shillings. The cost of the bed in
England cannot, as a rule, be less than 15 shillings per cubic yard.
As to the nature of biological purification of sewage there exist
two views. According to one, which is put forward by BauratBrettschneider of Charlottenburg, and which in its essentials
coincides with the so-called Hampton doctrine championed by
Travis, the whole so-called biological sewage treatment consists
of nothing more than a filtration of the organic filth, which, in
the main, would be present in the colloidal form in sewage
(together with the greater part of the so-called dissolved sub
stances) . This theory is opposed to that of Dunbar and his pupils,
according to whom biological sewage purification is to be explained
in the following manner : Each single portion of the bed is
gradually covered with a slimy surface of bacteria and other
organisms. During impregnation the greater part of the organic
matter is adsorbed by this covering. The film also adsorbs
90
SEWAGE DISPOSAL
oxygen in large quantities. With the help of this oxygen and of
the oxygen otherwise entering the bed, the adsorbed substances
are decomposed by the organisms in the intervals of rest between
each impregnation. This theory is supported by numerous
experimental data, so that there can be no doubt as to its truth.
(ii) Land Treatment.
Treatment of sewage on the land is the oldest form of sewage
treatment. Within the memory of man it has always been known
that the surface of the earth was able to remove the evil smell of
sewage and to make polluted water pure.
Two methods of land treatment must be distinguished, namely,
broad irrigation or sewage farming, and the intermittent sand
filtration of Frankland.
(a) Sewage Farming.
Broad irrigation or sewage farming was first practised in
England. To-day there is still in existence an irrigation bed that
has been in use two hundred years. As is well known, sewage
contains a number of substances which are valuable as nutri
ment for plants (nitrogen, phosphates, potash). The irrigation
process makes use of this fact, and on the farms all kinds of useful
plants are grown. Thus by this method of sewage disposal, the
sewage is purified and use is made of the nutritious substances
present in it.
In England alluvial soil is considered to be the best for sewage
farming. Soil lying over high waters generally in river valleys,
or sandy loam over gravel or gravelly sand, or even gravelly,
sandy subsoil with light or medium mainsoil about 40 centimetres
deep, are all good. Gravel without a finer covering layer serves
also as regards permeability (Schiele). The poorest earth is clay,
loam, clayey soil and turf. Clayey soil, since it is not permeable,
can only be used for the so-called surface or rude irrigation.
According to Dunbar, there are two main kinds of irrigation
processes. In the first kind the water flows down from the highest
point of the land. After trickling over the surface of one field
it is collected into a ditch, from which it is again uniformly dis
tributed over the next field. With a sharply inclined tract of
land, dams must be thrown up to retard the flow of the sewage
LAND TREATMENT
91
and to distribute it afresh. When the track is not so steep the
operation is carried out in the following manner : The sewage
flows from the distributors, passing transversely from the irriga
tion plant into smaller trenches arranged perpendicularly to the
larger. These are dammed up at the ends so that the sewage
must overflow from the trenches at the sides. It then flows over
the sloping surfaces of meadow into lower lying ditches. Then
from these second distributing ditches, in precisely the same
manner, the water is again distributed over a second series of
meadows. This process is generally used for surface irrigation
only, and in those cases where the land lies so low that it cannot
be drained. A good drainage is not usual, therefore, with the plant.
In Germany and also in France, as far as possible, it is en
deavoured to lay out sewage farms on the principle known as bed
irrigation. In this process surface treatment with sewage is done
away with, as the water passes through the ground. It is therefore
true irrigation. The sewage is led on to the farm in ditches.
The distributing canals are only allowed to fill so far with sewage
that this has to pass into the bed sideways and below the surface.
Wetting the stems and leaves of the plants is thus avoided. The
beds are usually only 1 metre broad by 20 to 40 metres long, as
otherwise uniform distribution of the sewage cannot be attained.
In this process many distributing ditches are required, and also
paths from which the beds can be attended to. This means,
therefore, considerable loss in working space.
Further, a process may also be briefly described here which,
up to the present, has not been widely employed, but which
might render good service in those places where no suitable land
for sewage farming is to be had in the neighbourhood of towns
and manufactories. The method consists in conducting the
sewage to farms, and here by means of hoses it is squirted on to
the fields. In the year 1897 it was first used by Nobel in Eduardsfeld, near Posen, with
million gallons of sewage yearly from
the town of Posen. The process is named after the inventor, and
is known as " Benobelung " (The Nobel Treatment), or the
Eduardsfeld process, and also as hose irrigation.
In most cases the subsoil is drained. The purified sewage is
conveyed to the river in collecting ditches. Under loam or clayey
soils drainage is naturally not effected, since it would serve no
purpose. The action in sewage farming is first of all a filtration
92
SEWAGE DISPOSAL
process, since all suspended matter exceeding in size the pores
of the ground is retained. Further, a large number of bacteria
are removed. Then again, in a manner similar to that occurring
with contact beds and percolating filters, but still more pro
nouncedly, dissolved organic matter is decomposed by the aid of
micro-organisms in the ground. The sewage flowing away in the
effluent drains differs from the raw sewage in that it is quite clear
and no longer capable of putrefaction. It contains considerably
less oxidisable matter, and the nitrogen compounds are to a great
extent removed and converted in part to nitrous and nitric acids.
The action in surface irrigation is not so effective as that in
true irrigation.
In all circumstances purification of the sewage before disposal
on the farm is to be recommended. If this be done larger amounts
of sewage can be disposed on the surface. In this preliminary
purification there come into consideration screens, grit chambers,
and septic tanks, as well as sedimentation processes with or
without chemical precipitation. Indeed, in certain cases the
sewage is treated in contact beds or percolating filters before
disposal on the farm.
With good management the purifying action of sewage beds
is quite unlimited. Bad working is generally attributable to
false application of principles, or to errors in the original plant.
Corn and potatoes are not suitable products to cultivate in the
view of English authorities (Schiele) ; on the contrary, grass,
carrots, and cabbages are very suitable. As regards pasturage
opinion is divided.
The main purpose of sewage farms must always be sewage
purification ; the yield of the process must not be increased at
the expense of good purification. It is inadvisable on this account
for towns to lease their sewage farms to farmers, as the latter
have always got the profit uppermost in their minds. Large
sewage farms can, as a general rule, be better and more rationally
arranged than smaller ones. In England, therefore, small
municipalities are advised rather to join with several others in
order to set up a joint sewage farm than to erect several small
plants. There are no scruples in England against keeping cattle
on sewage farms.
Heavy rainfall has naturally a very deleterious influence on
the capacity of a sewage farm to take up the sewage.
LAND TREATMENT
93
On the whole, according to Schiele, sewage farms can be
regarded as percolating filters. The fineness of grain demands
similar treatment to that with contact beds, viz. they must have
periodical rests. The sewage farm must consequently be chosen
so large that a portion of it can always remain unemployed.
The last English Royal Commission on Sewage Disposal con
cluded that the most useful ratio of working surface to surface
unemployed was in the case of surface irrigation 1:5. and for
true irrigation 1:3. The same Royal Commission has placed in
Volume IV of their Proceedings the results of searching experi
ments on the land treatment of sewage. Thereby the following
figures, per unit of land, are obtained as admissible amounts of
sewage which has undergone preliminary mechanical or chemical
treatment : —
24 hours.
At a given
time per
Soil.
per acre.
Gallons
23,000
Best kind for
(strong
filter purposes mixed
sew
(light sandy
age).
loam overlay
100,000
ing gravel and (rather
weak
sand).
sewage).
On year's working over
whole area.
Inhabitants
(calc. at 40 Gallons
gal. per head per
acre.
per acre
per day).
600
Over
10,000
2500
30,000
(rather
weak).
Inhabitants.
250
Soil less well
suited (sand
and partially
peaty soil lying
upon sand and
gravel).
25,000
to
46,000
600
to
1150
8000
to
23,000
750
200
to
600
Domestic
sewage
(weak).
Bad soils
(from gravelly
loam to heavy
loam or clay).
12,000
to
57,°°°
300
to
1400
4000
to
900a
100
to
"5
Combined
surface irri
gation and
filter farms.
Rents of sewage farms vary considerably. Whilst many sewage
farms lose large sums of money, others not only pay for the total
cost of working, but even create a surplus. This is explained on
the grounds that the original outlay, especially the cost of obtaining
94
SEWAGE DISPOSAL
land, shows great differences. Further, it must be borne in
mind that sewage farms making a profit are generally the leased
farms, in which case, as already mentioned, purification is often
insufficient, as the profit is the primary consideration of the
management.
The cost of sewage farming, apart from surpluses, amounts,
according to Fruhling, to 1.2d. in Berlin, o.37d. in Breslau,
o.87d. in Brunswick, o.25d. in Magdeburg, o.81d. in Dortmund,
and o.39d. in Freiburg per 1ooo gallons of purified sewage.
(b) Intermittent Sand Filtration, according to Frankland.
In the year 1871 Frankland showed that domestic sewage
could be effectively purified by irrigation if it were filtered through
a sufficiently large layer of sand. Choking of the filter could be
avoided if the sewage were not conveyed to the filter uninter
ruptedly, that is, if after each impregnation an interval of rest
were allowed to ensue. The sludge abstracted is then decomposed
by organisms as in contact beds, percolating filters, and sewage
farms. It was on account of these periods of rest that Frankland
named his process " Intermittent Sand Filtration."
Intermittent sand filtration differs from irrigation processes
chiefly in this, that filtration is effected in specially prepared beds
of sand which can be dosed with far more sewage than sewage
farms with equally effective purification. The portions of the
sewage valuable as plant nutriment cannot however be utilised
agriculturally, and so cultivation of the surface must be sacrificed.
The method was first used most frequently in England. It
was badly managed, and gave rise to various troubles such as
stoppages in the sand, evil smells, and the like, with the result
that the process was for a long time discredited.
Then the State of Massachusetts, U.S.A., demonstrated the
value of the process by means of searching experimental work,
using an experimental plant at Lawrence, and with large plants
based upon this. They established, as a consequence, the good
repute which the process to-day enjoys.
Henneking studied the plant closely in the State of Massa
chusetts, and reported in the " Mitteilungen der Konigl. Priifungsanstalt fur Wasserversorgung und Abwasserbeseitigung "
LAND TREATMENT
93
(Proceedings of the Royal Test Institute for Water Supply and
Sewage Disposal) upon his own observations on the spot and on
the results obtained. The practical knowledge gained during
more than eighteen years in Massachusetts shows that with the
conditions present there it is most suitable not to submit the
sewage to preliminary treatment before disposal on the filter-beds.
American sewage is always thin, about half as thin as mean
German domestic sewage.1 It also contains no noteworthy
amounts of industrial effluents. Purification is more complete
the sooner the sewage is conveyed to the filter-bed. Suspended
matter is retained on the surface of the bed, and can be scraped
off in a cheap and convenient manner after it has sufficiently
dried. In this process, for an unlimited number of years good
purification continually results with doses of 40,000 to 8b, 000
gallons per acre. The amount of impregnation within these
limits is adjusted according to the concentration and compo
sition of the sewage on the one hand, and to the nature of the
filtering medium on the other.
The most suitable soil' for the filter-bed is one free from organic
matter, porous sand, and gravel of 0.04 to 075 millimetre size
of grain. It should be of uniform nature throughout ; that is to
say, the whole bed must contain per unit volume approximately
the same number of sand grains of various sizes. Loamy surface
layers and intermediate layers must be removed. The surface
of the filter must be horizontal, or possess a slight inclination of
1 : 200 to 1 : 500. The depth of the filter layer should be at
least 4 to 5 feet on an average. The main purification of the
sewage is accomplished in the upper layer to a depth of 2 to
3 feet. A rectangular bed about 1 acre area has proved the
most suitable arrangement. The beds must be well drained
so that the treated sewage can flow away easily. It is distinctly
worth while striving to design the drainage on the separate
system (Trenn system).
Subsequent treatment of the purified sewage is unnecessary.
The periods of rest given after each application vary con
siderably. They vary between several hours and three days, and
generally last about 24 hours, so that the filter can be dosed once
a day. Since, as already mentioned, the filter-beds are much
1 English sewage of mean concentration is regarded as thin for German work
ing conditions. —Trans.
