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MODERN METHODS
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WATER PURIFICATION
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LONDON
EDWARD ARNOLD
PREFACE TO THE SECOND EDITION
So very considerable progress has been made in the methods
of water purification during the two years that bave passed
since the publication of this work, that an additional chapter
has been devoted to the description of processes which have
recently come into prominence. The sterilization of water-
supplies. that may be liable to contamination is now occupying
the attention of municipal authoritie?^ far more actively than
at any'previous time, and large developments in this direction
may be confidently anticipated. In America the application
of hypochlorite has been adopted at many important stations,
and on the Continent the ozone treatment is making rapid
headway. While neither of these systems has as yet received
any large measure of support in G-reat Britain, leading authori-
ties on water ])urification have expressed themselves favourably
with regard to both. As an alternative to ozone and hypo-
chlorite, we have Dr. Houston’s Excess Lime Process, which
is certain to receive ^ very attentive consideration in the near
future.
The question of sterilization has been fully entered into in
Chapter XIV., where typical installations and recent improve-
ments in purifying appliances are described. The whole book
has also been carefully revised and brought up to date, so as
to present to the reader the actual condition of the methods
of water treatment as they now exist.
J. I).
PREFACE TO THE FIRST EDITION
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-
tune to review the different processes, and 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 Conseil 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 officials are able to keep in touch with modern 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
Peeface
viii
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 modern 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 fully 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 influence 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-
Pbeface
IX
gress has been made in preparing crude waters for a final sand
filtration by means of successive prefiltration, whereby the
effluent comes to 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 prominence other
topics which directly bear on modern 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 obtaining permission to make full reference
to the work of many eminent 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 Examination, Metropolitan Water Board ;
to Director J. M. K. Pennink, Amsterdam ; to Dr. Kemna, of
Antwerp ; to Professor Dr. Zacharias, of the Plon Biological
Institute ; M. de Frise, Av. du Bois de Boulogne ; Mr. W.
Ciemence, 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 many 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 AnnaUn der PhysiJc, the authors are under obligation
X
Prepace
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, 25, 53, 58, 59,
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, Wasser und Ahwasser, The Trans-
actions of the British Association of Water Engineers, Engineering,
The Sanitanj Record, Gesundheits Ingenieur, and the Revue
d' Hygiene have been particularly helpful and instructive.
J. D.
J. C.
January, 1911 .
CONTENTS
CHAPTER I
INTRODUCTORY
Introduction and scope of tho work — Subdivisions of the subject - • - 1 — 7
CHAPTER II
SOUECES OF SUPPLY
Deep wells — Pollution of underground sources — Detection of, and 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 wells
adjoining rivers — Dangers of contamination — Suppilios at Dresden,
/Stuttgart, Brussels, Bedford, etc. — Shallow wells : construction of, and
regulation — Surface springs — Rain water - - . - « y — 23
CHAPTER III
STORAGE
Storage : effect on germs — London stored water : Dr. Houston’s researches —
Vitality of Bacillus iy'pliosus in stored river water — Dr. Rideal’s oxpori-
ments — Importance of searching for pathogenic bacteria — Effect of sto rage
onB. co^z— 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 suiiplios^ — Probable causes at
work- — Relative amounts of free and albuminoid ammonia — Storage
under laboratory conditions — General conclusions as to the benefits
accruing from storage — Copper sulphate treatment of plant growths- —
Dr. Kemna’s oxperiencos— Method of aj>plying tho treatment — Effect on
the service water 21—47
YI
Contents
xii
CHAPTER IV
CONSTEDCTION OF EESERVOIRS AND CAEE OF FILTERED
WATER
PAOEil
Construction of reservoirs — Reservoirs with compartments : Kansas, etc. —
Progressive sedimentation at Paris Waterworks — Circulating reservoirs
— 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 — Eflect 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
under-layers of sand — Pennink’s views on the action of the sand-filter —
Leiduin filters — Importance of uniform speed of percolation — Irregular
flow detaches germs — Method of obtaining uniformity of percolation
— 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 algae — 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 w^ater film on the sand granules, and the
bearing of this on the speed and efficiency of filtration — Uniformity of
the sand and coefficient of uniformity — Best grade of sand — Depth of
the sand-bed 50 — 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 percolation, 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 in use — The
Contents
Puech-Chabal system — ^Action of the digrossisseurs — Prefilter and finish-
ing-filter — Protection of the finishing- filter from growths — Aeration
during the procedure — Uniformity of the bacteriological results under
the Puecli - 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 —
Hr. Miquel’s experiments — Coagulants — Sedimentation after coagula-
tion — Methods of applying these — ^Turbine feed — Harris-Anderson dis-
tributor and solutioner — Principle of Mannock and Sibley’s inj ector —
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 filter — Mather and Platt’s filters — Special method of cleansing
the sand-bed — Coagulant feed — Purification cfTocted by Mather and
Platt’s pressure and gravity filters — ^The Tum-Over j)atent 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 Forrochlore treatment 164 — 201
CHAPTER VHI
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 — Bent form of electrical discharge — The Do Frise ozonizor —
Sterilizing tower — Details of the complete plant required — Power
xiv Contents
TAGES
necessary and cost of the treatment — Procedure followed in applying
ozone to river waters — Bacteriological 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 Niee — 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
Welter-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 — Desrumaux
and Doulton water-softeners — Special features of these — Mode of intro-
ducing the chemicals — Harris- Anderson softener — ^Thc solutioncr applied
to deliver the required chemicals — Bell’s softening apparatus — Review of
the various appliances — ^Pormutit 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. edi and pathogenic germs —
Concentration of samples imder 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
XV
PAGES
nitrites, and the importance attaching to their presence — ^Free ammonia
in different kinds of water — Estimation of albuminoid ammonia —
Relative 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 . , 2C0 — 285
CHAPTER XI
THE TESTING OF WATER— Coni*
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 animalculae, rotifers, flagellates, and rhizopods —
Plant life in reservoirs, green and blue algm, 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 organisms and how to restrict these — Mutual relationship
between plant and animal life - - , ... - 28G— 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 — ^hletliod of i>rotccting 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-solvcncy 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 — I’lumbo-protectivo substances — Reserve of plumbo-protective
power desirable — Protective treatment on a large 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 — Presence of small amounts of iron in the raw
water at various installations — Growth of Crenothrix 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-
ail— 335
mains -
XVI
Contents
CHAPTER XIII
THE PROBLEMS OF DISTRIBVTIOI^— Continued
PAGES
Water-hammer — Explanation of the cause of hammer in service 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 w'ater as the means of spreading cholera —
Typhoid from contaminated supplies — Pecuniary loss to communities
from typhoid — 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 - - - 33C — 340
CHAPTER XIV
RECENT ABVANCES IN STERILIZATION
Excess lime sterilization — Hard and soft waters — Removal of the excess lime
