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I
I
1
MODERN METHODS OF WATER
PURIFICATION
MODERN METHODS
OF
WATER PURIFICATION
BY
JOHN DON, F.I.C, A.M. 1. Mech. E.
AND
JOHN CHISHOLM, A.M. I. Mech. E.
BNCINBER AND MANAGEK OF THE AIVDRIB, COATBRIDGE, AND DISTRICT WATERWORKS
WITH 96 ILLUSTRATIONS
■* ♦ •
* • • • • » « fl
LONDON
EDWARD ARNOLD
1911
[AU rights r*stro*a\
K
•^
X
.(x-
• • •
• •
• •• • •
• . • • •
• • ••
• • •
• • • •
••• • ••
I • • •
• • •
•• • •
• • • <
• • • • • •
PREFACE
The favourable reception which was generally accorded to a
paper by one of the authors of this volume, read before the
Institution of Mechanical Engineers in London, on '' The
Filtration and Purification of Water for Public Supply," has
been the motive for the preparation of a fuller treatment of
the subject. As the methods now recommended for the purifi-
cation of water are both numerous and varied, it seems oppor-
time to review the diflEerent processes, €uid to consider how far
their usefulness is determined by the character of the water-
supply.
Much has been done to this end, though often in a more or
less detached way, by the existing periodical literature dealing
with water engineering and public health. In addition, there
are standard works on the purification of water of recent date
in different languages, the reports of the State Boards of
Health in America, also of the Imperial Board of Health in
Berlin, and of the CJonseil d'Hygiene in Paris, and the very
valuable reports of research work done at the laboratories
of the Metropolitan Water Board.
From these sources mostly it is that water authorities and
their oflBicials are able to keep in touch with modem develop-
ments and with experimental work in the domain of water
purification. In the present volume an attempt has been made
to bring together in a clear and compact way the materials
V
22526:5
vi Preface
with regard to which those interested in the treatment of
water should have reliable and up-to-date information. To
compress into a work of moderate dimensions even a summary
of all the useful and interesting facts that have come to light
in recent years with reference to water purification would have
been an impracticable task, and less appropriate to the object
in view than to devote attention to methods which appear to
stand in the forefront of modem practice.
Of first interest at the present time are the modem views
on the theory and practice of sand filtration, and the material
progress that has been made in raising the efficiency of this
widely-used process of purification by help of improved con-
struction and scientific management. It has therefore been
thought desirable to describe f uUy how the sand-filter does its
work, so that those who find that it does not act as efficiently
as they might have expected may be guided in the inquiry
into the cause of the defect and in the application of a remedy.
There are limits to the efficiency of sand-filters under normal
conditions, and as public opinion proceeds to favour more and
more stringent standards of purity in drinking water, irre-
spective of the quality of the source, the greater will be the
strain on the resources and skill of the engineer who seeks to
adapt the sand-filter to the purification of water.
Advances in the method of treating water have followed one
or other of three different lines. Arising from a knowledge of
the infiuence of coagulants on turbid waters, there has come
into use a large variety of mechanical filters, which in
many cases deal rapidly and effectively with waters that are
hardly amenable to treatment in the older fashion. Again,
the urgency of excluding pathogenic germs from service water
has favoured the adoption of some form of sterilization, either
by fluid bactericides or by ozone. Lastly, well-marked pro-
Preface vii
gross has been made in preparing crude waters for a final sand
filtration by means of successive prefiltration, whereby the
effluent comes t^ attain great uniformity of quality, with
freedom from undesirable bacteria.
These matters have been dealt with in some detail. The
discussion of them naturally brings into pronunence other
topics which directly bear on modem improvements. Such
are the storage of raw water, the care of filtered water and its
distribution, the vegetable and animal life in reservoirs and
filter-beds, and the methods at the disposal of the water
manager for testing the purity of the treated water.
The authors have been engaged for a considerable time in
experimental work in the purification of water, and have
visited many of the most important installations at home and
abroad. But it would have been impossible to prepare this
treatise without obtaiaing permission to make full reference
to the work of many enunent authorities. This permission
has been very cordially granted in all cases, and the authors
would desire to express their indebtedness to Dr. A. C. Houston,
Director of Water Examiaation, Metropolitan Water Board ;
to Director J. M. K. Pennink, Amsterdam ; to Dr. Kenna, of
Antwerp ; to Professor Dr. Zacharias, of the Plon Biological
Institute ; M. de Frise, 38, Rue de Louvre, Paris ; Mr. W.
Qemence, M.I.Mech.E., London; and MM. Puech-Chabal, Paris.
Their acknowledgments are also due to the makers of
mechanical filters described in the book, and to the patentees
of devices for regulating the introduction of coagulants, and
to the owners of mcuiy other special appliances. All of these
have willingly accorded assistance in the preparation of the
descriptive part, and have in many cases provided special
diagrams. For permission to reproduce Figs. 47, 48, and 50
from the Annalen der Physik, the authors are under obligation
viii PRKVAOX
to the publisher, J. A. Barth, Leipzig. Lastly, to the Council
of the Institution of Mechanical Engineers the authors are
indebted for permission to reproduce Figs. 3, 26, 53, 68, 69,
61, and 62 from the Proceedings of the Institution.
A bibliography of water purification is given in the Appendix,
and while all the works noted have been consulted, the valuable
contributions on the treatment of water which have appeared
from time to time in Water, Wasaer und Abtvasser, The Trans-
anions of the British Association of Water Engineers, Engineering,
The Sanitary Record, Gesundheits Ingenieur, and the Revue
d^Hygiine have been particularly helpful and instructive.
J. D.
J. C.
January, 1911.
CONTENTS
CHAPTER I
INTRODUCTORY
Introduction and scope of the work — Subdivisions of the subject - - - 1—7
PAGES
CHAPTER II
SOUBCES OP SUPPLY
Deep wells — Pollution of undeiground sources — ^Detection of, imd remedies
— ^Artesian wells — ^Protection of deep wells — Constructional details —
Upland sources : streams and lakes — ^Lowland sources : lower reaches of
rivers — ^Drainage of cultivated lands — ^Defilements, and safeguards against
such — ^Natural purification — Lands acquired by water authorities, and
costs — Infiltration of river water to adjacent wells — Supplies from weUs
adjoining rivers — Dangers of contamination — Supplies at Dresden,
Stuttgart, Brussels, Bedford, etc. — Shallow wells : construction of, and
regulation — Surface springs — ^Rain water 8 — 23
CHAPTER III
STORAGE
Storage : effect on germs — London stored water : Dr. Houston's researches —
Vitality of Bacillus typhosus in stored river water — ^Dr. Rideal's experi-
ments — ^Importance of searching for pathogenic bacteria — ^Effect of storage
on B. coli — Comparative results in Scotland — Vitality of the cholera vibrio
under storage — ^Vitality of pathogenic germs in relation to season —
Cholera epidemic in Russia — Chemical changes in stored water — Dr.
Houston's Reports on Thames and Lea supplies — ^Probable causes at
work — Relative amounts of free and albuminoid ammonia — Storage
under laboratory conditions — General conclusions as to the benefits
aocruing from storage — Copper sulphate treatment of plant growths —
Dr. Kemna's experiences — ^Method of applying the treatment — Effect on
the service water 24 — 47
ix
Contents
CHAPTER IV
CX)NSTRUCriON OP RESERVOIRS AND CARE OF FILTERED
WATER
PAOC8
Construction of reBervoin — ^Reservoira with compartmonta : Kansas, etc. —
Progressive sedimentation at Paris Waterworks — Circulating reflervoira
— Surroundings of reservoirs — Care of filtered water — Increase of germs
in service reservoirs and character of such — Growth of bacteria in spring
water — ^Difficulties of protecting service water — Influence of organic
matters — ^Effect of ozone and hypochlorites — General conclusions - 48 — 58
CHAPTER V
SAND-FILTRATION
Matters in suspension — ^Action of sand on dissolved substances — ^Ammonia
and its salts — albuminoid ammonia — ^Reduction of these in sand-filters
— Non-submerged filters — ^Dunbar's theory of absorption — Importance of
absorption in the purification of water — ^Retention of bacteria in sand-
beds — Experiments at Tegel and Miiggelsee — Growth of bacteria in the
imder-layers of sand — ^Pennink's views on the action of the sand-filter —
Leiduin filters — Importance of uniform speed of peroolation — Irregular
flow detaches germs — ^Metliod of obtaining uniformity of peroolation
— Defects of the filtering skin — ^Use of sand of fine grade — ^The effect of
the slimy coating of the granules — ^Aeration of the sand-bed — ^Rate of
filtration in relation to efficiency — ^Vegetable and animal growths on the
sand — Seasonal changes in the composition of the filtering skin — Influ-
ence of change of growth on the effluent — ^liberation of gases from the
film and the consequences — ^Films formed by quick growths — Odours
arising from decay of algse — Importance of a uniform film — ^Breaks due
to insects — Effective size of the sand grains — ^Efficient filtration with
reference to the character of the sand — ^Relation of effective size to rate
of filtration — Thickness of the water film on the sand granules, and the
bearing of this on the speed and efficiency of ffitration — ^Uniformity of
the sand and coefficient of uniformity — ^Best grade of sand — ^Depth of
the sand-bed 59—102
CHAPTER VI
THE MANAGEMENT OF SAND-FILTERS
Regulators — Importance of good regulation of the outflow from filters —
Siphon regulator — ^Telescope regulator — Burton's automatic device —
Weston controller — ^Management of sand-filters in Britain with reference
to speed of peroolation, regulation, purification antecedent to filtration,
sand paring and washing, etc. — Regulations recommended for the con-
struction and management of sand-filters — Form of daily report on the
working of the beds — Admission of water to the filters — Sand- washers —
Complete specification for the construction of sand-filters — ^Methods of
preparing crude water for filtration — ^Prefiltration — Sedimentation and
roughing-filters — Relative merits of the various systems iii use — ^The
CONTBKTS xi
PAoas
Poeoh-Chftbal system — ^Aoiion of the tUgroMisseurg — ^Piefilter and finish-
ing-filter — ^Pzoteotion of the finishing-filter from growths — Aeration
daring the procedure — ^Unifoimity of the bacteriological results under
the Puech • Chabal system — The Anderson process of treatment —
Hydroxide of iron as a coagulant — ^Results of the purification — ^The
Egham Waterworks — Successful prefiltration of Thames water — ^Arti-
ficial filming of the fine sand-filter — ^Non-submerged sand-filters —
M. Baudet's installation at Ch&teaudun — ^Bacteriological results —
Dr. Miquel's experiments — Coagulants — Sedimentation after coagula-
tion — ^Methods of applying these — ^Turbine feed — Harris-Anderson dis-
tributor and solutioner — ^Principle of Kent and Nixon's injector — ^The
difficulty of dealing with raw water of variable quality — ^Tests made with
various coagulants — ^The Aqua-Sana treatment .... 103 — 163
CHAPTER VII
MECHANICAL FILTERS
Advantages of mechanical filters in general — ^Time required for filming — Im-
portance of good filming — Chemical purification effected by mechanical
filters — ^The Jewell filter — Results obtained at Alexandria, etc. — Con-
struction and method of working — Cleansing the sand-bed — Application
of coagulant — ^Dr. Bitter's Report on the efficiency of the Jewell plant —
Jewell gravity filter — Contrivance for introducing wash water — ^Plant
at Little Falls, U.S.A. — Economy of working expenses — ^The Bell filter —
Details of construction and operation — Bacteriological results at various
stations — ^Bell's apparatus for the introduction of coagulant — Paterson's
gravity filter — ^Method of sand- washing — Construction of Paterson's
pressure ffiter — ^Mather and Piatt's filters — Special method of cleansing
the sand-bed — Coagulant feed — Purification effected by Mather and
Piatt's pressure and gravity filters — ^The Turn-Over patent filter — Con-
structional details and mode of washing the filter — ^The Candy filter —
Composition of oxidium and polarite — ^Their specific purifying properties
— ^Renewal of the oxygen absorbed by these substances — Method of
operating the Candy filter — ^Action of the filter on ferruginous and moor-
land waters — ^Analyses of the filtrate at different waterworks — ^Bacterio-
logical results — ^Reisert's filter — Construction and washing with com-
pressed air — Coke-filters — Specimen contract for the installation of
mechanical filters for the guidance of water authorities — ^Purification
by calcium hypochlorite — ^Method of disposing of the residual chlorine —
The patent De Chlor process — Satisfactory results and sterilization
of the effluent— -The Ferrochlore treatment 164 — 201
CHAPTER VIII
PURIFICATION BY OZONE
Nature of ozone and method of generating the gas — Importance of working
with dry air at low temperature— Study of " concentration " — Economical
production — ^Best form of electrical discharge — ^The De Frise ozonizer —
Sterilizing tower — ^Details of the complete plant required — ^Power
ZU CONTBKTS
PAOI
neoessaiy and oost of the treatmeat — ^Prooednre followed in applying
ozone to river waters — ^Baoteriologioal results — ^TheVosmaer battery of
ozonizers — ^Arrangement of the Vosmaer ozonizing plant and mode of
operating — The Otto process of sterilization — Special features and
details of the installation at Nice — Statement of the whole apparatus
required, with costs and usual working expenses — Ozone purifica-
tion at Ginnekin — ^Description of the installation — ^Results obtained
and working costs — ^The Howard-Bridge ozonizer — ^Economy of ozone
produced— Ultra-violet light as sterilizer 202—230
CHAPTER IX
WATER-SOFTENING AND HOUSEHOLD APPLIANCES
Defects of house filters in general — Charcoal as a filtering medium — ^The
Berkefeld filter — Its construction and method of working — Importance
of regular cleaning — ^The Forbes water sterilizer — Retention of aeration
after sterilizing by heat — Water-softening appliances — ^Temporary and
permanent hardness — Mode of dealing with these — Action of hard
waters on soap— Scale in boilers — ^Measure of hardness and cost of
chemicals for its removal — ^Mode of applying the treatment — ^Automatic
devices — Separation of the precipitate — ^Paterson's cold process — De-
scription of chemical feed and filter — ^Paterson's steam purifier — Lassen
and Hjort's water softener — ^Details of construction — Capital outlay and
working costs — Archbutt-Deeley water-softening process — Improved
method of throwing down the precipitate — Apparatus in use and its
employment — Traces of lime salts in suspension removed — Desrumauz
and Doulton water-softeners — Special features of these — Mode of intro-
ducing the chemicals — Harris- Anderson softener — ^The solutioner applied
to deliver the required chemicals — Bell's softening apparatus — Review of
the various appliances — Permutit as a water-softening medium — Prop-
erties and application of this substance — Its power of throwing out iron
and manganese — ^Easy method of estimating the degree of hardness of
water 231—259
CHAPTER X
THE TESTING OF WATER
Bacteriological examination — ^Apparatus for simple tests — Equipment of a
laboratory for the water manager — Method of conducting the experi-
ments, with particulars regarding the handling of the apparatus — Count-
ing the colonies of bacteria — ^Test for B, coli and pathogenic germs —
Concentration of samples under examination — ^The chemical examination
of water — ^Turbidity and its measurement — Standards of turbidity —
Turbidimeters — Influence of turbidity on the life of the sand-filter —
Colour of water and its measurement — ^Total solids in raw water —
Chlorides, and inferences to be drawn from isochlor lines — Nitrates in
natural sources — ^Amount of oxidized nitrogen as a standard of purity —
Reasons for rejecting this standard — ^Nitrites — Cause of the presence of
Contents xiii
PAOB
nitrites, and the importance attaching to their presence — ^Free ammonia
in different kinds of water — Estimation of albuminoid ammonia —
Kelatiye amounts of " free '* and albuminoid ammonia — ^Albuminoid am-
monia as an indication of pollution — Organic carbon and the '* oxygen-
consumed " test — ^Relation of carbon to nitrogen in different waters —
General conclusions 260 — 285
CHAPTER XI
THE TESTING OF WATEBr—ConUnued
Electrical conductivity of natural waters — Change of conductivity according
to the amount of matters in solution — Application of electrical tests to
determine the presence of defilements — Simple method of detecting
variations in the quality of the crude water— Standards of purity in
France, Britain, and America — ^Microscopic examination of water —
Capture of plankton — ^Water crustaceans — Commonest species and con-
ditions of their existence in reservoirs — Influence of sunlight — Various
commonly occurring animalculse, rotifers, flagellates, and rhizopods —
Plant life in reservoirs, green and blue algae, and diatoms — ^Periods of
abundant and scanty growth — The part played by various species in
forming the filtering skin at different seasons — Excessive growths of
microscopic oiganisms and how to restrict these — ^Mutual relationship
between plant and animal life 286 — 310
CHAPTER XII
THE PROBLEMS OF DISTRIBUTION
Cast-iron and steel pipes — Comparative merits — Joints in mains — Scour-
valves — Connection to the reservoir — ^Distribution within the area to be
supplied — ^Avoidance of " dead "ends — Various systems of branching —
Fire hydrants — ^Lead pipes for connections — ^Method of protecting iron
. and steel pipes from rust — ^Action of the service water on lead pipes —
Moorland supplies — ^Researches carried out by the Local Government
Board — Plumbo-solvency and the most suitable remedies — Dr. Houston's
conclusions regarding the origin of plumbo- solvency — ^The acidity of
peat — ^Mineral acids as a cause of plumbo-solvency — ^Erosion of lead
pipes — Plumbo-protective substances — ^Reserve of plumbo-protective
power desirable — ^Protective treatment on a laige scale — ^Usefulness of
various chemicals — ^Water-hardening — ^Treatment applied at different
waterworks, and the most economical and effective methods of working —
Exclusion of the worst runnings from the gathering area — ^Treatment
as corrective of both erosion and plumbo-solvency — ^Loss of carrying
power in iron mains — Presdnce of small amounts of iron in the raw
water at various installations — Growth of Oreiuj^rix and other allied
types — Evil effect on the carrying power of the mains — Removal of iron
from the ground water — Practice dependent on the conditions under
which the iron is held in solution — Methods adopted at different stations
and results obtained — Removal of deposits of rust from water-
mains ------------ 311 — 336
xiv Contents
CHAPTER XIII
THE PROBLEMS OF DISTRIBUTION— Cofatnuol
PAOR8
Water-hammer — Explanation of the oaiue of hammer in aeryioe pipes and
street mains — ^Maximum pressure— Method of avoiding or minimizing
the effects of water-hammer — Safety-valves and air-chambers — ^Best
form of water-taps — ^Electrolysis of water-mains — Conditions favourable
to this mode of protecting the pipes — ^Board of Trade regulations —
Galvanic action in cisterns — ^Public health in relation to water-supply
— Influence of various dissolved matters — Suspended impurities — Flood
epidemics — ^Dangers arising from gross impurities washed into the supply
by heavy rains — Impure water as the means of spreading cholera —
Typhoid from contaminated supplies — Pecuniary loss to communities
from t3rphoid — Contrast between the health conditions of towns supplied
with water of good and of doubtful quality — ^The case of Cherbourg in
relation to typhoid — ^Typhoid from unfiltered waters - - - 336 — 349
APPENDIX
USEFUL CONSTANTS AND DATA RELATING TO WATER FILTRATION
AND MEASUREMENTS
Table A. — Waste of water from taps left running 350
Table B. — ^Pressure of water in poimds per square inch for various depths 351
Table C. — Loss of head due to friction in water-pipes .... 351
Table D. — ^Discharge of pipes running full for different diameters and pipe
gradients 352 — 363
Table E. — Water-supply by gravitation — Dimensions of mains — Storage
reservoir — Gathering ground for given populations .... 353
Table F. — ^Discharge of water over weirs at depths stated .... 354
Table G. — Velocity of water in open channels - 354
Table H. — ^Weight of lead pipes per foot for various pressures - • - 354
Table K. — Weight of iron pipes for different pressures • . . . 355
Table L. — Cost of sand filtration — Purification by ozone and the De Chlor
process 355
Table M. — Relative costs of different mechanical filters and working
expenses 356
Bibuogbaphy 357 — 360
Iin)BX 361—368
LIST OF ILLUSTRATIONS
no. PAOK
1. Qeclogical Section across the London Basin - 11
2. Settlinff Basin at Kansas City. U.S.A. • - - - 50
3. Sundridge Park Ciroulatinff Reservoir - - - - 51
4. Method of Testing at Tegef ...... 74
5. Method of Testing at Mtiggelsee • • - - - - 76
6. Section of Ordinary Sand-FUter ... - - - 79
7. Watery Envelopes of Small Particle and of Sand Granule Uniting - 79
8. Chironomus (Larva) - - - - • - - 85
9. Number of Bacteria in Relation to Rate of Filtration • - - 88
10. Graph showins Advantage of Filtering at a Slow Rate, which is gradually
increased .-----.- 89
11. Spizogyra (Green Alga) and Fragilaria - - 90
12. AnahflBna (Blue Alga) 90
13. Hydrodiotyon --...-.- 90
14. Zooglcsa ......... 91
16. Beffgiatoa (Fungus) • • - 96
16. Didelon Automatic Regulator ...... 105
17. Glenfield and Kennedys Telescope Regulator .... 107
18a. Burton's Automatic Kegulator ....-- 109
18b. Burton's Automatic Regulator : Section • - 110
18g. Burton's Automatic Regulator : Plan - - 1 1 1
19. Weston's Automatic Reg^ator Controller • • - 112
20. Section of Outlet from (^nal to FUters - - 121
21. Section of Outlet from Filters to Reservoir - - 122
22. Greenway's Patent Sand- Washer - - - 124
23. Diagrammatic Section of Puech-Chabal System - - - 135
24. Puech-Chabal System at Magdeburg - • - - 139
25. Anderson Revolving Cylinder ...-.- 142
26. Egham Water Purification Works- .... facing 144
27. Graph showing Dr. Miquel's Results ..... 149
28. Non-Submergwl Filter at Ch&teaudun .... /aeing 150
29. Turbine Coagulant Feed - - - -152
30. Harris- Anderson Distributor ...... 154
31. Harris- Anderson Solutioner ...... 155
32. Kent and Nixon's Patent Injector- - - - - 157
33. Kent and Nixon's High Pressure Chemical Injector - 158
34. Aqua Sana Purifier - - - 162
36. Jewell Pressure FUter - - - - 169
36. Jewell Gravity Filter - - - - - - - 173
37. Bell's Pressure FQter 176
38. Bell's Coagulant and Chemical Feed - • - 179
39. Bell's Coagulant Feed and Filter - - 181
40. Paterson's Gravity FUter - • • - - 182
41. Paterson's Pressure Filter .-.--- 183
42. Mather and Piatt's Filter ..----- 184
43. Turn-Over FUter (Patent) - 187
44. Section of Candy Ozidizmg Filter - - • - 191
XV
XVI
List of Iixustrattons
no. PAOB
46. ReiMit'a PreaBore Filter - - - -194
46. Bnuh Diaoham ........ 203
47. Ck)mparative Yield of Ozone from Air and from Oxygen- . • 204
48. Decrease of Ozone Production in Moist Air .... 206
49. Output of Ozone with Increasing Voltage .... 206
60. Decrease of Yield of Ozone at Hiffh Temperatures . > - 207
61. Decrease of Output of Ozone as the Concentration Rises ... 207
62. limits of the Concentration of Ozone ..... 208
63. Siemens-De Frise Ozonizer ...... 210
64. Sterilizer at St Maur . - . . . .212
66. System Siemens-De Frise . . - • - - -213
66. Semicircular Electrode, showinff Water- Jacket : Cross-Section of Fig. 67 218
67. De Frise Ozonizer without Dielectric - - - - - 219
68. Vosmaer Ozonizer - ....... 220
69. Vosmaer Ozonizing Plant : General View . - - - - 221
(M). Otto Process, Compagnie Generate d*Ozone .... 223
01. Sterilizing Tower at Ginnekin. Holland - - ■ - - 226
62. Howard-Bridge Ozonizer -...--. 229
63. Berkefeld Filter - - 232
64. Lahmeyer Ozonizing Filter for Household Use .... 234
66. Forbes^ Patent Water Sterilizer - - . - - - 236
66. Paterson Water Softener - . . - -244
67. Paterson Steam Purifier ....... 246
68. Lassen and Hjort's Water-Softener - . - ' - - 246
69. Arohbutt-Deeley Water-Softener - - . - - - 248
70. Arohbutt-Deeley Water-Softener: Sectional Elevation - - - 249
71. Desrumaux Water-Softener - - - • .261
72. Doulton Water-Softener ....... 263
73. Bell's Water-Softening Plant - . - - -266
74. Permutit Water-Softener - . - - - - - 267
76. Laboratory at Airdrie, Coatbridge and District Waterworks • - 261
76. Incubator with Regulator . - . . - .262
77. Petri Capsule ........ 263
78. Reiohert s Temperature Regulator ..... 263
79. Colonies of Bacteria on Gelatine ...... 266
80. Photometric Turbidimeter - - . - - -273
81. Lanes of Equal Chlorine Content (Isochlor Lines) in Ground Water
Supplies ........ 278
82. Plankton Net - - - - - - . .292
83. Plankton Crustacea - - - .294
84. Plankton Crustacea - - - - - - - 296
86. Plankton Rotifera - - - - - • - 300
86. Plankton Magellata - - - - - -302
86a. Plankton Flagellata - - - - - 303
87. Plankton Rhizopods - - - - - - .304
88. Plankton Diatoms - - - - - - - 306
89. Plankton Algse ........ 308
90. Diagrammatic Scheme for Distribution - - - > - 316
91. Ball Hydrant ...-..-. 316
92. Glenfield and Kennedy's Fire Hydrant . - . - - 316
93. Dr. Houston's Apparatus for Examining Effect of Peat - - 322
94. Crenothrix ..-.-..- 331
96. Spraying Nozzle --.-.--- 333
96. Sedety Valve to Prevent Water-Hammer - 3.38
FoLDiNO Plates.
