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WATER PURIFICATION
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WATEK
PURIFICATION
BY
JOSEPH W. ELLMS
Member American Society of Civil Engineers, American Water
Works Association and American Chem.ical Society; Fellow
of The American Public Health Association and
The American Association for the
Advancement of Science.
Second Edition
McGRAW-HILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE
LONDON: 6 & 8 BOUVERIE ST., E. C. 4
1928
Copyright, 1917, 1928, by the
McGraw-Hill Book Company, Inc.
PRINTED IN THE UNITED STATES OF AMERICA
THE MAPLE PRESS COMPANY, YORK, PA.
PREFACE TO THE SECOND EDITION
The author, in preparing the second edition of this book, has
kept in mind the advance in the art of water purification as it
has developed during the past ten years. More recent data have
been employed to amplify the subject matter wherever it seemed
desirable. A new chapter has been written dealing with the
relation of the hydrogen-ion concentration of natural and purified
waters to purification processes.
The widespread use of the book both as a text and a reference
has been extremely gratifying to the author, and it is hoped that
in this new edition readers may find still more material of an
interesting and instructive character. The author has freely
drawn on the extensive and constantly growing literature of the
subject of water purification, and to the many writers quoted he
desires to express his acknowledgements in preparing this second
edition.
Joseph W. Ellms
Cleveland, Ohio,
Apnl, 1928.
vu
PREFACE TO THE FIRST EDITION
In writing this book the object has been to provide the reader
with a fairly complete account of the development of the art of
water purification. As a knowledge of the physical, chemical
and biological characteristics of natural waters is a prerequisite
to the proper understanding of purification processes, a considera-
tion of the properties of various classes of waters has been thought
advisable. The relation of polluted pubhc water supplies to
water-borne diseases has received especial attention because of
its importance. The various steps in purification processes,
such as plain sedimentation, coagulation, filtration and disinfec-
tion, are described in considerable detail. Special chapters are
devoted to water softening, and to the removal of iron and
manganese from ground-water supplies.
The rapid progress made in the art of clarifying and purifying
turbid waters in the United States during the past quarter of a
century has been notable. The evolution of the rapid sand
filter from its crude beginnings to its present well-developed
state for purifjdng waters of this type, is distinctly the result of
research work undertaken during the early part of this period.
It was the author's good fortune to have been identified with
some of the earlier investigations of this problem, and to have
been able to follow its solution closely in actual practice through-
out the whole period.
The experiences of other investigators, as disclosed by their
published papers, have been drawn upon freely, and while no
exhaustive examination of the extensive literature of the sub-
ject has been attempted, it is believed that the writers quoted
and referred to are sufficiently representative to provide the
reader with ample information upon the subjects discussed.
The wTiter is indebted to a number of his friends who have
kindly supplied him with original information, illustrations, or
assistance in writing technical descriptions of apparatus for
some parts of the book; and to manufacturers of special devices
used in filter-plant construction, who have loaned original draw-
ings and photographs for reproduction.
ix
X PREFACE TO THE FIRST EDITION
The author desires to acknowledge especially the contribution
of the subject matter in the appendices written by Mr. C. N.
Miller, Associate Member American Society of Civil Engineers,
deaUng with the hydraulics of the flow of water through filters,
and with the discharge of water from waste-water troughs in the
operation of rapid sand filters. The author is also under special
obligation to Mr. S. J. Hauser, Chemist and Bacteriologist of the
Cincinnati Water Purification Plant, for his kindly assistance in
reading the proof of the book and in preparing the index.
Joseph W. Ellms.
Cincinnati, Ohio,
March 1, 1917.
CONTENTS
Page
Preface to the Second Edition vii
Preface to the First Edition ix
Chapter
I. Introduction 1
II. Classification of Natural Waters 8
III. Transmission of Disease through Drinking Water. . 24
IV. The Effect of Improved Water Supplies upon Health . 34
V. Objects and Methods of Water Purification 49
VI. Sedimentation 54
VII. Types OF Settling Reservoirs AND Coagulation Basins. 66
VIII. Practical Efficiencies of Settling and Coagulation
Basins 91
IX. Filtration of Water 103
X. Preliminary Treatment of Water for Slow Sand
Filters HI
XI. System of Slow Sand Filtration 130
XII. System of Slow Sand Filtration {Continued) 150
XIII. Efficiency and Cost of Operation of Slow Sand Filters 168
XIV. Rapid Sand Filtration 178
XV. General Arrangement of Rapid Sand Filter Plants . 192
XVI. Details of Rapid Sand Filter Plant Construction. . 207
XVII. Details of Rapid Sand Filter Plant Construction
(Continued) 227
XVIII. Details of Rapid Sand Filter Plant Construction
{Continued) 243
XIX. Regulating, Measuring and Indicating Devices for
Rapid Sand Filter Plants 254
xi
xii CONTENTS
Chapter Page
XX. REnrLATiNG, Measuring and Indicating Devices for
Rapid Sand Filter Plants {Continued) 269
XXI. Equipment for the Handling and Storing of Chemicals
AND FOR THE PREPARATION OF SOLUTIONS 289
XXII. Apparatus and Methods for Applying Chemicals and
THE Preparation of Solutions 313
XXIII. Power Plant, Pumping Machinery, Air Compressors,
Air Tanks, Wash Water Tank and Miscellaneous
Equipment 334
XXIV. The Cost of Constructing Rapid Sand Filters. . . . 352
XXV. Rates of Filtration, Loss of Head and Washing of
Rapid Sand Filters 359
XXVI. Efficiency and Cost of Operation of Rapid Sand Filters 378
XXVII. The Physical and Chemical Changes Produced by the
Application of Chemical Coagulants, and by the Sub-
sequent FlLTR.\TION OF THE TREATED WaTER 409
XXVIII. The Effect of the Hydrogen-ion Concentration of
Natural Waters 426
XXIX. Disinfection of Water Supplies 444
XXX. Disinfection of Water Supplies {Continued) 479
XXXI. The Removal of Dissolved Mineral Matter from
Water 499
XXXII. The Removal of Dissolved Mineral Matter from
Water {Continued) 539
XXXIII. The Control of Water Purification Processes . . . 559
Appendix \ 5(37
Appe.ndix B 571
Tables 1 to 13, Inclusive 573
Index 585
WATER PURIFICATION
CHAPTER I
INTRODUCTION
Water purification may be broadly defined as the art of remov-
ing foreign and polluting substances from solution and suspension
in water. The character and amount of these impurities, and
the object for which their removal is undertaken, naturally
leads to the treatment of this subject under the following heads:
1. Rendering impure water potable and hygienically safe for
drinking purposes, and suitable for industrial uses.
2. Removing putrescible organic matter and disease-produc-
ing organisms from the fouled water supply or sewage of a
community.
In the following pages it is intended to treat only of the first
division of this subject, since the second covers too broad a
field to bring it within the scope of this volume.
Both the kind and the amount of impurities in a polluted water
affect the methods which can be employed for its purification,
and this is so peculiarly true of sewage that its treatment has
become an art in itself. Those waters which are to be purified
for drinking purposes demand that a degree of purity shall be
produced which is not possible and usually unnecessary in the
case of sewage. The purification of the latter is, as a rule, quite
incomplete as compared with that required for a safe drinking
water, and obviously the object to be attained is quite different.
In the case of waters to be treated for making them suitable for
steam-boiler purposes, or for general industrial uses, a slightly
different object is sought. The softening of hard waters or the
removal of compounds of iron or manganese may be an integral
part of the purification of a public drinking water supply, in which
case it is combined with those processes utihzed for making a
water hygienically safe. Of course, it is quite possible to carry
on purification for industrial purposes independently of the more
refined methods used for drinking water, and frequently this
course is pursued in connection with manufacturing plants.
1
WATER PURIFICATION
HISTORICAL
Ancient Systems of Water Supply. — Good water for drinking
purposes has doubtless been appreciated by the human race
from time immemorial, for it does not take a very high degree
of intelligence to discriminate between a clear, colorless and
odorless drinking water, and one that does not possess these
outward attractive physical properties. Among primitive
peoples the question of water supply was never of pressing impor-
tance, except in arid and semi-arid regions. In these latter
countries provision for securing and storing a supply of water
was usually necessary. Consequently, springs were sought for,
wells were dug and cisterns constructed in order that a supply
of water might at all times be available.
Wells were common in ancient Egypt, Greece, Assyria, Persia
and India, and from the sanitary point of view they probably
furnished a safer drinking water than could be obtained from the
surface waters in the rivers and lakes. Wells of great antiquity
may be found today in Egypt and India. Joseph's well at Cairo
in Egypt is one of the most famous ancient wells, and was
excavated in solid rock to a depth of 297 ft. The Chinese were
familiar with the driving of artesian wells and pursued methods
similar to those now in vogue in sinking them.
Where turbid surface waters had to be employed for drink-
ing, domestic filters of unglazed earthenware or of sandstone
were known to have been used by the ancient Egyptians and
by the Japanese. Clarification of muddy water by the siphoning
of the liquid from one vessel to another by the capillary action
of porous material, such as a strip of cloth, and the consequent
separation of the water from the suspended matter, was well
known to the ancients.
As population became more dense and people began to congre-
gate in cities, the need for larger volumes of water than could
be suppUed by springs and wells became urgent. Works for
the collection, storage and conveyance of water were built for
supplying many of the ancient cities, and the ruins of some of
these works yet remain.
Within a year or two archeological explorations in India have
shown that 5,000 years ago the peoples of the Sind and Punjab
were hving in well-built cities, and in possession of a relatively
mature civilization, with a high standard of art and craftsman-
INTRODUCTION 3
ship, and a developed system of writing. The excavations
brought to Hght houses and temples, massively built of burnt
brick, and provided with well-constructed water conduits covered
with marble slabs.
The ancient water tanks of Aden in Arabia for the collection
of surface water from the gorges of the volcanic crater, at the
bottom of which the old city was located, afford an example of
early impounding reservoirs of an elementary type. These
tanks may have been built by Persian engineers as early as 600
B.C., or possibly by the Romans; but they without • doubt
antedate the Christian era.
The infiltration galleries for collecting ground water at Athens
in Greece w^ere probably constructed over 2,000 years ago, and
the same m.ethod is still pursued to obtain a pure and satisfactory'-
water supply. The rain-water cisterns of ancient Carthage
(150 B.C.) were divided into several storage compartments, two
of which were apparently used for settling or possibly filtering
the water. Historians state that the city of Laodicea in Asia
Minor obtained its supply from the River Caprus. The latter
had its origin in springs. The water w^as conveyed to the city
through a masonry aqueduct over 4 miles in length. A settling
tank with double compartments formed a part of this water-
works system. In Jerusalem underground cisterns were con-
structed, which were supplied through masonry conduits.
Probably no more elaborate system of public water supply
was provided for any ancient city than that for Rome. Until
312 B.C., the Romans took their supply from the River Tiber
and from springs and wells in the vicinity of the city. The
increasing pollution of the river water, as well as the need for
a greater volume of water, evidently induced the Romans to
seek elsewhere for a supply. In consequence, three groups of
springs in the volcanic plain on the left bank of the Tiber were
made use of, and the water from them conveyed by aqueducts
to the city. A fourth group of springs was also used which were
located in the mountains of limestone formation somewhat more
distant than the three other groups. This latter group furnished
the best quality of water with which the city was supplied.
E. H. D'Avigdor, in his "Water Works of Ancient Rome"'
interestingly describes the character of the Roman water supply
as follows: "The Romans possessed three almost independent
^ Engineering, vol. xxi, p. 403.
4 WATER PURIFICATION
water services, for which they used water of different degrees
of purity. The least clear and most loaded with sand, such as
the Anio aqueduct supplied, was used for public baths and the
watering of streets; the clearer water from Tepula and Alsietina
served for tanks, fountains and washing troughs; while the very
best (Virgo, ]\Iarcia and Claudia) was confined to drinking
purposes, and these springs were undefiled even after the heaviest
rains."
Rome was supplied with water from the above-mentioned
four groups of springs through 19 aqueducts, which were built
between 321 B.C. and 305 A.D. The aggregate length of these
aqueducts was 381 miles.
There can be said to have been no real distribution system
for the water entering Rome through the system of aqueducts.
The aqueduct water flowed through small tanks in which the
hea^'iest sand and gravel were deposited. To a limited extent
the small distributing reservoirs (castella) near the city served
a like purpose. From these reservoirs the water was distributed
to cisterns, public fountains and private residences.
During the ]Middle Ages,^ when disease played such havoc with
the people of Europe, polluted water undoubtedly assisted in
conveying infection. At the time of the fall of the Roman
Empire many of the aqueducts built by the Romans at Rome and
in the provinces were either destroyed or fell into disuse. The
Moors in Spain during the ninth century constructed some
important works, as well as repairing in the twelfth century
some old Roman works.
Until 1183 A.D. Paris obtained its entire supply of water from
the River Seine. As late as 1550, Paris used only 1 qt. of water
per capita per day, and at the end of the seventeenth century
was using but 23^ qt. per capita per day. With such small
amounts of water being used one can easily imagine what sanitary
conditions must have been.
London was first supplied in small quantities with spring water
conducted through lead pipes, and masonry conduits. In 1582
a pump was erected on London Bridge to take water from the
River Thames, and to deliver it through lead pipes to the city.
By the invention of the steam engine, pumping machinery of
adequate capacity and power was made possible. The growth
and development of water-works plants in reality dates from
1 TuRXE.^URE and Russel: "Public Water Supplies." ^
INTRODUCTION 5
the eighteenth century. However, not until the latter half of
the nineteenth century was very rapid progress made. The use
of cast-iron pipe became general in about the year 1800, and
gradually replaced the wooden mains formerly used.
Development of Modem Purification Plants. — The methods
employed in securing and maintaining pure water supplies have
been in a large measure governed by topographical and geological
conditions. In different countries, where like physical condi-
tions prevailed, similar lines of development have not always
been followed. Allen Hazen, in his book on "Filtration of
Public Water Supplies," points out that "it is really marvellous
how each country has met its problems of water supply from its
own resources, and often without much regard to the methods
which had been found most useful elsewhere. England has
secured a whole series of magnificent supplies by impounding
the waters of small streams in reservoirs holding enough water
to last through dry periods, while on Continental Europe such
supplies are hardly known. Germany has spent millions upon
millions in purifying turbid and polluted river waters, while
France and Austria have striven for mountain-spring waters
and have built hundreds of miles of costly aqueducts to secure
them. In the United States an abundant supply of some liquid
has too often been the objective point, and the efforts have been
most successful, the American works being entirely unrivalled
in the volumes of their supplies. I do not wish to imply that
quality has been entirely neglected in our country, for many
cities and towns have seriously and successfully studied their
problems, with the result that there are hundreds of water sup-
plies in the United States which will compare favorably upon
any basis with supplies in any part of the world ; but on the other
hand, it is equally true that there are hundreds of other cities,
including some of the largest in the country, which supply their
citizens w^ith turbid and unhealthy waters which cannot be
regarded as anything else than a national disgrace and a menace
to our prosperity."
The above statement was undoubtedly true at the time it
was written. In the past 30 years, however, there has been a
marked improvement in public water supplies. This condition
has been chiefly brought about by an awakened public interest
in general sanitation, and especially in the better quality of the
drinking water supplied for public consumption. Most of the
6 WATER PURIFICATION
large cities of the United States are now well protected against
water-borne diseases, even though the source of supply is in
many cases badly contaminated. The barriers set up, however,
must be closely guarded, and extreme \agilance on the part of
those entrusted with this duty is the only safeguard for millions
of water consumers.