— Advantages and disadvantages — Costs — Various modes of treatment
tested at Marseilles — Desrumeaux — Duyk — Ozone — Pucch-Chabal —
Ultra-violet rays — Results and comparisons — Hypochlorite at Jersey City
— Absence of residual chlorine — Sterilizing and injecting appliances —
Newport sterilizing plant — Results obtained — The De Chlor process —
Dechlorinating filter — Injector — Rate of flow — Costs and results — Candy
compound filter — Construction and operation — Cleansing — Ransome
continuous filter — Sand- washing — The moving and the stationary bods
— Results at Merthyr-Tydfil — Paterson’s patent outlet controller — Mode
of control — Paterson’s automatic measuring gear for chemicals — Storage
and its effects discussed ------ 350 — 377
APPENDIX
USEFUL CONSTANTS AND DATA RELATING TO WATER FILTRATION
AND MEASUREMENTS
Table A. — Waste of water from taps left running - . - - 378
Table B. — Pressure of water in pounds per square inch for various depths 379
Table C.— Loss of head due to friction in water-pipes - - - 379
Table D. — Discharge of pipes running full for different diameters and pipe
gradients 380 — 381
Table E. — Water-supply by gravitation — Dimensions of mains — Storage
reservoir — Gathering ground for given populations - - - - 381
Table F. — Discharge of water over weirs at depths stated - - - - 382
Table G . — ^Velocity of water in open channels - 382
Table H. — Weight of lead pipes per foot for various pressures - - - 382
Table K.— Weight of iron pipes for different pressures - - - - 383
Table L. — Cost of sand filtration — Purification by ozone and the De Chlor
process - 333
Table M. — Relative costs of different mechanical filters and working
expenses 384
Bibliography - • - - - ’ ' ' \ ' • - 38G-- 389
Im)EX -
- 390—397
LIST OF ILLUSTRATIONS
V\yJ. I' AO 15
1. Geological Section across the London Basin - - ~ - 11
2. Settling Basin at Kansas City, U.S.A. - - - « - 50
3. Sundridge Park Circulating Reservoir - - - - 51
4. Method of Testing at Tegel - ' - . - - 74
5. Method of Testing at Miaggelsee - - - - - -7(5
6. Section of Ordinary Sand-111 ter - - - - - - 70
7- Watery Envelopes of Small Particle and of Sand Granule Uniting - 79
8. Chironomus (Larva) - - . . . . - 85
9. Number of Bacteria in Relation to Rato of Filtration - - - 88
10. Graph showing Advantage of Filtering at a Slow Rate, which is gradually
increased ------ . - 89
11. Spirogyra (Green Alga) and Fragilaria - - - . - 90
12. Anabmna (Blue Alga) - - - . . , - 90
13. Hydrodictyon ------ . - 90
14. Zoogloea ------- - - 91
15. Beggiat'^a (Fungus) ----- . - 95
1C. Didclon Automatic Regulator ------ 105
17. Glentield and Kennedy’s Telescope Regulator - - - - 107
18a. Burton’s Automatic Regulator ------ 109
18b. Burton’s Automatic Regulator : Section - - • - 110
18c. Burton’s Automatic Regulator: Plan - - - - - 111
19. Weston’s Automatic Regulator Controller - - - - 112
20. Section of Outlet from Canal to Filters - - - - - 321
21. Section of Outlet from Filters to Reservoir - - . 122
22. Hardy and Padmore’s Patent Sand-Washer - - - - 124
23. Diagrammatic Section of l^uoch-Chabal System - - - - 135
24. Puech-Chabal System at Magdeburg ----- 139
25. Anderson Revolving Cylinder ------ 142
26. Egham Water Purification Works - - . . facwg 144
27. Graph showing Dr. Miquel's Results ----- I49
28. Non-Submerged Filter at Chateaudun - - - - facing 150
29. Turbine Coagulant Feed ------- 152
30. Harris-Anderson Distributor _ - - - . . 454
31. Harris-Anderson Solutioner . . - - . - 155
32. Mannock and Sibley's Patent Injector - - - - - 157
33- Mannock and Sibley’s High Pressure Chemical Injector - . 158
34. Aqua Sana Purifier ----- - - 102
36. Jewell Gravity Filter ------- 169
36. Jewell Pressure Filter - - - - - - -173
37. Boll’s Pressure Filter - - - - - - - 170
38. Bell’s Coagulant and Chemical Feed - -
39. Bell’s Coagulant Feed and Filter - - - - - - 181
40. Paterson’s Gravity Filter - - 182
41. Paterson’s Pressure Kltcr ------ 183
42. Mather and Platt’s Filter ----- - - 184
43. Turn-Over Filter (Patent) « - - . . . I87
44. Section of Candy Oxidizing Filter - - - - - 191
xvii
xviii
List of Illustrations
no.
45. Kei serfs Pressure Filter -------
46. Brush Discharge --------
47. Comparative Yield of Ozone from Air and from Oxygen -
48. Decrease of Ozone Production in Moist Air - - - -
49. Output of Ozone with Increasing Voltage - - -
50. Decrease of Yield of Ozone at High Temperatures -
51. Decrease of Output of Ozone as the Concentration Rises -
62. Limits of the Concentration of Ozone - - - -
53. Siemens-De Prise Ozonizer - - - - -
54. Sterilizer at St. Maur -------
55. System Siemens-De Prise - - - - ‘ ‘
56. Semicircular Electrode, showing Water-Jacket : Cross-Section of Pig. 57
57. De Prise Ozonizer without Dielectric . - - - -
58. Vosmaer Ozonizer - - - -
59. Vosmaer Ozonizing Plant : General View - - - - -
60. Otto Process, Compagnie G6n6rale d’Ozono - - - -
61. Sterilizing Tower at Ginnekin, Holland - - - - -
62. Howard-Bridge Ozonizer - - - - - - -
63. Berk efi eld Filter -------
64. Ozonizing Filter for Household Use -----
65. Forbes^ Patent Water Sterilizer ------
66. Paterson Water Softener -------
67. Paterson Steam Purifier -------
68. Lassen and Hjorf s Water-Softener - . - - -
69. Archbutt-Deeley Water-Softener ------
70. Archbutt-Deeley Water-Softener: Sectional Elevation - - -
71. Desrumaux Water-Softener ------
72. Doulton Water-Softener -------
73. Bell’s Water-Softening Plant ------
74. Permutit Water-Softener -------
74a. Sectional Elevation and Plan of a Permutit Piker
75. Laboratory at Airdrie, Coatbridge and District Waterworks
76. Incubator with Regulator ------
77. Petri Capsule --------
78. Reichert’s Temperature Regulator - - - - -
79. Colonies of Bacteria on Gelatine ------
80. Photometric Turbidimeter ------
81. Lines of Equal Chlorine Content (Isochlor Lines) in Ground Water
Supplies --------
82. Plankton Net --------
83. Plankton Crustacea -------
84. Plankton Crustacea -------
85. Plankton Rotifers -------
86. Plankton Plagellata -------
86a. Plankton Plagellata -------
87. Plankton Rhizopods -------
88. Plankton Diatoms -------
89. Plankton Algm --------
90. Diagrammatic Scheme for Distribution - - - - -
91. Ball Hydrant - -- -- -- -
92. Glenfield and Kennedy’s Fire Hydrant -----
93. Dr. Houston’s Apparatus for Examining Effect of Peat - - -
94. Crenothrix --------
95. Spraying Nozzle --------
90. Safety Valve to Prevent Water-Hammer - . - -
97. Otto Process at Marseilles ------
98. Westinghouse-Cooper Hewitt 220-Volt Lamp - - - -
99. Puech-Chabal Sterilizer at Marseilles
PAOE
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100. Candy De Chlor Filtering Plant ----- • 365
101. Candy Patent Compound Filter ------ 369
102. Ransome Continuous Filter - - - - - - 371
103. Paterson Automatic Outlet Controller ----- 372
104. Paterson Automatic Measuring and Chemical Supply Gear (Weir Type)- 373
105. Paterson Osilameter Measuring and Chemical Supply Gear - 374-375
106. Paterson Pressure Chemical Suiiply Gear - - - - 376
MODERN MI^]TirOI)8 OF WATER
riTRIFIOATION
CHAl'TlOR I
1 XTHODUCTO II Y
Dksion'et) to roiidf^r an iuu-onnt, of inodfirn dovadojoiicntH in
tlui th(!ory and iiraolicu! of water purification, Huh work Ih an
attempt to briiif' nndor tins notice of Water Autiiorit ins atul
their officials the most (dlicient appliaiutes for tlie treatment of
water, toilet lier witii tlie (hdails of working an<l eosfs of con-
struction and management.
The present is ;i tim<>. of great activity in the domain of water
imrificution. At no period liave county and municipal
authorities been more kecidy inferesteif in the eomliat lietwefui
rm-dieal .sciences and e]iidemi(; disiaise. Tlie germ origin of
infeefious ma!adi<-s heing now no longer regardmi fjy tlie com*
muriity as a pure tlic«ory, hut as a certain fact, t he whole* weigh!
of puhlif! opinion gravitates towards oim central aim. Har fii<^
avenne.H by whicli the camses of bodily ailments apfiroacli tlie
imlivitiual, sed.- a watch on the supply of eoniesUhle.H and of
water, upon the very air of the streets niul of the habitations •
therein lies the true method of safeguarding the in-alth of tlu’
community. If any evhlence. were required of t he quickening
of puldic ojiinion in n-eent times with refer(«nc(^ to the expedi-
ency of striking at the roots of infection, it would be found
in the numerous ap]iointmenf s of Medical (Iflic,.rn of Health
and iSanitary Ins]iectors, in t he compulsory isolat ion of suffereru
from cjiidmnic diseases, and in the increa.sed attention that in
now being piaid to the bacteriological e.xamination of the water
supply. Practical Kcience lias become the hamlnmiden of sociid
life. They cannot be liissociated without obsmiring the wav
to efficiency. With the growth of expert knowledge, the ditJi*
f
2
Modern* Methods oe Water Purification
culties which beset the question of public health will be handled g
with increasing success.