96
SEWAGE DISPOSAL
more heavily charged with sewage than in the case of sewage
farms, expense is considerably less with intermittent sand
filtration. That is to say, whilst an acre of filter-beds can be
treated with the sewage of 1250 persons daily, an acre of sewage
farm can only purify sewage from 110 persons. Intermittent
filtration therefore only requires about one-eleventh of the total
surface necessary for sewage farming. The cost of intermittent
sand filtration fluctuates correspondingly between o.04d. and
1.34d. per 1000 gallons of sewage, and, according to Henneking, should only amount to 8.2 per cent of the cost in sewage
farming. The purifying action of the sand filter is never so
complete as that occurring in broad irrigation. In Germany the
process has not come into practical application up to the present.
(iii) Sewage Purification by means of Fish-ponds.
.
Frequently it has been proposed to purify sewage by con
veying it to fish-ponds. The putrefactive matter decomposes
there in agreement with the observations made in the section on
" Self-purification of Rivers " by various organisms, of which the
larger always prey upon the smaller. The organic matter intro
duced with the sewage is thereby converted into fish tissues.
Naturally, therefore, the sewage must be so diluted that, in the
first place, direct harm to the fish is avoided, and secondly, that
purification can proceed normally. In the former case with too
high concentrations of sewage, sulphuretted hydrogen and other
inimical substances cause damage.
Cronheim carried out experiments in this direction which
demonstrated the important fact that fish requiring little oxygen,
like carp and tench, withstood an introduction of sewage to the
extent of 10 per cent of the total volume of the pond. Decom
position did not occur in the water, nor did sludge collect on the
bottom of the pond.
In later experiments Cronheim introduced 10 per cent of
sewage every 4 to 8 days into a pond which, besides carp and
tench, also contained trout and perch. In these experiments
also, with fish needing oxygen in high degree like trout, no harm
resulted. Whilst an acre of sewage farm can only absorb the
sewage of 100 people, a pond containing carp, of half an acre area
RESIDUES
97
should, according to Hofer, continuously absorb the sewage of
300 persons without extensive decomposition setting in. This
method is especially suitable for flat land, single farms, hospitals,
etc., but Hofer also maintains that it is applicable to large towns
like Munich.
According to Schick, the method is employed with the best
results for the Kreisirrenanstalt, Kutzenberg in Oberfranken
(300 persons), with a pond 0-5 acre in area. At Bau the same
author points out that there should shortly be plants for the
South Bavarian townships of Weinding and Ichenhausen with
about 3000 inhabitants. Further experience with regard to
expense and management must be awaited.
IV.
THE DISPOSAL OF SEWAGE RESIDUES AND
THEIR VALUE.
(i) Residues from Grit Chambers and Screens.
Sludge from Sedimentation Tanks.
The residues resulting from sewage treatment are grit-chamber
residues, residues from screens, the sludge from sedimentation
tanks, and the sludge from the plants for purification of the
effluents from percolating filters. With the exception of the last
they are all more or less capable of putrefaction. The disposal of
sludge is the most difficult and most important question in sewage
disposal. A solution of the sludge problem that is satisfactory
in every case is not yet known.
The residues from grit chambers and screens are not large in
amount. Generally not more than 15 to 20 per cent of the un
dissolved substances present in the sewage is displaced in these
purification processes. Grit-chamber residues mainly consist of
sand, rags, bones, coffee grains, and similar substances. They
usually contain 60 to 70 per cent of water. The dried material
generally consists of two-thirds mineral and one-third organic
matter. In Frankfort, with about 400,000 inhabitants arid
22,000,000 gallons dry-weather flow per day, approximately
350 to 550 cubic feet of grit-chamber residues are obtained in
24 hours. Its disposal generally occasions no great difficulty.
The material is quite firm when it contains 60 to 70 per cent of
H
98
SEWAGE DISPOSAL
water. It is dried by being laid on level ground. No great area
is needed for this storage ; and it dries fairly quickly. The dried
residues are sold to farmers as manure. The Frankfort grit' chamber residues contain about 0.12 per cent N, 1.o1 per cent
phosphoric acid (P2O5), and 0.12 per cent potash (K20) in the
dried substance. The residues accumulating every day from a
fine screening plant are about as considerable as those from grit
chambers. They consist mainly of excreta and paper. They
contain about 80 per cent of water. The dried substance consists
almost entirely of organic matter. They also are stored, dried
in the air, and are sold either wet or dry as manure. Although
these residues do not occupy much room in their storage, still, on
account of the faeces they contain, and the consequent offensive
smell, they may be very disagreeable. Residues from the Frank
fort screens contain, when dry, about 0.82 per cent N, 1.57 per
cent P2O5, and 0.40 per cent potash (K2O).
By far the most important portion of the residue accumulating
is the sludge from the sedimentation tanks. It settles to the
bottom of the tanks, wells, etc., in the sedimentation process and
forms a continually decomposing black mass which is of pulpy
or watery consistency, always evolving an extremely offensive
smell. The sludge consists mainly of triturated faeces, paper
fibre, coffee dregs, sand, etc. Its black colour arises from small
quantities of sulphide of iron, formed by the interaction of the
sulphuretted hydrogen resulting from the fermentation in the
sludge with the iron salts present in the sewage. It generally
contains 90 to 95 per cent water. The composition of the dried
substance depends upon the local circumstances and the sedi
mentation process employed. Sludge separated mechanically
and without the addition of chemicals contains, in the dried
material, about 50 per cent organic and 50 per cent mineral
matter. It further contains, in substances of nutritive value to
plants, approximately 2 to 3 per cent N, about the same amount
of phosphoric acid (P2O6), and about 0.5 per cent potash (K20)
in the dry substance. The high grease content of the sludge
from sedimentation tanks is noteworthy. Frankfort sedimenta
tion sludge contains on an average about 18 per cent grease in
the dried substance. This grease arises in part from the grease
of factories, cooking refuse, and faeces, mainly, however, from the
soap used in washing. The alkali soaps are decomposed by the
DRYING THE SLUDGE
99
lime salts in the sewage and yield insoluble lime soaps, which are
precipitated in flakes and settle to the bottom of the tanks or
wells in the sedimentation process. The grease, which is separated
from the sludge by slightly acidifying with sulphuric acid, has
the following composition : 68 to 73 per cent free fatty acids
coming from the soaps ; 18 to 20 per cent neutral fats (faeces,
fat, grease from cooking effluents) ; 7 to 14 per cent unsaponifiable portion (lubricating oils). It can readily be understood
that these numbers may be very different with sludge from a
sedimentation plant which works up large amounts of industrial
effluents, as is the case in Frankfort.
The chief difficulty in sludge disposal is the large amount of
water it contains. Since this amounts to 90 per cent or more, it
not only occupies very valuable space, but also the large amount
of water offers to anaerobic or putrefactive fungi of the most
varied kinds a nutritive substrate which very quickly assumes
a foul and stinking condition.
The whole problem of sludge disposal is the removal of the
water.
(ii) Drying the Sludge.
The most widely disseminated process, and the one longest in
use for drying sludge, is to spread it on the land. A part of the
water thereby drains away into the ground and another portion
evaporates. The removal of water takes place very slowly,
however, on account of the slimy nature of the sludge. Months
and years go by before the sludge is dry. The consequence is
that the place where sludge is stored is very noticeable, especially
in warm years, on account of its extremely disagreeable smell.
The gas arising during the fermenting process from the sludge is
combated by covering the sludge with some protecting material
like turf, tar, etc., or decomposition is checked by covering the
uppermost layer with disinfectants (saprol, tar, chloride of lime,
etc.). As too deep a layer of sludge cannot be deposited on the
storage-ground if it is not to take too long to dry, the storage of
sludge becomes rather costly, as considerable expenditure is
entailed in purchasing land. Fresh sludge from sedimentation
tanks and wells shows all these unacceptable features when
spread out on the land, but septic-tank sludge has much more
favourable properties. It has a higher percentage of dry sub
100
SEWAGE DISPOSAL
stance than fresh sludge, its smell is less offensive, but, above all,
it gives up its water much more readily when brought on to the
soil.
According to Spillner, Emscher-well sludge should have all the
good properties of septic-tank sludge. It contains considerably
less water than sludge from septic tanks. With 70 per cent water
it is pulpy and quite mobile, and it has no offensive odour.
Spillner carried out parallel experiments on the removal of water
from fresh and from Emscher-well sludge. The experiments
showed that the fresh sludge needs a much longer time to reach
firm consistency than does the sludge which has been liquefied,
and also that fresh sludge gives up much less drain-water than the
liquefied sludge.
The favourable results obtained with liquefied sludge are due,
according to Spillner and Imhoff, to the higher content of dry
substance which septic -tank sludge possesses, to the greater
amount of gas which partially putrefied sludge contains, and to
the fact that in such sludge the colloids, which are the main cause
of the tenacity with which the water is held, are destroyed
during the decomposition process.
Sludge-drying by drainage is carried out on a large scale with
Emscher wells in the plants at Essen, N.W., Bockum, and
Recklinghausen-Ost. The results, so Spillner reports, are as yet
very favourable.
A drying process employed in England consists in bringing the
sludge into a freshly opened ditch. The water is drawn out more
quickly by the loosened soil. As soon as the sludge is so dry that
it can bear the soil which has been dug out, the latter is filled in.
With sludge from sedimentation tanks the drying is still a very
wearisome process.
In Gottingen and Kassel the sludge is compounded with refuse.
It is readily understandable that efforts have frequently been
made to replace the method of drying sludge on the land by a
process permitting quicker drying. Filtration is the most
important of the methods considered. It has given poor results
in many localities. The colloids in the sludge render the removal
of water by filter-presses impossible, since they very soon choke
up the filter fabric. If the mud be expressed when hot, or chemicals
be added, the results obtained are better, but the process then
becomes very expensive. To the knowledge of the author filter
DRYING THE SLUDGE
101
presses are on this account never used in Germany. In England,
nevertheless, they are not infrequently used for removing water
from sludge. In these cases the sludge is obtained in sedimenta
tion processes in which chemicals are employed, and therefore
contains considerable amounts of lime.
Much better results have been aimed at in recent times by the
use of centrifuges.
At Frankfort -on -Maine, Harburg, and
Hanover the sludge from the sedimentation processes is freed
from water by centrifuges of the Schafer-ter-Mer type. This
apparatus is, mechanically and hygienically, the most perfect
apparatus designed for the removal of sludge by the aid of
centrifuges. It works perfectly automatically, and the workmen
do not come into contact with the residues at all (Figs. 20 and 21).
The sludge flows from the feed reservoir through a vertical rotary
axle and into the centrifuge in such a way that it is distributed
into six presses arranged radially to the axle, and separate one
from another. These presses or compartments are divided by
vertically placed sieves into a sludge space and sewage space.
The sludge enters the sludge portion, in which the coarser
particles are whirled to the outside by centrifugal force (about
750 revolutions per minute), whilst the sewage is conveyed
through the sieves into the neighbouring sewage space. The
sieves are prevented from choking by an automatic cleaning
device. When the centrifuge has been working from one to two
minutes the sludge chambers are completely filled. The sludge
supply is then automatically cut off by a circular disc. Imme
diately subsequent to this another circular disc opens which
serves to close the presses usually, and through the opening so
obtained the centrifuged sludge is hurled out of the presses.
After the disc has automatically closed the press, the disc at the
sludge inlet opens, and the process is repeated. The machine
works without any stoppages. The opening and closing of the
discs is automatically set working by oil-pressure with the help of
a certain mechanism. The machine requires no attention apart
from the removal of the oil. The cost is rather considerable ;
it amounts, according to Reichler and Thiesing, to 1 shilling
per 10 cubic feet of dried sludge, whilst removal of water by
filter-presses should only amount to 8d. A further disad
vantage of the process is that the sewage flowing out of the
centrifuge still contains a large quantity of solid substances.
102
SEWAGE DISPOSAL
This disadvantage, however, does not alter the fact that the
method is at the present time the only one permitting rapid
removal of water from sludge in a relatively simple manner, and
one free from objection from the point of view of hygiene.
In Frankfort, experiments carried out on a small scale to
Fig. 20, Centr1fuge for Sludge : Schafer-ter-Mer System.
remove water by an electro-osmotic process have not yet been
tested on a large scale.
Towns near the sea often get rid of sludge in the handiest way
by sinking it in the sea. Though the method is one of the cheap
est, it is not so cheap as might at f1rst be believed, for sludge
vessels must proceed a good way out to sea if the tide is not to
throw up the sludge on the shore. According to Spillner, the
DRYING THE SLUDGE
103
method is employed, among others, in London, Manchester, and
Salford, and it is proposed for many other localities, e.g. Belfast.