Those impurities in water which render it turbid, and which
for the most part are in suspension, make it unattractive as a
drinking water. It was probably noted at an early period, that
a muddy water, if allowed to remain quiescent for a short time,
lost more or less of its suspended matter by settlement. In
storing muddy waters for irrigation purposes this phenomenon
could hardly have failed to have been noticed.
The appearance of a muddy water was obviously improved by
settlement, and its suitability as a drinking water enhanced.
If clear spring waters could not be obtained for a public supply,
resorting to surface waters was a necessity. Hence, we find
evidence that in some of the ancient water-works systems pro-
vision was made for settlement of muddy waters in tanks or
settling basins. The "castellee" and piscinse of the Roman
aqueduct system evidently performed the function of settling
tanks, whether originally intended for that purpose or not. In
other ancient systems the evident purpose of tanks for settling
purposes is more pronounced. Some of these works have been
cited in the preceding pages.
These early devices for improving the quaUty of a water supply
were crude and imperfect, and can only be recorded as the
beginnings from which the really modern art of water purification
sprang.
"\Miile sedimentation for the clarification of water may be
looked upon as the earliest step in the art, nevertheless, it can
only be regarded in most cases as preliminary to more complete
methods. The straining action of sand and gravel was doubt-
less also noted by keen observers at an early date, in the same
way that the clarification effected by settling tanks had been
observed. The application of this principle to the pubhc water
supply of London was made in 1829. Filters of sand and gravel
were also constructed for many of the Continental cities, more
especially in Germany, where the principles underlying the action
of filters of this type were carefully studied.
INTRODUCTION 7
Allen Hazen has divided the history of water purification in
the United States into three epochs, the first beginning with
James P. Kirkwood's report on the "Filtration of River Waters,"
in 1866, resulting from his study of European practice; the
second epoch commencing with the work of the Massachusetts
State Board of Health at its Lawrence Experiment Station, in
1887; and the third with the experiments on very turbid waters
beginning at Louisville, Ky., in 1896, and continued at Pitts-
burgh and Cincinnati during the 3 or 4 years following. To
these three epochs the author would add a fourth, which was
introduced in 1908 by the experiments at Chicago and at Boon-
ton, N. J., on the disinfection of water with hypochlorite of hme.
Chlorine and its compounds, as well as ozone and ultra-violet
light, have been carefully investigated as disinfecting agents both
in this country and in Europe. The widespread employment of
chlorine has amply demonstrated its usefulness as a practical,
efficient and economical agent in water purification. This phase
of water purification is well estabhshed, and marks an important
stage in the practical development of the art.
References
1. L. F. Vernon-Harcout: "Sanitary Engineering," 1907.
2. Bolton: "Ancient Methods of Filtration." Pop. Sci. Mo., vol. 16,
p. 495.
3. Arthur S. Riggs: "Ancient Water Tanks of Aden, Arabia." Eng.
News, vol. 52, p. 25, 1904.
4. "Ancient Water Supply of Athens." Eiigineer, vol. 101, p. 215, 1906.
5. Croes: "The Water Works of Carthage." Eng. Record, vol. 25, p. 8,
1892.
6. Edward Wegmann: "The Water Works of Laodicea, Asia Minor."
Eng. Record, vol. 40, p. 354.
7. Edward Wegmann: "Ancient and Modern Water Works." Eng.
Record, vol. 65, June, 1912.
8. E. H. D'Avigdor: "Water Works of Ancient Rome." Engineering,
vol. 21, p. 403, 1876.
9. Geo. Higgins: "The Old Water Supply of Seville." Proc. Inst. C. E.,
vol. 38, 334.
10. TuRNEAURE and Russel: "Public Water Supplies."
11. Allen Hazen: "Filtration of Public Water Supplies."
12. W. P. Mason: "Water Supply."
13. Engineering News-Record, p. 1028, Dec. 25, 1924.
CHAPTER II
CLASSIFICATION OF NATURAL WATERS
In order to understand intelligently the methods employed in
water-purification processes, it is necessary to have a knowledge
of the composition of the various classes of natural waters which
require treatment. Although all the water which is now flowing
on the surface of the ground, as well as that which is found in
the ground, has a common origin, nevertheless, this water has
acquired varied characteristics, which have been derived from
the substances with which it has come in contact.
RainfalL — From the water surfaces of the earth the sun is
constantly evaporating enormous volumes of water, which are
again condensed and precipitated upon the land and water
surfaces as rain, snow or ice. That which falls upon the land
surfaces of the earth is disposed of in different ways. Some of
the water is evaporated again; some is absorbed by growing
vegetation; some flows directly over the ground into the rivers
and lakes; and some sinks into the soil to become the subter-
ranean water of the earth. The amount of water precipitated
on the surface of the earth in any particular region depends upon
a number of factors. Warm air which is saturated with water
in the form of vapor will only precipitate this moisture when
sufficiently cooled. Air currents may be cooled by coming into
contact with the cold surfaces of the earth, or by being forced
upward by mountain ranges into colder air currents, or by
mingling directlj^ with colder air currents at lower levels. Pre-
cipitation of water will take place under these conditions.
The water thus precipitated is as near pure water as may be
found under natural conditions. It probably will contain minute
quantities of nitrogen compounds, such as ammonium salts, and
some organic matter consisting of plant spores and bacteria.
It will also contain in solution small quantities of the gases,
oxygen and carbon dioxide.
As the descending rain or snow approaches the earth, it washes
out of the atmosphere suspended particles of dust and thus puri-
fies the air. These impurities will, of course, be found in the
8
CLASSIFICATION OF NATURAL WATERS 9
rain water if collected before reaching the ground. Rain water
caught in or near our large cities is much more impure than that
collected in the open country. The impurities swept from the
air are relatively in small amounts as compared with those
acquired b}- the water after reaching the earth; but they are the
first of the dissolved and suspended constituents to be taken
up by the water, and are soon increased in amount and kind after
the water reaches the ground.
SURFACE WATERS
Flowing Surface Waters. — The character of the land surfaces
upon which rain or snow is precipitated naturally influences the
proportion of the volume of water which finds its way over the
top of the ground into the streams and lakes, and that which
sinks into the ground to become a part of the underground water
of the earth. If the land is mountainous, the rain rapidly runs
off the steep slopes into the valleys, and quickly enters the
rivers. If the soil is easily washed aw'ay, the water will carry
with it large volumes of sediment, the composition of which will
depend upon the geological characteristics of the denuded sur-
faces. On the other hand, if the precipitation occurs in a flat
level country, a much larger proportion of the water will per-
colate into the soil. If vegetation is abundant, some of this
water will be retained by the growing plants, and ui&y sensibly
retard the discharge of surface water into the natural water
courses. In water which has been subjected to such conditions
there will be found those dissolved salts with which the water
has come in contact, as well as organic matter derived from
vegetation.
Flowing surface waters may be characterized, therefore, as
those which contain relatively small amounts of dissolved mineral
compounds, more or less of suspended matter, depending upon
topographical and geological conditions, and variable amounts
of organic matter, likewise modified by the flora of the region.
Impounded Surface Waters. — Natural lakes and ponds are
composed of water which has found its way directly through
surface streams into the depressions in w^hich these bodies of
water lay, and of the water which has percolated for some distance
through the ground and reappears as a surface water at lower
surface levels. In a like manner the low-water flow of streams
10 WATER PURIFICATION
is very largely maintained by the ground-water flow from higher
levels.
In consequence, these lake waters are virtually mixtures of
surface and ground waters, and their composition is, in a large
measure, intermediate between them. Obviously local topog-
raphy and the very important factor of sedimentation will
materially affect their composition. They also have an im-
portant influence in rendering streams flowing from them more
uniform in their discharge on account of the storage for water
which they afford.
UNDERGROUND WATERS
The water which sinks into the ground does not all imme-
diately pass through the subsoil to underground channels. Some
is held by the surface soil, and in hot countries may soon be
evaporated into the au'; some of the water is absorbed by the
growing plants; and the remainder sinks slowly or quickly through
the ground depending upon the porosity of the latter.
The movement of this ground water is governed exclusively
by the character of the strata with which it comes in contact.
Impervious formations will block or divert the flow, while per-
meable strata will soon become filled and form the channel along
which the underground stream moves. The velocity of flow is,
of course, low, and depends upon the porosity of the soil in which
the water is moving.
All of these factors have a bearing upon the dissolved constitu-
ents which will be found in an underground water. The sus-
pended matter of the surface water will have been filtered out,
whether in a relativeh' coarse form like sand and silt, or in a
finer or colloidal condition like finely divided clay. On the other
hand, the solution of mineral compounds containing sodium,
potassium, calcium, magnesium, ii'on, aluminum, silica, etc.,
will have begun, and will continue as long as the water does not
become supersaturated, and until "a chemical system of balanced
values"^ is attained for the various salts with which the water is
in contact.
CONTAMINATION OF WATER
Natural Impurities. — For convenience the impurities in water
may be divided into classes according to the sources from which
^ Chase Palmer: "The Geochemical Interpretation of Water Analyses."
U. S. Geological Survey Bull. 479.
CLASSIFICATION OF NATURAL WATERS U
they are derived. As has been previously noted water in the
course of its flow over the surface or through the ground dis-
solves more or less material as well as carrying varying amounts
in suspension. Provided no contact with the wastes of human
life or activity has occurred, the acquired impurities might be
designated as natural impurities, in distinction from those
derived from sewage or manufacturing wastes. Water polluted
from the latter sources is unfit for human consumption without
purification as will be shown in a later chapter. Water which
has not been subjected to such contamination may or may not
be fit for drinking, depending entirely on the nature of the
dissolved and suspended impurities which it may contain.
Dissolved Impurities. — The solvent action of water upon the
seemingly insoluble constituents of the earth's crust is enormous,
aside from its erosive action. The surface and subsoil, as well
as the deeper rock strata, are all subjected to the decomposing
action of the water with which they come in contact. Erosion
assists the solution of the mineral compounds composing the
various strata by reducing them to a finely divided state.
Disintegration of minerals Kke orthoclase, for example, is
able to supply the bases sodium and potassium; dolomitic lime-
stones may furnish calcium and magnesium; and clay ironstone
and pyrite may give up iron, aluminum and silica. The acids
with which the above bases are usually associated are carbonic,
hydrochloric and sulphuric acids. These latter are derived from
the disintegration of the minerals in the rock strata the same as
are the bases. J\Iore or less carbonic acid is obtained directly
from the air and from the oxidation of carbonaceous compounds
in the breaking down of organic matter. Minute quantities of
nitric acid may be derived directly from the air, and from oxida-
tion of nitrogenous compounds. The oxidation of sulphur in
minerals supplies sulphuric acid in many cases. Sulphates,
chlorides, nitrates, carbonates and silicates exist as such in the
earth's crust in enormous amounts, and whenever they come in
contact with water are dissolved directly, and in amounts
depending upon the supply available and the solubility of the
salt being acted upon.
A classification of natural waters with respect to their dissolved
constituents, which is based upon the chemical nature and the
proportional amounts of the radicles present in solution, has
been suggested by Chase Palmer in a paper entitled "The Geo-
12 WATER PURIFICATION
chemical Interpretation of Water Analyses."' He states that:
"Nearly all terrestrial waters have two general properties, salinity and
alkalinity, on whose relative proportions their fundamental characters
depend. Salinity is caused by salts that are not hydrolyzed; alkalinity
is attributed to free alkaline bases produced by the hydrolytic action
of water on solutions of bicarbonates and on solutions of salts of other
weak acids."
According to his classification waters may possess five special
properties as follows:
1. Primary salinity; that is sahnity caused by the sulphates
and chlorides of the alkalies sodium and potassium.
2. Secondary salinity; that is sahnity produced by the sul-
phates and chlorides of the alkahne earths calcium and mag-
nesium, or in other words permanent hardness.
3. Tertiary sahnity; that is in reahty an " acidity " arising from
an excess of saline compounds over and above that due to primary
and secondary salinity.
4. Primary alkalinity; that is an alkalinity produced by car-
bonates and bicarbonates of sodium and potassium, or in other
words permanent alkalinity.
5. Secondary alkalinity; that is the property caused by alkaline
earth bicarbonates such as those of calcium and magnesium, or
in other words temporary hardness.
By various combinations of these properties five well-defined
classes of waters are possible and are found in nature.
Class 1. "Waters characterized by properties 1, 4 and 5 as
stated above.
Class 2. Those showing properties numbered 1 and 5.
Class 3. Those exhibiting properties numbered 1, 2 and 5.
Class 4. Those marked by properties numbered 1 and 2.
Class 5. Those possessing properties numbered 1, 2 and 3.
"Surface waters appear to belong chiefly to the first three
classes, class 4 is represented by sea water and brines, class 5
is exemphfied by mine (acid) waters and waters of volcanic
origin."
The less there are of dissolved impurities in a water, the better
it is fitted for a pubhc supply. Consequently, water supplies
are commonly rated as "soft," "hard," or "alkaline," although
these classes may merge into one another, depending upon the
lU. S. Geological Survey Bull. 479, 1911,
CLASSIFICATION OF NATURAL WATERS 13
earth strata with which they have come in contact. The "soft "
waters are ahnost always surface waters, containing Httle mineral
matter. This dissolved mineral matter is about equally divided
between sihca, alkahne earth salts, and alkali salts, although the
sihca is frequently greater than the other two classes of com-
pounds. The acid combining with the bases is largely carbonic
acid, and there are usually about equal amounts of sulphates
and chlorides present.
The "hard" waters derive most of their mineral matter from
limestone. Sihca and the alkalies are usually present in small
quantities, and may be in no larger amounts than are found in
"soft" waters. Sulphates and chlorides are generally present
in small amounts, except where the water has come in contact
with gypsum deposits or with mine drainage.
The "alkali" waters are quite variable in composition and few
are fitted to be used as public suppHes. They generally contain
large quantities of sodium sulphate and chloride; some may
contain large amounts of calcium and magnesium, and others
practically none. Some of these waters contain little dissolved
mineral matter other than sodium bicarbonate.
The average hardness of water used for public suppHes in over
300 cities of the United States is graphically shown on the
accompanying map. It clearly indicates the widely varying
character, as regards hardness, of the public water supplies in
the various states. Waters from 0 to 55 parts per million of
hardness are regarded as quite "soft," while those ranging from
56 to 100 parts per million are noticeably harder, yet are not
considered as being objectionable. However, waters ranging
from 101 to 201 parts per million of hardness become less and
less acceptable as they approach the upper limit of this class; and
the waters in the 201 to 500 parts per million class are decidedly
objectionable as pubhc supplies without treatment. Some of
them are too impregnated with mineral matter to attempt to
purify them by artificial means.
Suspended Impurities. — Intermediate between a solution, as
it is commonly understood, and a suspension of finely divided
particles, hke sand for example, there may be so-called colloidal
suspensions of certain substances in water which possess peculiar
properties, and which are of considerable importance in connec-
tion with water-purification problems. For example, silica is
found in this state in many natural waters, especially those
14
WA TER P I 'RIFICA TION
CLASSIFICATION OF NATURAL WATERS 15
showing primary alkalinity, i.e., waters containing sodium and
potassium carbonates. The silica compounds characteristic
of the clays show a marked tendency toward the colloidal state,
and render the problem of the purification of turbid waters of
this class almost a problem in itself.
The enormous amount of the heavier sediment carried by
many rivers consists largely of sand and clay. Any reduction
in the velocity of flow of the water laden with such sediment
causes it to be deposited on the bed of the stream. Gravel and
sand bars are thus formed in river beds, which may be shifted
from one point to another by any sudden increase in the velocity
of the current, such as might be produced by a flood. Lighter
material like clay is more slow^ly deposited and more quickly
moved again by any change in the rate of flow of the water. It
thus happens that almost all surface waters carry var3dng
amounts of suspended material in them which depend upon the
velocity of the currents of water and on the character of the
bottom and shores. The action of the wind on large bodies of
water like the Great Lakes, for example, may stir up the sediment
on the bottom and render the water, near the shore especially,
quite turbid.