26. Egham Water Works
28. Non-Submerged Filter at Ch&teaudun
- facing 144
160
f»
•
• • • V • ••
• ■ • • • •
> • • • * .
•• • mm
« ••• • • -
• • < • •
MODERN METHODS OF WATEE
PUJRIFICATION
CHAPTER I
INTRODUCTORY
Dbsignbd to render an account of modem developments in
the theory and practice of water purification, this work is au
attempt to bring imder the notice of Water Authorities and
their officials the most efficient appliances for the treatment of
water, together with the details of working and costs of con-
struction and management.
The present is a time of great activity in the domain of water
purification. At no period have coimty and municipal
authorities been more keenly interested in the combat between
medical science and epidemic disease. The germ origin of
infectious maladies being now no longer regarded by the com-
munity as a pure theory, but as a certain fact, the whole weight
of public opinion gravitates towards one central aim. Bar the
avenues by which the seeds of bodily ailments approach the
individual, set a watch on the supply of comestibles and of
water, upon the very air of the streets and of the habitations :
therein Ues the true method of safeguarding the health of the
community. If any evidence were required of the quickening
of public opinion in recent times with reference to the expedi-
ency of striking at the roots of infection, it woidd be found
in the numerous appointments of Medical Officers of Health
and Sanitary Inspectors, in the compulsory isolation of sufferers
from epidemic diseases, and in the increased attention that is
now being paid to the bacteriological examination of the water-
supply. Practical science has become the handmaiden of social
life. They cannot be dissociated without obscuring the way
to efficiency. With the growth of expert knowledge, the diffi-
1
•I • • •• • v • • -
2 • 'MoDfiitN 'MiTttqps OF Water Purification
.•. •:.•••/• ;'•/!: • : /•. * •
cultk^'whicir bWei tiie question of public health will be handled
with increasing success.
Among these problems there is, perhaps, not one more
important than that of providing an adequate supply of whole-
some water for household and dietetic use. The sUi of intro-
ducing disease into the midst of a population has so frequently
been laid to the charge of the drinking water that it has become
almost a necessity to place that commodity beyond the range of
suspicion.
" Nearly all great outbreaks of diseases, both in this country
and elsewhere," said the President of the Institute of Sanitary
Engineers at the meeting in 1908, '^ have been associated with
certain conditions of the water-level in the soil." Further, he
drew attention to the extraordinary circumstance that the
death-rate of children under five years — after excluding
diarrhcea cases — ^is inversely proportional to the quantity of
water present year by year in the soil. Now, these statements
may not be incontrovertible, but that there is a large element
of truth in them cannot be doubted. Typhoid fever is asso-
ciated with the fall of the year, when a more copious rainfall
begins to wash siuiace impurities and germs that have been
thriving near the surface down to the deeper strata from which
drinking water is drawn. The periodicity of the visits of this
fever is so noticeable in America that it goes by the name
of " fall fever." That a replenishment of the hospitals with
enteric patients takes place regularly in Britain in the months
of October and November is but too well known to the medical
profession.
We need dwell no longer on this point. Water is not by any
means the only vehicle by which the seeds of disease are con-
veyed to men, but its universal use in the household, the part
it plays in the preparation of food, its use as a beverage at all
hours of the day, confer upon it, when polluted, far-reaching
powers for mischief. A vitiated supply of milk, distributed
from a particular dairy, may be responsible for a greater per-
centage of victims among the consimiers of it, but the taint
will probably reach no more than a small fraction of the
community. Bad water, on the other hand, exercises its
influence on all — all ranks and all ages. Those who escape
its evil effects owe their immunity to a vigorous constitution
or to accidental circumstances. The stricken are those whose
Introductory 3
general tone is under par. Even the perfectly healthy suffer
when the degree of pollution is serious. Further, if the germs
of disease be present iu water drunk, no particular individual
can solace himself with the thought that he is safely entrenched
against their attack. The danger is real ; the risk cannot be
gainsaid.
The cognizance of the fact that pure water is not only
desirable, but also essential, in the interests of health, is no new
thing ; for history informs us that water from springs and wells
was sought for by prfeerence, and that in remote ages water
was carried from distant uplands to certain important cities.
What is new is the realization of the fact that water which was
generall}^ accepted as unexceptionable, either because it was
drawn from deep wells or because it had been passed through
sand filters, may be very far from pure, under aU conditions
and at aU seasons.
Filters which are efficient when tested in the ordinary way
may become unreliable when the conditions are varied in a
manner adverse to their prearranged operations, and also when
they are handled unskilfully. The removal of sediment by the
filter may appear satisfactory, but unless the sand surface be
properly filmed, or the efficiency of the bed otherwise established,
obnoxious germs may be passing through in thousands. There
is matter for reflection in the fact that certaia authorities are
so careful with regard to the proper formation of this filTn that
they do not hesitate to allow the effiuent from a freshly sanded
filter to run to waste for two or three weeks, before turning it
into the service reservoir. In general practice, however, the
time allowed for filming is limited to forty-eight hours or
less.
There is probably no system of purification yet devised that
can claim to be safe and reliable without constant supervision
and periodical examination of the results of its working.
Rapid mechanical filters, with or without coagulants, and
ozone purifiers, require to be adjusted to the condition of the
incoming water. There is but one way of ascertaining whether
the appliances are doing the work expected of them, and that is
examination of the effluent, consistently repeated at appro-
priate intervals during the operation of the filters.
Formerly it was the custom to attach supreme importance
to the chemical analysis of water, because it was supposed,
4 Modern Methods' op Water Purification
somewhat erroneously, that the percentage of certain in-
gredients indicated definitely the volume of sewage or other
foul liquor that had made its way into the supply. It is not
to be questioned that the presence of an undue percentage of
organic matter should raise suspicion, and lead to immediate
inquiry into its origin. " But," says Wankljnti,* " the nitrates
and nitrites have been erroneously regarded as measuring the
defilement of water " ; and other authorities of note hold that
the presence of considerable amounts of organic matter does
not warrant the analyst in saying that the water is bad, while
the absence of the same matter does not guarantee bacterio-
logical purity. From his quantitative measurements, the
chemist may entertain strong presumptions, but certainty
escapes him. A reliable test has been put into his hands in
consequence of the progress of that branch of natural science
which deals with microscopic germs. Not only does this test
remove all uncertainty, but it is also extremely delicate, so
that the remotest possibilities of any given supply causing
mischief can be detected. At length it would seem that water
authorities in general are approaching the question of water
purification from the right standpoint. It is generally the case
that sand filters do little to alter the chemical character of a
supply ; they may do a very great deal in the way of eliminating
the living content.
Keeping this in view, we have the essential criterion for
discriminating the relative merits of different kinds of filters.
Other important considerations there are which turn the
balance of opinion in favour of one particular kind or another.
None, however, can be put on the same level of urgency as
the capacity to deal effectively with bacteria. It is to be
remarked that in the meantime absolute sterilization is not
demanded by the great water authorities. So long as the
number of germs carried away by the effluent does not exceed
a specified maximum per cm®., and that Bacillus coli is
practically eliminated, it is assumed that pathogenic bacilli
have been either wholly arrested or so much thinned out
that the consumer need have no dread of them. Still, it is
plain that the health authorities do not place entire reliance
on this assumption. When an epidemic breaks out, they
promptly advise the householders to complete the sterilization
♦ "Water Analysis," p. 113, 10th edition.
Intbodttotoby 6
of the drinking water by boiling. Hence it is not to be won-
dered at that the preference of the public tends more and more
towards a supply as nearly germ-free as possible. This is
why they willingly bear the outlay of bringing water from
unpolluted gathering groimds in remote uplands. This also
is the reason why a comparatively expensive process of
sterilization by ozone has been adopted at many important
stations. A wineglassful of water well within the prescribed
limit of bacteriological purity may yet contain five to ten
thousand germs, so that the consumer may be excused if he
questions whether some of these may not be dangerous.
Unfortunately for its rehability, the purification of water
differs in an essential point from almost every other mechanical
process. Machines and other specific apphances produce a
desired result* with certainty when the material they operate
upon is uniform in form or quality. They are not expected
to do the work intended unless this is the case. If they do it
at all, they do so imperfectly. But purifying plants have to
contend with changes in the raw water, both periodic and
unexpected. If mechanical filters are to displace the open
sand arrangement, they must be capable of adjustment to
varying requirements, and this accommodation should be
automatic as far as possible. There are, of course, ways and
means of securing a great measure of uniformity in the raw
water before it is conducted to the purifying appliances. Thus,
for example, the storage of several months' supply in a large
reservoir, equalizes the content of sediment, germs, and other
offensive matter. Previous treatment over roughing filters
is an aid to maintaining an average of impurities to be subse-
quently eliminated. The same end is sought with the help of
sedimentation basins in which coagulants may or may not
be appUed.
Water undertakers have now a choice of several systems of
purification which, it is maintained, surpass the slow sand
filter in efficiency and reliabiUty. Some of these have proved
notably successful at stations where the older process failed.
In making choice of a system, the essential point is the
character of the raw water throughout the year. That
being determined, the probable efficiency of any system
may be judged from its success with waters of a similar
type. Storage Ughtens the duty of the filter-beds, and, if
6 Modern Methods of Water Purifioation
continued long enough, it is a safeguard against water-borne
diseases.
; ^ As the available sources of naturally pure water are limited,
while the population of cities and manufacturing districts
tends to increase, many communities must eventually be
dependent on supplies of water which in the crude state are
unwholesome. It is well that the general introduction of
sewage purification now serves to exclude from rivers the
grosser forms of defilement. As the methods of treating sewage
become more parfect, and as regulations against the discharge of
putrescible matters into streams are more stringently enforced,
it may be expected that sentimental objections to the use of
purified river water will disappear. Better water for house-
hold purposes than that which is to be furnished to Paris from
the St. Maur works it would be difficidt to imagine. By means
of filtration followed by ozonizing, the Mame water will rival
that of the springs of Vanne and Dhuys.
The future of water engineering promises a rich and varied
crop of interesting problems, the solution of which will become
more delicate as the standard of purity is raised. The most
significant addition of recent times to the conditions which
treated waters must conform to is that which relates to the
jB. colt. It was the great weight attached to the elimina-
tion of this germ which chiefly induced the Municipal Ck)uncil
of Paris to sanction the construction of an ozone plant at
St. Maur. The close relation which has been established
bstween the art of water purification and the progressive
sciences of bacteriology, biochemistry, and hygiene, will
in future control, not only expert, but also public opinion,
with regard to the degree of purity which drinking water
should exhibit.
Among the practical sciences there are few which demand
of the student a more varied range of technical knowledge than
that of water purification. Hence the need of a properly
organized course of training for the water engineer and water
manager. A well-defined scheme of instruction would com-
prise at least as many branches of knowledge, and subjects as
scholarly as those which are included in the University curric-
ulum of engineering students. It is to be hoped that the
establishment of a faculty of water engineering in technical
colleges will not be long delayed.
Intboduotoby 7
The large number of sciences which offer contributions to
the theory and practice of water purification occasions a diffi-
culty in choosing the best arrangement for a clear exposition
of the subject in hand. A study of storage involves the con-
sideration of the animal and vegetable life found in reservoirs,
and the vitality of the bacteria present in the crude water.
The latter topic claims attention in discussing the care of
filtered waters. Sand filtration involves many issues both
chemical and biological. The construction of reservoirs and
the distribution of the supply call for the application of
mechanical principles. There are also subsidiary topics that
have risen in importance owing to modem developments in
the practice of treating impure water. Among these are the
introduction of coagulants, the use of special purifiers, as oxidium
and permutit, the application of ozone, the protection of pipes
and fittings from corrosion, and the graded mode of successive
filtration.
Under the circumstances, it has been found best to follow
a natural order of discussion, beginning with the sources of
supply, and follow the water on its way to the consumer.
The chief divisions into which the subject-matter falls are
therefore as follows :
(i-
(ii.
(m.
(iv.
(V.
(vi.
(vu.
•••
VIU.
Sources of supply.
Storage and construction of reservoirs.
Filtration by sand, including non-submerged filters.
Filtration by mechanical filters.
Purification by ozone.
Chemical and biological features of water.
Water-softening.
Distribution, including plumbo-solvency.
CHAPTER II
SOURCES OP SUPPLY
The growth of urban communities and the continual extension
of water undertakings have greatly limited the available
sources of untainted supplies for household use. The practice
of replacing dry closets and cesspools by the drainage of sewage
into rivers has fouled many sources potentially in reserve.
River water which has received considerable quantities of
sewage, whether treated or not, is scarcely regarded with
favour by communities in quest of wholesome and palatable
drinking water. There is, indeed, a well-grounded preference
for waters that are clearly exempt from anything more than
insignificant defilement with sewage, manure, or any other
organic waste.
Among the sources against which no exception is apparently
admissible on the score of pollution are deep wells and borings,
the upper reaches of rivers and their tributaries beyond the
demesne of agricultural activity. Lakes fed by mountain
streams are in general natural reservoirs of good water. To
these must be added the natural drainage of moorlands, uplands,
and forests, even when this is chiefly surface water or the
outflow from shallow wells.
Deep Wells ; Sources of Pollution. — ^In the case of deep wells
and borings, the purity of the water results from natural
filtration, and very often the supply is perfectly free from
undesirable germs, and even from organic matter. But there
are exceptions. Wells located in the midst of a population
are rarely safe. The proximity of cesspools, manure-heaps, and
polluted streams, suggests the exercise of caution in all such
cases. Dr. Thresh ("Examination of Waters and Water-
Supplie3," p. 301) instances a number of wells in districts
8
SouBCBS OF Supply 9
adjacent to the Metropolis to which surface water, tidal water,
and organic impurities, had had more or less free access.
There is always the possibUity of water percolating to con-
siderable depths by way of fissures and " swallow-holes." If
this happens, it escapes the benefit of natural filtration.
Detection of Pollution in Underground Sources.— When
an underground source has been found to contain suspicioas
germs (B. colt, etc.), or if the organic content be high, the
natural conclusion is that surface matters have access to it
through crevices or breaks in the strata. The source of
contamination is presumably some cesspool, rubbish-heap,
or deposit of farmyard manure in the vicinity, and an inspection
of the neighbourhood may indicate one or other of these as the
origin. To bring the matter to a test, one must ascertain
whether liquids can pass from the suspected place to the well.
For this purpose a strong solution of a suitable chemical, as
common salt, is introduced at the spot indicated. The well
is then pumped continuously, and samples are taken for analysis
from time to time. Any decided increase in the amount of
chlorine woidd point to infiltration from the suspected locality.
In place of salt, one may employ Uthium sulphate, which is
easily detected with the spectroscope, or the dye fluorescein,
which has powerful colouring properties. Professor Henry
Bobinson found that lithia was easily applicable to the
investigation of undergroimd sources (Trans. Inst. Mech.
Eng., Jan., 1909). Better, however, than any chemical for
identifying a source of pollution is an abimdant culture of
some harmless microbe, as B, pi*odigio8U8 or B, violaceus. For
if it b 3 shown that bacteria are able to travel from the spot
tested to the well, it is manifest that the process of natural
filtration has failed, and that pollution from that quarter may
be looked for.