Among these problems there is, perhaps, not one more o
important than that of providing an adequate supply of whole- ^
some water for household and dietetic use. The sin 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. t]
“ Nearly all great outbreaks of diseases, both in this country
and elsewhere,” said the President of the Institute of Sanitary -^v
Engineers at the meeting in 1908, have been associated with
certain conditions of the water-level in the soil.” Purther, he
drew attention to the extraordinary circumstance that the ^
death-rate of children under five years — after excluding
diarrhoea 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- 3 ^ 3 ^^
ciated with the fall of the year, when a more copious rainfall
begins to wash surface impurities and germs that have been fjl
thriving near the surface down to the deeper strata from which j.
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 fj j^
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 i
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 consumers of it, but the taint inc;
will probably reach no more than a small fraction of the tlAi!
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 ‘ j
or to accidental circumstances. The stricken are those whose to
IlTTItODUCTOBY
3
general tone is belo-w par. Eyen the perfectly healthy suffer
when the degree of pollution is serious. Further, if the germs
of disease be present in 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 ns that water from springs and wells
was sought for by preference, 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
generally 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 all conditions
and at all 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 tho bed otherwise established,
obnoxious genus may be passing through in thousands. There
is matter for reflection in the fact that certain authorities are
so careful with regard to the proper formation of this film that
they do not hesitate to allow the effluent 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 ne system of purification yet devised that
can claim to be safe and reliable without constant su|.)orviHion
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 aHcortaining whctlier
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 supremo imp)f>rtane0
to the chemical analysis of water, because it was suppo.scd,
4 Modehk Methods of Water Pxjrificatiojs"
somewhat erroneously, that the percentage of certain in-
gredients indicated definitely the volnme of sewage or other
foul liquid 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 Wanklyn,* “ 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. Prom 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.
Introductory
5
of the drinking water by boiling. Hence it is not to be won-
dered at that the i)r<‘ferenco of the public tendn more and more
towards a KU])])ly as nearly germ-free as possible. This is
why they willingly bcuir the outlay of bringing water from
iinpolhited gatlundng grounds in remote uplands. This also
is the reason wliy a comparatively expensive process of
steriliz-ation by ozone has been adopted at many important
stations. A wiueglassful (.)f water well within the prescribed
limit of bacdsTiologica! purity may yet contain five to ton
thotisand germs, ho that the consumer may be excused if ho
questions wludJun- some of tluiso may not b(^ dangerous.
Unfortunahdy for its rc^liability, tlie })urification of water
diihu’s in an i^ssmitial point from almost ev(uy otlun* mcsihanical
])ro(u^ss. Maerhiutis and other s])ocifi,c ap])IianccH producer a
desired rc^sult with ccuiainty vvlum tlio matcuial tlioy o])erato
upon is unibn’in in form or ({uality. Tliey are not cx])(K;tod
to do the. work intmulcHl urdc^ss this is tlu^ (^as(^. If tlic\y do it
at all, they do so irnjxu’fectly. But ])urifying liavo to
contend with <^lning(is in tlu^ raw \vat(U‘, botli jxu’iodic and
lUiexpeetcxl. If nunthanical filhws an^ to (lisj)Iae(^ tlui ojxvn
sand arrangc*nuuit, they must be cu])abl(^ of adjustrruuit to
varying refpurenuints, and this accommodation should bo
automalit; as far as ]K)ssibl<5. Th(T(‘. arcs of (a)urs(^ ways and
mc^ans of scxMiring a great measure of uniformity in tlic^ raw
water hefont it is (uuuluctcjd to tlie purifying a])))lian(^eH. Thus,
for exampl(*, tlu^ storages of se.vm’al mf)nths’ sujiply in a largo
reservoir, e(|Ualizos tlu*. (jonhuit of scidirmxit, g(u*ruH, and other
offensive, mattitr, Pntvious tn*atm(mt ov^'er rougliing filters
is an aid to maintaining an averag<; of irnpuritic^s to Ixi subse-
quently (diininatfuL Thcj sairuj end is sought with the h(5l]j of
Kcx!inu‘ntaiion basins in which coagulants may or may not
he applied.
Water uiulertak(?rs have*, now a (;lioi(;e of sctvcu’al syshuns of
■purilieation wliinh, it is maintaincxl, surpass thc^ slow sand
niter in eflieicauty and reliability. fSonu) of th(?se Iiave proved
iiotatdy Kuceessfirl at Htations wlu?n‘. tlu^ oldcu* })roc;(mH fiiilcxl.
In making clniiee of a system, th(» csstmtial point is the
<;liaraeter of tho raw watc?r tlirougliout th<^ ycuir. That
iMiing deter mi nod, the probable (dli(deney of any systcun
may bc5 JiidgiKi from its huccchh with watcu’s of a similar
type. Ktorage liglitens the duty of the filter-btals, and, if
6 Modern Methods or Water Purification-
continued long enougli, it is a safeguard against water-bomo
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 bo
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 scwago
become more perfect, and as regulations against the discharge of
putrescible matters into streams are more stringently enforced,
it may be expected that sentimental objections to the ubo 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 difficult to imagine. By mc^ans
of filtration followed by ozonizing, the Marne 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 niout
significant addition of recent times to the conditions which
treated waters must conform to is that which relates to the
jB. coli. It was the great weight attached to the elimina-
tion of this germ which chiefly induced the Municipal Council
of Paris to sanction the construction of an ozone plant at
St. Maur, The close relation which has been establiBhod
between 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.
iNTROBUCTORr
7
rh.e large number of sciences which offer contriTbntions to
the theory and practice of water purification occasions a diffi-
culty in choosing the best arrangement for a clear exposition
of the s-ubject in hand. A study of storage involTes 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 modern 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.) Sources of supply.
(ii.) Storage and construction of reservoirs.
(hi.) Filtration by sand, including non-submerged filters,
(iv.) Filtration by mechanical fiJ.ters.
(v.) Purification by ozone.
(vi) Chemical and biological features of water.
(vii.) Water-softening.
(viii.) Distribution, including plumbo-solvency.
CHAPTER II
SOURCES OP SUPPLY
The growth of urban communities and the corLbirmal c*xt(‘nBion
of water undertakings have greatly limited the available
sources of untainted supplies for household use, Tile‘S practice
of replacing dry closets and cesspools by the dra^inage of HC‘wage
into rivers has fouled many sources potentially in renerve*.
River water which has received considerable quanliiicH of
sewage, whether treated or not, is scarcely regard(‘d with
favour by communities in quest of wholesonae a»nd ‘|>alatable
drinking water. There is, indeed, a well-groixmcied j>rc‘fcmica
for waters that are clearly exenapt from anytlaing more than
insignificant defilement with sewage, manure,, or any other
organic waste.
Among the sources against which no exception is a|>j>arciitly
admissible on the score of pollution are deep wells and boringn,
the upper reaches of rivers and their tributaries bc^yond the
domain of agricultural activity. Lakes fed by rnoiiritiim
streams are in general natural reservoirs of good water. To
these must be added the natural drainage of moorlands, uplandH,
and forests, even when this is chiefly surfaoe water or tlie
outflow from shallow wells.
Deep Wells ; Sources of Pollution. — In the cause of deep welk
and borings, the purity of the water results frojii natural
filtration, and very often the supply is perfectly free from
undesirable germs, and even from organic matter. Kut therc^
are exceptions. Wells located in the midst of a population
are rarely safe. The proximity of cesspools, manure-heapB, and
polluted streams, suggests the exercise of caixtion in all «ueh
cases. Dr. Thresh ('‘Examination of Waters and Water-
Supplies,” p. 301) instances a number of wells in districts
8
9
Sources op Su^^y '
adjacent to the Metropolis to which , water, tidal water,
and organic impurities, had had more or less free access.
There is always the possibility 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 suspicious
germs {B. coli, 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 would point to infiltration from the suspected locality.
In place of salt, one may employ lithium sulphate, which is
easily detected with the spectroscope, or the dye fluorescein,
which has powerful colouring properties. Professor Henry
Robinson found that lithia was easily applicable to the
investigation of underground sources (Trans. Inst. Mech.