Compounds of iron and of manganese are not infrequently met
with in the colloidal state in natural waters, and offer some of the
most interesting phases of water-purification work. Organic
matter found in natural waters is probably always present in this
form to a greater or less degree. Vegetable stain produced by
humic substances is a marked characteristic of a very large class
of natural surface waters, and as such has received considerable
attention in the study of purification problems.
How the removal of these impurities, whether in solution or in
suspension, is effected will be discussed under the description
of the various methods of purification now employed, rather than
in this place. It is only desired to emphasize the varied classes
of impurities which may be found in natural waters, and which
are virtually "natural impurities," as distinguished from those
derived from sewage and manufacturing wastes. This waste
material may furnish similar classes of polluting compounds to
those derived naturally, but their origin usually justifies their
consideration separately.
Whether the dissolved salts usually found in natural waters
are objectionable depends upon the use to which the water is
16 WATER PURIFICATION
to be put. A certain amount of the chlorides, sulphates and
carbonates of sodium, potassium, calcium and magnesium are
by no means deleterious, and may possibly be beneficial in a
drinking water. On the other hand, if too great amounts are
present these dissolved salts render the water unfit for domestic
and industrial uses, and actually cause financial losses of no small
amount to those obliged to use them. Compounds of iron or of
manganese are especially objectionable, and not infrequently
have caused waters containing them to be abandoned as sources
of supply. Excessive amounts of the fixed alkalies either as
salts of the strong acids like hydrochloric and sulphuric, or of
the weak acids like carbonic, make a water unsuitable as a public
supply.
Microscopic Plant and Animal Life. — In many of our natural
waters a luxuriant growth of algae and diatoms is found at certain
seasons of the year. The character of the mineral and organic
constituents of the water, as well as the conditions of light and
temperature materially affect the extent of these growths. They
occur in both still and running water. Accompanying the growth
and also the decay of certain of these organisms bad odors and
tastes are not infrequently developed, and where this occurs
in public water supphes, they become a nuisance entirely out of
proportion to their number and size. Certain microscopic
animal forms may also produce troubles of this same character.
The odor of growth appears to be due to secretions of an oil-
like character which they produce, and is usually somewhat
characteristic of the special organism producing it. When the
organisms are in large enough numbers they are capable of giving
an odor to large volumes of water, and not infrequently spoil
the taste and odor of the whole of a public water supply. Odors
of decomposition are usually very offensive, and notably so in
the case of the "blue green alga?" or Cyanophycea.
It is not probable that impurities of this nature in natural
waters produce disease in human beings, when swallowed in
drinking water. They are very objectionable if they produce
a marked odor, and in such cases are most frequently complained
of in pubUc water supplies.
Bacteria.— Even lower in the scale of plant life than the
diatoms and the algae are found the bacteria. They are present
in all natural waters, being the more numerous in surface waters,
and much less so in ground waters. By far the larger number of
CLASSIFICATION OF NATURAL WATERS 17
the various species of bacteria play a beneficient role in the
economy of nature, and appear absolutely essential to many of
the normal processes of development of both plants and animals.
A few species, however, are associated with disease in animals
and in human beings. So far as the contamination of water is
concerned, it is only the organisms capable of producing patho-
logic conditions in man that are of interest. These virulent
forms usually reach our natural waters through the medium of
domestic sewage and manufacturing wastes. This class of
impurities is considered in more detail in the next section.
IMPURITIES DERIVED FROM WASTE MATERIAL
Sewage, — The water carriage of waste material of human and
animal origin has become, in those countries which pay any atten-
tion to problems of sanitation, the most common method for
its transfer to some point of ultimate disposal. Wherever
public water supplies are installed, a system of sewers will of
necessity follow. Hence the disposal of large volumes of fouled
water has become a problem of great difficulty, and one that yet
awaits a completely satisfactory solution.
It is obvious that some method, even though it is not entirely
satisfactory, must be used to get rid of this polluted water or
sewage, and the easiest way has been to turn it into the natural
water courses. In this manner much of the surface water on
thickly settled land areas has become polluted with material
dangerous to the health of human beings, who unwittingly or of
necessity drink the water thus contaminated. Since disease has
been found to originate so largely from specific plant and animal
forms, microscopic in size, which, having produced the disease,
are discharged from the body chiefly in the excreta and the urine,
the conveyance of disease through sewage to water has been
pretty definitely proven.
Ground waters as well as surface waters may become polluted
by sewage. The discharge of sewage on the surface of the ground
or into cesspools, or the leakage or overflow of vaults, may furnish
the dangerous pollution to well and spring waters by direct
percolation through fissures in the rock strata, or by more
indirect routes through the soil itself.
Manufacturing Wastes. — In many industries there remains
after the mamifactured product has been completed, a great
deal of waste material, which for economic reasons it is not worth
18 WATER PURIFICATION
while to work over. Much of this material is in suspension and
solution in relatively large volumes of water. Its disposal by
the easiest method is to dump it into the nearest body of water.
Water fouled with such material is totally unfit for human con-
sumption. Frequently the material renders even the best
methods for the purification of domestic sewage inadequate, and
its proper disposal becomes a special problem in almost every
case.
The waste liquids from textile works, dye works, straw-board
factories, paper mills, abattoirs, meat packing establishments,
dairies, etc., furnish material which is obviously difficult to
dispose of, and which must pollute in the foulest manner any
natural water into which they may be turned.
NATURAL METHODS OF PURIFICATION
Sedimentation. — Some of the impurities which a natural water
acquires in the course of its flow may be lost under certain favor-
able conditions. For example, a water laden with suspended clay
or fine sand will deposit this material as soon as the velocity of
the water is sufficiently retarded as was previously explained.
This process of sedimentation is one of the most important of
the natural methods of purification, and plays an important part
in our artificial methods as well. In flowing streams the deposi-
tion of sediment is intermittent, being active during low stages
of the stream when the rate of flow is relatively low, and much
diminished or practically nil in flood periods. At such times the
scouring action of the current causes much that has been
deposited to be again placed in suspension, and thus carried
further toward its ultimate disposal in the sea. In this way the
immense deltas at the mouths of rivers like the Mississippi and
the Nile are formed.
Effect of Sunlight. — The purifying action of sunlight on certain
vegetable compounds in colloidal suspension, such as the brown
coloring matter in many of the streams and lakes in the north
central and northeastern parts of the United States, is worth
mentioning in this connection. A certain amount of bleaching
out of this coloring matter is apparently effected when this class
of waters are impounded in natural lakes or artificial reservoirs.
Oxidation of the carbonaceous matter probably occurs, and
sedimentation in the quiet water undoubtedly assists in the
clarification.
CLASSIFICATION OF NATURAL WATERS 19
Precipitation of Compounds from Solution. — Dissolved salts
are not usually readily removed once they have gone into solu-
tion. The chlorides, sulphates and nitrates of either sodium,
potassium, ammonium, calcium or magnesium will be retained
on account of their great solubility. Carbonates and bicar-
bonates of the fixed alkalies, as well as of ammonia, are also
very soluble. On the other hand, the bicarbonates of the
alkahne earths have a rather limited solubihty and may be
deposited from solution if the excess of carbon dioxide, which is
necessary for their retention in solution, is in any way removed.
Ground waters in particular may become heavily charged wdth
bicarbonates and, on being brought to the surface where the
pressure is diminished, wall lose some of their free carbon dioxide
and deposit their monocarbonates, which are much less soluble.
This is particularly true of calcium carbonate. Magnesium
carbonate, however, is considerably more soluble.
Oxidizable salts hke ferrous sulphate, ferrous carbonate, and
corresponding salts of manganese occurring in ground waters
may be deposited from solution on exposure to the air. Such
purification can be hastened by aeration and thus render some
unsuitable deep well waters entirely acceptable as a source of
water supply.
"Acid mine waters" are usually contaminated with dissolved
iron compounds, which not infrequently find their way into sur-
face streams. As much of this iron may be in an unoxidized
state, the exposure to the oxygen of the air, and to that dissolved
in the surface water, soon converts the iron to the form of the
insoluble ferric oxide. Organic matter in colloidal suspension
may retard the precipitation of the iron, and cause the latter to
assume a colloidal state itself.
In waters in which the alkahnity is due to sodium and potas-
sium carbonates, colloidal solutions of silica and alumina are
sometimes found, and on account of their slight solubihty may
be deposited, should this "primary alkalinity" be diminished.
Such a diminution can be effected if waters of this class come
into contact with chlorides and sulphates of hme and magnesia.
These latter salts will react with the fixed alkaline carbonates,
forming carbonates of lime and magnesia and the chlorides and
sulphates of sodium and potassium. The latter salts are without
power to assist in holding the sihca in solution.
20 WATER PURIFICATION
Filtration. — The natural filtration of water through the soil
effects a high degree of purification provided the ground is of the
right character. Sand and gravel, when not too coarse, afford
an excellent purifying medium. Suspended impurities, organic
matter and oxidizable salts are removed as a result of the strain-
ing action, and the chemical and biological changes induced
during filtration. The action of both sedimentation and filtra-
tion in purifjang natural waters is perfectly normal, and one
which is constantly going on. To these agencies we owe the
potability of most of our ground waters, and by a study of the
principles underlying these natural processes we have been able
to design and operate our modern water-purification plants.
PURIFICATION BY MEANS OF MINUTE PLANT AND ANIMAL
ORGANISMS
Thus far in considering natural methods of purification only
those agencies have been especially noted which are effective
without the intervention of organized plant and animal life.
In the cycle through which inert mineral matter passes into
organized matter, and then back again into inorganic compounds,
life in some of its most marvellous forms plays an important and
essential part. These forms belong both to the animal and
vegetable kingdom, and for the most part are microscopic in
size. The borderland between plant and animal, in these almost
invisible organisms, is extremely ill defined; but no matter
how classified their importance in the economy of nature is
fundamental.
All living organisms which float about in water between the
surface and the bottom are designated by biologists as "plank-
ton." They are moved about by the currents and the wind
chiefly, although they have shght powers of locomotion. They
also possess the peculiar ability to remain suspended in the water
with little effort on their part. The plankton can be divided
into two general classes:
"the food producers or plants, which assimilate inorganic matter and
build up organic compounds by means of their chromophyll coloring
matter; and the food consumers or animals, such as the microscopic
protozoa, rotifera, etc., together with the larger ones up to the fishes."
CLASSIFICATION OF NATURAL WATERS 21
In the lecture from which the above quotation was cited, Dr.
Marsson^ concisely epitomizes the relations of these two groups
by stating that the
"vegetable component of the plankton is the fundamental food supply
or condition of existence for all aquatic life. It comes from the prod-
ucts of the decomposition of the albumen which finds its way into the
water from decaying animals and plants, as well as from sewage. The
self-purifjdng power of natural waters is merely the maintenance
of the proper equilibrium between retrogressive and progressive
metamorphosis."
The groups of microscopic plant forms known as the algse,
diatoms, fungi and bacteria exist in enormous numbers in all
natural surface waters, and to some extent in ground waters.
The algse and diatoms through their pecuhar cellular structure
are hving laboratories in which light is the energy which tears
the carbon from carbonic acid, and the nitrogen from its simpler
compounds and convert them into starch, sugar and albumen.
Thus oxygen is liberated and becomes available for oxidizing
organic matter and preventing putrefactive changes.
The fungi and bacteria find their nutriment in dead organic
matter, and are the primary agents for its decomposition into
simpler compounds. Bacterial activity is associated with the
using up of large amounts of oxygen, where the latter is available;
and in such cases non-putrefactive disposal of contaminating
impurities in water is in process in distinction to putrefactive
changes where the oxygen is not present.
The bacteria are the natural food for many of the microscopic
animal organisms. The latter include the protozoa, infusoria
and metazoa, and where these organisms are found in abundance,
bacteria and food for bacteria will also be present. They thus
become indexes of pollution in water, quite as indicative as the
bacteria themselves. When the food supply is gone they must
die also.
Since the smaller plant and animal organisms are the source
of food for the fishes, and they in turn for human beings, the
cycle of matter from man through human wastes to mineralized
1 Max Marsson: "The Significance of Flora and Fauna in Maintaining
the Purity of Natural Waters, and How They are Affected by Domestic
Sewage and Industrial Wastes." Eng. News, Aug. 31, 1911. Trans, by
Emil Kuichlixg.
22 WATER PURIFICATION
compounds and back again to man is complete. The natural
methods of self-purification of water are going on ceaselessly and
effectively, but the agencies ordained for this purpose must have
time and opportunity to do their work.
References
1. United States Geological Survey:
(a) Water Supply Papers:
"Conservation of Water Resources." No. 234, 1909.
Herman Stabler: "Some Stream Waters of the Western United
States." No. 274, 1911.
R. B. Dole: "The Quality of Surface Waters in the United States."
No. 236.
Herman Stabler and Gilbert H. Pratt: "The Purification of Some
Textile and Other Factory Wastes." No. 235, 1909.
(b) Water Supply and Irrigation Papers:
D. D. Jacksox: "The Normal Distribution of Chlorine in the Natural
Waters of New York and New England." No. 144, 1905.
Herman St.\bler: "Prevention of Stream Pollution by Distiller}-
Refuse." No. 179, 1906.
Herman St.\bler: "Stream Pollution by Acid Iron Wastes." No.
186, 1906.
(c) Bulletins:
Chase Palmer: "The Geochemical Interpretation of Water Analysis."
Bull. 479, 1911.
2. United States Department of Agriculture:
Office of Public Roads:
A. S. Cushman: "A Study of Rock Decomposition under the Action
of Water." Cir. 38.
Bulletins:
A. S. Cushman: "The Effect of Waters on Rock Powders." Bull.
92, 1905.
Bureau of Chemistry:
J. K. Haywood and B. H. Smith: "Mineral Waters of the United
States." Bull. 91, 1907.
3. Mass. State Board of Health Report for 1892:
T. M. Drown: "On the Mineral Constituents of Some Natural Waters
in Massachusetts."
4. Engineering News:
Dr. M.\x Marsson: "The Significance of Flora and Fauna in Main-
taining the Purity of Natural Waters, and How Thej' Are Affected by
Domestic Sewage and Industrial Wastes." Aug. 31, 1911. Trans, by
Emil Kuichling. J. D. Watson: "Pollution of the River Taine."
Feb. 8, 1912.
5. Journal New England Water Works Association:
G. C. Whipple and D. D. Jackson: " Asterionella: Its Biology, Its
Chemistry and Its Effect on Water Supplies." Vol. 14, No. 1.
CLASSIFICATION OF NATURAL WATERS 23
F. S. HoLLis and H. N. Parker: " Chlamydomonas in Spot Pond
(Mass.)." Vol. 14, No. 1.
R. S. Weston : ' ' The Occurrence of Cristatella in the StorageReservoirs
at Henderson, N. C." Vol. 13, No. 1.
T. M. Drown: "Odor and Color of Surface Waters." Vol. 2, No. 3,
1888.
G. Transactions American Microscopical Society:
D. D. Jackson: "A New Species of Crenthroix (C. Manganifera)."
Vol. 23, May, 1902.
G. C. Whipple and H. N. Parker: "On the Amount of Dissolved
Oxygen and Carbonic Acid Dissolved in Natural Waters, and the
Effect of These Gases upon the Occurrence of Microscopic Organ-
isms." Vol. 24, May, 1902.
H. N. Parker: "Notes on the Growth of Synura in Lake Cochituate,
Mass." Vol. 30, No. 2, April, 1911.
7. American Naturalist:
D. D. Jackson: "Movements of Diatoms and Other Microscopic
Plants." Vol. 23, No. 461, 1905.