The experiments made at Lake Tegel (p. 73) indicate how
a test of the power of undergroimd formations to retain bacteria
may be carried out A chemical analysis would have served no
purpose, because the permeability of the strata to liquids was
not in question.
Should it have been proved that a solution of salt or lithia
has travelled from a rubbish-heap to a weU, that circumstance
alone does not show that dangerous ingredients would be able
10 MoDBBN Mbthods OF Watbb Pttbitioation
to come in by the same route. On noting the time taken by
the t38t liquid to travel through the intervening strata, and
comparing the rate of parcolation with that which obtains
in unfissured formations, one may b3 able to infer the actual
conditions which exist undergroimd. With compact gravel
and unbroken rocks, the rate of percolation vertically is slow,
and it is still more so in a lateral direction, probably not more
than a few feet per hour. A movement of the test liquid at
a speed greatly in excess of this would be a suspicious circum-
stance, and a confirmatory experiment with a culture of
bacteria should then be undertaken.
At the Cambridge County Asylum in 1905, the water from
a^ well in the chalk, 60 feet deep, was suspected of being
the occasion of a large number of typhoid cases among the
patients. It was shown that the imderground supply of the
well proceeded in part from the sewage irrigation, distant
1,200 feet, and that coloured liquids could travel that distance
in 103 hours through the underlying rocks (Trans. Assoc, of
Water Engin., 1907, pp. 108-137).
In considering the circumstances which may influence the
content of well waters, it is desirable to take full advantage
of the knowledge which is available regarding the geological
formations of the district. After studjdng the disposition of
the strata in the neighbourhood of the Cambridge County
Asylum, Dr. Thresh concluded that from beyond a certain line
the imderground water would travel avxiy from the well under
observation. Experiments with fluorescein proved that this
inference was completely justified.
Artesian Wells. — It often happens that underground supplies
have to travel from distant gathering grounds. Thus, the
waters which find relief in the artesian wells of Paris and London
are fed from the outcrop of the porous strata beyond the
area covered with impervious clays. In the case of London
the chalk formations which are the reservoir of the artesian
springs crop out in the Kentish Downs to the south, and in the
Chiltem HiUs on the north. The quality of the water is never-
theless affected to some extent by the condition under which
it is at first absorbed by the porous beds. For though the
journey of many miles underground filters out much suspended
matter, changes the organic content, and imparts a degree
SOUSOBS OF SUPFLT II
of hardness, impurities make their'appear- j
aaoe in the outflow, at particular seasons.
After heavy rainfall following drought, the
water of certain deep wells is discoloured,
and this is what might be expected if the
took formations are intersected by fissures.
Indeed, there can be little doubt that the
subterranean stores of water in the chalk
beds are here and there fed by swallow-
holes, and when they are tapped in the
vicinity of these openings the water cannot
be of reliable purity. 5
Yet the strata underlying the London n
Clay are productive of much excellent |
drinking water, for it is remarked, in the i
Sixth Report of the River Pollution Com- "f
missioners, that " in the whole course of g
their experience they had found do catch- 3
ment basin so rich in springs of the finest I
drinking water as that of the Thames." ^
A cross-section of the superficial strata s
from the Chiltems to the Kentish Downs g
is shown in Fig. 1. The topmost layer S
of impervious clay is twenty-eight miles g
broad, and beneath London it has a thick- §
ness of 300 feet. Beyond the clay the a
chalk rocks become the superficial forma- ^
tion, and much of the soil resting on theee o
pervious rooks is under cultivation. The ""
stratum of chalk beneath London is from
600 to 700 feet in thickness, and it is
supported by deeper layers of a sandy and
porous nature, so that the storage capacity
of all these rocks must be very large.*
Protection of Deep Wells from Pollu-
tion. — Precautions against the defilement
of deep wells are almost 'necessarily
* For a full aooount of the sources from which
waMr-aupplies are drawn, see "The Geology of
Water . Supply," by H. B. Woodward, F.E.S.
(Arnold's Oeologieal Series).
12 Modern Methods of Wateb Pubifioation
restricted to the immediate neighbourhood of the out-
flow. The greatest attention should be directed to that
quarter from which the underground flow comes to the well.
From what direction the well is principally fed may be ascer-
tained by a consideration of the geological formations, and by
suitably devised tests with fluorescein. Probable sources of
pollution can then be investigated, and measures taken to
safeguard the well water. Around the place where the bore
is sunk, an area should be enclosed and kept clear of decaying
matter. Local circumstances, as the slope of the ground and
the permeability of the rocks, will determine the extent of this
area, and it ought to extend farther towards the direction
from which the underground flow arrives. The bore of the
well must be made water-tight to some depth by iron pipes or
masonry. At Hastings and at Halstead (Essex) the wells are
lined with iron to a depth of 60 feet, and at Leighton Buzzard
all water above the 176 feet level is excluded. In the last case
the water-tight casing was extended considerably, not on account
of any risk from surface water, but in order to avoid the inflow
from certain strata containing iron oxide. At Hythe the first
6 feet of the brick lining of the well is backed with cemsnt to
keep out surface water. For the next 17 feet the backing
is of clay puddle, and the brickwork is carried to 70 feet, and
this is followed by iron cylinders to the bottom at 163 feet.
The iron casings of the wells belonging to the West Cheshire
Water Company are 130 feet deep. Thus, the depth to which
the casing of the well requires to be carried must b3 decided
by the existing conditions at each station.
The season in which there is the greatest risk of impinrities
from the soil reaching the well is that which is marked by
heavy rainfall after drought. This occurs frequently in the
autumn. The level of the ground water is then quickly raised
by the first washings of the superficial layers, which contain
organic matter and myriads of bacteria. Wells naturally
receive an abundant tribute of the new supplies, seeing that
the contour of the water-level underground slopes steeply
towards them. At such times the analysis of the outflow
should be carefully inspected.
Upland Sources of Supply : Streams and Lakes. — Supplies
collected from uplands beyond the limits of cultivation
Sources of Supply 13
generally furnish excellent drinking water. The defect most
commonly met with is a tendency to act upon lead when
the catchment area includes stretches of peaty soil. In that
case the influence of organic matter dissolved from the peat
is most felt when the storm waters descend. The greater the
proportion of spring water as compared with purely surface
drainage, the better will be the quality of the service water.
This subject is discussed at length in a later chapter. Forest
lands, especially those covered with pines and similar species,
yield drinking water of high grade. Hence the recommenda-
tion has b3en made by the Local Government Board that
lands acquired by water undertakers should be planted.
Trouble arises from fallen leaves obstructing the streams
and discolouring the water, so that it would appear to
b3 advisable to leave clear margins alongside the water-
courses.
Lakes situated in mountainous districts, with feeders draw-
ing from untilled land, are held in high esteem as natural
reservoirs of potable water. Many large communities in
Britain enjoy supplies of almost ideal purity from the lochs
of Wales, of Scotland, and the Cambrian hills. All the advan-
tages of storage accrue to these reservoirs hemmed in by natural
barriers. In som? cases, as at Loch Katrine and Thirlmere,
the original water surface is raised by the erection of a dam,
so as to meet the requirements of the installation. The great
lakes of North America provide service water for a number
of cities, as Chicago, Milwaukee, Cleveland, Erie, and Toronto.
It cannot, however, be said that these immense sheets of fresh
water now yield faultless drinking water. The supply is
unstinted, but the inshores are fouled with sewage, while the
great volume of traffic on the lakes contributes to the defile-
msnt of the waters. To avoid the grosser impurities, the intakes
are carried out by tunnels or submerged pipes reaching from
half a mile to a mile or more into the purer deeps. CMcago
has lately diverted its sewage from the old convenient dump-
ing-groimd on the shore, and carried tunnels four mUes
out into Lake Michigan, in order to tap the best water
that the lake can provide. The inlets of these tubes and
tunnels are naturally placed well balow the surface to
avoid passing ships, floating impurities, and ice in the cold
season.
14 Modern Methods op Water Purification |
Lowland Sources: Rivers and the Drainage of Cultivated
Lands. — Catchment areas which include cultivated lands, rivers I
in their lower courses, and shallow wells, may be reckoned the
principal sources of supply that are clearly open to contamina-
tion. Rivers in their lowland reaches are called upon to provide
drinking water for vast populations, and. thanks to storage
and purification processes, they merit no ban on hygienic
grounds. The Thames, the Seine, the Rhine, the Elbe, the
Nile, Ganges, and Mississippi, are fountains from which whole-
some and palatable waters are prepared by artificial expedients.
Water Authorities who draw from rivers may congratulate
themselves that the practice of sewage treatment is now becom-
ing general, and in many cases compulsory. Thus is avoided
pollution of the worst kind on a large scale. It is manifestly
impossible to exclude organic impurities from rivers and their
tributaries in traversing cultivated lands, in passing hamlets
and farmsteads, in coming within the reach of all kinds of
accidental or intentional defilement. But consumers need not
be seriously concerned at this, especially if the volume of water
flowing is very large compared with that of the foul liquids
which it may here and there take in. For the well-aerated
river water quickly sets to work on the particles of organic
origin, and the living things disseminated in the water join
in the attack. In a longer or shorter period the character
of the gross impurities is completely altered. The effect is
similar to that which occurs when surface water charged with
decaying matter filters into the earth. The final steps of the
process may not be completed, but they are approached.
That is to say, the organic substances tend to become mineral-
ized. If this happens they are innocuous to the consumer.
The bacilli of intestinal origin die off in river water. These
considerations dispose of sentimental objections to river water
in the lower reaches as a source of supply for a community.
With storage and scientific modes of filtration, the final result
may not be inferior to that which Nature throws up from the
stores which she hides underground, and which she constantly
replenishes from the surface.
Catchment areas which include buildings and cultivated
lands demand careful management and regular supervision.
Certain powers have been conferred upon those who under-
take to supply communities with water, and, in particular.
SoTJBOES OF Supply 15
some British authorities have embodied in their special Acts
a clause enabling them to protect their lands from pollution,
and their watercourses from defilement, through the operation
of any industry in the vicinity.* It is sound policy for
water authorities to become proprietors of their gathering
areas, so that they may restrict agricultural operations to
grazing, and forbid the use of any manures other than mineral
fertilizers. The watercourses should be kept open, cleared of
weeds and overhanging vegetation, and the access of the public
prevented. All drainage from buildings within the area must
be intercepted, and taken by well-laid conduits to a point lower
down than the intake. An examination of the watercourses
enables the practised eye to discover whether any leakage of
foul water is finding an inlet. Sewage and other offensive
matters occasion growths of a fungoid nature on the weeds
and pebbles, and leave a discoloration of the bed of the
stream where they enter, easily noticed when the water runs
low.
Attention must be paid to the effect of storm water, with
special regard to the nature of the suspended matters that
may be discharged into the streams from the wash of the
adjoining lands. When the groimd dips steeply, much
of the loose material lying above is swept downwards by
heavy rains. It is generally possible in such cases to divert
the storm water, or by artificial means to impede the free
access of turbid waters descending from slopes. Planting the
borders of reservoirs and watercourses has often been advocated,
and trees of the pine species are favoured. The planting need
not be carried close to the banks.
Where minerals, coal, ironstone, etc., are worked within the
catchment area, the drainage of the pits never forms a desirable
addition to the supply. Deep workings exhaust the under-
groimd waters that might otherwise contribute to the general
intake. Nevertheless, it is better to divert the discharge from
the pumps. It is not only fouled by the workers, but it gener-
ally is charged with iron and other ingredients of the seams
and veins with which it has bsen in contact.
♦ The olauBe is to the effect that " they may hold any lands or servitudes
which they may deem necessaiy for the purpose of preventing the fouling of
any water which they are authorized to take, and for the protection of their
waterworks against nuisances.'*
16
Modern Methods op Water Purification
Lands aequlred for Gathering Grounds. — The following water
authorities have acquired land within their gathering areas
for the purpose of preventing pollution :
' Birmingham
Bolton
Bradford
England ^
Liverpool
Leeds
Manchester
Newcastle
, Oldham . .
Ireland . — Belfast . .
46,662 acres.
2,366
9,000
23,000
16,000
11,000
6,600
2,000
13,322
Scotland. — Edinburgh and District Water Trust have
purchased about 6,000 acres, or nearly the whole of the area
draining to the Talla Reservoir.
Olasgow has acquired the f euing rights of the lands draining
into Loch Katrine.
Lanarkshire Middle Ward District Committee have specially
arranged to keep certain fields out of cultivation near their
reservoirs.
At Paisley the Water Engineer, Mr. Lee, states that the
drainage area at the old works of the Corporation extended to
about 900 acres, and that 600 acres have already been bought.
The land is let for the grazing of cattle and sheep, and no town
manure is allowed for top dressing.
Kirkcaldy and Dysart. — (a) The Water Commissioners have
purchased two estates in the vicinity of their waterworks,
with the object of having full control of them, so as to be able
to prevent pollution of the streams feeding their reservoirs,
and these estates are let, but in fields where there is access to
the watercourses sheep-grazing only is permitted. The total
area of the gathering ground is 3,900 acres, and the rental
derived from the leases with the restrictions mentioned repre-
sents 4 per cent, of the purchase price, which was at the rate
of £160 per acre.
Filtration of River Water into Adjacent Wells. — Instead
of drawing water directly from a river, it is now not an
uncommon practice to sap the moist strata adjoining by means
of deep trenches parallel to the banks. Advantage is thus
v^
SoTJEOEs OF Supply 17
taken of a natural filtration, and if the deposits which bound
the course of the stream are gravelly or sandy, an abundance
of water is secured, much superior in quality to that in the
open river.
Dangers ol Contamination ; Localities supplied from Under-
gromid Sources. — In an article upon water purification by
natural filtration (CerUralU. /. AUg. Oeaundheitspflege, 1908,
H. 9, 10), Professor W. Prausnitz refers to the large number of
important towns which are supplied from underground sources.
The water is frequently drawn from the immediate neighbour-
hood of a river, and is obtained either from wells and boreholes,
or from galleries excavated parallel to its banks. A wide range
of analytical researches has proved that these sources are very
liable to admixture with imperfectly filtered, or even raw,
water during times of flood. The proportion of impure water
which then finds access to the supply depends on local factors,
such as the nature of the strata, the distance from the flooded
stream, and the extent and depth of the inundation. Prausnitz.
gives instances in which the content of bacteria increased by
thousands per cm^. This is confirmed by Professor Kruse
{ZeiUchr. /. Hyg. u. Infektionakh., 1908, Bd. 59, pp. 6-94), who,
however, is not certain that epidemics have been caused by this
form of contamination. He suggests a number of remedies,
as the intercepting of flood water by dams and barrages, the
fortifjdng of the adjacent banks with clay and turf, raising the
level of the surrounding land, and the rejection of doubtful
water as occasion arises. On the whole Dr. Kruse is inclined
to favour natural filtration, especially as there is little risk of
the bed of the stream becoming choked up with algae or other
growths, and so preventing the water from percolating. The
current obviates this inconvenience, so characteristic of artificial
filter-beds. From time to time, also, floods sweep away all
slimy matters. It is not without significance that, when the
bed of the river has been scoured in this way, there is observed
a marked increase of bacteria in the neighbouring wells, and
Dr. Prausnitz concludes that part of the increase may be due
to direct percolation from the river-bed. The permeability
to bacteria of the intervening space between river and well
must depend on the nature of the ground.
In Dresden, after the service water had been rendered less
2
18 Modern Methods of Water Purification
pure in consequence of floods, Dr. Meinert recorded a far higher
mortality from diarrhoea among yoimg children, and a large
increase of stomach catarrh among adults. Dr. Prausnitz
confirms the appearance of diseases of this nature, concurrently
with heavy flooding at various localities. He strongly advo-
cates daily chemical and bacteriological analyses during periods
of danger. Also the temperature of the output from deep
wells should be noted, for any sudden alteration is probably
traceable to the admixture with surface water.
Natural filtration plays a part in the preparation of water
for the use of the city of Amsterdam. The collecting ground
consists of many acres of sand-dunes, the property of the
water undertakers. The terrain is a barren, undulating waste
which has been canalized and drained by a network of deep
channels. Bain water percolates downwards through the sand,
picking up on the way very considerable quantities of mineral
matter, so that on reaching the works at Leiduin it holds about
36 grains per gallon, largely salts of lime. It also dissolves
iron in its passage towards the canals, and this requires a
special treatment for its elimination.
The bacterial population is considerable, averaging about
2,000 per cm^., so that the raw water stands in need of
thorough filtration.
Water of better quality is obtained for the supply of Brussels
from galleries driven underground among sandy strata in the
direction of the Forest of Soignes. The main conduit is fed
by galleries driven sideways, so as to pick up as much as possible
of the rain which is absorbed by the sand. In order to husband
excess water during heavy floods, portions of the walls of the
underground passages are made water-tight at selected spots.
The well-soaked strata are thus forced to retain their charge
until the adjoining beds draw it away as the ground water
level sinks. These concrete-lined portions of the galleries,
or " serrements," as they are called, thus provide an ingeniously
cheap method of storage.
The town of Gratz in Austria receives its water from wells
sunk in alluvial sand alongside the River Mur. Flooding
occurred in May, 1907, and immediately there appeared in the
town a marked increase of cases of stomach and bowel com-
plaints. The alluvial bed is 30 feet deep, resting on an im-
pervious clay. Investigations proved that the supply water was
SouBOES OF Supply 19
very much polluted while the floods lasted. In response'^to a
public outcry, new wells have been constructed at a distance
of 120 yards from the Mur. These have jdelded good drinking
water. The old works now serve as a stand-by to be used
in dry weather. Much care has been taken to make the
linings of the wells water-tight.
Stuttgart meantime (1910) stands in pressing need of an
increased reserve of drinking water, seeing that the filtered
Nutz river water is strongly objected to by the towns-people
on account of its bad odour. There is a moderate supply
of spring water which was considered sufficient for the con-
sumers forty years ago, and which at the present day would
furnish a few gallons per head. Numerous localities, some
near, some very distant, have been explored with a view to
resolving the problem before the city authorities. It has been
proved that the sand and gravel beds lying close to the River
Neckar, though only 10 or 12 feet deep, effect a complete
purification of the river water, which percolates under ordinary
circumstances. But whenever the river comes down in flood,
the whole of the ground water in these river gravels is turbid
and laden with germs. Hence the project of augmenting the
supply from this source does not meet with great favour, and
it is likely that the choice will fall on the River Enz, forty miles
distant, in the Black Forest.
Ihiring the past year researches have been in progress near
the town of Landeshut in Silesia. By one scheme it is proposed
to tap the alluvial beds in the Bobertal, close to the River
Bober. Numerous borings from 12 to 60 feet in depth have
been put down, and in general the water foimd is of good
quality. In permeating through the gravels, the soft river
water adds three or four degrees (Grerman standard) to its
hardness, and in hot weather its temperature experiences a
welcome lowering of 6° to 6® Cent.*
The city of Worms was provided with a roughly filtered
service of Rhine water in 1888. The arrangement "was as
follows. ; An . iron cylinder 10 feet in diameter, with perforated
wall, was simk to a depth of 3 feet below the bed of the river.
Within this was set a large perforated cone connected with
a 16-inch service main. The remaining space between cone
and cylinder was packed with rough gravel. The result, as
* See Qhsbdewchlung und Waaaerveraorgung, October, 1909.
20 MoDBBifr MxTHOBs OF Watbb Pubifigation
might be expected, was never satisfactory, and after the town
of Mannheim began to pour sewage into the Rhine the water
was quite dangerous. A new supply has now b3en obtained
from boreholes in the Biirstadter Forest, eight miles distant.
This is of fine quality, but it contains much bicarbonate of
iron in solution, and this has to be dealt with by aeration and
filtration. At the same time traces of sulphuretted hydrogen
are oxidized.
Conditions very similar to the above may ba noted in con-
nection with the water-supply of Bingen. Formerly the town
obtained its water-supply from two wells, one 60 yards, the
other 60 yards, from the Rhine. The wells were built in to
some depth, but the bottom portions were left with the natural
walls. The water obtained was found to be fairly good ao
a rule, unsatisfactory only at times. Hence a new and better
supply ha.s been requisitioned from underground sources five
miles distant. The site was selected by an eminent geological
expert. Berlin now draws its domestic supply from deep
borings near the shores of Lakes Tegel and Miiggel (see
p. 73).
Contamination of spring water with sewage gave rise to a
serious outbreak of enteric fever in a small market-town of
Southern Austria; 386 of the inhabitants out of 1,700 were
struck down {CentraB)L /. Allgem. Oesundheitspflege, 1908, H. 9
and 10, M. Kaiser). The foul water percolated through the
ground for some distance without losing its dangerous germs.