Eng., Jan., 1909). Better, however, than any chemical for
identifying a source of pollution is an abundant culture of
some harmless miirobe, asR. prodigiosws otB. violaceus. For
if it be 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 underground 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 well, that circumstance
alone does not show that dangerous ingredients would be able
10 Modeen Methods oe Watee Pxjeificatioh
to come in by the same route. On noting the time taken by
the test liquid to travel through the intervening strata, and
comparing the rate of percolation with that which obtains
in unfissured formations, one may be able to infer the actual
conditions which exist underground. 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 underground 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 studying the disposition of
the strata in the neighbourhood of the Cambridge County
Asylum, Dr. Thresh concluded that from beyond a certain line
the underground water would travel avmj 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
Chiltern Hills 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
SOURCDS OF SUPPIT
11
t
of hardness 5 impurities make their appear-
ance in the outflow, at particular seasons.
After heavy rainfall folloving drought, the
water of certain deep wells is discoloured,
and this is what might be expected if the
rock formations are intersected by fissures.
Indeed, there can he 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.
Yet the strata underlying the London
Clay are productive of much excellent
drinking water, for it is remarked, in the
Sixth Report of the River Pollution Com-
missioners, that in the whole course of
their experience they had found no catch-
ment basin so rich in springs of the finest
drinking water as that of the Thames.’’
A cross-section of the superficial strata
from the Chilterns to the Kentish Downs
is shown, in Pig. 1. The topmost layer
of impervious clay is twenty-eight miles
broad, and beneath London it has a thick-
ness of 300 feet. Beyond the clay the
chalk rocks become the superficial forma-
tion, and. much of the soil resting on these
pervious rocks 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 he very large.*
Protection of Deep Wells from Pollu-
tion. — Precautions against the defilement
of deep wells are almost necessarily
^ Por a full account of the sources from which
water-supplies are dra.wii, see “ The Geology of
Water-Supply,” by H. B. Woodward, !F.E.S.
(Arnold’s Geological Series).
m
Fig. 1.— Geological Section across the London Basin.
12 Modern- Methods oe Wate:k Pxjrifica'TION
restricted to the immediate neigh.Tboiirhood of oiit-
flo-w. The greatest attention shoixld. be directed to that
quarter from which the nndergrouixdL flow comes to ttic‘ well.
Prom what direction the well is principally fed may asci*r“
tained by a consideration of the geological formations, and })y
suitably devised tests with fluoresceixi. Probable Bonrca^n of
pollution can then be investigated, and measurers taken to
safeguard the well water. Around t>lie place where tin* Ik ire
is sunk, an area should be enclosed and kept clear of dcK-aying
matter. Local circumstances, as the slope of the ground and
the permeability of the rocks, will determine tlie extcuit of this
area, and it ought to extend farther* towards the direction
from which the underground flow arrives. Tlie l)or«* of the
well must he made water-tight to some depth by iron or
concrete. At Hastings and at Halstead (Essex) tlie wells are
lined with iron to a depth of 60 feet, a.nd at Leighton Buzzard
aU water above the 175 feet level is excluded. In ih<» last ease
the water-tight casing was extended considerably, noton aee^uiut
of any risk from surface water, but in order to avoid tin* inihuv
from certain strata containing iron oxide. At Hytlicj the first
5 feet of the brick lining of the well iB hacked with cemruii to
keep out surface water. Por the next 17 fcK^t the hat^kiiig
is of clay puddle, and the brickwork is carried to 70 feet, and
this is followed by iron cylinders to the bottom at 103 feet.
The iron casings of the wells belonging to th(^ West Cfhesldre
Water Company are 130 feet deep. Hhus, the d(q)th to wliieli
the casing of the well requires to be carried must be dfautlfKl
by the existing conditions at each stahion.
The season in which there is the gircatest risk of impuriticH
from the soil reaching the well is that which is marked by
heavy rainfall after drought. This occurs frt^qiiently in I In*
autumn. The level of the ground waher is then quickly mined
by the first washings of the superficial layers, which eoiitain
organic matter and myriads of bacteria. WcIIb riiitumlly
receive an abundant tribute of the ixew supplies, seeing that
the contour of the water-level undLerground slopes stcr^ply
towards them. At such times the analysis of the oiitfiow
should be carefully inspected.
Upland Sources of Supply: Streams and Lakes. — «u|iplicf»
collected from uplands beyond the limits of cultiviiticiii
SouKCES 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 been 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
be 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 some 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 pollu-
tion 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. Chicago
has lately diverted its sewage from the old convenient dump-
ing-ground on the shore, and carried tunnels four miles
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 below the surface to
avoid passing ships, floating impurities, and ice in the cold
season.
14 Modern Methods oe Water Purification
Lowland Sources : Rivers and the Drainage of Cultivated
Lands. — Catchment areas which include cultivated lands, rivers
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 are not condemned 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 bilildings 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.
^QViWKH OF Supply
15
Bomr lirii iHii aiitluiritii'S liav(‘ (»inb(Kli(*(l in tluar Bp(‘(:ial Acta
a elariKc (niahiing tluan to j)rotf*c,t tluar lands from jxdlution,
and tlifir %vatf*n*oursi*s from dofilfajuait, through, tlui ojxTation
of any iiidu-stry in tlio. vicinity.^ ft is sound poli(‘,y for
watfT authorities to brooino proprietors of tludr gathorinf^
areas, ho tliai tliey may rc'Htricit agri<;ultural ojxTations to
graying, and forl>i<l the uhc^ of any manur(‘H otlna* than mineral
fc»rtili/*erH. The* \vatenmurHi‘.s should la* l<(*pt opcm, eh'anai of
weeds and oveiiiangiiig v(‘getation, and tin* a<uH‘BH of tlu^ public
jirewnted. All drainage* from buildings wHbin the* area must
l>e intfTCf‘pted, and take*n by \V(*ll”hu<l comluits to a |)oint lowc^r
down than the intake:*. An (*xaminatiori of tln^ watencourBeH
e'nabIe*H the* prindisf*d eye* to <liHcov(‘r whe*thc*.r any loikago of
f{>ul water is firniing an ink*t. Sewage*, and oilun* offemBivc
matte‘rH cK*eaHiofi growths of a fungeucl natain^ on the^ weeds
and pe!d)leH, and leave a diseadoration of tlu^ b(*<l of the
Htrcaim whi*n^ the‘y ente‘i% c*aHiIy noti(a*d whe‘n the waten: runs
low. Tiic'se examinations should fje made*, piuiodieally.
Atte*ntion must be* ]mid to the! <etT(*et of storm watc*r, with
F.pe’cdal ri'garel to the nature of th.e suspende^d matte*rB tliat
imiy be* elisoharged into the. Htr<*amH from the wash of the
adjoining landK. Wlion the*, ground elijm steH'july, much
of the- loose material lying above* is swe-pt dowuiwards by
heavy niiiiH. !t is ge-neraily possible*, in Hiicii (^aHe*H to <livc*rt
tin* Hteami wale‘i% eu’ by artificial mmm to impe‘de^ tlu^ fren*;
ac'CtesK ed turbiei wate-rs desetending from Hlop(‘H. Phinting the*
borderH of re-serve urn and wiitcT(anirs{*H has oftem, l)e.*eii advo(;ateal,
and Irei'H ed the pine Hpee-ies are* fnvemre*d,. Tlie^ planting rie(:*d
not III- earrie*ci e*Ios<» to the banks.
Wlie*re ifiiiterals, f-oak ireinsteme*, edee, are* worke*d within tho
eaitfiinieiit arsa, the drainage ed the* pits ne*v(‘r feernma de'sirablct
addition to the siippl^*. Deep workings e-xliaust th,ee unde*r-
grenind walers lluit might edherwise* earntril^ute^ t=e> tlie* gcmeral
intake. .XmmilieiesH, it is }ie*tleT to dive*rt the* eliHediarge^ from
tlie ptniips. It i?4 not only foule-el hy the worke-rs, tmt it geri<‘r-
ally is e-iiargi'd with iron and ot!ie*r ingri*ciieiiiH ed tin* HcniniH
iinel veifiM with whim'll if lens be*em in <’ontaeei.
* TI41! to *»flerf flmt- thiy rimy l!e4fl any larali-i «»r Heirviteidfw
wliii’fi ifpy iiew fur tlc’ iiurpfo^Mif |?n-.v<intin^ the feuling ai
liny %vii!i>r wLi^’h ih*y lae iPjlhori/.*uI to iwel for the |>rote«U.if.m of tlsdr
Wilt iTWf ir k.;i iigii! II -if. II ^ I i 'i i « 'eH. * *
16 Modern Methods oe Water Purification
Lands acquired for Gathering Grounds. — The following water
authorities have acquired land within their gathering areas
for the purpose of preventing pollution :
" Birmingham
. ,
45,562 acres.