London possesses a whole fleet of sludge vessels, each of which holds
1ooo tons and costs £30,000, not to mention the large iron
F1g. 21. Centr1fuge for Sludge: Schafer-ter-M er System.
tanks on the plant in which the sludge is stored prior to the arrival
of the vessels. The London vessels take the sludge sixty-five
miles out to sea, while Manchester and Salford have a ship which
goes fifty miles out to sea. On an average three journeys are
made per week.
104
SEWAGE DISPOSAL
Weldert reports in a preliminary communication that by
adding saltpetre, sludge from sedimentation tanks, as well as
sewage, loses its capacity to putrefy. As the foul nature of
sludge is one of its greatest nuisances, it may be possible to treat
it with nitrates and then dry it in the air.
The costs of the various methods of sludge disposal are given
by the last English Royal Commission on Sewage Disposal as
follows : —
Land treatment
About 2d.
Sinking in the sea
,, 5d.
Digging into trenches
,, 5d.
Filter-presses
,, 6d. to 1s.
Presses and combustion
,, 1s. 6d.
per ton of aqueous sludge containing about 90 per cent
(estimated)
of water,
inclusive of interest on plant capital and all expenses, charges,
and taxes, without reference to the value of the sludge as manure
or to its calorific value.
(iii) Profit from Sludge.
To cover at least a portion of the expense incurred, attempts
are continually being made to realise a profit from the disposal
of sludge.
Sale for agricultural manuring purposes is the method which
has been used most frequently. As has been already pointed out,
sludge contains in no inconsiderable amount substances nutri
tious to plants, especially nitrogen (generally 2 to 3 per cent in
the dried material).
Wet sludge, from which no water has been removed, is only
employed as manure in those places where there is agricultural
work in the neighbourhood of the sewage plant to which it can
be delivered. Damp sludge could not bear the cost of carriage
to greater distances, as its manurial value would not be in any
way proportional to this cost, apart altogether from the con
sideration that it would not be practicable, on account of the
nuisance due to smell. In Frankfort, till recently, the fresh sludge
was, in part, directly sprinkled over the fields in adjacent agri
cultural undertakings. For this purpose long pipes were laid
to which movable pipes could be attached.
PROFIT FROM SLUDGE
105
Frequently experiments have been carried out with a view to
further drying the sludge which had previously been freed from
a portion of its water by the above-mentioned methods, and with
a view to selling the dried product as poudrette (artificial manure).
Ten years ago in Frankfort such a plant was worked. The sludge
was freed from water on the storage-grounds until quite firm, and
was then dried further in a drying plant until it contained 10 to
20 per cent water. The " poudrette " thus obtained contained
about 1-7 per cent nitrogen and 2 per cent phosphoric acid. The
residue in nitrogen as compared with the above-mentioned
numbers, shows clearly that part of the nitrogen is present in the
form of ammonia which volatilises on drying. The method was
a failure, since a hundredweight of dried poudrette cost about
a shilling. Similar results have been obtained in towns that
have tried to prepare artificial manure from sludge, so that this
method of making a profit can now be considered non-existent.
The large amount of grease in sludge from sedimentation pro
cesses has over and over again provided an inducement for deter
mining a rational method of extracting the grease. When no
special circumstances are present requiring a recovery of the
grease, or when the sludge does not possess an abnormally high
percentage of grease, its recovery from the sludge coming from
domestic sewage has proved irrational.
The recovery of grease is fairly difficult, as it is so intimately
mixed with the remaining particles of sludge that the specifically
lighter fatty particles do not rise to the top, or do so with great
difficulty. With the aid of the previously mentioned grease ex
tractors, separation into layers of sludge rich in grease and poor
in grease could be effected. The sludge rich in fats could then
be worked up by extraction on the lines of the method described
below. In practice this method has not yet, to the knowledge of
the author, been applied.
Further, the greasy scum obtained from sewage from slaughter
houses, hotels, and the like might be worked up, as it consists
mainly of fats. Whether this is carried out in practice is also
unknown to the author.
According to Schiele, the sedimentation plant at Bradford
treats a sewage from wool scouring which is very rich in grease,
and a part of the sludge is worked up for grease in the following
manner : After addition of sulphuric acid the sludge is heated
106
SEWAGE DISPOSAL
to 1oo0 C. and expressed in hot filter-presses. The greater part ot
the water and the grease is thereby removed. The residue after
expressing still contains 30 to 40 per cent water and 25 per cent
grease. From the filtrate the grease separates out on the top,
and after washing and deodorising it is sold, generally to
America. In the Bradford plant the total sewage must be treated
with sulphuric acid to decompose the dissolved soaps. The
proceeds from the sale of grease cover about half the cost of the
sulphuric acid. The grease residues remaining over are burned
with one-eighth the amount of coal, as on account of the large
percentage of grease present it is not saleable as manure. In an
experimental plant the recovery of grease from the press residues
was tried. The residues are heated in retorts from which the
grease distils over. The residue remaining in the retort should
then be suitable for addition to artificial manure, since it contains
some phosphoric acid and about 1.5 per cent nitrogen.
The town of Kassel has for two or three years worked a greaserecovery plant with a machine attached to their sedimentation
plant. The sludge is acidified with sulphuric acid, expressed in
filter-presses, and then extracted with benzene. The reports
sounded very favourable, but the process was very soon dis
continued, due to the firm working it having experienced a loss
on the undertaking. The cause of the non-success lay, firstly, in
the high cost of drying the sludge, and secondly, in the yield of
grease being considerably lower than was anticipated.
In Frankfort, extraction of wet sludge with benzene was in
vestigated with a mechanical arrangement in a small experi
mental plant. A practical application of this process has not yet
been effected on the large scale.
To my mind, therefore, no solution of the problem of grease
recovery from sedimentation sludge need be expected. It is
easy to be attracted by the, no doubt, considerable value of the
grease present in these residues. Thus the grease present in
Frankfort sludge obtained in one year has a worth of
about £25,000.
If, however, in order to recover this sum
an expenditure of £50,000 must be incurred, the transaction
is not a profitable one. According to Schiele, an English
manufacturer whose attention the Royal Commission on Sewage
Disposal drew to the fact that in his effluents there was
contained so much valuable material, replied : " It is worth no
PROFIT FROM SLUDGE
107
more to me than a piece of gold at the bottom of the sea. It
costs me too much to get it up." This answer can be adapted to
practically all attempts at the recovery of grease from ordinary
sedimentation sludge. In addition I might also for a moment
call attention to something to which up to the present, as far as
I know, attention has not been directed. To a judge of the
circumstances it is at once probable—and the plant at Kassel
has established this in fact—that benzene extraction, grease
distillation (for the recovery of pure grease from crude grease),
and other operations cannot be conducted without smells ; on
the contrary, a very obnoxious odour is generally developed,
which is noticeable for a great distance around. Now municipal
sedimentation plants are by no means all far away from the town,
so that there is a danger that, with a diminution in the rental
value, that part of the town in which the sedimentation plant is
situated may depreciate in value. However, quite apart from
aesthetic and hygienic considerations, which must be urged
against a continual smell owing to the association of a plant and
dwellings, this disadvantage might possibly not be accompanied
by a profit from the sale of the grease. And so municipalities
occupied with the idea of recovering grease from their sewage
can only be pursued with the cry " videant consules."
A method of making profit frequently adopted of late years is
the destruction of sludge by fire, either by simple burning or by
gasification, in which processes the heat or the gases obtained
are employed in the production of other forms of energy. If the
sludge cannot be burned of itself, combustible material such as
turf, coal, borecole, must be added. Even if no profit results, or
the cost of disposal be only in part covered, this method of dis
posal or of realising a profit from these residues is the best, as it
is the one most worthy of recommendation from the hygienic
point of view.
The town of Frankfort now disposes of its sludge in the following
way : It is first pumped out of the sedimentation tanks into
large reservoirs which are situated over centrifuges of the Schaferter-Mer system. In these reservoirs a portion of the water is
separated and led back to the sedimentation tanks. The sludge
is then centrifuged. It is then mechanically forwarded to a
drying drum, in which the centrifuged material with about 70
per cent water is further dried by hot gases from the refuse
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SEWAGE DISPOSAL
destructor plant. The sludge coming from the drum still contains
about 25 per cent water, and is now burned in the refuse ovens.
Addition of other combustible material is unnecessary, as the
dried sludge burns of itself. From a kilogram of sludge about a
kilogram of steam is obtained. Burning of the sludge is therefore
attached to the refuse destructor, which is situated near the
sedimentation plant. The current obtained from the dynamos
driven by the burning of the sludge and refuse not only illuminates
the whole plant and yields power for the plant, but there is also
a considerable portion conveyed through high-tension cables to a
pumping-station in the Stadtwald, where by means of the current,
electric motor-pumps are worked and serve to raise drinkingwater. Besides this there is a considerable amount of current
delivered to the town supply.
In Bury the sludge is mixed with refuse and burned (Schiele).
In Pforzheim (Germany) sludge combustion is similarly
provided for alongside the refuse destructors.
In the years 1902 and 1903 gasification experiments were
carried out with Frankfort sludge by Bujard. He found, as the
mean of two experiments with gasification lasting four hours,
using 50 kilograms of dried sludge, the following volume per
centages were given :—
Yield per 100 lb. sludge= = 320 cubic feet of gas.
Carbon dioxide
Heavy hydrocarbons
Carbon monoxide .
Methane
Hydrogen
Nitrogen (residue) .
16.1%
5. 8%
22.8%
13.2%
35.8%
6.3%
Calorific value for 1 cubic metre =3620 to 4072 W.E.
Reichle and Dost report upon gasification experiments with
coal-pulp sludge : Its gasification is only possible with a certain
amount of water present, which must not be over 58 per cent ;
the gas gave on the average in volume percentages
Methane
Carbon dioxide
Nitrogen
Carbon monoxide
0%
n.o%
62.6%
14.2%
PURIFICATION OF INDUSTRIAL SEWAGE
Oxygen
Hydrogen
.......
109
1.o%
n.2%
The calorific value amounted to only 800 W.E. The gasifica
tion of 2.5 kilograms of the sludge with about 51 per cent water
yielded about 1 horse-power per hour. In the gasification a
grease-like substance distilled over ; the water gas in the dust-bag
contained 2208 milligram total nitrogen per litre, of which
1494 milligram was present as ammonia. Reichle and Dost
consider that the introduction of gasification with the sludge
from Degener's coal-pulp process would considerably reduce the
high cost of working which has been a hindrance up to the
present, and conduce to the more general introduction of this
otherwise very advantageous process.
In the town of Kopenick, near Berlin, coal-pulp sludge is
gasified on a large scale. The power gas obtained is converted
into electrical energy.
B.
Purification of Industrial Sewage.
I.
GENERAL.
Most towns take industrial effluents into their drainage system
in return for a fee ; they then demand that the sewage never
contains substances harmful to the drains (acids, alkalies, com
bustible material, etc.), and that the purification of the whole
sewage is not rendered much more difficult as a consequence of
the introduction. Consequently, there are already large manu
facturing towns whose sewage contains quite considerable
amounts of industrial sewage admixed. For purifying such
municipal sewage chemical precipitation is to be recommended
in the sedimentation plants. With contact beds and percolating
filters the plant must be larger in its dimensions than would be
necessary for the corresponding amounts of domestic sewage.
The reception of industrial sewage makes the process of sewage
purification more expensive for municipalities. Nevertheless,
the endeavour to receive industrial effluents into the ordinary
sewerage system is to be welcomed and recommended. Other
wise separate plants in the various manufactories must result to
a great degree. Now larger plants, for the reasons which have
already been frequently mentioned in other chapters,, are worked
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SEWAGE DISPOSAL
more rationally and with greater security than smaller plants.
Again, the erection of separate sedimentation plants is contrary
to all the fundamental principles of drainage systems, according
to which all refuse should as far as possible be conveyed out of the
town. With manufacturing plants, however, the residues must
be allowed to accumulate on the works' premises.
Although it seems desirable to convey industrial sewage
through the ordinary sewers, there are still very many cases in
which purification of industrial sewage itself is necessary. Where
towns refuse to receive the sewage or demand a previous slight
superficial purification, and where there is no sewage system as
in works and in isolated places, the industrial effluents must
themselves be purified if the stream conducting it away is not to
be harmed by the incoming sewage. Therefore the purification
of industrial sewage is a question becoming ever increasingly
important.