After the cause had been discovered and remedied, the whole
installation was disinfected with Ume, 300 grains per gallon
being applied for a time. The bacteria, which numbered on
the average 310 per cm®., were thus destroyed.
Following upon the closing of the Stralauer Waterworks at
Berlin, which gave uncatisfactory drinking water, the mortaUty
from bowel diseases decreased from an average of several
hundreds in the preceding twelve years to the present figure
of 64 per annum.
The town of Bedford (England) derives its water from wells
sunk near the banks of the Ouse. It is realized that pollution
is not excluded by the percolation from the river, and accord-
ingly the water is treated carefully at the works, being first
passed through Candy filters, and then sprinkled over non-
submerged sand-beds. Some part of the effluent from the
Sources of Supply 21
mechanical filters goes to sand-beds of the old type. The
service water is remarkably pure.
A very large amomit of water is pumped within the area
administered by the Kent Water Company along the lower
reaches of the Thames. It is mostly used for industrial
purposes, and Mr. Clayton Beadle (see his paper read to the
Royal Society of Arts, reproduced in WcUer, vol. x.) judges
it to be pretty near the raw Thames water in its general
characters.
On the other hand, the Kent and Lea valley wells, which
contribute to the MetropoKtan supply, jdeld very good water
from the standpoint of chemic&l analysis, and over 90 per cent,
of the samples tested bacteriologically showed no B, colt in
100 cm^. (Fourth Report Metrop. Water Board, 1910).
Water of good quality is obtained from wells sunk in the
alluvial sands alongside the bed of the Mississippi.
The city of Nashville, Tennessee, obtains water from a
filtration gallery which taps the imderground waters by the
Cumberland River. Peoria, Illinois, draws from gravel
deposits left by the River Illinois. In India, the town of
Trichinopoly is supplied from a number of wells sunk 26 feet
below the bed of the River Cauvery. Here a constant flow
of water is pumped, notwithstanding the fact that the Cauvery
is dry for five months of the year. In South Africa the popula-
tion of the Rand are dependent on deep wells, which provide
satisfactory water for domestic use. On the other hand, the
alluvial deposits in Lower Egjrpt do not yield good water, owing
to the richness of the Nile Delta in organic matter.
Shallow Wells. — Many small communities, agricultural
holdings, and private dwellings, depend upon shallow wells
which are fed by surface water purified to some extent by
percolation through the superficial strata. These are much
exposed to contamination, and are undoubtedly responsible
for many of the outbreaks of epidemic disease in country
districts. As it is in general impossible to dispense with this
method of obtaining a domestic supply in thinly-populated
districts, it is all the more necessary to adopt every reasonable
safeguard against pollution. County authorities in Britain
now have powers of examining the sources of drinking water,
and of enforcing compliance with the conditions laid down by
22 Modern Methods of Water Pitrificatton
their Medical Officers and Sanitary Inspectors. The most
obvious of the measures that should be taken to guard the
well from the easy access of defilement may be stated as
follows :
1. The well should be removed as far away as possible from
manure-pits, cesspools, and other possible sources of con-
tamination, and always towards the direction from which the
underground waters flow. It should not be situated in a hollow
to which surface water tends, but rather on a site which
naturally throws off the rainfall. Nor should it be placed on
ground which is hable to be inundated with flood water.
2. A space all round should be fenced in, and kept under
grass or planted. Local considerations may limit the radius
of this space to a few yards, but it is doubtful whether anything
less than 100 feet can be looked upon as a real safeguard in
gravelly strata. The enclosure should extend more in the
direction from which the subsoil water percolates.
3. The well should be cased water-tight to the bottom, or
in any case to not less than 20 feet. The casing should be
carried 2 or 3 feet above the surface, and the groimd surround-
ing should be laid with cement or otherwise made water-tight
to a distance of 4 feet. It is recommended that the pump be
separated from the well-head, and placed some distance away,
so as to minimize risks from spilt water finding its way inside.
The top of the well should be protected from dust by a suitable
covering.
4. Samples of the water should be taken for analysis from
time to time. In addition the consumer should observe the
character of the supply, noting how it changes with weather
and season. Wells which become turbid after heavy rainfall
are always to be suspected.
Surface Springs. — Springs other than artesian wells are gener-
ally called " surface springs," because they are derived from
the water gathered by superficial beds of porous rock. The
water issues from the ground at the junction of the permeable
bed with one that is less pervious.* The quality of the outflow
depends on the nature of the strata through which it has
permeated, the depth of the natural layer of filtering matter,
and the presence or absence of sources of contamination at the
• See " The Geology of Water Supply '* (H. B. Woodward), chap. vi.
Sources op Supply 23
surface, particularly in the vicinity of the spring. If cultivated
lands are near by, the annual manuring replenishes the surface
with organic matter. All farmste acings and dwellings on the
gathering area are possible sources of contamination. Springs
that formerly gave serviceable supplies have been abandoned
owing to the increase of population on the area which receives
the rainfall, that eventually issues at the surface. Such has
been the case with the Bagshot springs that furnished London
with water for many centuries.
Some of the cautions which have been stated as bearing on
the use of shallow wells would apply to surface springs. It is
almost unnecessary to say that the outlet of the spring should
not be lower than the site of the dwelling-houses in the vicinity.
A space around the spring ought to be reserved, and surface
water excluded by appropriate constructions. It is not to be
expected that the use of farmyard manure can be controlled
to any great extent, but at least in the neighbourhood of the
spring mineral fertilizers ought to be substituted. Periodical
analyses of the water should be made.
Rain Water. — ^At not a few homesteads in Britain, the best
water available for domestic use is that which is collected from
the roofs of the buildings. Rain water is carefully collected
in many countries where it is difficult to obtain water from the
ground. Bain water is soft and insipid to the taste. Its
purity is hardly open to question except in the vicinity of towns.
It acts very freely on lead, and cannot be stored in cisterns
made of that metal. The first runnings from the roofs are of
course rejected. The conduits must be kept clean, and the
cistern covered to prevent the growth of algse. With respect
to domestic supplies from shallow weUs and surface springs,
it should not be forgotten that, wherever there is any question
about the purity of the drinking water, all danger may be
avoided by the use of one or other of the excellent household
filters now obtainable at a moderate cost.
CHAPTER III
STORAGE
That storage exercises a wholesome influence upon impounded
water in the way of removing sediment is patent to all. But
that other important and far-reaching processes come into
play during storage is a circumstance which has been brought
to our knowledge by modem investigation and research.
Dealing with micro-organisms in impure water, Frankland
(in 1892) called attention to the rapid extinction of bacteria
in streams and ponds. Following this, it was generally accepted
by epidemiologists that the germs of typhoid and other in-
fectious diseases become extinct within a few days after they
are carried into watercourses. In 1903, Professors Jordan,
Russell, and Zeit, conducted experiments to determine the
longevity of the typhoid bacillus in natural waters (Journal
of Infectious Diseases, vol. i., pp. 641-689, 1904).
Working with Lake Michigan water and Chicago River
water, Zeit found that in the former case extinction of the
bacillus took place in eight days at latest, while in the river
no vitality could be detected after three days. His method of
experimenting was one that sought to imitate natural conditions
as closely as might be. The disease germs were added to
measured volumes of water enclosed in collodion or parchment
sacs, which were then immersed in the lake or river, thus
giving free scope to diffusion.
Professor Jordan made similar experiments at the Chicago
Drainage Canal, which carries a large volume of sewage. He
confirmed the disappearance of the living typhoid bacillus
from his sacs after two days in almost every instance. How-
ever, it does not appear that he tested a volume larger than
1 cm^. in making his cultures ; otherwise he might have obtained
traces of the bacillus after a greater lapse of time. On the
34
Storage
25
other hand, Zeit confirmed his results by searching much
larger volumes as soon as the smaller quantity failed to give
indications.
The vitality of the typhoid germ in river water is a subject
of the utmost importance in relation to the disposal of sewage,
and numerous investigations have of late been set on foot,
The inferences arrived at vary with the conditions, as might
have been anticipated, but there appears to be a general agree-
ment that 99 per cent, of the tjrphoid bacilli introduced into
a natural water perish within a week's time.
London Stored Water : Dr. Houston's Researches.— So far
as concerns the Metropolitan water-supply, this matter has now
been thoroughly investigated by Dr. Houston, who has made
the most important and conclusive research that has yet
been undertaken (First Report on Research Work, 1908).
Samples of raw water from the Thames, the Lea, and the New
River, were inoculated with the typhoid bacillus to a given
number per cm^., and the sample bottles were stoppered and
set aside in a dark place. They were tested at the end of one,
two, three weeks, and so on, successively, till no result could be
obtained from a volume equal to 100 cm^. (3 J ounces.) Dr.
Houston found that 99-9 per cent, of the bacilli had ceased to
possess any power of multiplication after one week. Of the
survivors, and these may be regarded as endowed with a special
measure of longevity, from 80 to 99 per cent., perished by the
end of a second week. Those that survived after this time
can only be looked upon as stragglers, seeing that they repre-
sent but 1 or 2 out of 100,000 in the highest count, and on the
average about 1 per 1,000,000. In no case was any trace of
the bacillus found after eight weeks. The following are the
precise figures of one experiment :
T3rphoid bacillus introduced
One week after
Two weeks after
Three Ti'eeks after
Four and five weeks after
Six weeks after
Seven weeks after
Eight weeks after
>f
t*
476,000 per cm^.
80
11
2 „
Trace found after careful isolation.
Not found in less than 10 cm^.
Not found in less than 100 cm^.
Absent from 100 cm^
The lesson which these figures convey cannot be mis-
apprehended. It is very lucidly exhibited by Dr. Houston in
26 Modern Methods op Water Pxjrifioation
its practical aspect, when he points to the " safety change "
which comes over river water under storage. Pathogenic
germs are very nearly eliminated in three weeks. Impounded
for that period, a raw water which is in a dangerous state
goes far to complete a process of regeneration. Any temporary
defect in the subsequent filtration can hardly now be a source
of danger to the consumers. Even without the purifying eflfect
of the filters it could hardly convey disease. It has reached
the safety condition.
During three weeks* storage the sum total of all the microbes
in river water, or in water contaminated from any source,
diminishes at a rapid pace. Dr. Houston foimd that 220
germs in a sample of New River water fell away to 48, 620 in
Lea water to 106, 450 in Thames water to 53, by the end of
the third week. Perhaps more remarkable was the fact that,
out of the bacilli that would grow on a special medium selective
of cxcremental (and therefore suspicious) germs, not 1 in 10
of the average persisted for three weeks in stored water.
Satisfactory as is the knowledge now brought to hand by
these investigations at the MetropoUtan Laboratory, it has, of
course, to be borne in mind that total extinction of the typhoid
germ, under laboratory conditions of experiment, must be
reckoned on the basis of several weeks. It further appears
that certain types capable of growing at blood-heat on an agar
medium with bile and lactose (excremental bacteria) do not
perish even after two months. Therefore, while storage is an
admirable preparation for the treatment by filters, it should
be regarded as a prehminary to, rather than as a substitute for,
that process. After adequate storage, filtration may well be
looked to, in order to deal the finishing blow upon the straggling
survivors of disease germs, if such really occur.
Dr. Rideal's Tests with River Dee Water. — In the course of
his evidence before the House of Lords in regard to the Aberdeen
Water Bill (1910), Dr. Rideal stated that he had infected samples
of Dee water with a culture of typhoid bacilli to the extent of
15 per cm^., and that a storage of eight days was sufficient to
cause their disappearance, so far as could be judged when
10 cm*, was examined. From his examination of the water of
the Dee, which is a stream comparatively pure as compared
with the Thames, he had come to the conclusion that, on being
Storage 27
stored for ten days, the water would be bo much improved
that, with the subsequent purification by sand filtration, it
would be entirely innocuous to the consumers.
. It is to be noted that Dr. Rideal's tests of Dee water were
on a less comprehensive scale than those carried out in the
laboratories of the Metropolitan Water Board. From his
evidence it did not appear that he had examined larger volumes
of the infected water than 10 cm^., otherwise it might reason-
ably have been expected that the disappearance of the bacillus
would have been indicated after three or four weeks.
Pathogenic Bacteria : Importance of Isolating these in the
Bacteriological Analysis. — In considering the bacteriological
analysis of a water, and the inferences to be drawn therefrom,
it has to be kept in view that the detection of *' specifically "
pathogenic bacteria is attended with very considerable diffi-
culties, and that consequently the recommendation has been
made that search should be directed to find the ordinary
excremental bacteria (J?, coli). In any case it is desirable
that an estimate of the latter should be made, in order that a
rational conclusion may be come to regarding the degree
of sewage pollution. The waters of the Thames and Lea
nearly always indicate the presence of B. coli in 1 cm®. Fre-
quently it is present in 01 cm®, and even in 01 cm®.
In neither of these two streams, nor in the New River, did
Dr. Houston succeed in isolating the typhoid bacillus, although
a most extensive and very carefully executed research wao
conducted by himself and the laboratory staff (see Dr.
Houston's Second Research Report, 1907-08). Needless to say,
the most recent and most reliable tests for the typhoid bacilluu
were applied, and the experiments were continued for twelve
months. Two himdred and ninety-four experiments were made
with waters drawn from the Thames, the Lea, and the New
River, and on each occasion 100 cm®, was the measure used for
the search. In the total volume submitted to culture there
were many millions of bacteria of all sorts, and of these some
7,000 that might possibly have been typhoid, seeing that their
growth up to a certain point conformed to that of typhoid,
were specially dealt with. Not a single B. typhosus could be
isolated. Clearly this was a thoroughgoing investigation, and
one which should be gratifying to the consumers of the Metro-
28 Modern Methods op Water Purification
politan area. Yet Dr. HouBton does not for a moment advise
any slackening in the purification of the raw waters from the
sources mentioned. All of them are subject to sewage pollution,
ai^d no one can predict the moment at which one or other of
these streams might begin to disseminate epidemic germs.
Thames and Lea Waters proved to contain very Few, if Any,
Pathogenic Bacilli. — More recently Dr. Houston has confirmed
the results which were published in his earlier reports. By
following the most stringent conditions of analji^ical work, he
has reduced the possibiUty of error in his deductions to a
minimum, and he has established his former conclusions beyond
the range of doubt (Fifth Research Report, 1910).
The method adopted was that to be described in connection
with the vitaUty of the cholera vibrio. Each sample of river
water was divided into two equal portions, and one half infected
with a definite number of typhoid bacilli (2-3 per cm®.) and
also with Gartner's bacilji (0-7 per cm®.). The other half of
each sample, which had not been infected, was subjected to
exactly the same analji^ical treatment as that to which these
pathogenic bacteria had been added.
It is plainly to be deduced from the series of experiments
thr.t it is possible to detect a single B, typhosus in 6 cm®., and
one Gartner's in 14 cm®. And as it was not found possible*
to isolate either of these bacilli from the non-infected water,
the inference is that there are at all events fewer typhoid
bacilli in the crude Thames and Lea waters than one in 6 cm®.,
and fewer Gartner's baciUi (B. enteritidis) than one in 14 cm®.
(Fourth Annual Report, 1910, p. 7).
The danger of epidemic diseases emanating from the chief
MetropoUtan sources of supply, if it exists at all, must be very
remote, especially when adequate storage and careful filtration
are interposed between the reception of the water and the
deUvery of it to the consumers.
B. Coli Test : Disappearance of the Germ in Stored Water.
— The importance of testing for B, coli as being a typical
microbe in sewage-polluted waters has already been referred
to, and it; is very germane to the subject of impounding
* From the large volume of non-infected water which was put to the test,
there were isolated one typhoid-like bacillos and one indistinguishable from
Gartner's.
Stobagb 29
water to discover how far this species is eliminated during a
period of comparative quiescence. Dr. Houston has settled
the question so far as the waters stored by the Metropolitan
Board are concerned, and in his Third Research Report he
conclusively shows that enormous advantage accrues from
storage. Experiments were made weekly, and often bi-weekly,
during the course of a whole year upon Thames and Lea raw
and stored waters. The general results as summarized by
Dr. Houston are remarkable. Fifty per cent, of the samples
of crude Tliames water contained typical B. coli in tV cm®., but
of the stored waters at Staines, Chelsea, and Lambeth, 27 per
cent, contained no typical B. coli in samples 1,000 times larger
— i.e.y in 100 cm^. Of all the tests made with Staines and
Chelsea stored water, only 33 per cent, could be got to give
indications of the bacillus in question with a quantity so small
as 10 cm®. The Lambeth reservoir did not quite approach
this high standard, typical B, coli having been found in 1 cm®,
of a goodly number of samples during December to February.
But on the whole the stored water is, with reference to typical
B, coli, from a hundred to one thousand times better than the
raw water.
Theoretically the water is stored for about fifteen dayB at
Chelsea and Lambeth, and for ninety-five days at Staines :
but it can easily be imderstood that the water which is brought
to the filter-beds may have been impounded for very different
periods, according to the exigencies of supply and demand.
Turning now to Lea water, Dr. Houston foimd results even
more satisfactory than those above quoted. In raw Lea
water B. coli is about as frequent as in the Thames. Sixty-
seven per cent, of all the stored samples yielded no result
at all with 100 cm®. Only one sample out of a hundred gave
the indication sought for with 1 cm®., and four only with 10 cm®.
In fact, there were fewer typical B, coli in 1,000 cm®, of stored
water than in 1 cm®, of raw Lea water. The nominal period
of storage here is fifty-eight days. With the reduction of the
number of JB. coli we are chiefly concerned at this point, but
it may be mentioned in passing that by storage of Lea water
there resulted a reduction to the extent of 97 per cent, of all
the bacteria capable of growing on a culture medium at blood-
heat, and of those that, being chiefly excremental microbes,
could germinate on a bile-salt medium.
30 Modern Methods of Watbr Purification
The Bacillus enteritidis sporogenea was also sought for, and,
dealing always withj 10 cm^. of raw or stored water, this microbe
was found in 36 per cent, of Thames water samples, and in
about 12 per cent, of the same water impounded. It also
occurs in 36 per cent, of the Lea River samples, but it actually
could not be detected in the Lea stored water at all, an
eminently satisfactory result.* The storing of Lea water brings
yet another advantage which Dr. Houston has discovered. He
has frequently noted in his reports the distinction between
typical and non-tj^icpj B. coli, the former giving, inter alia, the
" indol reaction." The discovery mentioned brings into relief
the circumstance that typical B. coli die faster in the Lea
reservoirs than do the non-typical, which are regarded as being
less objectionable. Out of every 100 coK-like microbes in
raw Lea water, 86 per cent, are typical. Out of 100 coK-like
microbes in the stored water, 63 per cent, only were typical.
We remember that the volume of stored water containing
100 coZf-like microbes would be about one thousand times
greater than that of the raw water holding an equal number.
In regard to this point, it may be added that the improvement
is not so well marked in the case of Thames stored water, but
there is a slight degree of betterment.
We can no longer doubt that storage for a sufficient time is
capable of eliminating to a very large extent the undesirable
flora of sewage.
Stored Water ; Comparative Results in a Scotch Case. — As
bearing on these conclusions with regard to the storage of river
water, the following facts relating to the storage of water
gathered from an area in the South of Scotland, partly
cultivated, are of special interest. There are several small
feeders of the main stream leading into the reservoir which
provides storage for over 250 days. The average number
of colonies of bacteria per cm^. in the stored water at its
outflow was 300. Of these, about half a dozen were able to
grow in McConkey bile-salt medium at blood-heat, and JB. coli
was not discoverable in 50 cm^.
On the other hand, the water entering the reservoir, and
consisting of the united flow of five or six contributory streams
was very much inferior, bacteriologically speaking. The average
"* Third Research Report, p. 8, and Third Annual .Report, Table £.
Storage
31
number of colonies of all kinds was 1,200 per om^., and of these
about 30 flourished at blood-heat on the special medium. B, coli
could be detected in 0-6 cm^. This water was distinctly below
the ordinary standard of purity. The reservoir water, on the
other hand, might be regarded as potable. Among the feeders of
the main stream, one at least was grossly polluted.* It is not a
large contributor, only delivering 2,000 gallons per hour, but the
intermingled sewage raised the number of excremental bacteria
to many thousands per cm*. This very objectionable tributary
polluted the water in the main stream appreciably for a con-
siderable distance below its entrance. Samples drawn near
this point showed results far inferior to those obtained lower
down. The number of bacteria of all kinds there rose to 3,000
per cm*., and of these 400 were clearly excremental, with B, coli
strongly in evidence. Flowing in a channel one and a half
miles long, and receiving a considerable admixture of other
waters, the main streams arrived at the reservoir in the con-
dition above stated.