8. Technology Quarterly:
D. D. Jackson and J. W. Ellms: "Odors and Tastes of Surface Waters
with Especial Reference to Anabaena." Vol. 10, No. 4, December,
1897.
9. Geo. C. Whipple: "Microscopy of Drinking Water."
10. Surveyor:
"Algae and Water Supplies." Aug. 25, 1911.
J.\mesScott: "TheChara: A Water-purifying Plant." Aug. 25, 1911.
11. Proceedings Engineers' Society of Western Pennsylvania:
T. P. Roberts: "Acids in the Monongahela River." November, 1911.
12. E7ig. Cont.:
Thorndyke Saville: "The Nature of Color in Water." January
10, 1917.
13. W. D. Collins: Water Supply Paper No. 496, U. S. Geological Survey,
1923.
14. "A Study of the Pollution and Natural Purification of the Ohio River."
Public Health Bull. 143, U. S. PubUc Health Service.
CHAPTER III
TRANSMISSION OF DISEASE THROUGH DRINKING
WATER
The discharge of sewage and waste material of all kinds into
the streams and lakes obviously affords ample opportunit}' for
disease-producing organisms to enter the sources of most of our
public water supplies. Those diseases peculiar to the intestinal
tract of the human body are the ones most likely to be dis-
seminated in consequence of this common practice; and hence,
typhoid fever, cholera, dysentery and gastro-intestinal disturb-
ances have come to be regarded as derived in a large measure
from polluted drinking water, wherever these diseases are endemic
or even epidemic. Anyone or all of these diseases may be trans-
mitted in other ways, but where the}' are widespread, some com-
mon carrier of infection is generally found to be the source, and
a common drinking-water supply usually offers the most favorable
opportunity, for transmitting the disease.
Probably most of the diseases transmitted by water are of
bacterial origin. The "spirillum cholera " of Asiatic cholera,
the ''bacillus typhosus" of typhoid fever, and the "bacillus
dysenteria3" of dysentery have all been found in contaminated
drinking water. Pathogenic protozoa ma}' also produce certain
diseases, and in the case of one form of dysentery, an amoeba
is known to be the cause. If the theory advanced by Sedgwick
and IVIacNutt, that inflammatory diseases of the respiratory
organs may be also to some extent water-borne, is accepted, then
polluted water supplies are chargeable with another group of
diseases particularly prevalent among all classes of people.
The virility of disease-producing organisms upon their entrance
to a water is of importance with respect to the real danger which
they possess. This ability to live and retain their vitality in a
medium foreign to their natural habitat is also of consequence,
for if the power to reproduce the disease is soon diminished and
eventually destroyed, then the length of time before their vitality
is lost is of the utmost importance. Much experimental work
has been done to determine the period elapsing before certain
pathogenic organisms die, when placed in water under varying
24
TRANSMISSION OF DISEASES 25
conditions. Laboratory experiments throw some light on this
problem, but are not usually conclusive, because of the artificial
conditions imposed. In almost all the experimental work the
number of organisms diminish in time, and usually very rapidly.
This may be the result of a decreasing food supply, or to toxic
compounds eliminated in the course of growth or decay, which
kill off rapidly the less resistant organisms.
The presence of pathogenic forms in a drinking-water supply
denotes, of course, all the possibilities of dangerous infection.
Nevertheless, sanitarians have of late regarded the number of
such organisms, and the length of time which they may have
been in the supply, as factors of much importance in the epi-
demiology of disease. This quantitative feature is of consider-
able significance in connection with the qualit}^ of a water
obtained by the methods commonly employed in the purification
of polluted waters.
Spiiillum Cholerae and Bacillus Typhosus.^ — The cholera
spirillum and the typhoid bacillus are the pathogenic organisms
which have been most studied in water-borne diseases. It is
very doubtful whether either of these organisms will multiply
outside the bod}', or in impure water. The cholera spirillum
is not very resistant to adverse conditions outside the human
bodJ^ It is killed in 10 min. by a temperature of 60°C., easily
destroyed by chemical disinfectants, and does not long retain
its vitality in association with the ordinary saprophj-lic bacteria
in the water.
The typhoid bacillus is probably more resistant than the
cholera organism to outside influences. Laboratory experiments
have demonstrated that the typhoid bacillus will live in sterile
water in glass vessels for 3 months, and in unsterilized ground and
surface waters for several weeks. Jordan' showed by his experi-
ments with typhoid cultures placed in sacks of collodion and
parchment and suspended in flowing water, that they would
retain their vitality under natural conditions for at least 4 or
5 day's. Geo. A. Johnson's experiments at Columbus Ohio,-
in which he modified Jordan's technique, showed that the
ability of the bacteria to pass through the walls of the parch-
ment sacks, might indicate that conclusions drawn from the
disappearance of the bacteria in Jordan's experiments, were
^Jordan, Russel and Zeit: Jour. Infect. Diseases, 1, p. 641, 1904.
-Eng. Record, vol. 52. Sept. 23, 1905.
26 WATER PURIFICATION
somewhat misleading. If the organisms actually escaped from
the sacks, failure of samples withdrawn from the latter to
develop typical cultures, did not necessarily mean that the
typhoid bacilli had died. Jordan concludes/ that:
"It is possible that water may continue to be the vehicle of infection
during a much longer period (than 4 or 5 days), but the available data
point to a comparatively short duration of life of the specific germ in
the water of flowing streams."
Houston- has shown that samples of Thames River water
inoculated with a typhoid emulsion and stored at temperatures
ranging from 32°F. to 98.6°F., developed negative tests for
typhoid in 9 weeks at the low temperature, and in 2 weeks at
the highest temperature. Intermediate temperatures gave nega-
tive results in conformity with the results stated above, viz.,
the higher the temperature of the water, the shorter the period
of life of the organism. The history of typhoid epidemics tends
to confirm in a measure the data obtained in these experiments.
It emphasizes the protective value of ample periods of sedimenta-
tion and storage of polluted waters used as public supplies.
Isolation of Cholera and Typhoid Organisms from Water. —
The actual isolation of these two organisms from polluted water
has been accomplished only in a comparatively few well-authenti-
cated cases. In the case of cholera the organism is discharged
from the intestines in enormous numbers, but not in the urine.
Its appearance in sewage and polluted water would, therefore,
be expected, and has been demonstrated. In 1892 Dunbar
isolated the spirillum of cholera from the polluted water of the
Elbe, during the epidemic in Hamburg. Koch^ also reports its
isolation from the water of two Altona reservoirs supplied also
from the Elbe.
The isolation of the typhoid bacillus from natural waters also
offers a great deal of difficulty, although it probably is more
virile and capable of living longer in natural water than the
cholera organism. The bacilli of typhoid fever are discharged
from the human body both in the urine and the feces. From
9 to 14 days after infection has taken place are required before
the disease fully develops. This characteristic feature of typhoid
fever makes the tracing of infection through natural waters much
^ E. O. Jordan: "General Bacteriology."
2 Eng. Record, vol. 65, June 1, 1912, p. G08.
^ Zeit. fur hygiene und Inject. Krank., 14.
TRANSMISSION OF DISEASES 27
more difficult, for although the bacilli may have been present
and caused the disease, they will have probably disappeared
before suspicion is thoroughly aroused as to their possible presence
in the water. Comparatively few cases have been recorded,
therefore, in which the bacillus has been isolated and shown to
have been the probable cause of a case of typhoid fever.
Other Water-borne Diseases. — Intestinal diseases and some
gastric troubles may be and probably frequently are caused by
organisms found in water. Among infants this perhaps is truer
than with adults. Epidemics of diarrhea and dysentery are not
uncommon and have been traced to impure drinking water.
The possible infection of a water supply by anthrax (B. anthracis)
derived from animals sick with the disease produced by this
organism is rather remote, but not impossible. It is of more
theoretical interest than practical that the pathogenic organisms
B. anthracis and B. tetani^ have both been isolated from river
water by Zeit and Fiitterer; but it goes to show the possibihties
of water-borne infection. Sewage-polluted waters may contain
all known pathogens as well as saprophytes, and what role the
latter forms may play in disease is by no means a settled question.
The relation between pneumonia, bronchitis and other inflam-
matory diseases affecting the respiratory organs and polluted
drinking water has been noted above. The ascertainable facts
relating to this phase of water-borne diseases are few and difficult
to satisfactorily classify. The data already collected by Dr.
W. T. Sedgwick and his associates are extremely valuable, and
further confirmation of their deductions is hoped for.
EPIDEMICS OF WATER-BORNE DISEASES
Cholera
Probably no disease is more truly characterized as a "filth
disease" than is cholera. In certain parts of India it may be
said to be endemic. Explosive outbreaks are not uncommon, and
the spreading of the disease by contact is probably constantly
going on. The insanitary nature of the personal habits of the
lower classes of natives affords ample opportunity for transmitting
infection, and the streams and lakes frequently serve as carriers.
1 "Report of the Sanitary Investigation of the lUinois River and Its
Tributaries." IlUnois State Board Health, p. 85, 1900.
28 WATER PURIFICATION
In 1817 a violent epidemic of cholera broke out in Jessore in
Bengal, which rapidly spread over a larger part of British India.
It continued unabated for 3 years, and then began to spread into
China and Persia. In 1823 the disease had reached Asia Minor
and Russia. For the next 7 years it did not advance westward
any further, but a fresh outbreak in 1830 in Russia caused the
disease to spread all ov^er the latter country and into northern
Europe and the British Isles. During the next 5 years it spread
southward, invading northern Africa.
Another epidemic started in India and China in 1841, reaching
Europe in 1847; another began in 1850 and entered Europe in
1853, and was carried across the Atlantic to North and South
America, where it was particularly severe. The epidemic of
1865-66 was less extensive than its predecessors. Since 1832
eight epidemics of cholera have occurred in the United States,
the last being in 1873.
With a better idea of the true cause for this disease in par-
ticular, and with improved methods for combating infection and
contagious diseases in general, cholera has not been widely
prevalent in Europe or the United States for a great many years.
Constant vigilance is required for its suppression, however, and
only by prompt action, where sporadic cases are discovered, have
the health authorities prevented epidemics. How many of these
epidemics have been directly transmitted through drinking water,
it is impossible to know; but that water acted as a carrier to a
greater or less extent in many of them is extremely probable.
In the period from 1831 to 1873, 373,000 people died in Prussia
of Asiatic cholera, and in 1886 alone 114,000. In 1892, 1,634
persons died from this disease in Prussia, and from the Hamburg
epidemic in this same year 8,616 deaths resulted. In 1910
Germany had but 10 cases of cholera.^
Circumstantial evidence of a very convincing character has
been collected, which proves that some cholera epidemics were
water-borne, and probablj^ no discussion of this subject is com-
plete without mentioning the disastrous Hamburg epidemic which
occurred in 1892-93. This city was using unfiltered water from
the River Elbe, which was contaminated by the sewage of over
800,000 people. During the fall of 1892, 17,000 cases developed,
resulting in 8,600 deaths. In fact, wherever the drinking-water
^ Dr. Arthuk Ledekeh; "The Modern Sewage and Water Problem."
Clinique) August, 1912.
TRANSMISSION OF DISEASES 29
supply was either filtered or obtained from some source other
than the river, few or no cases resulted.
In 1887 the city of Messina, Sicily, suffered from an epidemic
of cholera, during which 5,000 cases and 2,200 deaths resulted.
An investigation showed that water purposely diverted from a
conduit, conveying water to the city, ran into pools, which were
used for washing soiled clothing by the Messina washerwomen.
Much of this water found its way back into the open conduit,
and passed into the city. It was also found that the unglazed
tile used to distribute the water in the city were broken, and that
leakage from joints was common. Sewers laid on top and parallel
with the water mains were in a like condition and offered excel-
lent opportunity for further contamination. After a supply
of pure water, carried in tank ships from the mainland, was
provided for drinking water, the epidemic ceased at once.^
A similar outbreak of cholera in 1884 in Cuneo, Italy, which
resulted in 3,344 cases, was traced to a Uke cause, viz., washing
infected Hnen in a brook emptying into a public water supply. ^
Typhoid Fever
The prevalence of typhoid fever in civiKzed countries, where
no little attention is paid to matters of sanitation, seems at first
thought surprising. But not until 1880 was the organism which
causes this disease discovered by Eberth in the spleen of persons
dying from typhoid fever. Since it seems doubtful that this
disease, as it develops in human beings, can be reproduced in
animals, the evidence that the Eberth bacillus is the true cause
for the disease has been only slowly accumulating. Another
factor only recently discovered is that persons showing no cUnical
symptoms of the disease are genuine "culture factories" for
producing the bacillus and for its dissemination.
Epidemics resulting from these "typhoid carriers" have been
satisfactorily traced. The existence of such persons explains in
some measure the continuance of the disease, and its persistence.
The transmission by direct contact, by flies, by milk and by water
has been proven in scores of cases.
Dr. J. F. Anderson^ concludes from his study of typhoid fever
epidemics due to contaminated water, that they are characterized
by:
' W. p. Mason: "Water Supply."
2 "A Symposium on Typhoid Fever." Amer. Jour. Public Hygiene,
May, 1909.
30
WA TER P URIFICA TION
(a) A general distribution of cases throughout the area
supplied by a particular water.
(b) By the explosive onset of the outbreaks.
(c) By the trouble occurring in the late winter or spring.
(d) By the comparative freedom from the disease of persons
not using the suspected water.
(e) By evidences of sources of infection found by an inspection
of the watershed.
(/) By the outbreak beginning or ending after a change in the
water supply.
(g) And by indications of the pollution of the water when
analyzed.
TYPHOID FEVER
DEATH RATE
PER
100,000 OF POPULATION
RfC.Ar,_-a
rmany
Kng. dc Wulfs
lyio
.Ncthei'laaJs
Switzerlaad
Fic;. 1. — Typhoid fever death rate in various countries.
In the following table, a comparison is made between the
typhoid fever death rates in European and American cities for
the year 1910, and shows even at this period how much more
prevalent this disease was in America than in Europe.
Unit of comparison
Deaths per
Aggregate 100,000 from
population typhoid fever,
1910
Thirty-three principal European cities in Russia,
Sweden, Norway, Austria-Hungary, Germany,
Denmark, France, Belgium, Holland, England,
Scotland and Ireland
Fifty American cities of 100,000 inhabitants or
over
Excess of deaths, typhoid fever in American cities
per 100,000 population
31,590,000
■ 20,250,000
6.5
25.0
18.5
TRANSMISSION OF DISEASES
31
In Figure 1 is a diagrainmatic representation of the relative
prevalence of this disease in several European countries as com-
pared with the death rate in the United States for the year 1910.
Some of the more important typhoid fever epidemics which
have been traced to infected water are Hsted below:
Place
Number of
Year , Population
Cases Deaths
Caterham, England 1879
Plymouth, Pa 1885
Tees River VaUey, England
Lowell, Mass '1890-91
Lawrence, Mass 1890-91
1893
1893-94
Worthing, England
Grand Forks, N. D
Maidstone, England I 1897
Ithaca, N. Y 1903
Butler, Pa 1903
5,000
8,000
1890-91251,976
77,696
44,654
16,000
6,000
33.830
18,000
13,000
352
1,104
1,330
2,855
1,792
1,411
1,245
1,928
1,350
1,348
21
114
100
217
137
168 (Wells)
96
150 (Springs)
82
111
Outbreaks of water-borne typhoid fever, or a gradually increas-
ing prevalence of this disease, which forced the authorities to
provide remedial measures, have occurred at Erie, Pa.; Niagara
Falls, N. Y.; Coates^-ille, Pa.; Ironton, 0.; Winnipeg Canada;
Rockford, 111.; Memphis, Tenn.; Council Bluffs, Iowa; and
Omaha, Neb.