The sewage produced in works can be divided into three
groups :—
(1) Closet, cooking, washing, and bathing water.
(2) Condenser, cooling, and washing water.
(3) The particular works sewage.
The first group comprise effluents which are domestic in
character, whose purification has been described in the previous
chapter.
The kinds of sewage named in section 2 are generally very pure.
It is always advisable to keep them separate from the particular
forms of sewage of the third group, as if this is not done the
sewage is simply diluted and the difficulties of purification are
considerably increased. This is to be recommended, as the water
from the second class often very considerably preponderates over
that of the third. Cleansing and condenser water is frequently so
pure that it can be drained away without any purification or
after treatment in a sedimentation tank.
To give a general composition for particular works effluents is
naturally impossible, as this depends wholly on the nature of the
work carried out. It is therefore also impossible to set forth
general rules for the purification of industrial sewage. Only this
much can be said, that the general principles of purification are
the same as in the case of domestic sewage, and therefore consist
of either mechanical purification by sedimentation tanks, or
PURIFICATION OF INDUSTRIAL SEWAGE
111
biological purification by broad irrigation, contact beds, or
percolating niters. In the sedimentation process it is always
advisable to make use of chemical precipitation, with the addition
of chemicals which have been proved to be suitable by experi
ment for the particular kind of sewage.
It is to be recommended much more with industrial effluents
than with household sewage that tests be made, on the basis of
a chemical investigation of the sewage, to determine the most
suitable method of purification.
Frequently, of course, partial purification is to be attained by
combination of different kinds of effluents. Thus, acid and alkali
discharges partially neutralise one another. Effluents con
taining lime precipitate heavy metals or alumina and the like.
Such a combination of the various effluents is often sufficient to
effect sufficient purification after sedimentation.
An arrangement which can be recommended for works clari
fying plants is the keeping of a reservoir. It is now used in very
many works in which at one time highly polluted and large
amounts of sewage are produced, and at other times little and
only slightly polluted sewage is formed. For if large amounts of
strongly polluted sewage are suddenly conveyed to a stream, it
means much greater harm is being done to the river than if the
whole sewage of 24 hours was slowly and uniformly discharged
into the river. For this purpose tanks must be laid down capable
of storing the effluent resulting from a day's working. Now and
then, when the river is sufficiently high and the sewage does not
seem too filthy, further purification than is assured in these
reservoirs is quite unnecessary.
Lately, also, industrial effluents have been used to lay the dust
on the roads.
According to Weldert, for this purpose, under certain circum
stances, there come into consideration effluents from ammonia
works, potash works, cellulose works, sugar refineries, coke
plants, spinning mills, wool factories, fulling mills, and ammoniasoda works. Experiments of Weldert with ammonia effluents
yielded favourable results. The problem of dust-laying will be
more closely studied under the various particular classes of sewage.
For the purification of works sewage the filter is frequently
used. Under the term " filter " no biological filters are under
stood, but apparatus, constructed, of course, of similar materials
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SEWAGE DISPOSAL
to them, but which, however, are worked continuously. Their
action therefore is the purely mechanical one of retaining the
suspended matter. They are generally prepared of cheap unsieved material, clinkers from boiler-fires predominating. This
filter is used both for the subsequent purification of clarified
works sewage and also for the removal of water from sludge
(Magma Filter). For the treatment of percolating filter discharge
such filters are also used.
II.
THE PURIFICATION
IN PARTICULAR.
OF INDUSTRIAL SEWAGE
With Fowler and Ardern we can classify industrial effluents,
according to the substances through which they act harmfully,
thus :—
(1) Effluents with large quantities of suspended matter.
(2) Effluents with substances that may decompose.
(3) Coloured effluents.
(4) Effluents containing poisons.
(5) Effluents containing oils, tars, fats, soaps, etc.
Many effluents may naturally come under several of the head
ings mentioned.
Effluents of the first kind can generally be sufficiently purified
by settling devices, sieves, rakes, filters, etc. Effluents from
coal-washing and cloth factories, etc., might be named here.
Effluents of the second kind are very disagreeable. They are
purified by chemical precipitation with subsequent sedimenta
tion, or by the land treatment, or by means of contact beds or
percolating filters, as was set forth in the previous section. The
chief and most important effluents belong to this class, for
example, those from tanneries, cellulose works, breweries, sugar
refineries, etc.
The purification of coloured effluents is still an unsolved
problem. No method is yet known of decolorising coloured
substances in a satisfactory and continuous manner. In general
decolorisation is more difficult, the faster the colours. Chemical
precipitation and various biological methods are employed.
With contact beds and percolating filters the colouring matter is
absorbed by the beds for a time, but after a certain period the
colour passes through unchanged.
PURIFICATION OF INDUSTRIAL SEWAGE
11B
Purification of sewage containing poisons must naturally
depend on the chemical nature of the poison. Acids are generally
neutralised with lime, and alkalis with sulphuric acid. Heavy
metals are precipitated by lime, etc. Cyanides can be separated
as Prussian blue with sulphate of iron and caustic soda. Under
this heading is comprised sewage from metal works, gas works,
tanneries, sulphite cellulose works, etc.
Sewage containing oils, fats, and soaps are finally purified by
the separation of the fat particles, in the case of soaps after the
addition of sulphuric acid. Under this heading are the effluents
from margarine works, wool-scouring works, slaughter-houses,
etc., which may also all be reckoned under section 2.
According to this general point of view an industrial effluent
may be classified and the manner in which the purification
process has to be carried out may be given. The extraordinary
variety of particular effluents in the four groups makes a closer
examination of the particular kinds of sewage seem worthy of
attention. I shall endeavour to mention all the classes of sewage
coming at any time into consideration.
(1) Sewage from Cloth Factories or Factories whose Effluents
contain Fibrous Material.
Reichle and Zahn describe a drum filter by A. and A. Lehmann
that is very suitable for recovering fibre of any kind from sewage.
The apparatus consists of a movable drum which is covered with
wire netting 1 millimetre mesh. The sewage streams through
the drum and leaves the fibre behind. From the works in ques
tion 22 tons of wool were obtained in nine months.
(2) Sewage from Cardboard Factories.
According to the laboratory experiments of Sjollema, the
addition of monocalcium phosphate (superphosphate) is most
suitable for the purification of this sewage, as it forms tricalcium
phosphate with the free lime present in solution. This is pre
cipitated out and settles down along with the suspended matter,
together with, also, a portion of the dissolved substances. The
precipitate after drying can be used as manure.
1
114
SEWAGE DISPOSAL
(3) Sewage from Straw-board Works.
These works produce very large amounts of sewage, which
contain many fine particles of straw mixed with lime.
The sewage can be purified by sedimentation (capacity of the
tanks being one hour's supply) and by filtration through me
chanical filters without the addition of a precipitant (rate of
filtration equal to 95 cb.m. through 1 sq.m. of filter every 24
hours). The filtered sewage can then be used again in the works.
According to Kimberley, the sewage so purified can be drained
into the river without harm if the stream contains twice the
amount of water present in the sewage. Sjollema recommends
his above-mentioned precipitation method with superphosphate
for this sewage.
(4) Effluents from Mines (Coal-washing).
Effluents from waterworks in mines consist of waters from
washing coal and from quenching coke. It is not advisable to
purify these effluents along with domestic sewage, for then the
sedimentation tanks have to be built abnormally large. In the
quenching of coke the water is used over and over again ; from
time to time, however, it must be withdrawn from circulation
and purified. This is generally effected in settling tanks. The
Imhoff-Lagemann patent is especially suitable for this purpose.
The bottom of this tank is drained. The drains terminate outside
the settling tank and are closed during the settling process.
They are opened only to dry the sludge.
Sometimes before its entry into the river the sewage is allowed
to flow through a filter of boiler-clinkers. The coal sludge ob
tained is either burned or worked up as coke.
According to the experiments at the Halle AgriculturalChemical Experimental Station, the resinous water from borecole
coke works is especially suitable as manure, since it may develop
a considerable nitrifying action without fear of any harm being
done to the plants by manuring the roots. It is most strongly
recommended as a manure for meadow or pasture land.
(5) Sewage from works Granulating Slag.
Many works, e.g., smelting works, have plants for granulating
slag. The fluid slag is allowed to flow into water, by which means
PURIFICATION OF INDUSTRIAL SEWAGE
115
it is broken into small pieces. The effluents resulting from this
are hot and contain large amounts of fine slag, of which a part
sinks and another part floats on the surface.
The firm " Stadtereinigung und Ingenierbau-A.-G., BerlinWiesbaden " have constructed devices for the purification of
such effluents which should work quite satisfactorily. The idea
of these plants is that the sewage is led with fairly slow velocity
through a sedimentation tank, by which means the heavy
particles sink to the bottom. The floating material is removed
by the aid of several channels which are placed obliquely to the
direction of flow, and are provided with various devices cor
responding to the purpose for which they are constructed. The
floating slag skimmed off is led into a second tank which is at
rest, and in this the floating substances are stored up until the
layer has reached a certain strength. Thereupon the water
underneath is drained away, so that the scum sinks to the bottom.
The slag from the two tanks is then bagged.
(6) Sewage from Paper Mills and Cellulose Works.
In the manufacture of paper, rags, hemp, jute, esparto grass,
straw, and wood are all used.
The main effluent from all these raw materials is the alkaline
water obtained by boiling them. To this must be added the water
from washing and cleansing the raw materials after they have
been digested, the discharge from the Hollanders, the water
containing both acid and chlorine from the bleaching process,
and finally the discharges from the paper machines and dyeing
process.
Separate treatment of the different kinds of effluent is advis
able. The sewage coming from the paper machines allows of a
recovery of the fibrous material in specially erected settling
tanks, and the effluent therefrom may be used again. The above
sewage may be purified, however, to the requisite degree by
chemical precipitation and sedimentation or by means of sand
filters.
The effluents from wood-pulp or cellulose works are of great
importance. Cellulose in Germany is entirely prepared by the
sulphite process. Fir and pine is treated in so-called digesters
or boilers at high temperatures and under pressure with calcium
116
SEWAGE DISPOSAL
bisulphite. The soluble material is thereby removed and the
wood fibre isolated. The fibrous residue is then expressed and
washed free from the strong liquors. There thus accrue to the
sewage : boiler liquors and washing liquors, water from the sieves,
presses, and from the machines for removing water from the
cellulose, in addition to condenser water. The boiler liquors are
the worst, for they contain about 100 grammes of organic matter
per litre, and consequently, if conveyed to the river without
further treatment, cause grave inconvenience owing to putre
faction, and especially to the formation of fungi (Sphaerotilus) .
In most works the sewage undergoes a superficial purification.
The suspended matter is filtered off after a partial recovery of
the sulphur acids, and the liquors are cooled down and neutralised
with lime. The sewage is subsequently treated in sedimentation
tanks. Dissolved material is, however, scarcely influenced by
this process, and they are the substances that exert a harmful
influence on the river carrying the sewage away. The purifica
tion of the liquors by the biological process is impossible, even after
great dilution of the sewage, firstly on account of the difficulty
of decomposing the liquors, and secondly on account of the
harmful action on the micro-organisms of the sulphurous acids
present in the lye.
Possibilities of making a profit from such sewage have been
investigated, and the very numerous proposals made with this
object in view have only partly led to practical results. Evapora
tion and combustion of the product is very costly, and the works'
profit comes into the question. In rare cases only is the sewage
allowed to trickle away, and this depends on the local circum
stances.
Researches on the recovery of sulphur, on the employment
of the organic substances in the liquors as combustible material,
whether directly or after making briquettes of it with coal, coke,
or furnace dust, have not yet yielded any practical results.
Further, it is proposed, after the removal of harmful material,
especially the sulphur acids, to work up the liquors as feedingstuffs ; these proposals, also, have not been put into practice.
On the contrary, the liquors have been used, after certain sub
stances have been added, as adhesives, and most recently have
been used to lay the dust on the streets. Their value as manure
to be added to " Thomasmehl," and their application in tanneries,
PURIFICATION OF INDUSTRIAL SEWAGE
117
are still undecided questions. Fermentation of the sugar pro
ducts found in the residues and the recovery of alcohol is already
carried out in practice in Sweden, but in Germany the pursuit
of this process is not profitable owing to the big duty which is
paid on alcohol since the recent legislation concerning duty on
brandy. The recovery of colouring matter from the boiler liquors
is already a successful process, but the problem needs further
investigation (Pritzkow).