Bolton
2,356
5 J
Bradford
9,000
5>
England ^
Liverpool
. . 23,000
Leeds
. . 15,000
Manchester
. . 11,000
if
Newcastle
6,600
i)
^ Oldham . .
. . 2,000
J?
Ireland.—
-Belfast
.. 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.
Glasgoiv has acquired the feuing 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
Sources 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 of Contamination ; Localities supplied from Under-
ground Sources. — In an article upon water purification by
natural filtration {CentralbL /. Allg. Oesundheitsfflege, 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
(Zeitschr. f.Hyg, u. InfehtionslcJi., 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
fortifying 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 algoc or other
growths, and so preventing the water from percolating. The
current obviates this inconvenience, so characteristic of artificial
filter-beds. Prom 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 duo
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
18 Modern Methods oe Water Purification
pure in consequence of floods. Dr. Meinert recorded a far higher
mortality from diarrhoea among young 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 land is a barren, undulating waste
which has been canalized and drained by a network of deep
channels. Eain 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
SoTJucES OP Supply
19
very mucli 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 yielded 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 Eiver
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 Eiver Enz, forty miles
distant, in the Black Eorest.
During 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 Bobortal, close to the Eiver
Bober. Numerous borings from 12 to 60 feet in depth have
been put down, and in general the water found is of good
quality. In permeating through the gravels, the soft river
water adds three or four degrees (German standard) to its
hardness, and in hot weather its temperature experiences a
welcome lowering of 5^ to 6° Cent.*
The city of Worms was provided with a roughly filtered
service of Ehine water in 1888. The arrangement was as
follows : An iron cylinder 10 feet in diameter, with perforated
wall, was sunk 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 Gasbeleuchtung und Wasservarsorgung, October, 1909.
20
Moderit Methods oe Water Pttrification
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 been 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 be noted in con
nection with the water-supply of Bingen. Formerly the towr
obtained its water-supply from two wells, one 50 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 as
a rule, unsatisfactory only at times. Hence a new and better
supply has 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 [Centralbl. /. Allgem. Gesundheits'pflege, 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 lime, 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 unsatisfactory drinking water, the mortality
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
SoxTECES OF Supply
21
mechanical filters goes to sand-beds of the old type. The
service water is remarkably pure.
A very large amount 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 Water, 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 Metropolitan supply, yield very good water
from the standpoint of chemical analysis, and over 90 per cent,
of the samples tested bacteriologically showed no B. coU 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 underground 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 25 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 poi)ula-
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 Egypt 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 aU 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 MoDEEir Methods of Watee Pubieication
their Medical Of&cers and Sanitary Inspectors- The most
obvious of the measures that should he taken to guard the*
well from the easy access of pollution may he stated as
folloAvs :
1. The well should be removed as far away fbS possible fnim
manure-pits, cesspools, and other possible sources of
tamination, and always towards the direction from which
underground waters flow. It should not be sitixatcd in a hollow
to which surface water tends, but rather on a site whicdi
naturaRy throws off the rainfall. Nor should it bo placed on
ground which is liable to he inundated with flood watcu\
2. A space all round should be fenced in, and k(p)t under
grass or planted. Local considerations may lim it tlie X’adius
of this space to a few yards, but it is doubtful wlieth(*ranythiiig
less than 100 feet can be looked upon as a real safeguard in
gravelly strata. The enclosure should extend inoro in the
direction from which the subsoil water percolates -
3. The weR should he cased water-tight to tlu^ bottom, or
in any case to not less than 20 feet. The casing should he
carried 2 or 3 feet above the surface, and the ground Burrouiid-
ing should be laid with cement or otherwise naadc watcT-tiglit
to a distance of 6 feet. It is recommended that tlic pump he
separated from the well-head, and placed some distance, away,
so as to minimize risks from spilt water finding its way iiiKicli*.
The top of the well should be protected from dust by a Huitablc
covering.
4. Samples of the water should be taken for analysis from
time to time. In addition the consumer should oIjhctv<^ thc^
character of the supply, noting how it changes ‘vvith w^eatli(*r
and season. Wells which become turbid after licavy raiiifiill
are always to he suspected.
Surface Springs, — Springs other than artesian wcdls gencT-
ally called ‘"surface springs,” because they are derived from
the water gathered by superficial beds of poronB rock. The
water issues from the ground at the junction of the i)(*rim‘a! flu
bed with one that is less pervious.^ The quality of tln^ outflow
depends on the nature of the strata through vvhicli it him
permeated, the depth of the natural layer of filtering nuiitc r,
and the presence or absence of sources of contamination at the;
See “ The Heology of Water Supply (H. JB, Woodward), chap. vL
Sources of 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 farmsteadings 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. Rain 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 algae. With respect
to domestic supplies from shallow wells 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. Careful attention
must, of course, be given to the cleansing of domestic filters,
especially charcoal filters, from time to time, otherwise they
cease to yield pure water.
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 modern investigation and research.
Dealing with micro-organisms in impure water, Erankland
(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
indications of the bacillus after a greater lapse of time. On the
24
Stoeage
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 typhoid 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| 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 :
Typhoid bacifius introduced
One week after
Two weeks after
Three weeks after . .
Four and five weeks after .
Six weeks after
Seven weeks after . .
Eight weeks after . .
475,000 per cm^.
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 oe Water Purification
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 effect
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 found that 220
germs in a sample of Hew 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 excremental (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 Metropolitan 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 preliminary 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
1^7
stored for ten days, the water would be so 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. RideaFs tests of Dee water wore
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 specificallv ”
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 {B, coli). In aiiy 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 0-1 cm^. and even in 0*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 was
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 bacillus
were applied, and the experiments were continued for twelve
months. Two hundred and ninety-four experiments were made
with wa.ters drawn from the Thames, the Lea, and the Now
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 consumers within the Metro-
28 Modern Methods of Water Purification
politan area. Yet Dr. Houston does not for a moment advise
any slackening in the purification of the raw waters from the
sources mentioned. All of them are suh j ect to sewage pollution,
and 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 analytical work, he
has reduced the possibility of error in his deductions to a
minimum, and he has established his former conclusions beyond
the range of doubt (Fifth Eesearch Report, 1910).
The method adopted was that to be described in connection
with the vitality 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 bacilli (0-7 per cm^.). The other half of
each sample, which had not been infected, was subjected to
exactly the same analytical treatment as that to which these
pathogenic bacteria had been added.
It is plainly to be deduced from the series of experiments
that 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 bacilli {B. enteritidis) than one in 14 cm^.
(Fourth Annual Report, 1910, p. 7).
^he danger of epidemic diseases emanating from the chief
Metropolitan 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
delivery 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 bacillus and one indistinguishable from
Gartner’s.
Storage
‘5 I I 0 R 45,R y
water to discover how far this species is a
period of comparative quiescence. Dr. Houston i^fsettled
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. Eifty per cent, of the samples
of crude Thames water contained typical B, coliin u, em'^., 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., 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. coK 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 days at
Chelsea and Lambeth, and for ninety-five days at Staines ;
but it can easily be understood 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 found results even
more satisfactory than those above quoted. In raw Lea
water B. coli is about as frequent as in the Tliames. Sixty-
sevem per cent, of all the stored samjdes yielded no rcisult
at all with 100 cm^"*. Only one sample out of a hundred gave
the indication sought for witli 1 cnr^., and four only witli 10 cm^.
In fact, there were fewer ty;[)ical B. coliin 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 tlio
number of B. coli w'e are chi(‘fly concerned at tliis jioint, but
it may be mentioned in passing that by storage of Lea water
thcrci resulted a reduction to the extent of 97 per cent, of all
the bacteria capalile of growing on a culture medium at blood-
heat, and of those that, bedng chiefly oxcremental microbes,
could germinate on a bile-salt medium.
3053
6
30 Modebn Methods of Water Purification
The Bacillus enteritidis sporogenes was also sought for, and,
dealing always with; 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-typical B. coli, the former giving, inter alia, the
‘‘ indol reaction.’’ The discovery mentioned brings into relief
the circumstance that t 3 rpical B. coli die faster in the Lea
reservoirs than do the non-t 3 ;pical, which are regarded as beirg
less objectionable. Out of every 100 coK-like microbes in
raw Lea water, 85 per cent, are t 3 q)ical. Out of 100 coZ^'-like
microbes in the stored water, 63 per cent, only were typical.