The analjrsis shows that the stored water is greatly improved
as regards the bacterial content, and of course also in the
matter of turbidity. Table I. gives the average results :
TABLE I.
Raw water
Stored water . .
Pai-ts per 100,000.
Bacteria grow-
ing at—
Total
Solids.
24
12
Oxidized
Nitrogen.
37
24
Free Albuminoid
Ammonia. Ammonia.
1
Oxygen
consumed.
20^ C.
37^ C.
0-007 0-026
0-002 0-020
019
0-20
1,100
270
113
7
1
B. Coli Tests.
Raw water . .
Stoped water
present in O'S to 1 cm^.
not found in 50 cm^.
Effect of Storage of River Water in the Dark on B. Coli.—
When crude Thames or Lea water is kept in a stoppered
bottle in the dark, the B. coli perish so rapidly that after a
week it is generally impossible to isolate them from 1 cm®.
Taking 10 cm®., the average life under the above conditions is
eleven days, but occasionally they were detected after three
* All objectionable tributaries have now been excluded from this particular
supply.
32 Modern Mbthods of Watbb Purification
or four weeks. The B. coli persists for a shorter time than the
general flora of bacteria, so that while in raw Lea water there
is (roughly speaking) one typical B, coli to every 1,000 of all
sorts, in the stored water there is but 1 in every 10,000.
Of course, these ratios are struck from a large number of
analyses, giving here and there results widely different from
the average. But there is no uncertainty about the principle
stated, for Dr. Houston shows that the ten worst samples
of Lea stored water were superior to his ten best samples of
Lea raw water, so far as coK-like forms were concerned.
As a general deduction from considerations of the vitality of
different species of microbes, and from the resultiS of extensive
tests upon the wholesome influence of storage, it may be said
that, if a purification process succeeds in destroying B. coli,
it will a fortiori eliminate the more delicate microbes of typhoid
and cholera. This view is accepted by eminent authorities,
and, in particular, at the Paris Waterworks it is now considered
a necessary and also a sufficient mark of efficient filtration
that B, coli should not be present in the effiuent.
Vitality of the Cholera Vibrio in River Water.— The
appearance of cholera from time to time in the Western
Hemisphere, its rapid spread when once it has made good its
footing, and the deadly character of the malady, have led to
exhaustive researches in many countries regarding the manner
in which infection is conveyed. The important discovery,
due to Koch, of the cholera vibrio defined more clearly the field
of these investigations. It remained to find out precisely in
what media the vibrio might occur, its vitality in these, and
how far any one of them might serve as a carrier of the bacillus
to human beings.
It is generally accepted by bacteriologists who have studied
this question in connection with outbreaks of cholera in India,
Russia, and Germany, that the disease is quite capable of being
conveyed by water-supplies, and that infected water is presump-
tively responsible when a wide area is attacked.
Dr. Houston has recently turned his attention to the vitality
of the cholera vibrio in Thames, Lea, and New River water,
and he finds that there is no difficulty, deserving to be called in-
superable, of recapturing, as it were, by aid of his culture media,
1
I
Storage 33
specimens of the vibrio which have been previously dis-
seminated in the samples of river water. Yet there are
difficulties, the chief one which confronts the bacteriologist
being that the true cholera vibrio is imitated by other vibrios,
at present reckoned harmless, not only in microscopic appear-
ance, but also iu their behaviour under the delicate reactions
by which the Koch bacillus is identified.
The precautions which Dr. Houston took care to adopt
would seem to leave nothing to be desired from a scientific
point of view. Taking a definite volume (1 litre) of river
water, he divided it into two equal parts, infected one half
with a small dose of true cholera vibrios, added some peptone
to encourage growth, and, after incubating for eight hours at
37^ C, plated a number of samples from each portion, and
proceeded with the subculture of these. He repeated this
experiment on twenty-three occasions during a period of four
months, and made in all 1,050 subcultures of each of the two
kinds of water, infected and non-infected.
Dealing first with the subcultures of non-infected water,
none satisfied the tests for the cholera vibrio. The raw water,
therefore, while containing many bacteria of different species,
contained none possessing the characteristics of the true vibrio.
There was nothing, therefore, in the raw water that could give
rise to a doubt regarding the reliability of the tests if they were
satisfied by the contents of the infected portions.
Coming, then, to these latter, the subcultures were put to
the proof, and sixteen out of the twenty-three samples gave
the proper reactions. Of the seven that did not respond to
the tests, six had received very feeble doses of the cholera
vibrio — ^namely, from 1 bacillus in 30 cm^. to 1 in 3 cm^. In
the seventh sample the infection was about 3 per cm^.
All the sixteen samples which gave positive indications had
received very sparing doses of the vibrio, in order that it might
be distinctly shown whether a very few germs of this species
scattered through the water could be isolated and identified.
Hence the maximum number of vibrios introduced only once
exceeded 5 per cm®., and was in general only 1 or 2. In five
instances it was much less than 1 per cm®.
Effect of Storage on the Germs of Cholera. — It being, there-
fore, clear that scientific method can track out the germs of
3
34 Modern Methods op Water Purification
cholera three times m four when their number is sparse and
near the vanishing point, we can turn with interest to Dr.
Houston's experiments regarding the vitality of the germ
in river water. He was able to prove that, with an artificial
infection of millions per cm^., the very longest time that their
presence could be detected in so large a quantity as 100 cm®,
was less than three weeks. Further, the storage of the infected
water for one week brought about an enormous reduction
in the number of germs. On the average, only 1 in 1,000
survived for that short period. In two weeks the vibrios could
hardly be isolated from 10 cm®., and by the end of three weeks
no trace of infection could be detected when 100 cm®, was tested.
These notable experiments confii'm the conclusions which had
been already arrived at respecting the great advantages which
accrue from storage. The cholera vibrio is much less persistent
than the bacillus of typhoid. One may conclude that, even in
the very improbable event of London water becoming polluted
with cholera germs, the water would be rendered sterile, so
far as these were concerned, by a month's storage. In his
report, Dr. Houston replies to some possible objections that
might be suggested against a strictly literal interpretation of
his bacteriological results. For example, it is supposable
that the vibrios imported into river water alter their vital
character on account of the environment, and so fail to react
in the same way as those which are taken directly from a
patient. It is hardly within the power of the bacteriologist
either to prove or to disprove that vibrios disseminated in
water undergo a metamorphosis of the nature suggested.
If such really occur, one would have anticipated that, as the
samples were suboultured from week to week, there would
have been observed a progressive reluctance on the part of
the colonies recovered to yield the typical reactions. This,
however, was not so. Dr. Houston kept a mixed strain of
vibrios aUve in sterilized water for four weeks, and obtained
the indications looked for in the subcultures all that time.
One week later the vibrios were extinct, for no growth of any
kind appeared on the plates.
It may be said that the isolation of a few vibrios from river
water containing numbers of bacteria of other descriptions is
attended wth difficulties. We may admit this, and still look
with confidence on Dr. Houston's results, seeing that they are
Storagb 35
based on an ample array of experiments. As many as 100 to
180 subcultures were made of the various samples.
It is worthy of notice that bacteriologists favour the opinion
that pathogenic bacteria are more persistent in natural waters
during cold weather. This may well be due to the fact that in
winter the action of the sun's rays is neither so powerful nor
so prolonged as in the warmer season. Further, during warm
weather, the saprophytic bacteria, by their active growth, may
decimate or even.suppress entirely the pathogenic microbes.
The history of cholera epidemics contains no more striking
illustration of the evil consequences of infected waters than
the sombre record of the ravages of this disease in Russia
since its appearance in 1907. The presence of the malady
was first notified from Samara, a large town standing at the
most easterly bend of the Volga, and at the junction of lines
of railway branching eastwards. Whether owing to infection
conveyed by the river, or by the extensive traffic over its waters,
cholera very soon appeared at towns on its banks as far down
as Astrakhan at its mouth, over 600 miles to the south. Not
only were the lower reaches of the stream invaded, but towns
a long way up the river fell under the scourge. Numerous cases
occurred at Nijni-Novgorod, which lies 400 miles upstream,
nor did the march of the epidemic slacken till it reached the
province of Yaroslav, 200 miles beyond. In short, the whole
course of the river for 1,200 miles was thickly marked with
cholera-stricken towns and villages within a brief period after
its notification at Samara in the month of July. By the end of
the year many thousands of the inhabitants had been seized
with the malady, and one half of the cases terminated fatally.
From the infected spots alongside the great river the disease
spread rapidly, crossing into the Valleys of the Don and the
Dnieper, and making many victims at Kieff, where the river
water is used to furnish the town's supply. Many other
streams and waterways were polluted by drainage from cholera-
stricken towns, and by the dejecta from sufferers on board
the floating craft. However, by the end of 1907 the ravages
of the disease began to slacken, and in February, 1908, Russia
was understood to be clear of it. Once again in the following
summer it reappeared in the valley of the Volga, and claimed
more victims than in the preceding year. The same ill-fated
districts in the south and east were attacked, and many new
36 Modern Methods of Water Pttbifioation
ramificationB marked the progress of the epidemic, St. Peters-
burg, for example, being very severely visited. In the capital
there were no less than 2,600 deaths between September 11
and October 10. There was again a marked abatement during
the winter, the fresh cases reported monthly declining from
3,000 in October to 400 in March. Cholera apparently refused
to be entirely stamped out during the spring of 1909, and once
more in July it began to rage with increased virulence. From
June, 1908, to April, 1909, there had been 30,000 cases notified
and 1 3,000 deaths. To stamp out the germs of cholera when
once it has become epidemic over a wide area, and after millions
of vibrios have been disseminated over the land, is a task of
supreme difficulty. The utmost efforts of the Russian Govern-
ment from 1907 to 1909 failed to rid the Empire of cholera, and
in 1910 its ravages were, if anything, more sweeping than ever.
Chemical Changes In Stored Water: Dr. Houston's Re-
searches. — There are, however, other changes which proceed
in the reservoirs wherein river water or surface water is im-
pounded, which are of much interest to the student of bio-
chemistry. These changes are almost all in the direction of
betterment so far as the potability of the water is concerned.
In his Third Research Report (February, 1909), Dr. Houston
continues the results of his investigations, and shows that in
every case the stored water in the Metropolitan reservoirs
contained much less ammoniacal nitrogen* than the raw.
The average reduction for the Thames water would appear to
be about 36 per cent., and for the Lea water 52 per cent. As
regards the " oxygen consumed," or, rather, absorbed from
permanganate (in three hours at 27° C), the stored water again
shows results from 20 to 30 per cent, better. The oxidized
nitrogen (nitrites and nitrates) is diminished very considerably,
especially in the case of Lea stored water (44 per cent.). In
all cases the total " hardness " diminishes. We are to con-
clude, therefore, that changes of a physico-chemical nature
are in progress in reservoirs impounding river water. These
may be due to the activity of living things — algae, plankton,
bacteria — and to fermentation of dead matter accumulating*on
the sides and bottom, or to other agencies that cannot be
definitely specified.
* Nitrogen of the so-called " free '* or inorganic ammonia — NH3 and its
compounds.
Storage
37
We gain some light in regard to this alteration which
storage induces upon river water from p. 10 of Dr. Houston's
Third Research Report, where it is stated that the albu-
minoid nitrogen * suffers no diminution in the case of Lea
water, and is actually increased for Thames water in the
reservoirs at Staines and Lambeth. Only at Chelsea Reservoir
is there a decrease (29 per cent.). Now, it is pointed out
by Dr. Houston that the albuminoid ammonia test is an
empirical one — that is to say, the chemical process employed
is one which furnishes only a general idea of the amount of
organic matter present. Accepting this view (see also Thresh,
p. 216), we turn to the analysis for total organic nitrogen, and
this was determined for two samples. We find in the case of
Lea water that there is a moderate diminution of the total
organic nitrogen (6 to 13 per cent.) during storage. Yet in
these two very samples the albuminoid ammonia on being
estimated showed an increase of 40 per cent.
Probable Causes of the Chemical Changes.— Gathering up
these facts relative to the change that comes over stored water
— namely, the decrease of ammoniacal nitrogen, the decrease
of oxygen consumed, of total hardness, and of oxidized
nitrogen — one may hazard a suggestion as to the probable
causes at work in the particular waters here under con-
sideration. But first we shall consider how far these chemical
changes are related to the season of the year.
Tables II. and III. show the summer and winter averages,
taking the former from May 1 to September 30, and the latter
from October 1 to April 30.
TABLE II.
AhMONIAOAL NiTROOBK, PaBTS FEB 100,000.
Water.
Winter.
Summur.
Raw Thames
Stored fiAinbcth
Stored Chelsea
Stored Staiaes
Raw Lea
Stored Lea
00083
0-0048
0-0028
00061
00139
0-0048
0-0030
0-0043t
0-0013
00038
0-0064
0-0055
* Nitrogen of organic compounds, which can be estimated as ammonia in
the laboratory. -f May, June, July only.
38
Modern Methods of Water Purification
Thus, there is more ammoniacal nitrogen in the raw water in
winter, and the decrease due to storage for Thames water is
60 per cent, on the average of three reservoirs, and for Lea
65 per cent. In summer, with less ammoniacal nitrogen in the
raw water, the amount increases in two instances in Thames
stored water (though it is steady on the average of the three),
and decreases slightly in Lea water.
TABLE III.
Albuminoid Nitrooen, Parts per 100,000.
Water.
Winter.
00164
00152
00107
00233
0-0152
00136
Summer.
00138
00217
0-0109
0-0191
1 00159
1 00182
Raw Thames
Stored Lambeth
Stored Chelsea
Stored Staines
Raw Lea
Stored Lea
The albuminoid ammonia in Thames water is greater in
amount during the colder period of the year, and it diminishes
very considerably when stored at Lambeth and Chelsea.
But Staines shows a rise of 42 per cent. The summer albu-
minoid ammonia increases at Lambeth, and also again at
Staines, by 30 per cent, under storage, and falls away by
22 per cent, at Chelsea. In Lea water the winter and summer
albuminoid ammonias are nearly equal, but there is a diminu-
tion of 11 per cent, in winter through storage, and a rise of
14 pef cent, in summer. So far, then, as this constituent is
concerned, we may say that the tendency seems to be towards
a decrease in winter and an increase in summer.
From October to January the ammoniacal nitrogen in raw
Thames water increases four or five times over, and it sinks
to near its summer level in the following May. Its material
decrease in the reservoirs during the colder part of the year
is in all likelihood due to the activity of certain vegetable
forms,* and to the fact that there is less thrown oflF by fer-
mentation and decomposition among the sediment when the
general temperature is lower. That there is less ammoniacal
nitrogen in the raw water during the summer follows from
* For the action of Nitrifying Bacteria see pp. 68, 66, 280.
Storage 39
the circumstances that the water-level in the gathering area is
lower, and surface supplies send much less abundant con-
tributions. The average number of microbes of all kinds in
the raw water during the warmer months (May to September)
is less than one-fourth of the average for the whole year.
The tendency of the albuminoid ammonia to decrease in
stored water during the winter is probably due to the fact
that many living things which might thrive and multiply in
warmer weather subside with the general fall of sediment.
Much finely divided organic matter that has been carried away
by surface water by autumn and winter rains will also fall out.
To a large extent the contamination of surface waters is absent
in summer, so that one would anticipate a lower content
of albuminoid nitrogen from May to September. That the
albuminoid nitrogen shows in general a tendency to increase
under storage in the warmer period points to the more vigorous
growth of animal forms in the reservoir waters.
We have seen that the ammoniacal nitrogen is quite as
abundant in the reservoirs as in the raw water during the
summer ; and though plant forms must be continually making
use of it, the supply is no doubt maintained by the fermentative
changes which develop in the deposited sediment. In it the
organic matter is daily replenished from the impurities which
the incoming water conveys, as well as from dead organisms
which have completed their period of existence in the reservoir.
Relative Amount of Ammoniacal and Albuminoid Nitrogen. —
Dr. Houston calls attention to the ratio of ammoniacal to
albuminoid nitrogen in the raw and stored Lea water, and
shows that for the former the ratio is 69 : 100, and for the
latter 33 : 100 on the average. There is a special significance
in this which becomes more apparent when we consider the
summer and winter ratios. For the raw water these are
44 : 100 (summer) and 90 : 100 (winter), and for stored water
31 : 100 (summer) and 35 : 100 (winter). In the colder season
the amount of albuminoid nitrogen draws very close (it is
in excess, as a matter of fact, for January and February,
1908) to the ammoniacal in raw Lea water, but storage reduces
the ratio by no less than 55 per cent. The reduction for the
summer months is from 44 to 31 — that is, 30 per cent. In other
words, while both albuminoid and ammoniacal nitrogen are
40
Modern Methods op Water Purification
reduced by storage, the latter diminishes much more quickly
than the former, especially in the colder months. The agency
which withdraws so large a proportion of the ordinary ammonia
(or ammonia salts) without affecting the actual amount of
albuminoid matter to any great extent must be looked for in
the vegetable life of the reservoirs.
We gain some further insight into the vital activities which
are at work in these reservoirs by a consideration of the
oxygen-consumed test. This is now believed to furnish a
measure of the carbonaceous part of the organic matter without
specially signifying whether such carbon is derived from plants
or animals. The winter and summer averages (using the
terms in the same sense as above) are given in Table IV. :
TABLE IV.
OXTOEK ABSORBED BT PERMANGANATE, PaRTS PER 100,000.
Water.
' Winter.
0-2586
01883
01754
0-1817
.. j 0-2166
01336
Summer.
Raw Thames
Stored Ijambeth . .
Stored Chelsea
Stored Staines
Raw Lea
Stored Lea
01561
01710
01240
01296
01613
01259
Thus, it appears that there is a reduction of 30 per cent, from
raw to stored in the winter for Thames water, and of 38 per
cent, in the case of Lea water. In summer, again, the corre-
sponding figures are 19 per cent, and 22 per cent. We conclude
that the decreased percentage of reduction during the warmer
part of the year is traceable to the fact that the warmer
weather is more congenial to the growth of plants which draw
supplies of carbon from the air dissolved in the water.
Referring to Table I. (p. 31), which shows the effect of
prolonged storage on surface water, it will be seen that free
ammonia diminishes by 70 per cent., albuminoid by 25 per
cent., and oxidized nitrogen by 37 per cent. On the other
hand, oxygen consumed remains about steady, showing at
times a slight improvement.
Chemical Changes in River Water stored under Laboratory
Conditions* — ^In order to throw light upon the changes which
Storage 41
occur in stored river water, Dr. Houston made a series of
experiments of the following nature (Third Research Report,
pp. 12, 13). Samples of Thames and Lea water, along with
their proper sediment, were placed in bottles, partially filling
them. The bottles were plugged with cotton-wool, and set
in a room with a northern exposure. The temperature ranged
from 10° C. to 21° C. The samples were left for about five
weeks, and then subjected to analysis. Preparatory to this
operation the bottle containing the sample was shaken up.
In one set of experiments the sediment was allowed to subside
again ; in the second set the turbid water was immediately
withdrawn. Dealing first with the experiments to which no
sediment went to analysis, it is observed that the ammoniacal
nitrogen €dmost entirely disappears, the average loss being
94-4 per cent. Albuminoid nitrogen sinks by 33-6 per cent.,
and oxygen absorbed by 30 per cent. With regard to the
samples which were shaken up before being analysed, it is
again observed that the ammoniacal nitrogen has practically
vanished, about 6 per cent, only of the original amount being
left. Albuminoid nitrogen suflFers a smaller decline — ^namely,
21-8 per cent. — and the oxygen absorbed only 16-3 per cent.
Under the conditions of these tests, abundant opportunity
was given to the living things present in the raw waters to
continue their development. Many lowly forms thrive well
under such circumstances, and the disappearance of ammonia
salts was doubtless due to this form of life. The decomposition
progressing among the sediment would release more ammonia
as a by-product, and would tend to lessen the percentage of
albuminoid matter. The analyses recorded show that 12 per
cent, of the original albuminoid nitrogen still remains in the
sediment. In like manner it appears that 14 per cent, of the
oxygen absorbed in the raw sample can be determined in the
matter deposited after the lapse of five weeks. Of the whole
albuminoid nitrogen present at the beginning, 66 per cent,
still remains either in solution or in the bodies of animalcula
and minute plants which are suspended in the water.
Storage, then, imder laboratory conditions is more beneficial
to the water than is the impounding in the London reservoirs.