Besides the " sulphite " process, there is the " soda " process
for the preparation of cellulose, in which the wood is digested
with caustic soda instead of calcium sulphite. The method is by
no means as important as the sulphite process. The caustic soda
liquors are the worst effluents in this case, and are to be as care
fully treated as the sulphite strong liquors.
Logau evaporates the residues and ignites them ; the heat
obtained by the ignition is used in evaporating further quantities
of the liquors. Fire for combusting the material only needs to be
used at the commencement of the operation. Soda is recovered
from the ashes. Rimman saturates the liquors with carbon
dioxide after they have been raised to a certain specific gravity
by the addition of soluble salts. A part of the organic matter
present is thus precipitated.
(7) Sewage from Breweries.
The major portion of brewery sewage is cleansing and washing
water. It is consequently only slightly polluted. On the other
hand, the effluents of the process itself are greatly polluted,
especially those from the malting, from the drying of the hops
and grain, and from the yeast. This sewage has a strong
tendency towards putrefaction on account of the large amount
of organic matter that it contains. It has a tendency also to
form lactic acid.
Partial purification consists of chemical precipitation followed
by sedimentation.
This kind of purification is, however, generally insufficient.
Where more thorough purification is impossible, the sewage
should be immediately conveyed to the drains.
Brewery sewage is best purified by land irrigation.
After the addition of lime (neutralisation of the lactic acid)
118
SEWAGE DISPOSAL
these effluents can be purified on contact beds, but best of all in
percolating filters.
(8) Tannery Sewage.
In tanneries there are principally three classes of effluent,
from the liming process, the dye liquors, and tanning liquors.
The lime effluents, which result from the unhairing or depilation of the hide, contain lime principally, sodium sulphide, and a
large amount of decomposable organic substances (pieces of hide,
hair). Under certain circumstances, if foreign hides are being
worked up, napthalene may be present as a preservative for the
skins.
Tanning liquor contains either tannic acid or chromium salts.
The tanning effluents therefore contain these substances. Fre
quently, also, other chemical compounds like sodium thiosulphate, arsenic salts, etc., are present.
The dyeing liquors are used to dye the leather ; the sewage
resulting from this part of the industry has the same colour as
the dyeing liquors.
All tannery effluents are generally putrefactive to an unusually
large extent. They therefore have a very harmful action on the
stream conveying them away if they are led into it directly or
with insufficient purification.
They are therefore best run into the drains after preliminary
purification in settling tanks. According to Schmidtmann,
Thumm, and Reichle, they will even then frequently give trouble,
when, for example, tan sewage containing sodium sulphide comes
into contact with acid effluents, like those from breweries. The
resulting evolution of sulphuretted hydrogen will be a great
source of annoyance in the streets.
If it is not possible to run the sewage into the sewers, a large
reservoir is to be recommended for a works.
A partial purification can be attained occasionally by com
bining the various kinds of effluent. The lime from the liming
process precipitates chromium salts, and then the sewage is
clarified in settling tanks. In certain cases, therefore, chemical
precipitation can be dispensed with. It is better, however, to add
chemicals in calculated quantities.
When more thorough purification is necessary it is best to use
broad irrigation, preceded by treatment in septic tanks. If the
PURIFICATION OF INDUSTRIAL SEWAGE
119
artificial biological process is employed, double -contact beds
seem to work better than percolating filters. Arsenic and other
poisonous substances must be removed before any biological
purification is taken in hand.
(9) Sewage from Dairies and Margarine Works.
The sewage from such places contains particles of milk
collected together. One would therefore expect albumens,
carbohydrates, fat, lactic acid, etc., in such effluents, which are
therefore highly putrefactive.
Kimberley, acting for a Commission in the State of Ohio,
U.S.A., undertook a detailed investigation of the sewage from
dairies. If the amount of water in the river receiving the sewage
be thirty times as great as the sewage itself, then, according to
this author, dairy effluents can be discharged into the river after
treatment in settling tanks. These tanks should be twice as
large as a day's effluent requires.
In other cases, dairy effluents may be purified by intermittent
sand filtration until they are incapable of putrefaction (22,000
gallons per acre of filter surface).
In Germany they are frequently purified by ordinary land
irrigation. They are generally previously clarified in masonry
tanks. To prevent nuisances due to bad odours disinfectants
(chloride of lime) are added to the sewage in the tanks. According
to Guth a good soil cannot take up more than 6 gallons per square
yard. Grass, clover, and trees thrive very well on the fields
irrigated. In the opinion of Dunbar, an effluent from a dairy, if
not too concentrated, can be purified by the biological processes,
and most successfully with percolating filters continuously
employed. For the biological process the sewage must be pre
viously purified by chemical precipitation, to neutralise the lactic
acid, as otherwise purification would be insufficient. According
to Guth, not more than a cubic metre of sewage should be applied
to a square metre of surface, that is, 0.5 cubic metre of filter
material.
Harm precipitates dairy effluents with acid silicates (the waste
from the manufacture of alum) and with lime. He asserts that
he has obtained good results from lengthy investigations. Informa
tion is lacking as to the cost and the resulting sludge.
120
SEWAGE DISPOSAL
Partial purification can be attained by precipitation with
sulphate of iron and lime, followed by sedimentation.
(10) Sewage from Slaughter-houses, Knackers' Yards, and
Glue Works.
Slaughter-house sewage is generally very concentrated, is
readily decomposed, and has an especially harmful action on the
stream receiving it. It contains blood, fat, flesh, manure, and
slaughter-house refuse of every kind.
It may be partially purified by treatment with iron or alu
minium sulphates, followed by sedimentation.
For mechanical purification automatically working clarifying
boilers by Mertens of Berlin have been employed (Swinemiinde,
Paderborn-i.-W.).
In Kiel, during 1905, an experimental plant was erected for
the purification of slaughter-house effluents by means of the
biological process. Meanwhile, many towns have employed it
for the work with success. Preliminary purification in septic
tanks should be very suitable with such sewage.
Thiesing studied the sewage coming from the knacker's yard
and also its disposal. It comprises the water used in cleaning
the places in which the horses are killed, the glue liquors, the
waste liquors from steaming the carcases, the glue condenser
water, and mixtures of these kinds of sewage. They are all very
concentrated and readily decomposable. Up to the present,
according to Thiesing, the treatment employed with such effluents
has always been insufficient. It is necessary to observe that
rain-water does not pass through the purification plant. On the
other hand, domestic sewage may be treated along with it.
Broad irrigation and the biological process should be very
suitable for the purification of such sewage. With such treat
ment preliminary purification in septic tanks and grease separa
tors is to be recommended.
(11) Sewage from Sugar Refineries.
The sewage from sugar refineries, besides condenser water,
which is harmless, consists of water from the washing of the beet,
from the diffusers, and the filter-presses.
PURIFICATION OF INDUSTRIAL SEWAGE
121
The different kinds of sewage must be treated separately.
The water used in washing the beet is purified in sedimentation
tanks and then used again. Markwart would like to run the
water from the diffusers and from the presses into the diffusers
again without further treatment. It is then necessary to prevent
fermentation from being set up.
According to Herzfeld, the following important preliminary
must be observed before using the effluents again in the process,
viz. the particles of pulp must be removed by careful sedi
mentation.
Hoyermann and Wellensiek recommend for the purification
of sewage from sugar factories one of their own preparations,
which consists of humic acids which are hydrolysed with alkalies.
In the process of hydrolysis the solubility of the humins is quite
considerably increased. The sewage to be purified is treated
with humin suspended in water, and then lime is added till the
whole is weakly alkaline. As a result a flocculent precipitate
separates out, and the water becomes quite bright and clear ; the
precipitate settles quickly. According to Schone, the nitrogen
content of the effluent from the slicers should be lowered by
about 69 per cent after treatment by the Hoyermann-Wellensiek
process. The sewage should then also be incapable of putrefying.
According to the report of the Proceedings of the Technical
Association of Sugar Manufacturers at their conference in Magde
burg, on the 21st March, 1911, the following managers, Gehrke
(Alleringersleben) , Thiel, Griinanger (Niederdodeleben) , and Dr.
Dietrich (Gehrden), who have all employed the process for the
purification of their effluents, expressed themselves very favour
ably with regard to it.
A German ministerial decree of the 4th of July, 1910, by the
President of the Government, explains that the question of using
the effluents from the diffusion process and from the slicers has
proved to be practicable in technical work, so that, in those cases
in which nuisances arise from introducing these effluents into
the stream unpurified, the police authorities might be justified
in forbidding their introduction.
The water from the presses is often purified thus : It is first
heated in fermentation tanks, then neutralised, after which it
is drained on fields, being subsequently collected and used
again.
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SEWAGE DISPOSAL
De Plato treats the filtered water with milk of lime (150 Be)
until completely precipitated, and then, after sedimentation,
with a five per cent solution of calcium hypochlorite. The water
is next decanted and led through five cylinders filled with lumps
of coke. Analysis showed that about 50 per cent of the organic
matter is thereby removed ; the effluent should then be harmless
to the fish in the river.
(12) Sewage from Starch Factories.
Starch factories may use corn, maize, rice, or potatoes. The
sewage varies with the kind of raw material. Starch factories
employing rice and maize have effluents containing some free
alkali, and now and then some sulphurous acids.
Generally the sewage from starch factories is similar to that
from sugar factories. It contains a large amount of organic
matter, whilst fermentation and putrefaction readily occur.
In Germany potatoes are mainly used as raw material in the
manufacture of starch. From a hundredweight of potatoes
there is about 50 to 70 gallons of sewage, which consists of
waters from washing the potatoes, the by-products and the
starch, together with refuse from the pulp-presses.
The sewage is clarified in settling tanks. The effluent, which
is acid in reaction, is frequently drained away after this simple
clarification. The sludge is from time to time worked up for
starch.
With the Hoyermann-Wellensiek process mentioned under
sugar-factory sewage, 75 per cent of the organic matter from the
starch sewage is separated.
C. Zahn made a detailed investigation of the possibility of
purifying sewage from starch factories by means of the biological
process. The use of septic tanks instead of sedimentation
tanks is not to be recommended. Purification was better the
finer the material composing the beds, so that with starch-factory
effluents contact beds are superior to percolating filters. It is
advantageous here, also, to neutralise the sewage before passing
it on to the beds. Zahn effected this neutralisation by mixing
acid sewage with some alkaline effluents, or else by means of lime
stone laid down in the beds. For the preparation of the beds the
use of materials free from iron is to be recommended. With a
PURIFICATION OF INDUSTRIAL SEWAGE
123
diminution of 80 per cent in the oxidisability of the sewage there
was nevertheless subsequent decomposition, so that Zahn urges
the adoption, in the case of industrial effluents, of the views held
in regard to domestic sewage.
(13) Sewage from Distilleries and Yeast Works.
This sewage contains a large amount of organic matter both
dissolved and in suspension. It is therefore strongly putre
factive. The effluents from the yeast-presses and from the dis
tillation of the wort are the chief concern in these processes.
They are best disposed of as food for cattle. They may be
roughly purified by chemical precipitation (alum and lime) and
by sedimentation in tanks.
They may be thoroughly purified by land treatment, by contact
beds, or by percolating filters ; double-contact beds can be most
strongly recommended.
According to Dibbin, yeast refuse is decomposed very well in
contact beds composed of slate.
(14) Sewage from the manufacture of Sour-krout.
In this process there result effluents containing large amounts
of decomposable substances, which, as a consequence of the
sulphur contained in the cabbage, undergo decomposition
accompanied by a very strong smell.
The introduction of such sewage into the town drains is danger
ous, as good purification of the whole of the town's sewerage is
then brought into the question.
There is no information as yet with regard to the direct puri
fication of the sewage, but in my opinion the effluents would be
similar in character to those from dairies, and should be purified
therefore in a corresponding manner.
In certain places the sewage is purified successfully by allowing
it to trickle through deep pits.
(15) Sewage from Dye Works {Print Works).
More or less large amounts of organic colouring matter are
always found in this type of sewage, which is, consequently,
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SEWAGE DISPOSAL
always coloured. The opinion was formerly held that the colour
of the sewage caused little harm to the stream receiving it, that,
on the contrary, coloured effluents had an aesthetic value in that
they allowed the waters of the stream to be coloured with all the
colours of the rainbow over considerable distances.