We remember that the volume of stored water containing
100 coli-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 B. 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 E.
Storage
31
number of colonies of all kinds was 1,200 per cm^., and of these
about 30 flourished at blood-heat on the special medium. B, coli
could be detected in 0-5 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 e'ddence. 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 analysis 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.
Parts per 100,000.
Bacteria grow-
ing at —
Total
Oxidized
Free
Albuminoid
Oxygen
20° C.
Solids.
Nitrogen.
Ammonia.
Ammonia.
consumed.
Raw water
24
37
0*007
0*026
0*19
1,100
113
Stored water . .
1
12
24
0*002
0*020
0*20
270
7
B. Coli Tests.
Raw water . . . . . . . . present in 0 '5 to 1 cm^.
Stored water . . . . . . not found in 50 cni^.
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 Modben Methods of Watee Pueification
or four weeks. Tte 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 tjrpieal 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 sampk'.s
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 results of extensive
tests upon the wholesome influence of storage, it may bo 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 authoritic^s,
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 effluent.
Vitality of the Cholera Vibrio in River Water. — I’fu^
appearance of cholera from time to time in tho WcKtiTn
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 tho mannew
in which infection is conveyed. The important disco v(<ry,
due to Koch, of the cholera vibrio defined more clearly tho fiedd
of these investigations. It remained to find out prccisidy in
what media the vibrio might occur, its vitality in thoMts, and
how far any one of them might serve as a carrier of tho baiiilius
to human beings.
It is generally accepted by bacteriologists who have studitul
this question in conneef ion with outbreaks of cholera in India,
Russia, and Germany, that the disease is quite capable of hoin«f
conveyed by water-supplies, and that infected water is prosumiv
tively responsible when a wide area is attacked.
Dr. Houston has recently turned his attention to tho viflilitv
of the cholera vibrio in Thames, Lea, and New River water
and he finds that there is no difficulty, deserving to bo called in-
superable, of recapturing, as it were, by aid of his culture media,
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 in their behaviour under the delicate reactions
by which the Koch bacillus is identified.
The precautions which Dr. Houston took care to adop^
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 those. He repeated this
experiment on tw'enty-three occasions during a period of four
months, and mad© 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 tho 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 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 bo 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 tho germs of
3
34 Modeen Methods of Watee Pueieication
cholera three times in 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 wrecks 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 confirm 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 5o 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 subcultured 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 alive 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 vfith difficulties. We may admit this, and still look
with confidence on Dr. Houston’s results, seeing that they are
Storage
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. Nximerous 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 Purification
ramifications marked tke 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 13,000 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 62 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 sorcalled “ free ” or inorganic ammonia — NH 3 and its
compounds.
Storage
37
. some light in regard to this alteration which
nces upon river water from p. 10 of Dr. Houston’s
3arch Report, where it is stated that the albu-
rogen * suffers no diminution in the case of Lea
is actually increased for Thames water in the
t Staines and Lambeth. Only at Chelsea Reservoir
decrease (29 per cent.). Now, it is pointed out
)uston that the albuminoid ammonia test is an
ae — that is to say, the chemical process employed
h furnishes only a general idea of the amount of
iter present. Accepting this view (see also Thresh,
mrn to the analysis for total organic nitrogen, and
^ermined for two samples. We find in the case of
that there is a moderate diminution of the total
ogen (5 to 13 per cent.) during storage. Yet in
rery samples the albuminoid ammonia on being
lowed an increase of 40 per cent.
Causes of the Chemical Changes. — Gathering up
elative to the change that comes over stored water
he decrease of ammoniacal nitrogen, the decrease
consumed, of total hardness, and of oxidized
le may hazard a suggestion as to the probable
vov'k in the particular waters here under con-
But first w© shall consider how far these chemical
related to the season of the year,
and III. show the summer and winter averages,
)rmer from May 1 to September 30 , and the latter
r 1 to April 30 . ^
TABLE II.
Ammoniacal Nithogen, Parts per 100,000.
Water.
Winter.
Summer.
0'0083
0*0030
th . .
0-0048
0-0043t
i. . .
0-0028
0-0013
. .
0-0051
0-0038
1
0*0139
0-0004
;; ;; ;; i
1
i
0-0048
[
i
1 0-0055
1
organic compounds, which can be estimated as ammonia in
t 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
50 per cent, on the average of three reservoirs, and for Lea
65 per cent. In summer, wdth 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 Nitrogen, Parts per 100,000.
Water.
Winter.
Summer.
Raw Thames
0-0164
0-0138
Stored Lambeth . .
0-0152
0-0217
Stored Cholsoa . , . . . .
0-0107
0-0109
Stored Stoines
0-0233
0-0191
Raw Ijca . .
0-0152
0-0159
Stored Lea
0-0135 :
0-0182
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
all)uminoid ammonias are nearly equal, but there is a diminu-
tion of 11 per cent, in winter through storage, and a rise of
14 per 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 off by ferr
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. 63, 06, 280.
Stoeage
39
the circunistances 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 of 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.
Oxygen absorbed by Permanganate, Parts per 100,000.
Water.
Winter.
Summer.
Haw Thames
0-2586
0-1561
Stored Lambeth . .
0T883
0-1710
Stored Chelsea
0T754
0-1240
Stored Staines
0-1817
0-1296
Haw Lea . .
0-2155
0-1613
Stored Lea
0-1336 1
0-1259
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. W'e 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.
Kef erring 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 almost 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 suffers 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 amraonia
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, under 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 Modeei^ Methods of Water Purification
recently pumped water with many, or even most, of the
reservoir samples. Further, as Dr. Houston points out, i\L
sides and bottoms of the reservoirs are always covcrc^d with
deposits, which by their fermentative changes infiuence the
chemical aspect. It would appear to him hliar advantage
might result if the raw water were first put tli rough a sedi-
mentation basin, or roughly filtered after the Puecli-CdialMil
system, whenever the sources are unusually fcurhid. ^ Thc^ twin
sets of experiments which were made seem to indicate tliat
this recommendation is sound.
General Conclusions. — It is not to be overlooked that tlio
foregoing discussion has immediate reference to the storage
of river water, but there can be no doubt tlmt any HUj)ply
composed largely of surface water, contaminated more or Ichb
with sewage, would under storage exhibit corr(^H])oncIing
changes. The impounding of water from deep) spriiigH and
wells, and from other sources that are ordinarily Ix^yond tiie
reach of pollution, is a step which is justified by tho c^xigcmcies
of supply and demand, and not by any expectation that the
•quality of the raw water will be improved. It may c*ven
happen that over-abundant growths of algae in the rc^KiTVoirH
will tend to a deterioration of their contents, but if cfire in
taken to anticipate excessive development among the* algoici
forms by the use of very small doses of copper sulphatt^. t}u*r«
need be no serious anxiety regarding this matter.
The benefits accruing from the storage of rivcT watc*r are
largely influenced by local circumstances. A certain fraedicin
of the ordinary flow of the stream is abstracted, and tlio larger
this fraction is, the more difficult it is to make a Hcdc^ction of
the best water. This is especially the case wlierc3 thc^ vmmxHnr
is fed from a pumping-station, but it is very often not tuny to
build up a reserve when conditions are favourable.
When flooding occurs, the supply is interrupjfled for a thrio,
during which the volume of water in the reservoir in continually
decreasing. The filters, as Dr. Houston says, are then borrow
ing on capital. The subsequent replenishment with criicla
water produces a mixture of raw and stored material whicli is
undoubtedly very different from the normal. Unless storage
has been provided equivalent to the volume of service w«it4ir
required for a lengthy period, say, for three months, tlie
Storage
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 filters 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 baffly without apparent reason. This very
circumstance was pointed out to the writers 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
liis conclusions are here briefly recapitulated :
1. The microbes of disease, and those which are indicative
of sewage (R. wli), perish rapidly in stored water. In about
three weeks, generally speaking, the safety change is com-
44
Modebn Methods op Water Purification
plote, 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 of Plant Growths.
During the warmer months of the year it frequently happens
that algse 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,
Analoena 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 the 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 undesirable 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 unfavourable 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
Storage
45
waters with a suitable chemical, 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 algse. 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 will be a prevention which is here much
better than a cure after the evil has developed. Eor 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
abundant 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 until August 12 did the
manager consider it desirable to accept the effluent 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
this 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
MoDERisr Methods oe Water Purification
position of dead filaments was at an end, and the bacteria,
lacking food, decreased steadily, to the advantage of the
effinent.