Even ground-water supplies, which through carelessness or
ignorance are not protected properly from pollution, are not
infrequently the distributors of infectious material. An instance
of this character occurred some years ago at Lincoln, Neb., where
an outbreak of typhoid fever resulted and severe intestinal
troubles affected several thousand people. The cause was found
to be leakage from a broken sewer which found its way through
the ground and an abandoned pipe that connected directly with a
well from which the public water supply was drawn.
The improvement in general sanitation during the past 25
years has been well summarized by C. A. Holmquist in a study
of typhoid fever statistics for the State of New York as a whole,
and for certain cities of the state. He finds that in 1900 the
average death rate from typhoid fever in the registration area of
the United States was 31.3 per 100,000 of population. For the
same area for the period from 1918 to 1922, this death rate had
32 WATER PURIFICATION
fallen to 5.3 per 100,000 of population. Comparing these rates
with those for the State of New York, he finds a similar reduction.
Death R.\te from Typhoid Fever ix the State of Xew York
„ . , _ , Average Rate per 100,000
Period Covered of Population
1885 to 1906, 22-year period 23 . 6
1900 l-j-ear period 26 . 7
1918 to 1923, 6-year period 33
1923 1-year period 2.9
These reductions in typhoid fever death rates are due in part
to improved water supplies, and are well illustrated in the
following chapter.
To illustrate the decrease in typhoid fever between 1910 and
1925 in American cities, statistics show that of the 77 largest
cities in the Um'ted States, 30 had typhoid fever death rates
below 2 per 100,000 of population in 1925, while only two cities
had rates over 20 per 100,000. In 1910, out of a similar group of
51 cities, not one had a rate below 2 per 100,000 of population,
and 17 had rates over 20 per 100,000.
The pollution of the Great Lakes in the United States by the
cities built upon their shores is to a large extent local; but since
these communities draw their water supply from the same source,
the problem of preventing the drinking water from becoming
contaminated, and still obtain a satisfactory disposal of the
sewage, is a troublesome one. The common remedy of extend-
ing the water supply intakes out from 3 to 5 miles from the shore
has been resorted to with fair success, and with marked decreases
in the typhoid death rate in most cases. The City of Chicago
has diverted a large part of its sewage through a drainage canal
into the lUinois River, thus keeping a constantly increasing
volume of sewage from polluting the lake water farther and
farther from the shore line. Other lake cities are contemplating
partial purification of their sewage in order to conserve the purity
of their water supplies.
The effect of the wind on these large bodies of water in causing
currents, the influence which the shore lines may have on these
currents, and the movement of ice polluted with sewage from the
shore out into the lake in the spring months are all factors which
may at times be the cause for water-borne epidemics. '
ID. D. Jacksox: "Chlorination at Cleveland, O." Eng. Record vol
65, June 15, 1912.
^
TRANSMISSION OF DISEASES 33
References
1. "Report of the Sanitary Investigations of the Illinois River and Its
Tributaries." IlUnois State Board of Health, p. 85, 1900.
2. Vitality and Isolation of Cholera and Typhoid Organisms:
{aj~~Jo2ir. Infect. Diseases, vol. 1, p. 641, 1904.
(6) Eng. Record, vol. 52, Sept. 23, 1905.
(c) Eng. Record, vol. 65, June 1, 1912.
(d) Zeit. fur Hygiene und Infect. Krank., 14.
(e) E. O. Jordan: "General Bacteriology."
3. D. D. Jackson and T. W. Melia: "Differentiation Methods for
Detecting the Typhoid Bacillus in Infected Water and Milk."
Jour. Infect. Diseases, vol. 6, No. 2, Apr. 1, 1909.
4. "A Symposium on Tj^phoid Fever" (8 papers). Am. Jour. Public
Hygiene, May, 1909.
5. "Epidemic of Typhoid Fever at Columbus, Ohio." Jour. Mass.
Assoc. Boards of Health, vol. 14, May, 1904.
6. Allan J. McLaughlin: "Sewage Pollution of Interstate and Inter-
national Waters." Public Health and IMarine Hospital Service. Hy-
gienic Lab. Bidl. 83, March, 1912.
7. D. D. Jackson: " Chlorination at Cleveland, Ohio." Eng. Record, vol.
65, June, 15, 1912.
8. "A Polluted Well at Lmcoln, Neb." Eng. Record, vol. 65, June 1, 1912.
9. Typhoid Fever Epidemics and Statistics:
(a) Eng. Record, vol. 55, p. 131, February, 1907.
(6) Eng. Record, vol. 58, p. 444, October, 1908.
(c) Eng. Record, vol. 61, p. 263, 677, March, 1910.
(d) Eng. Record, vol. 62, p. 630, December, 1910.
(e) Eng. Record, vol. 63, June, 1911.
(/) Eng. Record, vol. 65, pp. 254, 300, 591 and 601.
(g) Eng. Record, vol. 66, p. 95, July, 1912.
(h) Eng. News, vol. 67, June 13, 1912.
10. Charles ~Bv Boldrean: "Typhoid Fever in New York City, etc." /LC
Am. Jour. PubliJ Health, vol. 2, 1912.
11. H. DE B. Parsons: "Our Typhoid Streams." Stevens Inst., Janu-
ary, 1911.
12. Nicholas S. Hill, Jr. and Leon R. Whitcomb: "The Relation of a
Pure Water Supply to Chronic Intestinal Tract Infection." Eng.
News, vol. 69, No. 5, Jan. 30, 1913.
13. George A. Johnson: "The Typhoid Toll." Jour. Am. Water Works
Assoc, June, 1916.
14. C. A. Holmquist: "Typhoid Fever and Improvement of Water Sup-
pHes." Eng. Contr., p. 797, Oct. 8, 1924.
15. Roger G. Perkins: "Typhoid Fever in Cleveland, 1873-1926."
Jour. Preventive Medicine, Sept, 1927.
CHAPTER IV
THE EFFECT OF IMPROVED WATER SUPPLIES UPON
HEALTH
As the relation between impure water and disease becomes
better understood and appreciated, more attention is being given
to the quaUty of pubUc water suppHes. Sometimes the method
pursued is to seek a purer water from some uncontaminated
source, or to render a polluted supply better by some process of
purification. By substituting a pure drinking water supply for
an impure one, the reduction in the death rate from water-borne
diseases has been notable, and the improved health of the com-
munity has usually been demonstrated beyond question.
In the United States the typhoid fever death rates undoubtedly
furnish the best indicators of the quality of public water supplies.
The following table taken from Dr. Geo. M. Kober's paper on
the "Conservation of Life and Health by Improved Water Sup-
ply" summarizes the statistics of 61 cities in the United States for
the years 1902-06.1
Mean Typhoid Fever Death Rate from 1902-06 per 100,000 of
Population for Cities Using Various Classes of Water
4 cities using ground water from large wells 18. 1
18 cities using impounded water and conserved rivers
or streams 18.5
8 cities using water from sm.all lakes 19.3
7 cities using water from the Great Lakes 32 . 8
5 cities using both surface and underground water. . . 45 . 7
19 cities using polluted river water 61 . 1
From the same paper is reproduced a diagram (Fig. 2) showing
in more detail the typhoid fever death rates in different cities
according to the character and the source of their water supply.
Spring waters, ground waters from wells, and filtered waters
evidently furnish the safest supplies. Surface waters, whether
from streams or lakes, may furnish safe drinking water, but they
are much more likely to be polluted.
Probably the most striking effects in reducing typhoid fever
have come from the purification of polluted supplies. By filter-
^Eng. Record, vol. 57, June, 1908.
34
IMPROVED WATER SUPPLIES
35
ing an impure water supply marked reductions in water-borne
diseases have almost invariably resulted. Even where the
0 10 20 30 40 50 CO TO 80 90100U0120
70
Co
60
55
50
45
40
35
30
20
15
10
PURE MOUNTAIN SPRINGS
FILTERED WATERS
EUROPEAN CITIES
FILTERED WATERS
AMERICAN CITIES
GROUND WATERS
LARGE WELLS
J_
IMPOUNDING RESERVOIRS
PROTECTED WATER SHED3
3P:
4_l PROTECTED RIVER
OR STREAM SUPPLY
u.
m
n
SMALL LAKES
I I
GREAT LAKES
SUBJECT TO POLLUTION
H
MIXED SURFACE AND
UNDERGROUND WATERS
/Munich
*"\ Vienna
r Berlin
Zurich
O.GS Hamburg
I Paris
LLondon
Paterson
Binghamton
18.1
ia.5
18.3
RIVER WATER
SUBJECT TO
POLLUTION
IQ,'2\ Albany
J ; Lawrence
1 ; Watertown
Richmond Borough
Queens Borough
Camden
Lowell
Fitchburg
Cambridge
Somerville
Worcester
Bridgeport
Hartford
Maiden
Boston
Chelsea
New Bedford
.Waterbury
Holyoke
Bronx Borough
Manhattan Borough
Fawtucket
Newark
Jersey City
Baltimore
Eochester
Syracuse
Fall Eiver
Brockton
Taunton
Haverhill
Portland
Salem
Milwaukee
Detroit
Chicago
83.1 Bu Halo
J , Erie
J Cleveland
J iDuluth
St. Paul
Canton
Brooklyn Borough
Columbus
.McKeesport
Minneapolis
Seattle
New Orleans
Toledo
Evansville
Springfield
Covington
Grand Rapids
Wilmington
Richmond
Cincinnati
Louisville
Philadelphia
Lancaster
Atlanta
Harrisburg
Wheeling
Allegheny
Pittsburgh
45.7
Cl.U
0 10 20 30 40 50 60 70 80 90 100110120
Fig. 2. — Typhoid fever death rate according to water supply.
community has been only partially supplied with purified water,
the effect on the typhoid death rate has been noticeable.
36
WATER PURIFICATION
Typhoid Death Rates per 100,000 of Population for Cities Changing
FROM Polluted TO Purified Water Supplies
1907
190S
Columbus, Ohio,,
New Orleans, La,
Louisville, Ky . . .
Pittsburgh, Pa. . .
Philadelphia, Pa.
The filter plant for the City of Columbus, Ohio, was started
in August, 1908; the high rate for this year was due to an epidemic
in the early part of the year. The filter plants in New Orleans
no
130
120
110
100
90
80
70
60
50
40
30
\
K
1 :
>
O
3
O
\
\
A
^
A
o
■ii
a
3
a,
V
\
\ i
/
\ -S
1 u
\/
n
CT 3
V
1
1
a
u
a
3
'
FROM HYGIENIC LABORATORY
BULLETIN No. 83
BY
ALLAN J. McLaughlin
U.S.)
1 o:
1
1 ^;,t
i
a
a
i
a
3
\ o
\
1
■
V
--
in
J900 J901 1902 1903 1904 1903 191)6 1907 1908 1909 1910
Fig. 3. — Typhoid death rate by years for city of Pittsburgh, Pa.
and Louisville were started in 1909. In Pittsburgh and Philadel-
phia filter plants were placed in operation in 1907 and 1908,
respectively; but in neither city was the entire population sup-
plied with the purified water.
IMPROVED WATER SUPPLIES
37
Figure 3 is of special interest in this connection, in showing how
pronounced a reduction in the death rate followed the introduc-
tion of even a limited volume of purer water.
From the typhoid fever statistics of Cincinnati, Ohio, a most
convincing argument for the purification of a polluted water
supply can be presented.
Number of Cases and Deaths from Typhoid Fever
Unfiltered water from old works
Filtered water from new works
Year
1904
1905
1906
Total
for 3
years
1908
1909
1910
Total
for 3
years
Cases
Deaths
1,646
270
746
155
1,940
239
4,332
664
235
67
218
45
183
21
636
133
The figures for the year 1907 are omitted because water from
both the old and the new works was supplied to the city.
Tf the above figures are expressed as cases and deaths per
100,000 of population, a better comparison may be made with
other statistics.
Number of Cases and Deaths per 100,000 of Population
For 3 years before int
filtered watei
roducing
For 3
years after introducing
filtered water
Average 1908 1909
1910
Cases
Deaths
Cases
Deaths
417
64
Percentage n
67
19
jduction from
84
70
62
13
the average.
85
80
50.0
5.7
88.0
91.0
In a report on the purification of the Montreal water supply
Messrs. Hering and Fuller present a table showing the effect of
purification by filtration on the death rate from typhoid fever in
a number of American cities.
The relation between impure water supplies and certain intes-
tinal diseases other than typhoid fever, is more or less obscure.
38
WA TEH P URIFICA TION
Death Rates from Typhoid Fevek per 100,000 Population in American
Cities Using Filtered Water
City
Before
Year filtra-
plant was tion
com- !
pleted ''
Before
filtra-
tion
After
filtra-
tion
Years averaged
Death rate
Sand filters
Albany, N. Y. . .
Lawrence, Mass.
Pittsburgh, Pa. .
1
1899
10
9
90
1893
7
15
114 !
1907
S
1
133
1
22
25
471
Mechanical filters
Bingham ton, X. Y
Cincinnati, Ohio . .
Columbus, Ohio...
Paterson, X. J. . . .
Watertown, X. Y.
York, Pa
Hoboken, X. J
1907
5
5
1908
4
1
1908
11
1
1902
5
7
1904
5
5
1899
2
8 i
1905
/
4
47
50
78
32
100
76
19
15
16
20
10
38
22
14
Infant mortality from diarrhea and enteritis is probably both
directly and indirectly the result of drinking impure water,
although other causes contribute more frequently to death.
About 85 per cent, of the deaths listed under "diarrhea and
enteritis" in the United States census mortality statistics occur
in children under 2 years of age. Dr. A. J. McLaughlin- in
discussing this subject says:
"Instead of one disease designated under different names we are
probably considering several diseases with common factors of trans-
mission. Whatever the real relation between typhoid fever and enteritis
or diarrhea of children may be, one fact is clear, the same causes operate
to cause excessive prevalence of both. It is probable that cases of
typhoid in children under 2 years in man}^ cities are often incorrectly
diagnosed as enteritis. It must be remembered, however, that the
causative agent of bacillary dysentery is transmitted in the same waj'^
and by the same media as that of tj-phoid. There are too manj^ cases
of fatal illness in children under 2 years classed as diarrhea and enteritis,
and an exhaustive investigation should be made to establish the real
1 Including Allegheny, supplied with unfiltered water.
* Public Health and Marine Hospital Service. Hygienic Lab., Bull.
83, March, 1912.
IMPROVED WATER SUPPLIES
39
cause of death in enteritis and diarrhea of children. Without such an
investigation it is impossible to assign the real cause of the excessive
child mortaUty from diarrhea and enteritis. In cities of less than 50,000
population without slums and which are not 'mill' towns an enteritis
rate in children under 2 years above 100 deaths per 100,000 indicates
prevalence of an acute intestinal disease preventable by the same
measures that prevent typhoid fever. It is probable that in such cities
proper enforcement of prophylactic measures against typhoid fever
would reduce the enteritis rate below 40 deaths per 100,000. Enforce-
ment of prophylactic measures would include the installation of pure
water supplies and proper sewerage systems, coupled with a vigorous
campaign against the insanitary outdoor privy and the equally dangerous
shallow well.'"
Dr. McLaughlin gives the following table which emphasizes
the complexity of the problem.
City
Typhoid
death rate
per
100,000,
average for
10 years,
1900-1909
Character
of water
supply
Death rate
enteritis,
average
for 5 years,
1904-1908
Keiiiarks
Rochester, N. Y
Syracuse, N. Y
Albany, N. Y
Binghamton, N. Y. . . .
Utica, N. Y
Schenectady, N. Y. . . .