A research of Tienemann of very recent date has, however,
shown that this view is not quite correct. On the contrary, many
colouring matters used in the manufacture of paper, although
they are not poisonous at all to men, have a strongly poisonous
action, even at great dilutions, on the most varied kinds of
organisms present in water. Victoria blue, methyl violet, char
coal-black, and diamond green B have proved especially fatal to
fresh-water organisms even at very great dilutions, so that
sewage containing these colours may be^ very harmful to the fish
in the river. This may arise from direct destruction of the fish
or from the destruction of the lower organisms in the water,
whereby the source of the fishes' livelihood is either ruined or
impaired. Besides colouring matters this sewage often contains
mordants (mainly aluminium, ferric and zinc salts).
The removal of colouring matters from sewage is still an un
solved problem. The difficulty of removing the colour increases
the more permanent the colours are. By biological means,
whether by land treatment or by the artificial biological process,
the colour is only incompletely removed. The surface of the
land or the beds is gradually saturated with the colouring
matter, and then allows further quantities to pass through un
changed.
Partial decolorisation is attained in the case of many dyestuffs by chemical precipitation, using sulphate of iron and lime.
After precipitation the sewage is passed through sedimentation
tanks or filtered by means of mechanical filters.
The following is a method of decolorisation which has come
into general use : The dye-stuffs are reduced to the leuco base and
then the colourless sewage is run away. The process cannot be
recommended, however. The leuco bases are again oxidised in
the river and give coloured compounds, taking from the riverwater the oxygen necessary for the oxidation process. In this
way, therefore, not only do the colours reappear in the river, but,
in addition, the removal of the oxygen from the river-water
causes the harm done to the river to be greater and more serious.
PURIFICATION OF INDUSTRIAL SEWAGE
125
It should be best to dilute such sewage considerably, and then
run it into the town's sewers.
(16) Sewage from Chemical Works.
Sewage from chemical works varies so greatly according to the
class of work that it is impossible to give a definite mode of
purification ; indeed, this is all the more true as the methods of
manufacture are frequently kept strictly secret. Generally
speaking, it may be said of this class of sewage that suspended
matter may be removed in sedimentation tanks. Substances
which are lighter than water (tar, oil, etc.) can be removed from
the sewage by means of grease separators.
Nearly all chemical processes require acids or alkalies. By
mixing acid and alkaline effluents sufficient neutralisation is
attained in some cases. Acids are generally neutralised with
lime.
Large amounts of Glauber's salt often result from neutralisa
tion processes. The effluents from organic dye works are often
very rich in this salt. In general these salts should be harmless
to the living matter in the river, but I might point out that such
sewage, in my experience, is capable of destroying extremely
rapidly sedimentation tanks made of concrete. These data,
which I found in the course of quite different investigations, were
confirmed by a manager of a large dye works. The destruction
results from the conversion of the free lime of the concrete into
gypsum by means of the Glauber's salt. This is accompanied by
a disintegration of the concrete.
Very many, chemical processes yield coloured effluents. The
previous section may be referred to for their purification.
The erection of reservoirs can be strongly recommended for
such works, as the sewage is sometimes greatly polluted and large
in amount, while at other times it is less polluted and in much
smaller quantity.
Occasionally separate treatment of the individual effluents
can be recommended. In other cases mixing will be advantage
ous, as the dissolved substances may precipitate one another.
All these circumstances, and, in general, the best methods of
purification for sewage from chemical works, are determined in
practice by experiment.
SEWAGE DISPOSAL
(17) Sewage from Bleach Works.
In bleach works, sewage is formed which contains alkaline and
acid boiler liquors in addition to chloride of lime. The most
harmful are the alkali boiler liquors. According to Schiele,
superficial purification can be attained thus : The alkaline liquors
are stored up in reservoirs, the acid liquors are gradually mixed
with them, and then the whole is clarified in settling tanks. The
sewage so purified can then be further treated in biological plants.
According to a patent process, Keller (Stuttgart) makes the
alkaline boiler liquors applicable anew, as he adds dissolved or
undissolved lime to them with constant stirring, by which the
solution assumes a brighter colour. The liquid decanted from
the lime is then used again as it is, or concentrated in some way
or another.
(18) Sewage from Gas Works.
Sewage from gas plants is generally chocolate-brown in colour,
has an obnoxious odour, and contains free alkali, sulphocyanides,
phenol, cyanides, tarry products, etc. The disposal of such
sewage is a matter of great difficulty, owing to the poisonous
substances present. Its admixture with the town's sewage
makes purification of the latter considerably more difficult, if
there are in any way considerable amounts of sewage from the
gas plant.
Chemical precipitation followed by sedimentation is one method
of treatment, not, however, very effective.
Radcliffe has worked out and tested a process which proceeds
as follows : First, the suspended lime is removed in settling
tanks, then the water is pumped into a fractionating apparatus,
allowed to trickle down over plates, whilst from below hot ex
haust gases containing carbon dioxide and air are blown in.
The dissolved lime is thus precipitated and the phenols are
destroyed. The lime is separated off in a tank, and the liquid is
then driven into a fractionating plant, serving as an auxiliary to
the first. Here a stronger stream of air removes the phenols and
other substances. They are led into a furnace and burnt. The
sulphocyanides are decomposed by dropping in sulphuric acid.
After passing through a second settling tank and then being
filtered over coke the water should be quite clear. In St. Albans,
PURIFICATION OF INDUSTRIAL SEWAGE
127
England, such a plant is used. Many well-known English sewage
experts have tested the process and expressed themselves favour
ably with regard to it.
If gas-works effluents are to be purified by the biological
process they must be greatly diluted. Even after considerable
dilution or admixture with domestic sewage, the beds may not
be loaded too greatly with sewage if sufficient purification is to
be obtained.
(19) Sewage from Ammonia Works.
This sewage is characterised by a high content of mineral and
organic substances. It contains calcium chloride and free lime,
under certain circumstances calcium sulphydrate and free sulphur ;
of organic substances, tarry matter, thiocyanates, pyridine bases,
phenol, and other substances are present.
The free caustic lime can be removed by allowing the sewage
to trickle over inclined planes, whereby it is converted into
calcium carbonate.
By adding caustic soda (1 to 2 lb. per 10,000 gallons of sewage)
the sulphur, which is often present in a finely divided condition,
should be precipitated along with the calcium carbonate which
has separated out. Sulphocyanides are generally present in
small amounts, but may amount to 1 per cent. Such large
quantities can be precipitated with copper salts and further
recovered.
(20) Sewage from Potash Works.
Sewage from potash works contains inorganic salts in large
amounts, especially magnesium and calcium chlorides. Such
sewage cannot be purified by the usual methods. It is gener
ally conveyed directly to the river, and frequently considerably
increases the hardness of the river-water and the quantity of
salts that it contains. This may be very unpleasant from the
point of view of health if towns situated lower down the river
draw their drinking-water from the river concerned.
The Imperial Health Commission of Germany has been occu
pied with the question of this type of sewage. It recommends
that the limit be fixed at an increase to 500 of hardness in the
river-water. Further, the following procedure was recommended
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SEWAGE DISPOSAL
to prevent the river-water receiving excessive amounts of such
salts : —
(1) Arrangement of suitable distributors and regulation of
the discharge in the case of the final liquors.
(2) Provision of reservoirs large enough to contain the final
liquors in individual works.
(3) A number of controls working through a central enquiry
office.
Lately these effluents have been used for laying dust on the
roads. Owing to the calcium and magnesium chlorides present,
which are very hygroscopic salts, the sewage keeps roads moist
and thus lays the dust. In Frankfort, with such liquors, it has
been shown by investigation that they are specially useful in
winter during a dry frost. On such days the streets cannot be
watered, as they would very soon freeze. Each watering-cart set
in motion on the unwatered streets generates big clouds of fine
ice particles. If, however, the streets are sprayed with these
liquors, owing to their considerably lower freezing-point, not only
is no ice formed, but the surface of the street (asphalt) remains
moist for eight days without requiring further watering.
(21) Sewage from Metal Works and works manufacturing
Mordants.
Such sewage is generally acid and contains metallic salts. It
is very harmful if led directly to the river. It discolours the
river-water, moreover, owing to the separation of iron and other
metallic salts.
Purification can be effected by neutralisation with lime and
subsequent treatment in settling tanks. One disadvantage of
this process is that it yields large amounts of sludge.
It is better, therefore, to evaporate the effluents and recover the
metallic salts. In England, according to Schiele, it pays to use
this method.
(22) Sewage from works manufacturing Photographic Paper
and Cards.
The sewage from such concerns can be divided into two classes,
concentrated sewage and washing-waters. The concentrated
PURIFICATION OF INDUSTRIAL SEWAGE
129
effluents contain the most diverse chemicals (acids, alkalis, etc.),
as must naturally occur in such manufacturing operations.
Pritzkow recommends either leading the concentrated effluent
directly into sewers, in which case difficulties should not arise, or
the effluent should receive a special treatment. Pritzkow
advises the following method of purification : The strongly
concentrated sewage (dyeing machines ; the working up of the
residues) is freed from acids, alkalis, and harmful salts by
methods worked out from individual tests. To take one example,
it would perhaps pay to recover thiosulphate from the water
containing it. Then the water thus obtained, and the concen
trated effluent, with which such treatment is impossible, are
collected in a tank. Here the various kinds of sewage can mix,
decompose, and, as far as possible, neutralise one another. The
discharge from this tank might be mixed with the washing-waters,
which are freed from suspended matter in a special sedimentation
tank, and can then be run away into the river.
(23) Sewage containing Cyanides.
This type of sewage has been the object of an enquiry by the
Imperial Health Commission (Reichsgesundheitsrates) (Rubner
and von Buchka). Many sugar refineries work up their molasses
for cyanides. Gases from smelting furnaces are often freed from
their impurities by washing with water, and are then used again
in the process. The sewage resulting from this washing process
generally contains large amounts of cyanides. In the sugar
refinery at Dessau, according to the description of the Imperial
Health Commission, the cyanides are removed from the sewage
in the following manner : The effluents containing cyanides are
collected in pits. Sacks containing sulphate of iron are hung in
the water, and the salt dissolved by the hot sewage. Then caustic
soda is added, and it is next made weakly acid with sulphuric
acid. The whole is well stirred by blowing in a rapid current of
air. The addition of caustic soda and sulphuric acid is made in
calculated amounts corresponding to the analytical results from
tests of the contents of the pits. The mixture thus obtained is
then expressed in filter-presses. Should the water from the
presses not be clear, or if the qualitative test (Prussian blue) still
shows the presence of cyanides, it is sent back to the pits, and
K
130
SEWAGE DISPOSAL
from thence back once more to the presses. The blue sludge,
which comes from the presses containing about 70 per cent water,
is dried in pans and then contains about 45 per cent of potassium
ferrocyanide.
(24) Sewage from plants employed in scouring, combing, and
finishing wool.
The most concentrated and unpleasant effluent from this
manufacturing process is the effluent from the scouring of the
wool, containing soap. It is to be recommended that, in all
circumstances, such sewage should be worked up by itself. It
is generally freed from the threads by means of screens, sieves,
or similar apparatus, and is then acidified with sulphuric acid to
decompose the soap. Good mixing is obtained by blowing in a
rapid current of air or steam. The acidified sewage is then
allowed to stand for a time in large settling tanks. The sludge,
which is rich in fats, is worked up for fat (see p. 106). The sewage
can then be further purified by means of intermittent ground
filtration, or by the artificial biological process (percolating filters
or double-contact beds being the best) . The small amount of free
sulphuric acid should not occasion any trouble in the biological
treatment. In some plants, however, the acid effluent is neu
tralised with lime before the biological process. Frequently the
sewage is conveyed directly to the river without any biological
treatment, after acidification with sulphuric acid and sedimenta
tion.
(25) Sewage from Petroleum Refineries.
The sewage resulting from the refining process consists of
waste acid, acid washing-water, caustic soda, and alkaline washwaters. According to a decree of the authorities in Austria, the
disposal of such sewage is to be effected somewhat in the following
manner : The waste acid is allowed to stand some time, during
which the tar separates out on top ; this can be skimmed off and
burned (mixed with sawdust), or it is worked up as asphalt.
The dirty and dilute acid may be sold to artificial-manure manu
facturers. If the acid cannot be sold it is neutralised with lime ;
the resinous mass thus separating out is skimmed off, and the
PURIFICATION OF INDUSTRIAL SEWAGE
1S1
neutralised effluent is freed from suspended material, oily, tarry,
and such substances, both in settling tanks and by filtration
through wool-waste or peat, etc.