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 distribution. 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 unsuitable 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 algse 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 difi&culty 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 alg^ 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 dijffiicult 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. Rideal, 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 hypochlorite 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 small percentage
of hypochlorite serves to destroy bacteria. It is also strongl37'
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 hypochlorite 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 OP RESERVOIRS AND CARE OP PILTERED
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
algse, the whole extent of the reservoir should be made as deep
as possible, and never less than 25 or 30 feet. Por 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.gr., Selby) are lined throughout
with concrete over 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
Reservoirs and Filtered 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 is bad policy to have the inlet and outlet in the same tower.
IReservoirs 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
Dtreservoirs (Third Research Report, p. .3), the latter, not re-
commended by him, being used to conserve a considerable
■v'olume of water as a stand-by, while the raw water in ordinary
circumstances goes to the filters. , Such passive reservoirs may
Ibe perfectly appropriate under certain circumstances, enabling
■fclie water manager to shunt storm- water and to supplement
t;lie natural sources in time of drought ; but wherever the raw
■water is subject to surface pollution, the active reservoir
•fclirough which the whole supply must pass is the one worthy
of recommendation.
Reservoirs with Compartments in America. — There are
Bcveral advantages of dividing the storage area into compart-
ments. The grosser sediment is mostly collected in the first
t>a,sin, and this (or any one of the other units) may be cleaned
f jrom 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
tlae outlet without enjoying the normal average period of
B-tiorage. Unusually turbid supplies may be confined in the
4
50 ]yi:oX)EBN MethoX^s op Watjejb- Purification.
first chamber for a longer period, U.SS't
One of tb-ese reservoirs constructed. l^ansab,
represented, io P'^S- 2.
Prnffressive Sedimentation. — Where the main object jh to
get rid of tbe larger portion of the sediment of a turbn _
fn Wed space and tixxae. it has been found advardag.-c,^
to induce a contimaous amd
means of slow movement, with frequent change of dm < twn.
ThHest installation of this kind is that of the Compatmie
Generale sti} the Paris Wa^taxworks. IFirst the water rkmerndm
into a set of narrow t>rouglis, and its flow is directed alternately
to right and left, rnnking nximerous hnmings. The»© trciiiglis
are made of concrete and. tttere is a slight fall from each ssigmg
to the nesi-t. The Ineavier sediment falls down abtintlaiilly.
In sequence to the ‘troughs cx)mes a series of wider chaiinrlit
or basins so constrixcted tha.t the inflow and outflow cmnuit
are always in opposite directions. The rate of flow tei;-
diminished, considera^bly, and sediment of a finer grad© now
52
Modern Methods oe Water PrrR^tFiCATi^
settles. Lastly, the water reaches a train of clcciint iii^ t».i .m ,
which are divided up into numerous ii4« iii
of baffle-walls {murettes). These latter a.re ko c'lifi-t rtiri. .|
that the water must flow over one and under the m^xt in »'it|r r
On the whole, this sedimentation is satisfa-ctoon .'ind unit L
more rapid than if the water were kept stationary
period. At the particular installation hero refc*rr#*fl tL*
river water has passed through the Andersoia cylinder !mi,
it is transferred to the settling troughs, so tliat tfi**
with iron oxide accelerates any precipitaution \vhi#’h lusnhi
natural!}^ occur. Slow movement with clriingc of diririjiifi
not only promotes the silting out of suspeixclocl mat Inii it
also prevents very largely the growth of ih
sometimes caused in deep reservoirs by f iirr* ii! ..
which are set up after any considerable fall of uri jn
the surface stratum, and such are avoided I)y tip* pri f I’lii
system. There is also a material reduction of tin* gf-'n ii
of the raw water during the rapid sedimenfca.t ion, }>tif of
the main duty of eliminating offensive bacberia rentH tin*
fiJter-beds.
Circulating Reservoirs. — Circulating resei’voirn Im v» - In in
constructed at several waterworks in England for tfi# |iiii
pose of storing water which is derived from df*o{# ^
and is sufficiently pure to be used withox.at.t filtriif ion Tin
construction of Sundridge Park Reservoir ir Hhovrii in *1,
and it will be observed that the water circir la
clockmse round the outside annular space, axTcl f linn l urd-^
in the next channel. The outlet is central. Tlu^ t luripni
at by drawing the water round these circnilar vltaiin*
according to the engineer, that of keeping tlin vvafrr
and preventing it from becoming dead nnd iriHfiiitL TIp^
growth of fungi on the walls is also avoided.
Reservoir Surroundings.-Land in the vi.,r„tv ..|
stored ivater shoiild receive careM attention, an<l i.f.
to prevent the acceHs of
matter, it has been recommended thab i
50 to 100 yards wide all round should be acq ninwl nji jtirut,'
vith pines or shrubs which do not throw clown nr, J *
crop of W« in the autunm. ais ^iT rlrcl ,.
to tom. „tent from d« blown from bill, r.m,l„ i’'::,:
Reservoirs and Filtered Waters
53
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 impound 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.
Care of Filtered Water and of Service Water
IN General.
It is an undeniable 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 un-
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 Asterionella 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 dear-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 difficult 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 algae, and most of the plankton species, cease to grow.
It is a distinct advantage to keep the water in motion if the
dear-water basin is uncovered, and it has been found useful
54
MoDEEiiT Methods oe Water Pfeificatioi^
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 corered 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, Mew 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 influence of storage, no matter whether
the water is filtered or un-filter ed.
Rapid Growth of Germs in Spring Water under Storage. —
According to Dr. Miq[uel ('"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 ddrh at
25^^ C. each cm^. had more than 100,000. Leone at Munich,
by keeping the supply water in sterile flasks 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 increa^se 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 Zeitschrift fiir Hi/giene, vol. i., 188S.
Eeservoirs and Filtered Waters 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 still 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 increase their bacterial content, while if the water is running
clear and comparatively pure the same faculty 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, asitwere, 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 25*^ 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 {Zeitschrift fur 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
Moder]^- Methods oe Water Purification
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 possibihties 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. Rideal found that B. coli 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. colL He concluded
that chance infection of the pure mountain water would cause
a multiplication 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. FranMand found nearly 800 per cm^. under these
conditions (Proceedings of the Royal Society, 1893).
Reservoirs and Filtered Waters 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 aU 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 fiir 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 Niirnberg seltzer water,
as did Pfuhl in samples at Altona, and Slater in the aerated
waters sold in London.
Effect of Ozone and Hypochlorites. — 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 bo left
for six hours, and especially if it has been shaken, bacteria
flourish with vigour. A trace of hypochlorite or chlorine is
an admirable preservative. A dose of -ixi 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 5s. 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 Pubitication
to face the responsibiUty of sterflizing drinking Abater in bulk.
Prom 1905 ouwards he treated with chloros (sodium hypo-
chlorite) the water-supply of Lincoln (50,000 inhabitants), and
with highly successful results. Here, then, we seem to have
one pra“ ticable 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 eonsamer,
would seem to be the best remedy- If, indeed, there were any
fear that traces of chlorine would impair the quality of the
serTice 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, the 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, beheves 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
SAISTD-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
abundance 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
0-011 to 0-017 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 perform 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
* ‘‘ Micro-Organisms in Water,” p. 117,
59
Mobben Methods of Watee Pueifi cation
aninial. The effects which the filter is able to produce upon
tlie «*niclc^ water are in general the consequence of agencies
t!iat may ])e classed under more than one of the divisions here
m(‘nt iuiK‘d, bacteriological developments generally going hand
hi hand with chemical change, so that the term biochemical ”
wotild appropriately designate the joint work.
1. Action of the Sand-Filter on Matters in Suspension.—
Wlam turbid water is run slowly through a bed of clean sand,
all tlie pai-ticles which cannot negotiate the minute passages
an% of course, retained, and very many of smaller grade are
df*posited on the granules, where the feeble currents do not
nuidily dislodge them. The surface layer soon acquires a
c*c>ating of finer and coarser particles, the interstices of which
ari^ closcw than those of the sand-bed itself, so that after a time
thc' x)art of the purely mechanical action is performed
by tlu* top layer, and little filling of the interstitial passages
o(‘cmr.s bedow the ui)permost half-inch. But this thin filtering
Hhc*id is able to make a turbid inflow perfectly clear and trans-
parent, provided there bo nothing in solution to cause a visible
tint. That the greater part of the sediment is arrested at the
su])(‘rfi(ual layer is clearly shown by the fact that the sand is
discolotired to a depth of only a very few inches. Thus, the
mud constructs the screen which ultimately hinders the
|)aHsag(‘ 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,
ffust as prt^cij)itated sulphur will filter through blotting-paper,
so tlic 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 Egliam Waterworks.