Amsterdam, N. Y
Yonkers, N. Y
Cohoes, N. Y
13.7
14.8
21.9
20.9
17.3
22.4
18.6
9.5
83.8
129.1
148.5
27.0
Good
Good
Good
Good
Good
Good
Good
Good
Polluted
Polluted
Polluted
Polluted
89.5
105.5
80.0
104.7 .
133.7
164.7
150.7
207.7
170.9
173.2
175.0
151.6
Sanitary conditions
good.
Mill and factory
towns; bad sanitary
conditions.
Sanitary conditions,
Niagara Falls, N. Y . . .
Ogdensburg, N. Y
Buffalo, N. Y
exclusive of water,
good. Mill and fac-
tory towns.
Some striking evidence of the effect of purer water supplies in
cities in the State of New York has been brought out by C. A.
Holmquist in a study referred to in the previous chapter. The
cities of Albany, Cohoes, Niagara Falls and Binghamton suffered
severely from impure water supplies until measures were taken
to purify their drinking waters. The following table summarizes
this evidence in a concise form.
40
WA TER P I ^RIFICA TION
City
Period
Death rate
per 100.000 of
population
Albany^
Before slow sand filters were used
89 4
First j-ear after filters were used (1899)
40.0
Five years 1919 to 1923
4.1
Cohoes
Prior to filtration and disinfection
S.T ^
Six years 1918-1923
3.7
Niagara Falls
Prior to filtration, 1912
Year preceding filtration and disinfec-
131.8
tion
179.1
First year following filtration and disin-
fection
65.2
Second year following filtration and dis-
infection
26.6
Six years, 1918-1923
5.0
Bingliaiiitom
Before filtration
56 2
Six years, 1918-1923
4.0
1 At Albany added pre-filters to slow sand filter plant in 1908. Chlorina-
tion of this supply commenced in 1909.
In a paper by H. Burdett Cleveland published in the Natiori's Health
in October, 1924, a graphical representation of typhoid fever statistics for a
number of cities in the State of New York, including several of the above-
mentioned cities, gives visible evidence of the effect of improved water
supplies. Mr. Cleveland's statements in his paper are given in part in
order to explain the charts.
"Typhoid mortality curves for eight of the larger cities have been
plotted on semi-log paper with a circle interposed to show when pasteuri-
zation of milk was required by ordinance. Sanitary control of milk
supplies cannot be so definitely fixed, either in point of time or degree,
and has not been indicated. The periods during which each water
supply was untreated and, later, treated together with the treatment
employed are shown by these curves."
"A curve of the typhoid rate for the combined population of all the
cities for the 25-year period is also shown on a cross-section chart as well
as a curve for this period showing the percentage of population served
with untreated water. Supplies have been classified as treated, if
filtered, sterilized, or both."
"It is not to be claimed that all of this reduction, more particidarly
tluring the past 10 to 15 years, has been due to water purification.
Much of the decrease in typhoid mortality has undoubtedly been
IMPROVED WATER SUPPLIES
41
a o o o
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42
WATER PURIFICATION
no
90
80
70
60
50
Unfreafed
F,7-hred
Filtered and Sier'iUzed =
Sferi/ized
16981900
1920 1922
Fig. 36. — Mortality rate from typhoid
and water supply conditions in Albany
and Utica during the twenty-five year
period covered. In all the charts the
official health records supply the vital
statistics and in most instances the water
conditions are drawn from reports of
inspection bv the State Department of
Health.
190
140
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1898 1900 1905
1910
1915
1920 1922
Fig. 3c. — The correlations are quite
as marked between water suppHes and
typhoid fever incidence in Niagara
Falls and Buffalo. Circle shows when
pasteurization of milk was required by
ordinance.
no
100
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i 60
^ 70
§. fco
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Fig. 3d. — Further proof that sani-
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downward plunge at each introduction
of new sanitary requirements.
Q-
O
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SO
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Fig. 3 e . — R o c h ester and Elmira
afford further proof of the general prop-
osition.
IMPROVED WATER SUPPLIES
43
brought about by better sanitation of watersheds and, in some of the
larger cities and more progressive communities, by sanitary control of
milk supplies and especially, by milk pasteurization."
"To an indeterminate degree, also, typhoid vaccination since the
World War, as well as closer control by public health authorities of the
typhoid carrier problem and of infected food transmission, and a gradual
o
a.
-o
a>
c
E
o
o
100
90
80
70
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30
ZO
10
Percemage oftoialWaferSupp/y
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50
45
40 :i
35.1
E
30
Z5 4!
o
ex
20 ~
15 -o
o
10
1898 1900
1920 1922
Fig. 3/. — A curve of the tvphoid rate for the combined population of
all the cities for the twenty-five year period. Shows also the percentage
of population served with untreated water.
improvement in general sanitary conditions, have all contributed to this
noteworthy decline in the typhoid fever death rate."
"Beyond question, however, the effect of filtration and sterilization
of water supplies in reducing typhoid rates has been very much greater
than that of all other preventive measures. This is clearly indicated
by the table and curves presented herewith,"
44
WATER PURIFICATION
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IMPROVED WATER SUPPLIES
45
The follovdng mortality statistics taken from reports of the
Health Department of Cincinnati, Ohio, point pretty plainly
to the fact that a change from an impure water supply to a
purified supply made a marked difference in the number of
deaths from dysentery, diarrhea and enteritis in persons over 2
years of age.
The following figures show a reduction in deaths from dysen-
tery for 3-year periods before and after the introduction of
filtered water of 64.3 per cent, and for diarrhea and enteritis
of 55.1 per cent.
Unfiltered Water from Old
Works.
Filtered Water from
New Works.
Year
1904 1905
1906
Total
for 3
years
1908
1909
1910
Total
for 3
years
Dysentery
Diarrhea and enteritis over 2
years of age
27 21 22
152 167 174
70
493
9 11 5
90 60 ! 71
25
221
N. B. The year 1907 is omitted because water was supplied to the
city both from the old works and from the new works.
THE MILLS-REINCKE PHENOMENON AND HAZEN'S THEOREM
The available evidence clearly proves that cholera, typhoid
fever, dysentery and gastro-intestinal troubles are commonly
transmitted by infected drinking water, and that there is reason
to believe that other diseases are also conveyed in the same
manner. The effect of purifying a polluted water supply, in
decreasing the deaths from diseases other than cholera and
typhoid, has been studied recently by W. T. Sedgwick and J.
Scott MacNutt. They point out that in 1893-94, IVIessrs.
Hiram F. Mills, C. E., of Lawrence, Mass., and Dr. J. J. Reincke
of Hamburg, Germany, respectively, noted independently a
decHne in the general death rate of each of these cities as a result
of improving their water supplies. Professor Sedgwick and his
associate have collected numerous mortality statistics in a paper ^
on this subject, and have termed the coincidence between a
1 W. T. Sedgwick and J. Scott MacNutt: "On the Mills-Reincke
Phenomenon and Hazen's Theorem Concerning the Decrease in Mortality
from Diseases Other than Typhoid Fever Following the Purification of
Public Water Supplies." Jour. Infect. Diseases, vol. 7, 1910.
46
WA TER P URIFICA TION
lowered death rate and a purified water supply as the "Mills-
Reincke Phenomenon." In 1904, Allen Hazen in a paper read
before the International Engineering Congress held in St. Louis,
gave a quantitative expression for the phenomenon by stating
that: "Where one death from typhoid fever has been avoided
by the use of better water a certain number of deaths, probably
38
36
34
32
30
a
S28
a
^ ?
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t-,
-26
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c
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e
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a
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= 12
\^
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y ■
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\\
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/
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>
/
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A
^
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LEGEND
-— Filtered Wafer
Population
—•—Typhoid Fever
Death Rates
^— '*'
-^
—
"^
38
36
3t
32
30
28
26
21
22
20
13
16
1*
12
10
8
6
4
2
3 S S
Fig. 4.
-Growth of water filtration and decrease in typhoid fever death
rate in the registration cities of the United States.
two or three, from other causes have been avoided." Sedgwick
and MacNutt have called this expression ''Hazen's theorem,"
and have concluded from the studies which they have made,
that the statement appears sound and conservative, but not
necessarily precise. The ratios they worked out varied widely.
For example, at Hamburg, Germany, for every death less from
IMPROVED \VATER SUPPLIES 47
typhoid fever after filtration, there were 15.8 deaths less from
other causes; at Lawrence, Mass., the ratio was 1 to 4.4; at
Lowell, Mass., 1 to 6.0; at Albany, N. Y., 1 to 4.1; and at Bing-
hamton, N. Y., 1 to 1.5.
From the data which they compiled with respect to diseases
of the respiratory organs, the evidence in many cases is striking
and warrants a more extended study. Factors not specifically
related to an improved water supply may have been potent in
reducing the death rate in the cities studied. Greater knowledge
of methods for the prevention of disease must have played its part
in diminishing mortality, and in extending the length of the
average life. On the other hand, the real causes for many dis-
eases are still unknown, and the probability that some of them
can be transmitted through polluted drinking water is by no
means unreasonable.
The elimination of disease germs from a water supply would be
a direct cause for a decrease in the death rate, while an indirect
cause could come from an increased vital resistance produced by
the use of purer drinking water. Probably both of these factors
are instrumental in bringing about a lowered death rate.
The accompanying diagram (Fig. 4) from George A. Johnson's
paper "The Typhoid Toll," in the Journal of the American
Water Works Association for June, 1916, is a striking graphic
presentation of the effect which water purification has had in
reducing typhoid fever in the LTnited States.
References
1. Geo. M. Kober: "Conservation of Life and Health by Improved
Water Supply." Eng. Record, vol. 57, June, 1908.
2. Arthur Lederer: "The Modern Sewage and Water Problem."
Clinique, August, 1912.
3. E. BoxjEAx: "Les eaux d'alimentation publique observations generales
sur leur role epidcmiologique; leur choix; etat actuel de I'epuration."
Rev. Scient, 49, An. 5, pp. 138-146.
4. W. T. Sedgwick and J. Scott MacNutt: "On the Mills-Reincke Phe-
nomenon and Hazen's Theorem Concerning the Decrease in Mortality
from Diseases Other than Typhoid Fever Following the Purification of
Public Water Supplies." Jour. Infect. Diseases, vol. 7, 1910.
5. Geo. A. Johnson: "The Typhoid Toll." Jour. Amer. Water Works
Assoc, June, 1916.
6. F. H. Waring: "The Typhoid Fever Epidemic at Xenia, Ohio." Jour.
Amer. Water Works Assoc, p. 167, June, 1919.
7. M. C. Sjoblom: "Typhoid Fever at Moline, 111." Jour. Amer. Water
Works Assoc, p. 230, June 1919.
48 WATKR PURIFICATION
8. M. C. Sjoblom: ''The Outbreak of Typhoid Fever and Dysentery at
the Chicago and Alton Shops at Bloomington, III." Jour. Anier.
Water Works Assoc, July, 1920.
9. ''Comparative Death Rates and Sanitary Conditions." The forty-
eighth Semi-annual Report of the Sewerage and Water Board of N«w
Orleans, La. {Ahst.) (Eng.) Contr., p. 820, Oct. 8, 1924.
10. J. W. Ellms: "A Sanitary Survey of Lake Erie Opposite Cleveland,
Ohio, in 1920." Jour. Water Works Assoc, IMarch, 1922.
11. Russell Suter: "Stream Pollution in Terms of Sanitary Quality of
Drinking Water." Jour. Amer. Water Works Assoc, March, 1923.
12. Abel Wolmax: "Cooperative Research in Water-purification Prob-
lems." Jour. Amer. Water Works Assoc, July, 1920.
13. E. Sherman Chase: "Quality of Water Supply." Engr. Contr., May
9, 1923.
14. H. W. Streeter: "Some Recent Developments in Stream Pollution."
Proc Seventeenth Annual Convention of Indiana Sanitary Water
Supply Association.
15. "Changes in Water Treatment." Editorial, Engr. News-Record, Aug.
21, 1924.
CHAPTER V
OBJECTS AND METHODS OF WATER PURIFICATION
The purpose of purifying a drinking water is obviously to make
it more pleasant and more wholesome to drink. The removal of
suspended sediment and of vegetable coloring matter, in order to
convert a dirty water into a clear and colorless one, commends
itself if for no other reason than that the water becomes more
acceptable to the senses of taste, smell and sight. If in addition
to improving its appearance, it is possible to reduce materially
or eliminate entirely the bacteria, some of which may be capable
of producing disease, a second important reason for the purifica-
tion of a drinking water can be advanced. By rendering a water
hygienically safe for drinking purposes, sickness and death, as
well as economic losses of no small magnitude are avoided. It is
not difficult to show that a pure and wholesome water supply is a
sanitary investment which pays in dollars and cents, as well as in
health and happiness.
For industrial purposes many waters are entirely unfitted for
use without purificarion. Usually the dissolved salts which pro-
duce hardness make a water unsuitable for use in steam boilers.
The softening of hard waters is a method of purification which
has long been practised, and which could be even more exten-
sively employed today to the financial advantage of users of
boiler scale-forming waters. In general, soft waters are more
desirable for most industrial purposes. In such industries as
brewing, distilling, starch and sugar manufacturing, the bacterial
content of the water is of some importance, since certain organ-
isms may produce fermentations which are undesirable. Waters
containing iron in solution or suspension are especially objection-
able for domestic purposes and for such industries as dyeing,
paper making and bleaching.
General Methods of Purification. — The impurities in water
which it is necessary to remove are in suspension and solution, and
purification methods fall naturally into two classes in consequence.
For the removal of matter in suspension two processes are em-
ployed, namely, sedimentation and filtration. These processes
49
50 WATER PURIFICATION
occur normally in nature, but being uncontrolled produce re-
sults of varying degrees of excellence. When artificially controlled,
sedimentation and filtration, properly carried out, are able to
purify waters of very poor quality, and with a degree of certainty
that have established these methods upon a scientific basis.
Mineral matter in suspension can be entirely removed, as well as
practically all of the organic matter, which latter includes the
bacteria. Chemical reagents may or may not be employed to
facilitate either or both of these processes. The chemical com-
pounds used in this connection are mechanical agents exclusively,
and merely assist and hasten the bringing together of finely divided
suspended particles into larger masses, which will settle and filter
out with greater ease.
For the removal of dissolved impurities, such as salts of lime
and magnesia, chemical reagents are usually resorted to. A pre-
cipitation of the bases in an insoluble form, and their subsequent
removal by sedimentation and filtration, constitute the usual
methods of purification. In the case of easily oxidizable soluble
salts, such as those of iron, aeration is effective in breaking down
the ferrous compounds by the removal of dissolved carbon dioxide,
and the introduction of sufficient oxygen to bring about the oxida-
tion of the ferrous to the insoluble ferric compounds.
Filtration usually follows the process of sedimentation, and is
carried out in various ways. Sand, gravel, coke, charcoal, coal,
porous tile and sponges are some of the materials which have been
and are still used as filtering media. Onh^ the first two media,
viz., sand and gravel, are commonly employed in large filtration
plants.
Purification methods which do not fall under any of the above-
mentioned classes, are those of distillation and sterilization by
chemical or physical agents. In the case of distillation all dis-
solved and suspended impurities are removed, as well as the
bacteria being killed. It is obviously the most perfect method of
purification, but not necessarily the most desirable. Its cost
makes it prohibitive for all practical purposes so far as large
supplies are concerned.
Disinfection and sterilization present the most advanced
phases of water purification, and furnish methods of great prac-
tical value for supplementing other methods, as well as in some
cases, furnishing themselves all the purification needed.
The action of these agents is primarily upon the readily oxidiz-
WATER PURIFICATION 51
able matter which may be in a water, whether it be of organic or
of mineral origin. The bacteria being a low form of plant life are
thus attacked, and are either destroyed or their vitahty so im-
paired that they no longer are able to reproduce themselves.