But in truth, under the conditions of the two sets of experi-
ments, the results are not directly comparable, seeing that
there may possibly have been a considerable admixture of
42 MoDERK Methods of Water Purification
recently pumped water with many, or even most, of the
reservoir samples. Further, as Dr. Houston points out, the
sides and bottoms of the reservoirs are always covered with
deposits, which by their fermentative changes influence thft
chemical aspect. It would appear to him that advantage
might result if the raw water were first put through a sedi-
mentation basin, or roughly filtered after the Piiech-Chabal
system, whenever the sources are unuGually turbid. The twin
sets of experiments which were made seem to indicate that
this recommendation is sound.
General Conclusions. — It is not to be overlooked that the
foregoing discussion has immediate reference to the storage
of river water, but there can be no doubt that any supply
composed largely of surface water, contaminated more or less
with sewage, would under storage exhibit corresponding
changes. The impounding of water from deep springs and
wells, and from other sources that are ordinarily beyond the
reach of pollution, is a step which is justified by the exigencies
of supply and demand, and not by any expectation that the
quality of the raw water will be improved. It may even
happen that over-abundant growths of algae in the reservoirs
will tend to a deterioration of their contents, but if care is
taken to anticipate excessive development among the algoid
forms by the use of very small doses of copper sulphate, there
need be no serious anxiety regarding this matter.
The benefits accruing from the storage of river water are
largely influenced by local circumstances. A certain fraction
of the ordinary flow of the stream is abstracted, and the larger
this fraction is, the more difficult it is to make a selection of
the best water. This is especially the case where the reservoir
i s fed from a pumping-station, but it is very often not easy to
build up a reserve when conditions are favourable.
When flooding occurs, the supply is interrupted for a time,
during which the volume of water in the reservoir is continually
decreasing. The filters, as Dr. Houston says, are then borrow
ing on capital. The subsequent replenishment with crude
water produces a mixture of raw and stored material which is
undoubtedly very different from the normal. Unless storage
has been provided equivalent to the volume of service water
required for a lengthy period, say, for three months, the
Stobaoe 43
recurrent irregularities in the quality of the intake cannot
fail to show their effect on the subsequent process of filtration,
and therefore on the purity of the effluent which goes to
service.
Not only is the water taken in after a flood likely to be
more than ordinarily polluted, but it is called upon to meet
the daily requirements after a shorter term of purification under
storage than the crude water normally receives. Where there
are likely to be pronounced irregularities in the quality of the
water which is distributed to the filter-beds, Dr. Houston
considers that water authorities might turn their attention to
supplementary processes of purification (Fourth Report Metro-
politan Water Board, 1910, p. 29).
It has been asserted by some authorities that the construc-
tion of reservoirs large enough to insure for the raw water a halt
of about three weeks before passing to the sand-beds is an
unnecessary addition to the initial expense, seeing that efficient
filtration removes all the objectionable matter, and yields an
effluent which is of even quality, no matter what the state of the
raw water may be. Speaking generally, there is some truth in
this contention, but fflters are by no means perfect machines,
and in the presence of adequate storage it is most reassuring
to have the knowledge that, even should a filter-bed function
badly for a time, there will be no serious harm to the con-
sumers. To those who systematically analyze the output of
filters it must be well known that the efficiency varies, and
that, out of a group of a dozen, one or two may from time to
time function badly without apparent reason. This very
circumstance was pointed out to the ^vrite^s at Antwerp
Waterworks by Dr. Kemna. Two of the beds had been giving
results much poorer than the others, as was, indeed, evident
from a glance at the turbidimeter. As, however, the raw water
had been twelve hours in a sedimentation basin with coagu-
lants, and had subsequently been roughly filtered after the
Puech-Chabal system, the manager had no anxiety regarding
those temporary defects. Dr. Houston lucidly sums up the
advantages which he has proved to accrue from storage, and
his conclusions are here briefly recapitulated :
1. The microbes of disease, and those which are indicative
of sewage (JB. coli), perish rapidly in stored water. In about
three weeks, generally speaking, the safety change is com-
44 MoDEBN Methods or Water PimnncATioN
plete, and the dangers imminent from sewage pollution are
minimized.
2. After being impounded for two or three weeks, the water
is in a better state from a chemical point of view, seeing that
there is a well-marked decrease of ordinary ammonia, oxygen
consumed, oxidized nitrogen, lime salts, and occasionally of
albuminoid nitrogen.
3. Storage deprives the raw water of nearly the whole of its
sediment, and therefore serves to prolong the life of the filter-
beds.
Copper Sulphate Treatment op Plant Growths.
During the warmer months of the year it frequently happens
that algae and minute plant species increase in the reservoirs
to an extent which is both harmful to the quality of the water
and unfavourable to its filtration. Certain species of water-
plants give rise to disagreeable effects, notably the blue algae,
Anaboma and Uroglcena, which during their decay disseminate
oily matters with offensive smell. When the water is loaded
with an excessive growth of minute forms (plankton, etc.), the
life of the filters is shortened. Not infrequently (as at Antwerp)
the filter basins themselves show a tendency to become choked
up with rank growths of algae, so that the period of working is
decreased. Much difficulty has been experienced in America
on account of these water-plants. They do not flourish so
vigorously in spring waters, but they favour river and sur-
face waters containing a good deal of ammonia and other
ingredients washed from tKe land. The result is that such
waters may actually deteriorate under prolonged storage, and
many of the good effects that follow from a few weeks'
quiescence may be counterbalanced by the imdesirable conse-
quences of abnormal plant growth.
One at least of the considerations which have led water
undertakers to adopt a method of rapid sedimentation is the
possibility of trouble arising from these cryptogamic growths.
Exclusion of light would also arrest their development, but this
may be regarded as imfavourable to bacteriological purification,
and on the score of expenditure it may be impracticable. The
procedure which is most generally applicable without entailing
any considerable outlay is that of treating the impounded
Stobagb 45
waters with a suitable ohemioal, which will check the plant
growth, and yet leave no residue appreciable to the consumer.
^ Experiments with sulphate of copper have been made in
America, England, and many other countries, and it has been
shown that a very small dose of that substance will effectively
arrest the growth of algae. One part in ten millions is algicidal,
and if this exceedingly small proportion be added to the
reservoir in anticipation of growths which have previously
given trouble, there wiD be a prevention which is here much
better than a cure after the evil has developed. For the
addition of copper sulphate to a reservoir or filter-bed choked
with algae results in the death of myriads of living members,
which straightway commence to decompose and foul the water
with the resulting products. If blue algae are present, the
chemical applied ruptures the oil-sacs, and the smell which
proceeds from the water is temporarily many times worse than
before.
Dr. Kemna's Experiments. — The following statement by
Dr. Kemna regarding the application of copper sulphate to a
filter-bed at Waelhem is of interest. There had been a most
abimdant growth of algae, which brought the filters to a stand-
still after a brief run. The sulphate was added on August 4
and 5 at the rate of one part per million, from August 6 to 13
at half the above strength. Not imtil August 12 did the
manager consider it desirable to accept the efSuent of the
filter-bed for service use. During the first four days (August 4
to 7) the ordinary ammonia in the filtrate increased. It then
began to diminish, and the normal condition on this respect was
reached about eight days later. In the meantime the filter
gradually became obstructed by. the dead organisms, and it
could be run for only four days after restarting ; it was cleaned
on August 16.
Most noticeable was the circumstance that the number of
microbes which passed through the filter rose quickly soon
after the treatment was begun. The effluent was, indeed, very
bad on the fourth, fifth, and sixth days. Dr. Kemna explains
tiiis fact in stating that the dead algae afforded material for an
enormous increase in the number of bacteria at the surface of
the filter-bed (see also p. 95). However, within a few days
more the filter resumed its normal efficiency. The decom-
46 MoDEBN Methods of Water Purification
position of dead filaments was at an end, and the bacteria,
lacking food, decreased steadily, to the advantage of the
effluent.
Method of applying Copper Sulphate. — Water engineers who
have knowledge of this mode of treatment have found that it
answers better to add the chemical in two doses. The first
disposes of species which more readily absorb the copper
sulphate, and when these are destroyed the second application
reaches the others with greater certainty. The sulphate may
be introduced into a reservoir in the following way : A weighed
quantity is tied up in canvas bags, which are towed from side
to side so as to make a fair (Ustribution. With filter-beds
spraying may be resorted to, or the solution may be added to
the inlet by a perforated pipe, or a bag containing the crystals
may be submerged in the water which comes in.
It is evident that the copper sulphate treatment applied to a
reservoir already beset with algoid growths occasions a certain
amount of inconvenience, and renders the water imsuitable for
consumption for a number of days. Unless the use of the
reservoir can be dispensed with for a week at least, the treat-
ment is to be advised with much caution. It has been found
from experiments in America that the bad odours arising from
the disintegrating algae disappear, but some time is required.
The treatment has this to recommend it, that its influence
possesses a degree of permanency. Algse grow only with reluc-
tance for a considerable period subsequently. The after-effects
continue, and are appreciable in the case of filter-beds after
several cleanings. There may be difficulty at first in obtaining
a satisfactory film, for the precipitated copper appears to
linger in the sand-bed, and even in this passive state to inhibit
the growth of algae to some extent.
As already stated, copper sulphate should be applied more
as a preventative than a cure. This is Dr. Kemna's opinion.
By regular use of the plankton net, one can judge with accuracy
regarding the condition of the reservoir water. Each case
requires special examination and consideration, for some waters
are able to take larger doses than others. The presence of
carbonate in solution tends to precipitate the sulphate of copper
as carbonate, and thus to reduce its algicidal potency. To
what extent the above reaction actually occurs with very dilute
Storage 47
solutions has not been determined. Carbonate of copper at
any rate is slightly soluble in ordinary waters. Dr. Hewlitt
thinks that the copper is quickly thrown down as oxide or
carbonate. It may be that in the highly diluted condition the
copper sulphate dissociates, the copper or basic ion being
absorbed by the algae, while the acid radical combines with
dissolved carbonates.
Filtered Water is not affected by the Copper Sulphate.—
However this may be, it would seem that the filtered water
contains no trace of copper even when doses of 1 part in
2,000,000 have been employed. It may be dijfficult to obtain
proof of the absence of a trace of copper in the effluent, and
there would seem to be no ground for supposing that infinites-
imal quantities have the slightest effect on the health of the
consumers, especially as any contamination from this source
would be temporary. Dr. Bideal, however, appears to have a
doubt regarding the total elimination of the copper salts, and
he prefers to apply another chemical. There is no serious
objection to the use of a hj^ochlorite or free chlorine on the
score of after-effects. Only a very slight increase of the total
amount of combined chlorine results, and this is in no way
harmful. As will be seen (p. 198), a very smaU percentage
of hypochlorite serves to destroy bacteria. It is also strongly
algicidal. A solution of bleaching lime of suitable strength
can be applied to the reservoir water by spraying, or by a
suitable conduit at the intake, or by other methods, as may
prove convenient. It is found, however, that in sunny weather
the dose of hjrpochlorite has to be largely increased. Again it
may be said that the treatment should be in anticipation. No
matter what chemical is applied, there will be the objectionable
consequence of destroying dense overgrowths of plants, result-
ing in the suspension of the use of the reservoir for a time.
CHAPTER IV
CONSTRUCTION OF RESERVOIRS AND CARE OF FILTERED
WATER
Water engineers are in agreement as regards the leading
principles of reservoir construction. One of the main objects
in view being to discourage the growth of water-plants and
algae, the whole extcipit of the reservoir should be made as deep
as possible, and never less than 25 or 30 feet. For the same
reason the sides are to be perpendicular, or as nearly so as may
be practicable, in order to restrict the width of the shallow
margin on which algae grow most profusely. The deposited
sediment will not collect on the steep slopes, nor afford pabulum
for plants to germinate in.
Many modern reservoirs (e.g., Selby) are lined throughout
with cement or bitumen sheeting, and others are built of
reinforced concrete (Suresnes), but in the case of very large
constructions the question of expenditure would set this
excellent method aside. When, however, a dam is formed by
impounding the waters of a valley, a judicious selection of the
site is a matter of the first importance. The sides should be
pitched with set rubble, or laid with cement to a depth well
below the probable low level. This further serves to protect the
banks from the action of waves during windy weather. Deeper
down the sides may be laid with loose stones. The bottom
should be cleared of vegetable matter, and during construction
every care should be taken to keep the bed of the reservoir
free from excremental material. It is a good plan to fill up
the newly-made reservoir with water, and allow it to run to
waste after standing a few days. Bottom growths do not occur
in deep reservoirs, but sediment, of course, accumulates apace if
turbid waters are admitted. If the suspended matters which
subside amount to 30 grains per gallon, and the reservoir water
48
Besebvoibs and Filtbred Waters 49
is renewed once in ten days to a depth of 20 feet, each square
foot of the bottom will receive a deposit of 3 pounds of matter
per annum. Part of this, being organic, may be removed by
decomposition and solution, but there will be a permanent
yearly addition, which may amount to a foot in twelve or
fifteen years. The greater portion of the suspended matters
precipitates near the inlet, and tends to reduce the depth there
more rapidly.
It has been recommended that the intake of reservoirs be
guarded by catch-pits to intercept the heavier portion of the
sediment. These can be cleaned out very easily when occasion
demands.
In order that the freshly admitted water may remain as long
as possible in the reservoir, and may not become mixed with
the outflow to the filter-beds, it is important that the outlet
and inlet should be as far removed from each other as possible.
It \a bad policy to have the inlet and outlet in the same tower.
Reservoirs which are capable of holding supplies for one or two
days should be divided, so as to insure a period of quiet, more
especially during the times when the intake is unusually turbid.
Dr. Houston distinguishes between active and passive
reservoirs (Third Research Report, p. 3), the latter, not re-
commended by him, being used to conserve a considerable
volume of water as a stand-by, while the raw water in ordinary
circumstances goes to the filters. Such passive reservoirs m^y
be perfectly appropriate under certain circumstances, enabling
the water manager to shunt storm-water and to supplement
the natural sources in time of drought ; but wherever the raw
water is subject to surface pollution, the active reservoir
through which the whole supply must pass is the one worthy
of recommendation.
Reservoirs with Compartments in America. — There are
several advantages of dividing the storage area into compart-
ments. The grosser sediment is mostly collected in the first
bcksin, and this (or any one of the other units) may be cleaned
from time to time without interrupting the work of the other
basins. The arrangement would also seem to afford greater
security against the freshly admitted water finding its way to
the outlet without enjoying the normal average period of
storage. Unusually turbid supplies may be confined in the
4
60
Modern Methods of Watbb Pumfioation
first chamber for a longer period, or a coagulant may be applied.
One of these reservoirs constructed at ELansas, U.S.A., is
represented in Fig. 2.
Progressive Sedimentation.— Where the main object is to
get rid of the larger portion of the sediment of a turbid water
in limited space and time, it has been found advantageous
to induce a continuous and progressive sedimentation by
means of slow movement, with frequent change of direction.
The best installation of this kind is that of the Compagnie
Fig. 2.— Settling Basin at Kansas City, U.S. A.
G^n6rale at the Paris Waterworks. First the water descends
into a set of narrow troughs, and its flow is directed alternately
to right and left, making numerous turnings. These troughs
are made of concrete, and there is a slight fall from each zigzag
to the next. The heavier sediment falls down abundantly.
In sequence to the troughs comes a series of wider channels
or basins so constructed that the inflow and outflow currents
are always in opposite directions. The rate of flow has
diminished considerably, and sediment of a finer grade now
Reservoibs and Filtered Waters
61
SectUm^ aX/ A. B .
Fio. 3.— SuNDRiDOB Pabk Cibculatiko Rbsebvois.
52 Modern Methods of Water Pxjripication
settles. Lastly, the water reaches a train of decanting basins,
which are divided up into numerous compartments by means
of baffle-walls (murettes). These latter are so constructed
that the water must flow over one and under the next in order.
On the whole, this sedimentation is satisfactory, and much
more rapid than if the water were kept stationary for an equal
period. At the particular installation here referred to, the
river water has passed through the Anderson cylinders before
it is transferred to the settling troughs, so that the mixture
with iron oxide accelerates any precipitation which might
naturally occur. Slow movement with change of direction
not only promotes the silting out of suspended matters, but it
also prevents very largely the growth of algae. Trouble is
sometimes caused in deep reservoirs by vertical currents,
which are set up after any considerable fall of temperature in
the surface stratum, and such are avoided by the present
system. There is also a material reduction of the germ content
of the raw water during the rapid sedimentation, but of courpe
the main duty of eliminating offensive bacteria rests with the
filter-beds.
Circulating Reservoirs. — Circulating reservoirs have been
constructed at several waterworks in England for the pur-
pose of storing water which is derived from deep sources,
and is sufficiently pure to be used without filtration. The
construction of Sundridge Park Reservoir is shown in Pig. 3,
and it will be observed that the water circulates first counter-
clockwise round the outside annular space, and then backwards
in the next channel. The outlet is central. The object aimed
at by drawing the water round these circular channels is,
according to the engineer, that of keeping the water fresh,
and preventing it from becoming dead and insipid. The
growth of fungi on the walls is also avoided.
Reservoir Surroundings. — ^Land in the immediate vicinity of
stored water should receive careful attention, and every pre-
caution must be adopted to prevent the access of objectionable
matter. It has been recommended that a belt of ground
50 to 100 yards wide all round should be acquired and planted
with pines or shrubs which do not throw down an abundant
crop of leaves in the autumn. This will protect the waters
to some extent from dust blown from highroads and from
Bbsbbvoibs and Filtebed Waters 63
cultivated fields. The margins of the reservoir should be kept
clear of grass and weeds. By means of suitably-placed channels,
surface water draining from adjacent agricultural grounds in
flood-time is to be carried clear away.
The constructions made to impoimd water may be classed
according to the object they are intended to serve — ^namely, for
the storage of raw water, for the purpose of a brief period
of sedimentation with or without coagulants, and lastly for
retaining a reserve of filtered water. It is of great moment
that the latter should be properly constructed and protected
from all possible sources of pollution.
Cabe of Filtered Watbb and op Sebvice Watbb
IN Genebal.
It is an imdeniable if somewhat disconcerting fact that
filtered water is very liable to deteriorate if kept for any
length of time before being distributed. The same is true of
water drawn from springs and deep wells. Stored in an open
reservoir, water of excellent quality may be invaded by
plankton and micro-organisms which would render it im-
palatable to the consumer. New reservoirs are generally
exempt from such visitations, but soon the side-walls and
bottom become seeded with minute plants, and under favour-
able conditions an abundance of living things pervades the
whole contents. Whipple instances the case of a Brooklyn
reservoir in which the microscopic Aateriondla increased to
such an extent that each cm^. contained many thousands.
Algae and diatoms are most to be feared, particularly the latter,
if there be much mineral matter in solution. The obvious
remedy for algoid and plankton growths is to exclude light
by covering the clear- water reservoirs. This plan has been
followed at many installations, as at Paris, London, Antwerp,
Eltham (for pumped spring water), Nancy, Bedford, etc.
Without this precaution it is diflScidt to maintain the purity of
filtered water. Germs drop from the atmosphere or are
carried by wind. Thus the reservoir becomes a gathering
ground for micro-organisms. In the absence of light, blue and
green algse, and most of the plankton species, cease to grow.
It is a distinct advantage to keep the water in motion if the
clear-water basin is uncovered, and it has baen found useful
54 MoDBBN Methods of Water Purification
to do this when the water is stored in the dark (see Circu-
lating Reservoir, p. 51). At most of the principal waterworks
filtered water is stored in covered basins. The largest in the
world is that for the Metropolitan supply at Honor Oak.
Mr. Bryan, Chief Engineer to the Board, has expressed the
opinion that filtered water should not again see the light till
it issues from the consumers' taps.
Increase of Germs in Filtered Water. — ^What seems at first
sight to be a peril to pure waters, whether filtered or drawn from
springs, is a revival of bacterial activity. The germs which
have escaped from the filters, or which are naturally present in
deep well waters, may increase many times in a brief period.
At Poughkeepsie Reservoir, New York, the filtered water stored
in the light failed to preserve its bacteriological purity. The
organisms in the reservoir far exceeded in number those in the
raw water. The average count per cm^. in the latter for the
summer months was 180, while for the reservoir the number
had risen to 1,100.
Later it will be indicated that it is only the harmless germs
which undergo this . multiplication. Pathogenic microbes
eventually yield to the infiuence of storage, no matter whether
the water is filtered or unfUtered.