It is generally believed that the eflficiency of the filtering
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 algse has taken place. Supplies
Sand-Filtration
61
from lowland streams and from lakes usually develo-p a
rigorous growth on the filter-beds, while purer waters from
springs and uplands do not encourage the development of
alg^ 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 algse 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 round. 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
account, 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^ per
cent, of the capital outlay per bed. These showed an efficiency
equal to that of the open filters ; and as their period of run
62 Modebn 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 (Proc. Inst. Civil 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, 0-0028 part per 100,000, while the filtered
supply did not contain 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 obtained 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 0-00036 part per 100,000. In contrast
with this, the sand-filters at a large installation in Scotland
often leave the free ammonia unchanged, while at other times
it is reduced by one half, from 0 002 to 0-001 part per 100,000.
On first consideration it might s ^em 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 Metropolitan stations 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 0-5 milligramme per litre (0 05 part per 100,000)
to 0-01 milligramme in the same volume, a reduction of 98 per
cent. Yet the prefilters are under cover, and no film of vegetable
Sakd-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 efiiuent 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
Rideal (“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 ejQduent.
Hence, where the ammonia has suffered a decrease, we should,
on the hypothesis 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 prefiltered, 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 simOar 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 hypothesis ; fo-r 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 0-003
64 Modern Methods of Water Purification
part per 100,000 — that is, 0-02 to 0-03 milligramme per litre.
Expressed as nitric anhydride, this would mean an increase
of about O-Ol to 0-02 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 ammoniacal
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 nitrif 3 dng 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
SAI^-D-FlLTItAa^IO]^
65
natural food of many saproph5^ic tacteria, among wkich
may be mentioned Bacillus termo, seyeral species of micro-'
coccij vibrios, and spirilla. Ey the activity of micro-orgaiiisms'
albuminoids are peptonized, then split up into simpler bodies^
as fatty acids, tyrosin, leucin, ammonia carbonic acid, marsh,
gas, snlplixiretted hydrogen, and water. Further decomposi-
tions ensue, and, if conditions be favourable, nothing is left of
the albuminoids that could be called organic, the ultimata
residues being water, nitrates, ammonia, carbonic acid.
These putrefactive chauges go on with ease in the soil, but
they also mako good progress in water. The River Seine, for
example, after receiving all the organic dehris of Paris, exhibits-
at Menlan, 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
Elbe and its tributaries, did not prevent the water of that
river from being used as drinking water at Hamburg, without
ary process of filtration, for years previous to the cholera-
outbreak. The Eiver Dee in Aberdeenshire was examined
bacteriologically in 1892 by Er. Erankland. At that time
it was receiving considerable amounts 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 Ms examination, the volume of sewage from
any one village was so small in comparison with the flow of
water in the river that he could not detect by chemical analysM
tany 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
0-105 milligramme, and the finished supply 0-084 milligramme, a.
decrease of 4-4 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 June to August
66
Moderj^- Methods of Water Purieicatioh
36 per cent. Stored Lambeth water contains (Report for
1908-09) 0*0162 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 0-0056, a diminution of 61 per
cent.
riltration 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 ‘'Bulletin 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 conne-ction 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 mad© on the
Contment of irrigation and natural percolation through soil
as a means of purifying water for household purposes. The
experience of Dr. Roch [Wasser und Ahwasser, 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-Filtratioijt
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 algse 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 ground, 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-Suhmerged Filters on Sewage. — It is not,
however, in the topmost layer alone that organic matter is
acted upon. The investigations which 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 (Dunbar, “Principles of Sewage Treatment,’’
p. 138). Some days must elapse before the “ oxygen con-
sumed ” declines by 50 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.
The astonishing thing about the mature filter is the rapidity
with which it does its work. Dunbar has shown that, if a volume
Modebn Methods oe Water Purification
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 tliat
sewage is completely purified and rendered non-putrcscible irx
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 he quite reasonable if
the process occupied two or three days. But the rapid elimina-
tion of organic matter noticed by Dunbar is beyond the powT^.r
of bacteria. Hence the inference that the dissolved orgatiio
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 Sowagf:“>
Treatment,” p. 140). It is clear that the separation of dis-
solved organic matter cannot be a mechanical effect dopendingf
upon the minuteness of the pores, seeing that solutions of
albuminoids pass unchanged through filter - paper and urx-
glazed porcelain which intercepts bacteria. Nor is it tho
outcome of chemical changes; for if chemical reactions do occur,
they are limited to certain favourable coincidences, such
the encounter of any iron salts in the filtering material vvitli
sulphuretted hydrogen, and the chance concurrence of ammonia,
with this same compound of sulphur. But such roactiouH^
account for very little of the whole change, and it is difficult
to conceive of any possible chemical action as occurring ini
the filter that would explain the disappearance of albuminoid
bodies in solution.
The Theory of Absorption. — Hence it was that Dunbar* pu-fe
forward his theory of absorption. The absorptive agency i»
the gelatinous slimy film which covers each granule in the
matme filter. At first this film is thin, but it gradually gaiiin
m thickness and in water-retaining capacity. Just as the
gelatinoi^ covermg becomes thicker, so does the filter act
more and more effectively on dissolved organic substances.
^ Principles of Sewage Treatment,’’ p. 142.
Sand-Jilteation
69
The surface of the filmy coat is not an even, and smooth one,
hut 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 he 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
wort 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.
Tiiere 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 oe Water Purification
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 “a&orption,’’ “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 ammonia, 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, COg, 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 — ^from 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.
SAli^'D-FlLTEATIOiT
71
Importance, of Adsorption in Water Purification. — The bearing
of the foregoing 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. Baudot, 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 state of 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 Frankland 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 Modeen Methods oe Watee Pueieication
3. Bacterial Purification. — The retention of bacteria by
the sand-filter has variously been credited to the skin of algse
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 Nantes the average reduction is from 10,000 germs
per cm^. to 4,000, a fall of 60 per cent. At Cherbourg the
degrossisseurs 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 (Zoogloea) soon develop,
and the characteristic slime is drawn over the whole surface.
The coarse sands and gravels of the prefilter in the Puech-
Sand-Filtbation
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 Penninkand others have shown, there are bacteria distributed
right through the under-layers. In the finishing filter, which is
composed of fine sand, no viscous JSlm 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 {Gesundheits Ingenieur, 1909, No. 41). Their
tests were made in the neighbourhood of the boreholes at
Tegel Lake and Miiggelsee, from whiph 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 flow 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 fineness. 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 5 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. prodigiosus. On nine subsequent days at
somewhat irregular intervals the tests gave positive result;.
The experimenters calculated that in all not more than 0*0025
S AISTD -Filtbation 7 5
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. 5). 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. prodigiosus discovered. Many thousand
billions of bacteria had been poured into the horizontal tube,
washed down into the gravels with water from a side-tube (i^),
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. violaceus and
B, prodigiosus) 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 different thicknesses of the filtering material. The results
are given in Table V. :
TABLE V.
Number of B. Violaceus per
cms. in Crude Vater.
Number of B. Vioiaccus in
Filtered Water.
Depth of Sand.
100,000
Nil in 10 cm^
8 foot
100,000
Nil in 10 cm^.
7 „
100,000
5 in 10 cm^.
c „
100,000
5 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
15,000
36 in 1 cm^.
li ”
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-fidters {Zeit-
Sand-Filtbatioist
77
schrift fur Hygiene, vol. viii., 1890) found that the Berlin
filters were inhabited by a rich flora of germs down to end
including the layer of flints on which the sand rested. A
pound of sand taken at the depth of 1 foot contained 40,000,000
of micro-organisms, approximately 180,000 per cm^. of material.
The flints contained about half as many, and the sand near
the surface far more. As the Berlin filters were at the time pro-
ducing a satisfactory effluent with only a moderate number of
germs per cm^., it follows that the sand was quite able to retain
the immense host of bacteria that were lodged in it. We shall
further refer to the manner in which
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