The effect of these agents is not selective, except in so far as they
react first with the more easily oxidized material. If not ex-
hausted on the latter, they will react slowly upon the more re-
sistant matter, but may fail to effect a complete oxidation or to
hinder vital processes. Those bacteria which are capable of form-
ing spores, and which may be in this stage, are sometimes not
affected, on account of their well-known resistance to injurious con-
ditions. The effect of these disinfectants upon the pathogenic
forms is the same as upon the non-disease-producing bacteria
which may be present in a water. If practically all the bacteria
are destroyed, therefore, the water is rendered hygienically safe.
The agents used for disinfecting water are the hypochlorites of
calcium and sodium, pure chlorine gas, ozone, copper sulphate,
and the rays of ultra-violet light. Other chemical compounds
have been suggested and experimented with, and the use of the
electric current has frequently been tried. None of these agents
is of much practical value excepting chlorine and its compounds
in the form of the hypochlorites, ozone gas and the ultra-violet
light. All of the chemical disinfectants are used in very minute
amounts in water-purification work; nevertheless, they are ex-
tremely effective when properly applied. The relative merits of
these various agents will be discussed in a later chapter.
The use of copper sulphate as an agent for killing off growths
of algse and diatoms in water supplies is of practical importance,
and of much value. The troublesome character of these growths
in the operation of water-woi'ks, and even of purification plants
will be considered in detail later.
Statistics of Purification Plants. — Sixty years ago in the United
States no plants for the purification of a public water supply were
in existence. In Europe plants which clarified the water were
in use, and incidentally effected a certain degree of bacterial puri-
fication. They were operated upon an empirical basis and with
no true understanding of the scientific principles underlying the
art. In fact, the modern theory of the cause for many diseases
was unknown, and the part played by minute vegetable and
animal organisms in the dissemination of disease was undreamed
of. By the wonderful investigations and deductions of Pasteur
52
TT'^ TER P URIFICA TION
and Koch, the relation between polluted waters and the trans-
mission of certain diseases became apparent and furnished
a rational basis upon which methods of purification could be
constructed.
Statistics compiled by Prof. Geo. C. Whipple in 1911 show
the growth of water purification plants from 1880 to 1910. The
figures are given in the accompanying table.
Populations Supplied with Filtered Water at Different Dates
Total urban popu-
lation in U. S.,
places of more
than 2,500 inhabi-
tants
Population supplied with filtered water
Per cent, of
Year
Sand filters
Mechanical
filters
Total
urban popu-
lation sup-
plied
1870
1880
1890
1900
1910
None
None None
0.00
13,300,000
21,400,000
29,500,000
38,350,000
30,000
35,000
360,000
3,883,221
275,000
1,500,000
6,922,361
30,000
310,000
1,860,000
10,805,582
0.23
1.45
6.30
28.20
Since these statistics were compiled the filtration of public
water supplies has steadily increased, and must continue to
increase as the population grows and the pollution of the sources
of water supply becomes greater.
From figures compiled in 1924 by C. G. Gillespie, Director of
the Bureau of Sanitary Engineering of the State Board of Health
of California, it has been found that there are 634 cities in the
United States which have filter plants of one million gallons, or
over, capacity daily. His summarized statistics are as follows:
Type of plant
Number of
cities having
plants
Total
installed ca-
pacity m.g.d.
Total popu-
lation served
Slow sand filters. .
Rapid sand filters
Total
47
587
634
916.0
4,048.4
4,964.4
5,054,000
18,610,000
23,664,000
Statistics Relating to Disinfection of Water Supplies, — The
phenomenal increase in the number of disinfected water supplies
during the past 15 years is evidence of the value of this form of
treatment for rendering drinking water safe from a sanitary
standpoint. It is estimated by Linn H. Enslow that in 1911 over
800 million gallons of water per day were being treated with
WATER PURIFICATION 53
bleaching powder in a score of the larger cities of the United
States and Canada. In 1913, liquid chlorine began to replace the
use of bleaching powder, although over 1,700 millions of gallons
of water per day were being treated with the latter reagent.
By 1915, approximately one billion gallons of water per day were
being treated with bleaching powder and a like volume with
liquid chlorine. In 1918, more than a thousand cities and towns
in North America were employing disinfection; and by 1924,
3,750 million gallons per day were being treated with liquid
chlorine, and 50 million gallons per day with bleaching powder.
It is estimated that 6,000 installations of apparatus are required
for this purpose, of which 12 are electrolytic-cell plants where
the chlorine is produced at the point of application to the water,
25 hypochlorite plants, and the balance liquid chlorine plants.
The above figures presumably include filter plants using
chlorine for disinfecting the water after filtration as well as those
public supphes which do not have the water filtered.
The investment represented by purification plants mounts into
many millions of dollars, but the conservation of life effected by
them, measured in dollars, is very many times more than their
first cost. Efficiency of these plants is of the utmost importance
both from the hygienic and economic standpoint, and is becoming
more and more appreciated by communities owning them. To
the technical problem of purification much study has been given
in the past, and is still being given at present; but the art as a
whole is on a thoroughly scientific and practical basis, as the
beneficial results of water purification amply testify.
References
1. Allen Hazen: "Filtration of Public Water Supplies." Appendix IV.
2. "Water Purification in the United States." E7ig. Neivs, vol. 47, p. 310.
3. Rideal: "Water and Its Purification."
4. G. C. Whipple: "The Present Status of Water Purification in the
United States, etc." Proc. Congress of Technology, Boston, 1911.
5. Eng. Record:
(a) Geo. W. Fuller: "Importance of Proper Operation of Water
and Sewage Purification Plants." Vol. 58, p. 498, 1908.
(6) George C. Whipple: "Policy of Water Filtration." Vol. 60, p.
718, 1909.
(c) Rudolph Hering and George W. Fuller: "History of Devel-
opment of Water Purification — Report on Montreal Supply." Vol.
62, p. 539, 1910.
6. C. G. Gillespie: "Filtration Plant Census." Jour. Amer. Water ^-^i
Works Assoc, August, 1925.
CHAPTER VI
SEDIMENTATION
The removal of suspended mineral and organic matter from
water supplies is most easily accomplished by settling in reser-
voirs. The clarification and purification effected by settling in
this manner is usually spoken of as plain sedimentation. By the
addition of certain chemical compounds to naturally turbid
waters, an artificial flocculation or coagulation of the suspended
particles is produced whereby they settle out more rapidly.
This process is termed "sedimentation after coagulation" or
"precipitation with chemicals."
PLAIN SEDIMENTATION
Turbid surface waters flowing into impounding reservoirs be-
come partially clarified in passing slowly through or in standing
undisturbed in them. This result is produced because the veloc-
ity of flow of the water, which has maintained these minute par-
ticles in suspension, is lessened or reduced to practically zero.
The reduction in the velocity of flow permits the sediment to
gravitate toward the bottom of the reservoir, and to be finally
deposited thereon. Provided the wind does not set up surface
currents, nor temperature changes produce vertical currents, the
sooner will the deposition of the sediment be effected. For ob-
vious reasons a perfectly quiescent condition of the water can not
be produced, and complete clarification, therefore, is not usually
practicable.
The ponds and lakes are, as a rule, natural setthng reservoirs,
in so far as the turbid surface waters which may flow into them
are concerned. The water in them is, therefore, usually quite
clear. The factors tending to disturb the water and to retard
settlement are of course active at times.
Artificial settling reservoirs and coagulation basins form a
most important part of purification plants treating clay-bearing
waters. As a preliminary treatment for filtration they are
absolutely essential for efficiently and economically handling
these turbid waters. They may be also of much assistance in
.54
SEDIMENTATION 55
purifying waters which are only turbid during portions of the
year. In water softening, settHng basins are essential to obtain-
ing a well-clarified effluent.
Theory of Sedimentation.- — The very practical importance of
sedimentation in water purification has caused the conditions
which influence the phenomena to be carefully studied. Much of
the experimental work has of necessity been empirical in charac-
ter, because of the number of factors which are involved. Some
investigators, however, have approached the problem from a
theoretical standpoint, and many of their deductions are valuable
and suggestive. The early work of Brewer, Durham, Hunt,
Barus and Seddon is of interest in connection with this general
subject. The more recent paper of Allen Hazen,^ however,
has a more practical bearing on sedimentation, although discuss-
ing in a theoretical manner certain important factors.
From the simple assumption, "that whenever a particle of sus-
pended matter hits the bottom, it remains where it strikes, and
is never carried forward on the bottom, or picked up again;
second, that all the sediment in the water is of the same hydraulic
value, that is to say that every particle settles through the water
at the same rate as every other particle," Hazen proceeds to
develop mathematically fifteen special propositions. He dis-
cusses the velocity with which particles of sediment settle
through still water, and the effect of temperature, flocculation
and coagulation upon the rate of settlement.
The minute size of the particles, their very slow subsiding
velocities, and the mixing action produced by surface and vertical
currents, all tend to maintain the finest particles in practically
constant suspension. Hazen gives a table of the subsiding
velocities of various-sized particles which is reproduced on the
following page.
Hazen's resume of the deductions and conclusions at the close
of the paper is clearly and concisely stated as follows:
Resume
"The fundamental proposition, in clearing water by sedimentation,
seems to be that every particle of sediment moves downward through
the water at a velocity depending upon its size and weight and upon
the viscosity of the water. Particles of sediment are generally so far
apart that they do not influence each other; and, while there is no doubt
1 Trans. Am. Soc. C. E., vol. 53, p. 45, 1904.
56 WATER PURIFICATION
Velocities at which Particles of Sediment Fall in Still Water
T-.. , r .-1 Hydraulic value in
Diameter of particles .^ifii^eters per second
in millimeters ^qoq = 50°Fahr.
Remarks
1 . 0000
100.0
0.8000
83.0
0.6000
63.0
0.5000
53.0
0.4000
42.0
0.3000
32.0
0.2000
21.0
0.1500
15.0
0.1000
8.0
0.0800
6.0
0.0600
3.8
0.0500
2.9
0.0400
2.1
0.0300
1.3
0.0200
0.62
0.0150
0.35
0.0100
0.154
0.0080
0.098
0.0060
0.055
0.0050
0.0385
0.0040
0.0247
0.0030
0.0138
0.0020
0.0062
0.0015
0.0035
0.0010
0.00154
0.0001
0.0000154
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Experiments by the writer.
Interpolated from connecting curve.
Interpohitcd from connecting curve.
Interpolated from connecting curve.
Interpolated from connecting curve.
Interpolated from connecting curve.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's formula.
Wiley's fornuila.
Wiley's formula.
Wiley's formula.
Note. — These values are not given as being precise, but they arc believed
to be sufficiently accurate for the purpose of this discussion.
that they do sometimes collect in groups and thus change the condi-
tions, it seems to be generally true that each particle will settle as if no
other particle were present.
"If the water in a basin were absolutely quiet there would be a
regular sequence of clearing beginning at the top. The coarsest particles
would go down fastest, but at any given point there would be a gradual
clearing, and this clearing would take place most rapidly at the top,
and, after longer intervals, at lower points in the basin.
"Seddon started out with this theory, but found it to be not in
accordance with the facts. His observation showed that while the
amount of sediment in the water in the top was a little less than in the
water in the bottom, the distribution was nearly equal throughout
the mass, a condition of affairs inconsistent with the theory. He
SEDIMENTATION o7
accounted for this distribution of sediment by the constant mixing
of the water from top to bottom, and to the sustaining power of vortex
motions in the water. These motions he thought arose from the internal
motion of the water at the time of entrance, and from wind, and from
temperature changes.
"The writer has taken Seddon's development of the case as his
starting point, and has carried the discussion further. He believes that
while the internal motions keep the water mixed, and with nearly the
same density of sediment from top to bottom, the tendency of the
particles of sediment to settle is nevertheless an unbalanced force always
acting to take the particles to the bottom, and the number of particles
that hit the bottom in a given time is proportional, first, to the velocity
at which the individual particles settle, and second, to the density of
sediment in the water immediately above the bottom.
"With these fundamental relations in mind, it is easy to compute
and to express by simple formulas the proportions of particles of sedi-
ment of a given hydraulic value which will hit the bottom under given
conditions and which, therefore, presumably will be removed.
"The fundamental propositions may be very concisely expressed.
They are: First, that the results obtained are dependent upon the
area of bottom surface exposed to receive sediment, and that they
are entirely independent of the depth of the basin; and second, that the
best results are obtained when the basins are arranged so that the
incoming water containing the maximum quantity of sediment is kept
from mixing with water which is partially clarified. In other words,
the best results are obtained where any given lot of water goes through
the basin with the least mixing with the water which enters after it.
Tills is practically accomplished by dividing the basins into consecutive
apartments by baffles or otherwise.
"Thus far, the discussion is easy and apparently certain. The next
step is a more difficult one. It relates to bottom velocities, and has to
do with the question whether these velocities are such as to allow the
particles to remain on the bottom when they get there, or whether
they will be taken up again and be kept in motion with the body of the
water. This is a point upon which further experimental data are
needed. The problem of securing such data seems to be difficult.
The observations must be made at the bottom of a layer of liquid of
considerable thickness, where the conditions of observation are not
favorable. The observations, further, must be made on very low
velocities and on particles so small as to be practically microscopic.
"Whatever view may be taken of the second part of the problem, or
whatever researches upon it may show, the arrangements of basms
most favorable to taking particles to the bottom should stand."
58 WATER PURIFICATION
Coagulation of Sediment.— The collection of minute particles
of suspended matter into larger aggregates is a process which
appears to occur only to a limited extent in natural waters, al-
though it may be artificially produced by the addition of certain
chemical compounds. Since the deposition of these finely divided
particles greatly facilitates sedimentation and subsequent filtra-
tion, when the latter forms a part of the purification process, the
phenomenon is of much practical interest and importance in
water purification.
Colloidal Character of Sediment. — The analogy between the
physical properties of liquid suspensions of certain chemical com-
pounds, and those of turbid clay-bearing waters is so marked that
some description of their properties will be of interest. In a paper^
published some years ago by the author attention was called to
Dr. A. A. Noyes'2 classification of colloidal mixtures, in which he
defined non-viscous, non-gelatinizing, but readily coagulable
mixtures as ''colloidal suspensions." He regarded them as
really suspensions of minute particles and not true solutions. He
differentiates further by designating mixtures in which the par-
ticles may be visible under the microscope as "microscopic sus-
pensions," reserving the term "colloidal suspensions" for those
containing particles beyond the Hmit of microscopic visibility.
Physical and Electrical Properties.— Natural waters furnish
many examples of colloidal suspensions. Most turbid waters in
their natural condition may be considered as mixtures of "mi-
croscopic and colloidal suspensions." A beam of light passed
through Ohio River water, even after the water has stood for
many weeks, is plainly visible, in the same manner as when a sun-
beam passes through dusty air. This is a fairly good proof of the
presence of minute particles in suspension, which reflect the light
from their surfaces. Colloidal suspensions of gold and arsenious
sulphide artificially prepared act in a similar manner to a ray of
light.
Another property of colloidal and microscopic suspensions,
appai-ently depending on the presence of electric charges upon
them, is seen in the migration of the colloidal particles by the
passage of an electric current through the mixture. Thus the
particles of a colloidal suspension of ferric hydroxide or aluminum
i"The Coagulation and Precipitation of Impurities in Water Purifica-
tion." Eng. Record, vol. 51, May 13, 1905.
' Jour. Am. Chem. Soc, vol. 27, No. 2.
SEDIMEN TA TION 59
hydroxide migrate with the positive current toward the cathode,
while kaoHn and other similar colloidal or microscopic particles
migrate with the negative current toward the anode. The col-
loidal suspension of clay particles characteristic of turbid Ohio
River water act in a precisely similar manner to those of kaolin.