Rapid Growth of Germs in Spring Water under Storage. —
According to Dr. Miquel ("Manuel Pratique d'Analyse Bac-
teriologique des Eaux," Paris), spring water shows a remark-
able tendency to deteriorate when kept for even brief periods.
At a temperature of 25° C, Vanne spring water which contained
160 bacteria per cm®, was found to be swarming with germs
after twenty hours, as many as 30,000 per cm®, being common.
Dr. Frankland mentions a similar experience in the case of
water from a deep well in the chalk. This contained less than
100 germs per cm®., but after standing one day in the dark at
26® C. each cm®, had more than 100,000. Leone at Munich,
by keeping the supply water in sterile fiasks for a few days,
proved that the trivial number of bacteria originally present
multiplies to tens of thousands per cm®.* Using water from the
Lake of Zurich, Cramer showed that an enormous increase of
bacteria takes place every day for a week or longer, and that
eventually a maximum is reached. After that there is a
* See also ZeUachrift fur Hygiene, vol. i., 1886.
Besebvoibs and Filtebed Watebs 55
gradual decrease. It may further be said this observation
was confirmed by Dr. Miquel, who emphasizes the rapid
development of germs in spring water, the maximum being
reached within a week. He also states that the decline is
almost equally prompt up to a certain point — that is to say,
till about nine-tenths of the maximum number of germs have
disappeared. The subsequent decrease was always much
more gradual, so that after seven weeks the bacterial content
was stiU far beyond that of the freshly-drawn water.
Dr. Miquel further demonstrated that crude river waters
containing a rich flora of microbes show but little tendency
to incre€ise their bacterial content, while it the water is running
clear and comparatively pure the same f acidty of rapid multipli-
cation is invariably manifested by the germs present. The
behaviour of filtered waters depends to some extent upon
their previous history. If they have supported a rich crop of
bacteria before filtration, they are less able to nourish the same
species, and the water seems, as it were, to have become immune.
But such immunity is not to be looked for save in special cases,
and at best it may amount to checking the growth of one or
two species.
We may therefore conclude that bacteria have the power
of multiplying vigorously in all kinds of water usually dis-
tributed to consumers. This faculty of rapid increase is
greatly enhanced by high temperatures, and astounding
figures have been occasionally obtained after one day's in-
cubation at blood-heat. Most of the experiments referred to
above were arranged at 26° C. — ^that is, at a temperature which
would only be reached in this country exceptionally, and in the
warmest weather. But Dr. Frankland found that multiplica-
tion goes on even when the sample is placed in a refrigerator,
and Kruger {Zeitachrift fiir Hygiene, vol. vii.), working at 10^ C,
showed that the bacteria increased five times in twenty hours.
The authors have dealt with samples of filtered surface water
containing on the average 107 germs per cm^., and after incuba-
tion in the dark for one day at 10° C. found the average number
had mounted to 433.
Experiments made at Massachusetts prove that the purest
water — e.g., water which has been sterilized by boiling — is
highly susceptible to contamination. It has been suggested
that boiling destroys the substances which serve to give the
56 Modern Mbthods of Water Pxtrification
water some degree of immunity from bacterial attack. The
vital activity of micro-organisms produces toxic compounds
which are unfavourable to their multiplication.
Difficulty of protecting Filtered Water from the Multiplication
of Germs. — However that may be, it is evident that the care
of service water is a matter of difficulty, and the prevention of
a material increase of the bacteria may be difficult or im-
possible. Exclusion of light will not avail. That, of course,
saves the water from contamination by aerial microbes, but it
seems to have little influence on the possibilities of increase
on the part of those conveyed by the water itself. A low
temperature inhibits growth to a marked extent, and restrains
the vitality of the germs, so that the multiplication may only
attain to three or four times in twenty-four hours.
It is agreed among the authorities on this subject that the
susceptibility of different waters to microbial increase after
purification is widely divergent. Water undertakers should as-
certain by frequent tests at all seasons how far the service water
deteriorates, and the tests made should include the examina-
tion of tap water as it comes into the hands of the consumer.
Dr. Bideal found that B. colt increased in the water of a pure
mountain stream when he infected samples with that bacillus.
The increase was noted after two days' storage, and on the
fourth day B. coli began to disappear. On the other hand, his
tests made on the River Dee water, which is considerably
polluted, failed to show any increase of B. coli. He concluded
that chance infection of the pure mountain water would cause
a multiphcation of the germs he had under observation (see
his evidence on the Aberdeen Water Bill, 1910).
It is a familiar fact that spring water gets stale in less than a
day when kept in vessels, particularly in warm weather. This
is partly due to loss of aeration ; but after consideration of
the experimental work recorded, we can hardly doubt that there
is a deeper cause at work. What is true of spring water applies
to waters of excellent quality brought from mountain lakes
and streams. Glasgow receives water from Loch Katrine, and
in this the bacterial content is inconsiderable. But if a sample
be kept for two days at 10° C, there is a large development of
germs. Dr. FranUand found nearly 800 per cm^. under these
conditions (Proceedings of the Royal Society, 1893).
Bbsbbvoibs and Filtered Watebs 57
Influence of Organic Matter on the Growth of Bacteria. —
Organic matter encourages the multiplication of bacteria, but
the absence of it does not prevent it — at least for a time. This
has been fully demonstrated by a number of Continental
experts. Bacteria were introduced into distilled water, and
precautions were taken to exclude traces of organic substances.
In all cases the growth was large, and it appears that the
multiplication of certain species of germs is independent of
putrescible substances. Rosenberg, however, discovered that
there is a great possibility of ordinary water germs dying out
quickly in distilled water, even though they may have increased
very much at first (see Archiv fur Hygiene, 1886).
Free exposure to the air would seem to be most favourable
to the increase of bacteria in filtered waters. But water which
is charged with carbonic acid tends to inhibit growth, and
in some cases at least brings about a reduction of the actual
content. It must not be assumed from this that aerated
waters which are usually charged with carbonic acid are sterile,
for Merkel found hundreds per cm^. in Niimberg seltzer water,
as did Pfuhl in samples at Altona, and Slater in the aerated
waters sold in London.
Effect of Ozone and Hypochlorites. — A very small percentage
of ozone serves to preserve filtered water intact from bacterial
multiplication. Experiments made by the authors show that
bacteria do not propagate in water which has passed through
an ozonizer, if the infection be introduced within three hours
after the treatment. If a sample from the ozonizer be left
for six hours, and especially if it has been shaken, bacteria
flourish with vigour. A trace of hjrpochlorite or chlorine is
an admirable preservative. A dose of xV ^ ^V grain of hypo-
chlorite per gallon is fatal to bacteria introduced there and
then, and the effects continue for at least twelve hours. The
chlorine slowly loses its potency, and it does this much more
quickly if the sample to which it has been added is exposed to
daylight. In his lecture to the Seventh International Congress
of Applied Chemistry, 1909, Dr. Thresh discussed the steriliza-
tion of water by chlorine, and added that the cost would not
exceed 6s. per 1,000,000 gallons, provided the water were
fairly free from organic matter in suspension or solution
(see also pp. 198, 199). Dr. Houston, however, was the first
58 Modern Methods of Water Purdtioation
to face the responsibility of sterilizing drinking water in bulk.
From 1906 onwards he treated with chloros (sodium hypo-
chlorite) the waternsupply of Lincoln (50,000 inhabitants), and
with highly successful results. Here, then, we seem to have
one practicable method of curbing the tendency of residual
microbes to multiply in clear water. An infinitesimal dose of
hypochlorite, less than would be appreciable to the consumer,
would seem to be the best remedy. If, indeed, there were any
fear that traces of chlorine would impair the quality of the
service water, these might be removed by passing the water
through a rapid filter of iron borings and polarite or through a
layer of coke or carbon just before it entered the mains.
Of the organisms which grow in underground reservoirs and
in the distributing system, bhe only one that has pertinently
drawn attention to itself is Crenothrix. The activity of this
minute species is so detrimental to the visible character of the
tap water and to the carrying power of the iron mains that
steps must be taken to check its operations at very many
waterworks.
The question of the multiplication of bacteria in service
water has been considered at some length because the subject
is generally regarded as one of great importance. Dr. Houston,
however, believes that only harmless bacteria multiply, and
that all the germs of water-borne disease perish in filtered,
spring, and well water even more rapidly than in river water
impounded in storage reservoirs.
CHAPTER V
SAND-FILTRATION
The chief duty of a filter being that of intercepting matters
in suspension, and more particularly the retention of germs
of a pathogenic character, we have to consider how far the sand-
filter is serviceable for the work which it is so often called upon
to perform. There is no question that the sand-filter is able
to remove visible sediment from almost every kind of crude
water, and change the turbid flow into a transparent stream.
But even when the effluent is clearest, it may contain an
abimdance of living specks which are only visible with the
highest powers of the microscope. The ability of a filter to
retain bacteria must now be regarded as the touchstone by
which its efficiency is to be judged.
" The entire exclusion of sewage from supplies drawn from
rivers," says Dr. P. Frankland,* " is practically impossible,"
Yet such water is not objectionable on the ground of the total
organic matter which it contains, but simply because the
water undertaker is aware that the source from which it comes
is liable to contamination. Raw Thames water contains from
0011 to 0017 part of albuminoid nitrogen per 100,000,
which is not appreciably beyond the limit often set by chemists
to the quantity of that ingredient permissible in potable waters.
Untreated Thames water could not by any means be con-
sidered potable. Filtration does something to reduce the
organic content, but it is intended to p3rform other duties
which are of higher consequence.
The work of the sand-filter may be considered from three
standpoints : (1) The mechanical action of separating suspended
solids ; (2) its chemical influences on matters in solution ;
(3) its relations with the lower forms of life, vegetable and
♦ " Mioro-Organisms in Water," p. 117.
69
60 MoDEBN Methods of Water Pubificatiok
animal. The effects which the filter is able to produce upon
the crude water are in general the consequence of agencies
that may be classed under more than one of the divisions here
mentioned, bacteriological developments generally going hand
in hand with chemical change, so that the term " biochemical "
would appropriately designate the joint work.
1. Action of the Sand-Filter on Matters in Suspension. —
When turbid water is run slowly through a bed of clean sand,
all the particles which cannot negotiate the minute passages
are, of course, retained, and very many of smaller grade are
deposited on the granules, where the feeble currents do not
readily dislodge them. The surface layer soon acquires a
coating of finer and coarser particles, the interstices of which
are closer than those of the sand-bed itself, so that after a time
the greater part of the purely mechanical action is performed
by the top layer, and little filling of the interstitial passages
occurs below the uppermost half -inch. But this thin filtering
sheet is able to make a turbid inflow perfectly clear and trans-
parent, provided there be nothing in solution to cause a visible
tint. That the greater part of the sediment is arrested at the
superficial layer is clearly shown by the fact that the sand is
discoloured to a depth of only a very few inches. Thus, the
fine mud constructs the screen which ultimately hinders the
passage of very minute specks.
If the sediment be to a large extent composed of very finely
divided silt, the sand-filter does not operate so satisfactorily.
Just as precipitated sulphur will filter through blotting-paper,
so the silt of the Nile and the Mississippi and the Ganges is
imperfectly retained by a sand-bed. The remedy is to apply
a coagulant, as sulphate of alumina, and it is quite practicable
to do this at the beginning of a run after the sand-filter has
been cleaned, and so at small expense economize the time which
is usually needed for filming with mud in the ordinary prac-
tice. As we shall see later (p. 145), artificial filming is employed
at Egham Waterworks.
It is generally believed that the efficiency of the filt/cring
skin is enhanced by the crop of vegetable species which soon
begin to germinate in it. According to season and circum-
stances, it may be from two or three days to as many weeks
before any marked growth of algae has taken place. Supplies
Sand-Filtration 61
from lowland streams and from lakes usually develop a
vigorous growth on the filter-beds, while purer waters from
springs and uplands do not encourage the development of
algse in the film. This may be due to the lack of certain nutrient
ingredients in these purer waters, such as salts of ammonia,
and nitrates, which are known to force the growth of plants.
There is also little in underground or upland waters which
' would serve to sow the muddy film with spores or with frag-
ments of plants. Experience with that part of the Paris
supply taken from springs has shown that sand-filtration does
not improve the quality of the water, bacteriologically at least.
The growth of algae on the filter is not an unmixed good ; in
fact, a too abundant crop is objectionable, because it is apt
to detach itself from the surface, and rise to the top in patches,
carrying away the film in its train. Thus the continuity of
the surface layer is broken, and the water finds an easier
passage through the patches of sand exposed, and escapes
without undergoing searching treatment. From spring to
autumn the algoid flora are for the most part in season.
Diatoms are less dependent on temperature, and are met with
all the year roimd. We shall consider the advantages and
disadvantages of plant and animal life in the sand-filter in
a section dealing with the biology of the same. Meantime it
is to be noted that at various places satisfactory filtration
goes on without the presence of algae. At the Amsterdam
Waterworks as good results are obtained before the algae have
had time to grow as afterwards. The Puech-Chabal finishing
filters at Paris run for long periods because they do not become
encumbered with growths. The covered filters at Nancy do
their work with a film of purely inorganic material. Covered
filters are receiving favourable attention from various water
authorities. Especially in warm climates, the abundant and
rapid growth of algae shortens the life of the filters, and
correspondingly raises the cost of working. Largely on this
accoimt, mechanical filters have replaced the open sand-filter in
America, Egypt, and India. Covered sand-filters are installed
at Chateaudun, Durham, Nancy, Philadelphia, and elsewhere.
The experience of Zurich in this respect is of interest. At
first some of the filters were covered at an extra cost of 27 j^ per
cent, of the capital outlay per bed. These showed an eflSciency
equal to that of the open filters ; and as their period of run
62 Modern Methods of Water Purification
was one and a half times greater, and the output larger, they
worked 10 per cent, more cheaply. All the filter-beds there
have now been roofed over (Ptoc. Inst. CSvil Engineers,
vol. cxi., p. 282).
2. Action of Sand-Filter on Dissolved Substances.— The action
of the sand-filter upon dissolved substances is most marked
in the case of ammonia and organic matter. The latter is
usually estimated by determining the albuminoid ammonia
and the amount of oxygen consumed. Chlorides pass through
the sand without noteworthy decrease ; nitrates vary slightly,
sometimes decreasing, more often increasing; sulphates and
carbonates are not appreciably affected.
Free Ammonia; Decrease by Sand-Filtration. — ^In Chelsea
stored water, the ordinary or free ammonia averaged for
the year 1908-09, 00028 part per 100,000, while the filtered
supply did not contein a twentieth of that amount. Stored
Lea water sampled during the same period showed 0*004 part
of free ammonia, and the filter effluent gave 0-0004 part,
a diminution of 90 per cent. These remarkable results are
not obteined from sand-filters in general, but they may be
regarded as typical of the work of the Metropolitan installa-
tions. Indeed, the average amount of free ammonia at eleven
of the Metropolitan stations in the service water for the years
1907-1909 was only 000036 part per 100,000. In contrast
with this, the sand-fflters at a large installation in Scotland
often leave the free ammonia imchanged, while at other times
it is reduced by one half, from 0002 to 0001 part per 100,000.
On first consideration it might seem that the reduction of
free ammonia is due to the activity of plant growths in the
filtering skin. But this cannot be the only cause, since the
decrease was quite as marked in the month of December at
the Metropoliten stetions as at any other time. The averages
are certainly higher for January to March, but even for the
seven stations at which an increase over the normal occurred,
the average amount was still very low, reaching only 0-0004
part per 100,000.
At the Amsterdam Waterworks the prefilters reduce the free
ammonia from 0-6 milligramme per litre (006 part per 100,000)
to 001 milligramme in the same volume, a reduction of^98 per
cent. Yet the prefilters are under cover, and no film of vegetable
Sand-Filtration 63
matter is formed. During eleven months of the year 1908 these
prefilters removed the whole of the free ammonia. Little was
left for the finishing filters to do in this respect, and but for
one analysis, which showed 0-098 milligramme per litre in the
service water for October (the prefiltered effluent being then
quite clear of ammonia), the average for the year would have
been nil.
Cause of the Reduction of Free Ammonia. — To what, then,
are we to ascribe the reduction of free ammonia in the sand-
filter ? One cause may be the oxidation of ammonia into
nitrous and nitric acid by nitrifying bacteria. According to
Dibdin ("Purification of Sewage and Water," p. 12) and
Bideal ("Water and its Purification," p. 171), nitrifying
bacteria live in soil and water, and require the presence of
animal or vegetable matter and dissolved oxygen for their
action. All these constituents are present in river and surface
waters. The ammonia is transformed by these organisms
into oxides of nitrogen, which may be estimated in the effluent.
Hence, where the ammonia has suffered a decrease, we should,
on the hjrpothesis put forward, expect a corresponding increase
of oxidized nitrogen. This is actually the case at certain water-
works.
At the Amsterdam installation the oxidized nitrogen in-
creases from 1-2 milligrammes per litre in the raw Dune water
to 2*0 milligrammes in the preffltered, and to 2-3 milligrammes
in the finished service water. We saw that in this case there was
at the same time a remarkable diminution of the free ammonia
content. Exactly similar results are obtained with the Vecht
water at Amsterdam. The free ammonia diminishes from
0*5 to 0-04 milligramme per litre, while the oxidized nitrogen
rises from 2-32 to 3*92 milligrammes per litre. At Prestwick,
Ayrshire, the free ammonia diminishes, and the oxidized nitro-
gen increases during filtration.
The statistics for the Metropolitan supplies do not in the
main support our hjrpothesis ; for although there is a decided
reduction of the free ammonia, there is not as a rule any
marked alteration of the oxidized nitrogen content. Here,
however, it is to be remembered that the amount of free
ammonia in the stored waters of the Metropolitan area is
small, and the average reduction amounts to 0-002 to 0003
64 Modern Methods of Water Purification
part per 100,000 — that is, 002 to 003 milligramme per litre.
Expressed as nitric anhydride, this would mean an increase
of about 00 1 to 002 part per 100,000 ; and as there is about
ten times that amount ordinarily present in both stored and
filtered waters, the difference would hardly be perceptible.
This is all the more true, because the analyses issued by the
Metropolitan Water Board only express the oxidized nitrogen
to two places of decimals.
At the Paris Waterworks there are various systems of puri-
fication, but, of the two which depend chiefly upon sand-
filtration, neither effects any decided change in the amount
of oxidized nitrogen. This is shown by the reports of the
" Bulletin Officiel Municipal," from which it appears that in
the raw and filtered waters at Choisy-le-Roi (System Anderson)
the nitric nitrogen is nearly always denoted by the same
figure. This is also the case with the Puech-Chabal system
at Nanterre and at Ivry. As, however, the analyses are not
calculated beyond one place of decimals, and as the anmioniacal
content of the crude waters is low, it is not necessary to infer
that nitrification is at a standstill in the Paris filter-beds.
One thing is clear from the same reports, that the nitrous
nitrogen is in general wholly oxidized at all the stations.
Dr. P. Frankland("Micro-Organisms in Water," p. 118) shows
that sand-filtration increased the total nitrates in River Ouse
water from 0-077 to 0-089 per 100,000. Both organic carbon
and organic nitrogen decreased slightly.
It has to be remembered that some part of the ammonia
on which nitrifying bacteria operate would be derived from
the decomposition of organic matters present in the water,
so that we may not trace the whole of the increase of oxidized
nitrogen in a filtrate to the oxidization of free ammonia in
the unfiltered supply. Besides, Dunbar (" Principles of Sewage
Treatment," p. 150) asserts that there are bacteria which
transform nitrogenous organic matter directly into nitrates.
It is obvious, therefore, that there are difficulties in the way
of laying one's finger upon the ultimate destination of the free
ammonia which disappears in the sand-bed.
Reduction of Albuminoid Ammonia. — ^Abundant statistics
are to hand to prove that albuminoid matter undergoes
important changes in the sand-filter. Such matter is the
Sand-Filtration 65
natural food of many saprophytic bacteria, among which
may be mentioned BtzciUus tet^mo, several species of micro-
cocci, vibrios, and spirilla. By the activity of micro-organisms
albuminoids are peptonized, then split up into simpler bodies,
as fatty acids, tyrosin, leucin, ammonia carbonic acid, marsh
gas, sulphuretted hydrogen, and water. Further decomposi-
tions ensue, and, if conditions be favourable, nothing is left of
the albuminoids that could be called organic, the ultimate
residues being water, nitrates, ammonia, carbonic acid.