The acid and alkaline washing-waters are mixed ; if the acid
is not sufficient to neutralise the alkaline portion, part of the
muddy acid from above (after the removal of the resinous mass)
is added to the mixture. This mixture should still have a dis
tinctly acid reaction ; it is then boiled to decompose the petroleum
soaps. After skimming off the oily layer on top, the aqueous
and still acid liquid underneath is also purified in the abovementioned settling tanks and filters.
For larger works a special clarification plant for acid and
alkaline sewage is to be recommended.
(26) Sewage containing Soaps.
If it is a question of an effluent containing soap without the
addition of other polluted water, as is the case with many
laundries, good purification can be effected, according to Heydt,
in clarifying wells having large plates to oppose the passage of the
sewage, which is made to flow at a very small velocity. Milk of
lime is automatically added to the sewage at the inlet to the
well. The amount added must be estimated by experiments
on the particular effluent. After passing through a sand filter
of small depth the sewage is sufficiently purified for it to be led
without harm to any small stream. It is important to take care
that the floating particles which are formed are retained in the
clarifying plant and do not reach the filter. It is advantageous
to have the sewage exposed suitably to the air (to absorb carbon
dioxide) before coming on to the filter, and to interpose a
reservoir or second clarifying well.
Use of septic tanks for this class of sewage is considered in
advisable by Heydt, and only a biological plant with a very large
surface is practicable. Lubbert also regards the biological
process for the purification of laundry sewage as unsuitable, and
likewise recommends precipitation with lime.
In the opinion of the author it must be possible to purify such
soapy liquors by the addition of sulphuric acid till weakly acid,
followed by the separation in a grease separator of the precipi
tated fatty acids, which could then be recovered. The fatty
132
SEWAGE DISPOSAL
acids would be separated all the more easily, as such sewage
generally reaches the sewers warm.
(27) Sewage from Oil Works.
The sewage, on account of its high content of organic sub
stances, was used in South France as manure for pasture-land.
Its success, however, was very small. The reason for this is, no
doubt, the large amount of acid in the sewage. According to
Ventre, the sewage should lose its acidity on standing in the air,
and then after mixing with superphosphate or with animal
manure it should give a good manurial material.
G. The Disinfection of Sewage.
Sewage generally has a germ-number of one or more millions.
As Spitta has shown, most of the bacteria are associated with the
undissolved matter, so that by separating off the suspensions a
considerable reduction of the germs is effected. The bulk of these
bacteria are of a harmless nature, but there are undoubtedly
also many disease germs among them.
Since these disease germs under ordinary circumstances can
only exist a limited time in the river under the changed and
hostile conditions there, disinfection of the sewage is generally
unnecessary, the more so as nowadays river-water is no longer
used by municipalities for the water supply without undergoing
some treatment.
It is naturally very advisable in this state of affairs that the
excreta from people suffering from all infectious diseases, espe
cially typhoid, should be disinfected. The Prussian law takes
this into account, since it prescribes disinfection of all the refuse
from persons suffering from notifiable diseases.
It is best, likewise, to disinfect the sewage of houses where there
is sickness, before it enters the general sewage system.
Disinfection is necessary in times of epidemic, as the many
disease germs deposited in the river favour the spreading of
contagion. In most sewage plants there are for cases such as
these devices which disinfect the whole of the sewage. Chloride
of lime has proved the best disinfectant, but this only acts
sufficiently well when all suspended matter over 1 millimetre
DISINFECTION OF SEWAGE
188
in size has been removed. According to Schmidtmann, Thumm,
and Reichle, in times of epidemic the storm overflow-water of the
town constitutes an especial danger.
Industrial sewage in general need not be disinfected. Only
in the sewage from slaughter-houses and knackers' yards can
disease germs be present. Tannery sewage also may contain
inflammatory spores. Chloride of lime is the best disinfectant
for such sewage also.
According to Kurpjuweit, good regulations for the amount of
chloride of lime required cannot be given. In general, treatment
for two hours is sufficient. With a concentration of I part of
chloride of lime in 5000 parts of water, arid with treatment lasting
two hours, Kurpjuweit was able to disinfect the sewage in Charlottenburg sufficiently.
On the contrary, Kranepuhl asserts that for certainty a con
centration of 1 : 1000 must be employed for two hours' treatment,
or a concentration of 1 : 2000 for four hours.
LIST OF AUTHORS
A
Abraham and Marmier, 20
Agga, 32
Ardern, 112
Arnold and Schirmer, 42
B
Baudet, 10
Becker, 35
Bell, 11
Berkefeld, 43
Bieske, 32
Bischoff, 30
Bitter, 14
Blacher, 59, 61
Blunt, 27
Bock, 33
Bollmann, 33
Braikowitz, 16
Breda, 11, 33
Brettschneider, 89
Breyer, 42
von Buchka, 129
Biihring, 33
Bujard, 108
Buttner, 33
Bujwid, 29
Dibbin, 123
I Dietrich, 121
Dobrowolski, 22
Dolezalek, 22
Dost, 108
Downes, 27
Dunbar, 49, 79, 89, 90, 119
Duyk, 24
E
Erlwein, 22, 28
von Esmarch, 41, 45
F
Fiddian, 88
Fischer, 32
Fliigge, 30
Fowler, 112
Frankel, 9, 30
Frankland, 90, 94
Freund, 76
Friedberger, 14
Fruhling, 68, 94
G
Gartner, 23, 42
Gehrke, 121
] Gesellschaft fiir Abwasserklarung, 73
C
Candy, 11
Gottschlich, 13, 14
Chamberland, 42
Gotze, 9
Chemischen Fabriken fiir Laboratori- Grimm, 28, 29
umsbedarf, 61
Grosze-Bohle, 75
Chlopin, 22
Grove, 45
Continental Co., German, 45
Griinanger, 121
Courmont, 27, 28
Guth, 119
Craven, 26
Cronheim, 96
H
D
Halbertsma, 22
Degener, 84, 109
Halvor, 11
Dehne, 33, 55
Harm, 119
Deseniss and Jacobi, 49
] Helm, 33
135
136
LIST OF AUTHORS
Henneking, 95, 96
Herzfeld, 121
Hess, 33
Hesse, 42
Heydt, 131
Heyer, 37, 38
Hilgermann, 13, 17
Hofer, 97
Howatson, 20, 24
Hoyermann, 121, 122
Humboldt, 55
1
Imhoff, 25, 29, 100
Imhoff-Lagemann, 114
J
Jensen and Co., 42
Jewell, 11, 13, 14, 33
Johnson, 25, 29
K
Kaibel, 73
Keller, 126
Kimberley, 114, 119
Konig, 6, 8, 9, 44
Koerting, 32
Kranepuhl, 133
Kremer, 71, 72, 73
Kremcr-Schilling, 73
Krcssling, 48
Krohnke, 11, 32
Kurpjuweit, 133
Kurth, 32
Mertens,
Mezger, 1 120
Middledorf, 82
Miquel, 10
Mouchet, 10
N
Neiszer, 30, 48
Nobel, 91
Nogier, 27
Noll, 35
Novak, 1
O
Oesten, 32
Ohlmullcr, 22
Olschewski, 42
Otto, 21
Otto and Vosmacr, 20
P
Pape and Henneberg, 45
Pasteur Institute, 22
Permutit Filter Co., 61
Pfeiffer, 32
Piefke, 8, 31, 32, 42
dc Plato, 122
Prall, 22
Pritzkow, 129
Proskauer, 22, 48
Puech, 11
Pucch-Chabal, 9
Q
Quartz Lamp Co., 28, 29
Lahmeyerwerke, 48
Lanz, 32
Lautenschlager, 43
Lehmann, 113
Lepsius, 76
von der Linde, 33
Logau, 117
Lubbert, 131
Liihrig, 35
M
Markwart, 121
ter Mer, 101, 107
R
Radcliffe, 126
Reeves, 11
Reichle, 84, 101, 108, 109, 113, 118, 133
Rcichling, 32
Reisert, 33, 53, 55. 59
Richcrt, 15, 10
Rideal, 23
Rien, 70
Rimman, 117
Ritschel and Henneberg, 46
Rubner, 129
LIST OF LOCALITIES
s
Sauna, 23
Saville, 25, 29
Schafer, 101, 107
Schaffer and Walcker, 45
Scheelhaase, 15, 37
Schick, 97
Schiele, 24, 25, 76, 77, 78, 86, 87, 89,
90, 92, 93, 105, 108, 126, 128
Schmidt, 43
Schmidtmann, 84, 118, 133
Schmidt and Sons, 46
Schone, 121
Schreiber, 13, 22, 23, 51
Schuder, 22
Schwers, 32, 33
Sellenscheidt, 33
Siemens and Co., 45
Siemens and Halske, 20, 28, 47, 48
Sjolemma, 113, 114
Spillner, 82, 100, 102
Spitta, 132
Stadtereinigung und Ingenierbau, 73,
"5
Sucro, 11
T
Taacks, 32
Thiel, 121
Thiem, 15, 32
Tienemann, 124
Thiesing, 101, 120
Thumm, 24, 25, 84, 109, 133
Travis, 79, 89
Trindall, 20
U
Uhlfelder, 69
Ultra-Violet, 29
V
Ventre, 132
Vincey, 17
Vogelsang, 72
Volger, 1
Voran, 33, 55
Walker, 26
Warren, 11
Wehner, 40
Wehrenpfennig, 55
Weldert, 28, 29, 104, m
Wellensiek, 121, 122
Westinghouse, Cooper, Hewitt Co.
Wingen, 32
Z
Zahn, 113, 122,,123
LIST OF LOCALITIES
Alexandria, 14
Alleringerslebcn, 121
Altona, 9
B
Belfast, 103
Berlin, 31, 42, 43, 45, 61, 73, 94, 115
Bochum, 100
Bradford, 105
Breslau, 35, 94
Brunswick, 16, 94
Bury, 108
Celle, 43
Charlottenburg, 51, 133
Chateaudun, 10
Chemnitz, 16
Cologne, 55, 75, 76
Constantinople, 64
D
Darmstadt, 73
Delitzsch, 31
Dessau, 38, 45, 129
Dortmund, 94
Dresden, 70
E
Eduardsfeld, 91
Elberfeld, 69
Elbing, 31
Essen, N.W., 100
138
INDEX OF SUBJECTS
F
Frankfort-on-Maine, 15, 33, 37, 48, 51,
55. 69. 74. 75. 76, 97. 98, 99, 101, 102,
106, 107, 128
Freiburg, 94
G
Gerhden, 121
Gelsenkirchen, 30
Gothenburg, 16
Gottingen, 100
H
Halle a. S., 55, 114
Hamburg, 9, 17, 42, 45
Hanau, 28, 29
Hanover, 101
Harburg, 101
Hermannstadt, 20
Magdeburg, 94, 121M
Manchester, 89, 103
Middlekerke, 24, 25
Minneapolis, 26
N
Niederdodelcben, 121
Nizza, 20
Norwich, 79
O
Offenbach, 16
Ohama, 26
P
Paderborn, 20, 22, 120
Paris, 17, 20, 23, 29
Pforzheim, 108
Posen, 33, 91
R
Recklinghausen, 100
S
I
Ichenhausen, 97
Salford, 103
Schweinfurt, 16
St. Albans, 126
St. Mans, ,20
St. Petersburg, 20, 22
Sternberg, 31
Stuttgart, 126
Swinemiinde, 120
K
Kalk, 55
Kassel, 100, 106
Kiel, 120
Konigsberg, 9, 14
Kopenick, 109
Kutzenberg, 97
W
Warsaw, 9
Weinding, 97
Wiesbaden, 73, 115
Wismar, 31
L
Lawrence, 94
London, 5, 103
INDEX OF SUBJECTS
A
Aeration of water to remove carbon
dioxide, 38
Algae, 65
Alluvial soil, 30
Ammonia works, sewage from, 127
Apparatus
boilingfordrinking-water,
adding chemicals,
45 38, 77
Arsenic, 118, 119
Asbestos filters, 42
Assimilation, 65
B
Bacteria, 2, 3, 17, 18, 22, 23, 28, 31, 41,
45. 48- t13. 132
— anaerobic, 78
INDEX OF SUBJECTS
Bacteria, destruction of, 3
— pathogenic, 10, 22, 25, 28, 45, 92,
132
Bacterium
Baryta
Bank nitration,
process
coli, 28,
of
natural,
water
48 15
softening,
66
59
Bacterial
decomposition,
— — advantages, disadvantages, 59
Bastard
49
pump of Deseniss and Jacobi,
purification, 51
Baths, river, 64
Bed irrigation, 91
Beds, biological, 85
distribution of water, 87
impregnation permissible, 87
layer of slime on, 86
material for, 85
, protection against cold, 87
Beet, wash waters, 120
Biological process, artificial, 85
cost of, 89
nature of, 89
— purification of sewage, 85
Bleach works effluents, 126
Boiler corrosion, 59, 61
— fire clinkers, 112
— scale, 52
preventatives, 61
— sludge, 52
— water, corrosive action, 58
Boiling, the, of drinking-water, 45
advantages and disadvantages,47
Breslau water calamity, 35
Breweries, sewage from, 117, 118
Bromine, 18
C
Calcium hydrate, 54
— permanganate, 1 8
— sulphydrate, 127
Carbolic sulphuric acid, 30
;
Carbonic acid removal, 36, 52
Cardboard works sewage, 113
Cascade for removal of air, 19, 22
Cellulose works, sewage from, 115, 116,
117.
Central water supply, 40
Centrifuge Schafer-ter-Mer, 101, 102,
i°3
139
Chamberland Filter, 42
Charcoal niters, 41
Chemicals, action of, 76
— addition of, 10, 76
— disadvantages, 77
— mode of addition, 77
— quantities added, 77
Chemical works sewage, 125
Chloride of lime, 18, 132
• process for sterilising drink
ing-water, 25
Chlorine, 1 8
Cholera, 2, 17, 22, 45, 64
Chrome iron alum, 18
Chromium salts, 118
Ciliata, 65
Clarifying tanks, 4, 74
.arrangement of the tank bed, 74
— towers, 74
— welLs, 74, 79
Clay filters, 42
Clinkers from refuse destructors, 85
Cloth factories, sewage, 113
Coal-pulpgasification
process, 84of sludge, 108
— sludge, 114
Coke, 86
Coke aerators, 33
Coli bacteria, 28, 48
Colour, removal of, from water, 13, 18
Coloured effluents, 112, 118
Condenser waters, 110, 116, 120
Contact beds, 86
— advantages, disadvantages, 88
choking of, with sludge, 88
distribution of water on to, 87
single and double, 86
size of material for, 86
Cooling waters, no
Copper chloride, 18
Cost
29 of all water-purification processes,
biological processes, 89
chloride of lime process, 25
intermittent sand filtration, 96
mechanical filtration, 18
ozone process, 23
removal of iron, 34
manganese, 36
—, sand filtration, 9
140
INDEX OF SUBJECTS
Cost of sewage farming, 94
sludge disposal, 104
ultra-violet light process, 29
Cyanides, 113, 126
Cyanides, sewage containing, 129, 130
D
Dairy effluents, 119
Dams, 3
De Chlor process, 26
Destructors, refuse, 108
clinkers from, 85
Diarrhcca germs, 2, 22
Diffusers, effluents from, 120, 121
Diluvial soil, 30
Disease germs, 2, 25, 63, 133
Disinfection of sewage, 132, 1 33
water-mains and wells, 30
Disposal and profit from sludge resi
dues, 97
Distilleries, sewage from, 123
Double filtration, Gotze, 9
Drinking-water purification, 2
in other directions than health,
30
on large scale, 4
on small scale, 40
Drying of sludge (see Sludge)
Dunbar Filters, 49
Dust-laying with sewage, III, 128
Dye works sewage, 123, 124
E
Eduardsfeld process, 91
Elbe water, 1 7
Emscher wells, 82
Emulsifiers, 21
England, sewage disposal, 85
Epidemic, 17
Filtration pressure, 7
— velocity, 6, 8, 10, 11, 14
Fish life, harm to, 64, 124
— ponds, sewage disposal through, 96
Flies, plague of, 88
Floating material in sedimentation
tanks, 76
Fungi, formation of, 116
G
Gas works, sewage from, 126, 127
Glue liquors, 120
Granulation works, sewage from, 114
Gratings, 68
Grease in sludge, 98
— recovery, 105, 106, 107
— separators, 72
Grit chambers, 73
Grit-chamber residues, 97
composition of, 97
drying of, 98
H
Hampton doctrine, 89
Hardness of water, 52
— degrees of, English, French, German,
52
— due to chlorides, 60
gypsum, 59
nitrates, 60
— permanent, 52, 53, 59
— temporary, 52, 53, 54, 59
Havel, 85
Hops and grain drying, sewage from,
117
Hose irrigation, 91
Household filters, 41
Howatson Filter, 20, 24
Humin process (Hoyermann and
Wellensiek), 121
Hydrogen peroxide, 18, 27
F
Ferricprocess,
chloride,241 8
Fibrous material, recovery of, 115
Fiddian sprinklers, 88
Filter, in, 114, 131
— film, 8, 11
— film in biological processes, 89
Filtration, 4
1
Industrial sewage for dust-laying, in
purification of, 109
by chemical precipitation, 109
by combination of different
effluents, in
reception into the drainage sys
tem, 109
INDEX OF SUBJECTS
Industrial sewage, reservoirs for, 111
Infiltration, 14
Infusoria, 65
Intermittent sand filtration, 94
— cost, 96
- doses,
depth of
95 filter layer, 95
drainage, 95
filter beds, 95
nature of soil, 95
periods of rest, 95
preliminary treatment, 95
purifying action, 96
Irrigation, infiltration, 91
— rude or surface, 91
Iron bacteria, 31
— colloidal, 3 1
J Jewell Mechanical Filter, 11
K
Kalmann formula, 54
Kieselguhr Filters, 43
Knackers' yards, sewage from, 120
Kremer apparatus, 71
— septic well, 73
L
Land irrigation, 90
Lime, 18
Lime-soda softening process, 55
Liming process, effluents from, 118
Liquefying chamber, 82
M
Magma Filter, 112
Maine River water, 15, 31, 66
Malting liquors from breweries, 117
Manganese, removal of, 35
Manure, 98, 104, 105, 114, 132
— artificial, 105
Margarine works, sewage from, 119
Mechanical filtration, 10, 11, 13, 17,
— 114,
purification
124
of sewage, 68
Mercury-vapour lamps, 27, 28, 29
Metal works, sewage from, 128
141
Mines (coal-washing) effluents, 114
Mordants, 124
— sewage from manufactories of, 128
X
Naphthalene, 118
Neutralisation of drinking-water, 36
— plant, Frankfort, 39
Neva, 20
Nitrogen, 90, 98, 104, 105
Nobel treatment, 91
O
Oil, sewage containing, 113
— works sewage, 132
Ozone, 18, 20, 21, 22, 23
— concentration, 21
— plant, St. Petersburg, 20
— plants, small, 47
stationary, 47
transportable, 47
P
Paper works sewage, 115
Percolating filters, 86
advantages and disadvantages,
88
distribution of sewage on to, 87
subsequent purification of ef
fluent, 89
Pcrmutit, 35
— process, 60
advantages and disadvantages,
60
Petroleum refineries, sewage from, 130
Phenol, 127
Phosphoric acid, 90, 98, 105
Photographic papers, sewage from, 129
Plague of flies, 88
Plankton, artificial, 11
Porcelain filters, 42
Potash, 90, 98
— works, sewage from, 127
Potato wash waters, 122
Poudrette, 105
Preliminary filtration (Puech-Chabal),
9
— purification, 85
Press waters, 116, 120, 121
142
INDEX OF SUBJECTS
Prufungsanstalt, Konigl. fiir Wasserversorgung und Abwasserbeseitigung, 22, 28
Prussian blue, 113
Ptomaines, 2
Pumps, sump, 74
Purification of domestic sewage, 67
industrial sewage, log
drinking-water, 2
for technical purposes, 51
in other directions than of
health, 30
on large scale, 4
on small scale, 40
Pyridine bases, 127
Q
Quartz lamps, 27, 28, 29
R
Rakes, 69
— coarse, 69
— residues from, 97
drying of, 97
water content of, 98
Recovery of fibrous material, 115
Removal of iron, 30
action, 34
for industrial purposes, 32
from single wells, 49
plants for open and closed, 34
systems for, 32
Reservoirs, ill
Resinous masses, 130
Revolving sprinklers, 88
Rien Sieve, 70
River baths, 64
— bed, mud upon, 66
— pollution, 63, 64, 65
— water, 3, 15, 63, 64, 66
application to technical pur
poses, 64
capacity for absorbing acid, 66
Rotatoria, 65
Ruhr Talsperren Co., 16
S
Sand filters, 5, 15
covered, uncovered, 7
filter layer, 7, 8
percolating, 1 o
Sand filters, period of running, 8
— washing, 8
filtration, double (Gotze), 9
— natural, 15
— preliminary (Puech-Chabal), 9
slow, 5, 16
Screens, 68
Scum on septic-tank sewage, 78
Sedimentation tanks, 4, 74
(Patent Imhoff-Lagemann), 114
Self-purification of rivers, 65
Septic tanks, 78, 79
Sewage disposal, 97
— domestic, 67
— industrial, 109
— purification by fish-ponds, 96
Sewage farms, 90
bed irrigation, 91
cost, 94
drainage, 91
impregnation permissible, 93
periods of rest, 93
preliminary purification, 92
rents from, 94
suitable produce, 92
surface treatment, 90
Sieves, 69
Sieve waters, 116
Slaughter-house effluents, 120
Sludge centrifuges (Schafer-ter-Mer) ,
101
— composition of, 98, 99
— deposits, 99
covering material for, 99
disinfection of, 99
— destruction by burning, 108
— disposal, 76, 83, 97
by addition of saltpetre, 104
by sinking in the sea, 102
in Frankfort, 107
— drying by admixture with refuse,
100
burial, 100
drainage, 100
— electro-osmose, 102
- — filtration, 99
cost,
- Magma
104 Filter, 112
on the land, 99
— . Emscher well, 83, 100
INDEX OF SUBJECTS
143
Sludge, fresh, 100
Sulphocyanides, 127
— from effluents from percolating Superheated steam for sterilising
filters, 97
wells, 30
Surface treatment in sewage farming,
septic tanks, 100
91
— grease content, 99
experiments in recovery of, — waters, 1, 2, 3, 14, 15, 63, 64
in Frankfort, 106
— grease recovery, 105
T
in Bradford, 105
112,
118, 133
Tannery
sewage,
in Kassel, 105
Tar, 127, 130
— pumps under water, 83
Travis wells, 79
— vessels, 103
Small filters used in technical work, 42 Turbidity, removal of, 13, 18, 41
Typhoid, 2, 22, 45, 132
Smells, trouble from, 88, 98, 99, 107, —bacilli, 10
118
— disease, 17
Smelting furnaces, sewage from, 129
— epidemic, 30
Soap in sewage, 113, 131
— mortality, 17
Sodium hydrate, 54
— hypochlorite, 25
U
— sulphide, 118
screen, 69
Uhlfelder's
revolving
— thiosulphate, 118
Ultra-violet
apparatus,
small, 48
Softening of boiler-feed waters, 52
— formula for calculating the addition j —- — rays, 27
required, 54
V
— with
lime-soda,
baryta, 5955
Vacuum process for removing carbon
dioxide from water, 40
advantages and disadvan
tages, 58
W
permutit, 60
Wagner
suction
apparatus
for sludge
Softening plant, Voran system, 56
removal, 83
Sour-krout, 123
Weights and measures, table of, xiv
Spores, inflammatory, 133
Weston Controller, 1 1
Spree, 85
Wool scouring, combing, and finishing,
Spring water, 1
sewage from, 130
Staphylococcus, 44, 48
Works clarification plants, 109
Starch works, sewage from, 122
— sewage in detail, 11o
Sterilisation, processes of water, 18
— towers (Ozone process), 21, 22
Y
Stone filters, 42
Strawboard works sewage, 114
Yeast works, sewage from, 123
Sugar refineries, sewage from, 120, 121,
122
Z
Sulphite cellulose, sewage from, 1 1 5
Zeoliths, to
UNIV. OF MICHIGAN,
JAN 20 1914
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*3
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50
50
50
00
50
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50
50
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50
00
00
50
50
75
50
00
50
00
25
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1
2
*2
*2
*2
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50
50
50
25
00
00
00
25
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