These putrefactive changes go on with ease in the soil, but
they also make good progress in water. The River Seine, for
example, after receiving all the organic debris of Paris, exhibits
at Meulan, forty-four miles down the stream, only the slightest
traces of organic impurity. The refuse of Prague, Dresden,
Magdeburg, and other populous towns, discharged into the
Ellbe and its tributaries, did not prevent the water of that
river from being used as drinking water at Hamburg, without
any process of filtration, for years previous to the cholera
outbreak. The River Dee in Aberdeenshire was examined
bacteriologically in 1892 by Dr. Frankland. At that time
it was receiving considerable amoimts of raw sewage from
villages situated at intervals of ten to twenty miles on its
banks. It was shown that the stream was distinctly polluted,
from a bacterial point of view, after each receipt of sewage,
and was as regularly purified again in the course of its travel
from one village to the next (see Report to the Corporation
of Aberdeen, P. Frankland, 1892). At the time when Dr.
Frankland made his examination, the volume of sewage from
any one village was so small in comparison with the flow of
water in the ri\er that he could not detect by chemical analysis
any distinct rise in the amount of organic matters in samples
taken a short distance from the sewage outfall.
Destruction of organic matter goes on in the ordinary sand-
filter. The raw dune water at Amsterdam contains 0-15 milli-
gramme per litre of albuminoid ammonia, the prefiltered water
0105 milligramm3,and the finished supply 0084 milligramm3, a
decrease of 44 per cent. These numbers represent the averages
for the year 1908, but it may be remarked that this percentage
of decrease does not vary much throughout the year. For
the three winter months the fall in the content of albuminoid
ammonia was 44 per cent., and for the months Jime to August
5
66 MoDEBK Methods of Wateb Purification
36 per cent. Stored Lambeth water contains (Report for
1908-09) 00162 part of albuminoid ammonia per 100,000,
while the filtered effluent holds but 0-0055 part as the average
of 234 samples. Thames stored and filtered waters show very
similar decreases. With Lea water the figures are, for stored
and filtered samples, 0-0146 and 00056, a diminution of 61 per
cent.
Filtration at Paris on the Puech-Chabal system largely reduces
the organic matter present in the crude water. Decreases of
40 to 50 per cent, as judged by the oxygen consumed are
common (see " Bulletm Officiel Municipal," 1907-1909).
Estimated by the oxygen consumed method, the improvement
as between the stored and filtered waters of the Metropolitan
installations exceeds 40 per cent. At Amsterdam the decrease
of organic matter from raw to filtered water as estimated
by the oxygen consumed reaches 40 per cent, at times, but
the average for dune water is about 30 per cent. This
average is maintained with the Vecht supply at the same
station.
An experimental sand-filter under control of one of the
authors of this volume was put in connection with a reservoir
holding about 200 days' storage. When the filter was
" mature," and the rate of percolation 4 inches per hour, the
decrease of organic matter ranged from 35 to 45 per cent.
After cleaning, the filter still caused a diminution of the organic
substances, as much as 25 per cent, reduction having been
noted after forty-eight hours' continuous working.
It has already been said that the final stage of the dis-
integration of organic matter is reached when the contained
nitrogen appears as nitric acid (or combined with bases in the
form of nitrates). Nitrifying bacteria are required to com-
plete the last step from the albuminoid compounds and from
ammonia, and, as these operate best in the presence of humic
matter, attempts have been made to encourage their activity.
Thus, at the Zurich filters a layer of garden soil 4 inches thick
has been tried in the filter-bed. Much use is made on the
Continent of irrigation and natural percolation through soil
as a means of purifying water for household purposes. The
experience of Dr. Boch (Wasser und Abwasser, Band 2,
No. 3, 1909) does not go to show that this process, is reliable
from a bacteriological point of view, though there can be
Sand-Filtration 67
little doubt that the chemical work done m the soil is very
important, and the nitrification often complete.
The decomposition of organic matter is due in part to the
vegetable and animal life in the slimy film which covers the
sand. Algae and diatoms^ and all the forms of plankton
occurring in the raw water, collect in the film, and pursue an
active life among the sediment, drawing some portion of their
nourishment from dissolved matters in the water. Bacteria
swarm in myriads, and the saprophytic species live and
multiply by the disintegration of organic substances. The
indefatigable activity of bacteria replenishes the store of food
on which the algse thrive, and organic matters are, as it were,
prepared for their consumption. Plant and animal debris
alike come within the scope of bacterial operation. When
the algae die, their filaments are invaded by micro-organisms,
and transformed into food for future crops of the same kind.
Bacteria are indeed the handmaids of the more highly organized
plants, and a necessary link in the biological chain. Just as
a crop of land plants with the aid of soil bacteria exhausts
the organic matters of the groimd, and leaves very little in
the drainage water save dissolved minerals, so do the plants
of the filter-bed with co-operation of bacteria break down the
same substances and purify chemically the water which passes
through.
Action of Non-Submerged Filters on Sewage. — It is not,
however, in the topmost layer alone that organic matter is
acted upon. The investigations AVhich have been made with
regard to the purification of sewage by contact beds have
served to throw much light upon the biochemical action which
goes on in the deeper layers. If sewage be discharged upon
clean sand, no reduction of the dissolved organic matter takes
place at first (Dimbar, " Principles of Sewage Treatment,"
p. 138). Some dajrs must elapse before the "oxygen con-
sumed" declines by 60 per cent., the filter being meantime
worked intermittently. Time is required for the granules to
clothe themselves in the slimy coating which acts as a purify-
ing agent. The filter-bed is considered to be " mature " when
nitrates begin to show in the effluent. i i
The astonishing thiag about the mature filter is the rapidity
with which it does its work. Dunbar has shown that, if a volume
68 MoDBBN Mbthods of Water Pubifioation
of sewage be poured over a filter still retaining the dregs of
a previous charge, the newly added liquid does not force out
the liquid already adherent to the sand, but passes through
without displacing it. Further, it has been proved that
sewage is completely purified and rendered non-putrescible in
ten minutes by passing through a mature filter-bed 3 feet thick.
Purification can be obtained, though possibly not so thoroughly,
with much thinner beds, and in correspondingly shorter in-
tervals, as, for example, in half a minute with a 9-inch filter.
Formerly the idea prevailed among bacteriologists that the
purification of sewage in filters was due to the action of micro-
organisms, a conception which would be quite reasonable if
the process occupied two or three days. But the rapid elimina-
tion of organic matter noticed by Dunbar is beyond the power
of bacteria. Hence* the inference that the dissolved organic
substances are withdrawn from the liquid as it percolates, are
retained in the filter, and are decomposed by bacteria in a
subsequent period of rest (Dunbar, " Principles of Sewage
Treatment," p. 140). It is clear that the separation of dis-
solved organic matter cannot be a mechanical effect depending
upon the minuteness of the pores, seeing that solutions of
albuminoids pass unchanged through filter - paper and un-
glazed porcelain which intercepts bacteria. Nor is it the
outcome of chemical changes; for if chemical reactions do occur,
they are limited to certain favourable coincidences, such as
the encounter of any iron salts in the filtering material with
sulphuretted hydrogen, and the chance concurrence of ammonia
with this same compound of sulphur. But such reactions
account for very little of the whole change, and it is difficult
to conceive of any possible chemical action as occurring in
the filter that would explain the disappearance of albuminoid
bodies in solution.
The Theory of Absorption. — Hence it was that Dunbar* put
forward his theory of absorption. The absorptive agency is
the gelatinous slimy film which covers each granule in the
mature filter. At first this film is thin, but it gradually gains
in thickness and in water-retaining capacity. Just as the
gelatinous covering becomes thicker, so does the filter act
more and more effectively on dissolved organic substances.
* *< Principles of Sewage Treatment," p. 142.
Sand-Filtration 69
The surface of the filmy coat is not an even and smooth one,
but is corrugated and honeycombed, so that its external surface
is enormously increased. In certain cases it appears that the
surface is enlarged by such convolutions many thousand times.
Besides its outer surface, the gelatinous film possesses an
internal one, which probably has its own part to play. Such
as it is, this slimy envelope has the power of absorbing gases
with eagerness, and of withdrawing both organic and inorganic
matters from solution. If, for example, the slime from a
mature filter be washed into a bottle full of oxygen or carbonic
acid, and the stopper with a manometer attached be replaced,
there is seen to be a rapid diminution of the pressure, owing
to the absorption of the contained gas. Solutions of albumin,
or the peptone-like products of its decomposition, colouring
substances, enzymes, tannins, and other things, are forced to
part with more or less of the dissolved bodies. Strongly
putrescible sewage, or a solution of peptone, when treated by
a mature filter, becomes non-putrescible.
Examined with the microscope, the gelatinous film is ob-
served to be full of micro-organisms, which live upon the
absorbed matters and disintegrate them. They do this con-
tinuously in spraying and sprinkling filters, which permit
of uninterrupted aeration, and with " contact " beds they
work vigorously when the filter is emptied and the air per-
mitted to enter. Experimentally it has been shown in the
laboratory that much oxygen is absorbed and carbonic acid
is exhaled. Oxygen is required for the vital processes at work,
and as a final result the organic nitrogen appears in an oxidized
state as nitrate. To exclude atmospheric oxygen or to sterilize
the mature filter results in arresting the decomposition of the ab-
sorbed materials. The organic bodies are no longer mineralized.
Dunbar states that oxygen is not readily absorbed by a
filter which is standing full of liquid, but that it is quickly
taken up when the bed is drained, and just so much fluid left
as can be retained by capillary action. He believes that there
is a condensation of the oxygen molecules, so that ozone is
formed in the gelatinous film which surrounds the granules.
There is generally some proportion of iron in the composition
of the slimy coating, which may lend assistance to the fixing of
the oxygen. As throwing light on the action of iron, it may
be stated that gravels containing large quantities of iron, show
70 Modern Methods op Water Pubipication
marked power of absorption when sewage is poured upon them.
Gravels of this kind abound in North Germany.^
The purifying action of the film indicates the possession by
it of a power quite outside the agencies previously familiar
to science. It is not to be explained by surface attraction
nor by dialysis. There is no reason to believe that surface
attraction could withdraw dissolved matters from liquids in
the way that the gelatinous film does. Dialysis is at best
only a partial explanation, because non-dialysable substances
(colloids), like albumin, are more readily absorbed than
dialysable bodies. Dunbar considers the action of the film
to be one of the nature of suction, and it has been variously
named "adsorption," "resorption," or simply "absorption." It
is this which makes the purification of sewage by natural means
so simple, manageable, and economical. The range of sub-
stances over which the influence of resorption prevails is very
wide. Not only are nitrogenous compounds, like albumin,
peptone, and urea, withdrawn from solution, but sugar and
saccharine bodies are removed from the effluents of sugar
factories and other industries where these things go to waste.
The final outcome of a mature filter is the mineralization of
the organic compounds, and a liquid is discharged which is
non-putrescible. As has been already said, the nitrogen is
discharged mostly as nitrate. Part escapes nitrification, and
appears as ammonia, and there is a residue of organic nitrogen
which is non-putrescible. About 60 per cent, of the total
nitrogen in the crude liquid is converted into nitrate, 20 per
cent, into anunonia, and the remainder is still combined with
carbon in various ways. Sulphur of the crude liquid is oxidized
to sulphuric acid. Much of the carbon separates out as car-
bonic acid, and the air over a biological filter operating on
sewage has been shown to contain an excess of this gas. Pure
water introduced into a mature filter carries out a considerable
quantity of carbonic acid. The end products are nitrates,
ammonia, sulphates, CO^i some non-putrescible organic matter,
and water. Such, then, are the ultimate products which issue
from the biological filter, and such the transformations of
molecular structure which it effects — ^f rom organic to inorganic,
from putrescible to non-putrescible, and therefore to substances
unfit to"'serve as food for the micro-organisms which flourish
in decomposing matter.
Sand-Filtration 71
Importance of Adsorption In Water Purification.— The bearing
of the foregomg exposition of absorption and mineralization
on the work of the sand-filter is of great interest. When the
layer of sand has assumed its gelatinous coating, it is able to
perform the de-solution of dissolved organic matter. In water
which is intended for household use, the quantity of such is
generally very small, so that the slimy film may go on for long
periods actively sucking up organic matter, and doing some
work in the way of mineralizing. Hence the decrease of albu-
minoid ammonia in the effluent, and the increase of oxidized
nitrogen, which have already been commented on. In the bio-
logical filter for treating sewage, opportunity must be given for
ample aeration, but this is less necessary when the crude water
has but a minute content of putrescible substances. Possibly
the oxygen dissolved in the water may suffice for the needs of the
bacterial population. At any rate, the usual methods of work-
ing sand-filters do not make any provision in general for aera-
tion. During cleaning it is now a common practice to let the
water sink a few inches below the level of the sand, so that the
free entry of air is precluded. With non-submerged filters, of
the type devised by M. Baudet, the aeration is continuous,
and the mineralizing process has full play.
It may be thought that too much has been made of the reduc-
tion of organic matter by filtration, and that no apprehension
need be entertained about the hygienic statejof service water
which does contain minute amounts of putrescible substances.
That is no doubt true, but it has to be remembered that filtered
water is easily infected by chance contamination, and that
bacteria introduced therein multiply with surprising rapidity.
It may be assumed that the increase of germs is limited to a
great extent by the amount of organic food available for their
subsistence.
There are probably, as Fr€mkland has pointed out, other
circumstances to be taken into account, as the presence or
absence of inhibiting matters, but we may reasonably assume
that organic food is necessary to the saprophytes for their
development. Therefore, the greater the scarcity of their
natural food in filtered water, the less the risk of the bacteria
accumulating, and the better the chance that, if they do
happen ^to increase, they will speedily be reduced to normal
conditions.
72 Modern Methods of Water Purification
3. Bacterial Purification. — The retention of bacteria by
the sand-filter has variously been credited to the skin of algae
and other living things which spread over the surface, to the
gelatinous film which coats the sand and gravels, and to
the combined effect of both of these agencies. The fine silt
which gradually overspreads the top layer also plays a part in
trapping germs, but it is not essential to good bacteriological
results, seeing that these are often obtained when the raw
water has little in suspension, as, for example, after lengthy
storage. We know, however, that artificial films of alumina
and iron oxide serve to exclude 99 per cent, of the micro-
organisms, so that a share of the bacterial purification must
be ascribed to the film of inanimate silt.
It is probable that both silt and sand act upon bacteria
in the same way. The arrest of bacteria is due not so much
to the minuteness of the interspaces as to the gelatinous coating
which the particles assume. MM. Puech and Chabal have
shown that an extensive capture of germs goes on in their
roughing filters, in which the materials are of coarse grain,
with the particles of the last compartment not smaller than
peas. At Nantea the average reduction is from 10,000 germs
per cm^. to 4,000, a fall of 60 per cent. At Cherbourg the
degrossisseura retain over 80 per cent, of the germs, and at
Suresnes the average reduction from January to November,
1907, was over 90 per cent. (Trans. Assoc, of Water Engin.,
1907, p. 328).
According to Dr. Kemna (Trans. Assoc, of Water
Engin., 1907, p. 331), the diminution in the number of
bacteria in the gravel strainers is independent of the speed
of percolation. We have therefore to deal with an agency
totally distinct from the artificial filter of paper, cotton-wool,
or porcelain. Dr. Kemna explains that the bacteria are
retained by a sticking or adhesive force (p. 86), which comes
into play as soon as they come into contact with the surface
of the pebbles. The gelatinous covering of these must be the
main seat of that force, though no doubt the action is a mutual
one between the film and the jelly-like bodies of the micro-
organisms. At first, when the pebbles are clean, the bacteria
are able to lodge upon them, colonies (Zooglcea) soon develop,
and the characteristic slime is drawn over the whole surface.
The coarse sands and gravels of the prefilter in the Puech-
Sand-Filtration 73
Chabal series still further reduce the bacterial content. From
an average of 600 per cm^., the number is brought down to 100.
There is, of course, a filtering skin formed on the prefilters,
which performs its part ; but there is reason to believe that
elimination of microbes proceeds in the deeper layers as well.
As Pennink and others have shown, there are bacteria distributed
right through the under-layers. In the finishing filter, which is
composed of fine sand, no viscous film of vegetable growth
is formed on the top, because the water arrives there free from
spores or fragments that would initiate its growth. Yet the
final stage of the Puech-Chabal process again reduces the
number of microbes by about 60 per cent. At Suresnes the
figures for the year 1907 were 100 from the prefilter, and
30 for the finished effluent of service water. As will be seen
later, the authorities at the Amsterdam Waterworks do not
set much store on the efficacy of the filtering skin.
Retention of Bacteria In Natural Beds of Sand. — The reten-
tion of bacteria in natural beds of sand and gravel is a well-
established fact which accounts for the purity of underground
sources of supply. Recently Drs. Ditthom and Luerssen have
made experiments to determine how far this natural elimina-
tion of germs may be depended upon to render sewage-polluted
waters innocuous {Oeaundheits Ingenieur, 1909, No. 41). Their
tests were made in 'the neighbourhood of the boreholes at
Tegel Lake and Miiggelsee, from which the Berlin water is
pumped. At Tegel the borehole chosen begins to admit
water at a depth of 120 feet, and a wide tube 60 feet long,
perforated below for a length of 3 feet, was sunk into the
ground between the lake and the borehole, at a distance of
22 yards from the latter (Fig. 4). It was thus in the line of
underground fiow from the lake to the well. Between the lower
end of the sunk tube and the well intervened layers of gravel
and sand of varying fmeness. Rich cultures of B, prodigiosus
were then poured into this tube, and water was continuously
run in so as to keep the level within from 3 to 6 feet higher
than that of the ground water. ' The cultures were introduced
at intervals of four days for a fortnight. After nine days the
pumped water, which totalled 300,000 gallons daily, began
to show signs of B. prodigioaus. On nine subsequent days at
somewhat irregular intervals the tests gave positive results.
The experimenters calculated that in all not more than 00025
74
Modern Methods op Water Purification
2M'.a-
66-'
t
s
L.
F
Fia. 4. — Mbtbod of Testino at Teqel,
(From the Oesundheits Ingenieur, By peimiasion of
B. Oldenbouig, Munich.)
The perforated portions of the tubes are shown cross-hatched.
^>
3
Sand-Filtration
76
per cent, of the germs poured into the tube had succeeded in
reaching the well.
Similar experiments were then conducted at Miiggelsee,
but with a horizontal perforated pipe sunk in the ground to
simulate a leaky sewer (Fig. 6). Layers of sand and gravel
intervened between the tube and well, their total depth being
about 70 feet. Tests were made from December, 1908, to
February, 1908, and again from the latter date to the end of
March with the horizontal tube put some 6 feet deeper. Large
volumes of the pumped water were regularly tested, but on
no occasion was B, prodigioaua discovered. Many thousand
billions of bacteria had been poured into the horizontal tube,
washed down into the gravels with water from a side-tube (<),
but none percolated into the borehole.
It is thus manifest that deep layers of sand are almost
perfect safeguards against the intrusion of bacteria, and the
inference is that artificial filter-beds should not be too shallow.
The authors found, by experimenting with a wide glass tube
nearly filled with fine sand which had been kept moist
for a fortnight, that no test bacteria {B, molaceua and
B. prodigioaua) were able to pass through 8 feet of the sand.
On gradually diminishing the depth of the filtering layer,
by removing sand from below so as not to disturb the upper
layers, it became possible to determine the retentive power
of diflferent thicknesses of the filtering material. The results
are given in Table V. :
TABLE V.
Number of B. Violaetu$^^r
cm*, in Crude Water.
1
Number of B. Violaeeut in
Filtered Water.
Depth of Sand.
1
100,000
NU in 10 cm3.
8 feet
1 100,000
Nil in 10 cm3.
7 „
100,000
6 in 10 cm^.
6 „
100,000
6 in 10 cm'.
5 „
120,000
13 in 10 cm'.
4 „
120,000
18 in 10 cm'.
3 „
120,000
109 in 10 cm'.
2 „
16,000
36 in 1 cm'.
H..
1,000
27 in 1 cm'.
1 foot
Number of Bacteria Inhabiting the Under-Layers of Sand.—
Fraenkl and Piefke in their research on sand-filters {Zeit-
76
Modern Methods of Water Phrificatton
Pia. 5. — ^Method of Testtno at MtJaoBLSKE.
(Prom the Qesundheits Ingenieur. By permission of
R. Oldenbourg, Munich.)
The perforated portion of the pipe is shown cross-hatched.
.L
Sand-Filtration 77
schrift filr Hygiene, vol. viii., 1890) found that the Berlin
filters were inhabited by a rich flora of germs down to and
including the layer of flints on which the sand rested. A
pound of sand taken at the depth of 1 foot conta
…[truncated]