Experiments by the author with slightly turbid Ohio River water
produced an average rate of travel of the particles toward the
anode of 0.29 cm. per hour for a potential gradient of 4 volts per
centimeter. These results are of the same order of magnitude as
were obtained by Whitney and Blake for the migration of par-
ticles in a colloidal suspension of silicic acid,^ Silica doubtless
formed the larger proportion of the particles in the sample of
Ohio River water with which the above experiments were made.
The clearing of the water at the cathode and the movement of the
particles toward the anode indicated them to be negatively
charged.
Coagulation with Chemicals. — Turning now to another impor-
tant property of colloidal suspensions in general, viz., their coagula-
tion, we find that turbid natural waters possess similar properties
to colloidal suspensions artificially prepared. Non-electrolytes
do not have the power of coagulating colloidal suspensions;
but all electrolytes will do so with a proper degree of concentration
of the latter, and a sufficient length of time. Acids, bases and
salts, therefore, will coagulate colloidal suspensions, all being
more or less dissociated in aqueous solution and capable of con-
veying an electric current. In a similar manner hydrochloric acid,
caustic soda, caustic lime or an ordinary salt solution will each, if
of the proper concentration, coagulate the colloidal claj^ of a natu-
rally turbid water like that in the Ohio River. It should always
be borne in mind in dealing with natural waters that we are work-
ing with extremel}^ dilute solutions of salts, even in those waters
which we commonly speak of as high in soluble compounds. In
other words the concentration of the electrolytes is very low.
In a number of modern purification plants in which lime is used
to soften the water, in addition to the employment of sulphate of
iron or aluminum sulphate to effect clarification, the action of the
caustic alkali is virtually that of a coagulant, especially if the lime
is added in sufficient amounts to produce a slightly caustic con-
dition. Some quite extensive experiments undertaken on a large
scale some years ago, clearly proved that by rendering the Ohio
* Jour. Amer. Chem. Soc, October, 1904.
60 WATER PURIFICATION
River water caustically alkaline with lime, the suspended clay
could be coagulated, and could be subsequently removed by
rapid filtration through sand. The explanation of the phenom-
enon seems to be that the introduction of the base calcium hy-
drate in excess, furnished an electrolyte of sufficient concentration
in the water to effect coagulation of the colloidal clay.
The similarity between artificiall}^ prepared colloidal suspen-
sions and the verj^ small suspended particles characteristic of tur-
bid waters as above described, seems to warrant the classification
of the latter mixtures with the former. If we seek further analo-
gies in the co-precipitation or absorption by colloids of other sub-
stances in solution and suspension with them when these colloids
are coagulated, the true character of turbid waters seems even
more apparent.
When a turbid water containing carbonates of lime and mag-
nesia in solution is treated with sulphate of alumina, for example,
a reaction results setting free aluminum hydroxide. The liber-
ated aluminum hydroxide absorbs or mechanically traps the
finely divided material in suspension, and in the course of time
the finer particles come together to form larger particles which
settle out readily. This process of coagulation of the colloidal
clay suspension and co-precipitation of the larger suspended par-
ticles, appear to be started by the coagulation of the aluminum
hydroxide. It is evident, as Dr. Noj^es points out in the paper
referred to, "that the mechanism of this coagulation is not j^et
understood," although it appears, "that it is the ion with a charge
opposite to that of the colloid particles that is mainly responsible
for their coagulation." It is also probable that it is the electric
charge upon the particle which tends to hold it in suspension.
Time Required for Coagulation. — The time factor in the
coagulation of turbid waters is an important one. The length of
time required to bring about the proper degree of coagulation
varies with different waters. It is apparently influenced by the
character of the suspended colloids, by the kind and amount of
salts in solution, by the quantity of the coagulating chemical
applied, by the temperature of the water, and by the agitation to
which the mixture is subjected. The presence of much organic
matter may retard the formation of the floe. An ordinary clay
suspension is usually quickly coagulated. Complete flocculation
and partial clarification may take place under favorable condi-
tions in as short a time as 10 or 15 min.; on the other hand, the
SEDIMENTATION 61
author has seen a water which was not affected at the end of 4
his. This water had only a slight turbidity. Two hours after
applying the coagulating chemical to this water it could be passed
through a sand filter without removing the suspended matter or
all of the coagulant. The large amount of soluble organic
matter present in the water evidently produced a colloidal sus-
pension with the aluminum hydroxide, formed by the decomposi-
tion of the aluminum sulphate which was added, and was only
slowly precipitated.
Under ordinary conditions a period of 3 to 5 hrs. is sufficient to
properly coagulate and settle a turbid water. Of course a proper
arrangement of basins, inlets, outlets and baffles is requisite for
bringing about effective coagulation and clarification. The con-
struction of typical coagulation and settling basins will be de-
scribed in a succeeding chapter.
Loss of Chemical by Adsorption. — Another phenomenon
common to the coagulation of turbid waters is the adsorption of
the applied chemical compound by the flocculent material pro-
duced by the reaction and the associated suspended matter. The
particular significance of this fact in water purification was pointed
out by George W. Fuller in his report on the experiments
on Ohio River water made at Louisville, Ky., some years ago.
While adsorption or concentration of a liquid on the contact-
surface of the particles is not alone pecuHar to colloids, but is
characteristic of all solid precipitates, it has a practical bearing
on coagulation in that there is some loss of chemical on account
of this property. The amount of chemical thus lost is probably
proportional to the surface area of the particles of the precipitate,
and is a function of the nature of the solid and dissolved bodies,
and of the concentration of the latter.
Natural Colloids.— The" schmutzdecke," which forms on the
top of slow sand filters, is doubtless a true colloid, and by its
adsorptive power removes the organic and inorganic suspended
matter. The difference between the appearance of the sand m
the beds of slow sand filters receiving water carrying considerable
dissolved and suspended organic matter, and those which receive
water holding more or less clay in suspension, as pointed out
by George W. Fuller in his discussion of Allen Hazen's paper
"On Sedimentation," previously quoted from, may possibly be
explained by a difference in the character of the colloids pro-
duced or carried by the two types of water. The colloid formed
62 WATER PURIFICATION
by the soluble and suspended organic matter in a water has prob-
ably the characteristic of a true colloid, i.e., a viscous, gelatinizing
compound not coagulated by salts, like gelatine for example. On
the other hand clay-bearing waters produce or carry a colloid
which is non-viscous and non-gelatinizing, but which may be
readily coagulated by compounds like aluminum sulphate or
sulphate of iron. Bacterial activity very likely aids in the forma-
tion of the natural scums found on slow sand filters.
In the absence of any artificially applied coagulant like alumi-
num hydrate the ''granular appearance" of sand beds receiving
clay-bearing waters indicates the formation of a colloid whose
ability to prevent the passage of finely divided suspended matter
is limited. The colloidal particles pass deeper into the sand than
would a true gelatinous colloid, and their power of adsorption is
soon exhausted. The "ripening" of the sand beds of both slow
sand and rapid sand filters, is, therefore, probably a process of the
formation and deposition of colloidal particles upon the sand
grains, by which their adsorptive power is slowly increased.
It is, therefore, in the character of the colloid formed that one
must seek for the explanation of the phenomena connected with
the coagulation and filtration of natural waters. It is evident
that much more light is needed on a great many of these prob-
lems, but that some of them are associated in some way with the
colloidal state of the clay, of the organic matter and of the artifi-
cially appHed coagulants, is self-evident. While the above points
may at first sight appear to be only of scientific interest, they
are in reality intimately associated with the most efficient de-
sign of purification plants. The size of coagulation basins, the
mixing and the agitation of the raw water with the coagulant, the
ability to vary the period of coagulation for any given water, the
best chemical compounds to use for the proper coagulation of the
suspended matter in the water, the advisability of providing
for plain sedimentation before attempting coagulation and the
size and character of the sand grains composing the filter bed arc
all factors entering into the practical design of water-purifica-
tion plants. The poor results often obtained in the operation
of plants is quite as frequently the result of improper design as
of faulty methods of handling the plant.
SEDIMENTATION 63
Character of Forces Affecting Coagulation and Filtration. — It is
cbvious that the nature of the forces in play in coagulation and
filtration phenomena is but imperfectly understood, and that
their magnitude is so small as practically to place them in the
same class with those affecting molecules. Nevertheless, some
speculation regarding these microforces, as Hannan^ has so
aptly termed them, may be profitable. He discusses the prob-
able influence of forces of "low potential energy" only capable
of acting on masses of practically molecular dimensions, and
within exceedingly small ranges. In the hquid-liquid, gas-
liquid and Hquid-solid interfaces, Hannan believes that the
molecules of liquid "marshall themselves in layers, each layer
differing probably to some slight extent from its neighbors."
This orientation of the molecules in fluids (gas or liquid) is
probably replaced by minute stresses in the case of solids. "For
brevity the whole may be referred to as an interfacial system."
At the intersection of interfacial systems and particularly at the
solid-liquid-gas junction, Hannan believes that these micro-
forces are especially manifest.
Hannan regards water surfaces as layers of oriented molecules
probably thousands deep. "When the water surface takes a
curved form, the electromagnetic field thereby developed is
such that the following laws obtain: (a) convex attracts convex,
(b) concave attracts concave, and (c) convex and concave are
mutually repellent. Not only so, but the degree of attraction or
repulsion is seen to vary with the curvature." If curvature,
fineness of division or degree of dispersion are all virtually synony-
mous terms, we have the stage set for the play of forces in inter-
facial phenomena that must produce the characteristic results
observed in and around the capillaries formed by the deposits
of coagulum about the sand grains of a filter bed.
Hannan again in this extremely suggestive paper quotes a
statement of Bancroft'- in which the latter refers to mordanting
with alumina as follows: "The substance adsorbed and held
firmly is colloidal alumina. Coagulated alumina may be
absorbed to some extent, but it easily rubs off the material."
Hannan goes on to state that "by colloidal alumina is here under-
1 Frank Hannan: "Microforces: with Reference More Especially to
Orientation and Curvature." Jour. Amer. Water Works Assoc, Nov., 1923.
2 W. D. Bancroft: "Mordants-alumina." Jour. Phys. Chem., vol.
26, pp. .501 536.
\
64 WATER PURIFICATION
stood the hydrosol. Water filtration is quite closely analogous
to dyeing. Complete purification of the water, the main object
sought, corresponds to absolute exhaustion of the dye bath. The
fabric in our case is the filter bed; and fastness to washing is, for
us, undesirable. In these two short sentences of Bancroft may
be discerned a complete vindication of the empirically developed
mechanical filtration process. The preliminary intimate mixture
of alum and water yields colloidal {i.e., hydrosol) alumina which
adsorbs, or is adsorbed by, the impurities to be removed; a
very rapid process. Coagulation follows; the alumina is left
upon the sand in that condition in which it "rubs off easily."
"Massive alumina is found to adsorb color with great readi-
ness; but bacteria less readily," Gore^ observes; "the act of
catching impurities by the alum is the fundamental point of
coagulation, and must not be confounded with the precipitation
which follows it . . . Unless the impurity is caught before
filtration very little prospect remains of its being caught at all."
It is not to be doubted that bacteria were the impurities which
Gore had in mind, and Clark's- results, while not bearing him out
to the letter, yet show that, so far as bacteria are concerned.
Gore's statement really conveys the gist of the matter. An
ingenious plan, in principle akin to Clark's was developed by
Maddock^ at Oshkosh, Wis. His results should throw further
light on this problem. It is desirable we should know to what
extent the hydrosol form of alumina is indispensable for effective
purification. Whenever it can safely be dispensed with, the
way to marked economies in coagulation is clear."
"" References
Theories of Sedimentation:
1. Brewer: Proc. Nat. Acad. Sciences, November, 1883.
2. Durham: Chem. News, vol. 30, p. 57, 1874; ibid., vol. 37, p. 47, 1878.
3. Hunt: Proc. Boston Soc. Natural History, February, 1874.
4. Barus: Bull. U. S. Geological Survey, No. 36, 1886.
5. Seddon: Jour. Assoc. Eng. Soc, p. 477, 1889.
6. Hazen: Trans. Amer. Soc. C. E., vol. 53, p. 45, 1904.
7. Longley: Eng. Record, vol. 57, pp. 793, 813.
Coagulation :
1. Ellms: Eng. Record, vol. 51, p. 552, 1905.
1 William Gore: Eng. Conir., vol. 58, No. 6, pp. 134-135, 1923.
' H. W. Clark: Eng. Contr., vol. 58, No. 2, pp. 16-17.
3R. A. Maddock: Eng. Contr. vol. 54, p. 23, Dec. 8, 1920, ibid., vol.
59, No. 2. p. .381, 1922.
SEDIMEN TAT I ON 65
2. Eng. Record, vol. 54, pp. 439, 475, 1906.
3. Eng. Record, vol. 58, p. 292, 1908.
4. Eng. Record, vol. 61, pp. 176, 215, 247, 599, 1910.
5. Eng. Record, vol. 64, p. 476, 1911.
6. J. W. Ellms: "Coagulation and Sedimentation with Chemicals."
Jour. Amer. Water Works Assoc, May, 1922.
7. Malcolm Pirnie: "Application of Colloid Chemistry to Study of Filter
Effluents." Jour. Amer. Water Works Assoc, p. 247, March, 1922.
8. John R. Baylis: "The Solution of Corrosion and Coagulation Problems -^
at Montebello Filters, Baltimore, Md." Jozir. Amer. Water Works '■^-^
Assoc, p. 408, May, 1922.
9. James W. Armstrong: "Some Observations and Experiences in the
Operation of Coagulating Basins." Jour. Amer. Water Works Assoc,
p. 160, June, 1919.
10. F. A. Dallyn and A. V. Delaporte: "Preparation of Water for Filtra-
tion." Eng. Contr., p. 271, Aug. 8, 1923.
General Experimental Data:
1. Fuller: "Report on Water Purification at Louisville, Ky."
2. Fuller: "Report on Water Purification at Cincinnati, Ohio."
3. Weston: "Report on Water Purification at New Orleans, La."
4. "Report of Filtration Commission of Pittsburgh, Pa."
5. George F. Catlett: "Colloidal Theories Applied to Colored Water."
Eng. Record, June 3, 1916.
6. Thorndyke Saville: "The Nature of Color in Water." Eng. Contr.,
January 18, 1917.
7. Abel Wolman: "Cooperative Research in Problems of Water Purifica-
tion." Jorur. Amer. Water Works Assoc, p. 572, July, 1920. C'-U^J'
8. Report of Committee on Colloidal Chemistry, Council of Standardiza- C
tion, p. 273, Jour. Ayner. Water Works Assoc, March, 1923. /
CHAPTER VII
TYPES OF SETTLING RESERVOIRS AND COAGULATION
BASINS
The design of reservoirs and basins for efficient sedimentation
has received considerable attention in water-purification work,
but not as much as the subject deserves. The complexity of the
problem has not always been appreciated, and too frequently this
portion of the plant has been made to accommodate itself to other
features of the design instead of being properly coordinated with
them.
A certain amount of flexibility in the design of these reservoirs
is quite possible without materially sacrificing efficiency. Never-
theless, it is the author's opinion that much more of the work of
clarification should be thrown on this part of the purification
plant than is now the practice. They are by far the least com-
plicated portions of the works, and the least expensive to operate.
Their tendency to make more uniform the operation of the filters
strongly commends them to the operators of such plants. It is
believed that in designing settling reservoirs of all kinds more con-
sideration should be given to obtaining efficient sedimentation
and to making them as large as good engineering practice will
permit, due regard being had for other portions of the plant, in
order to produce a well-balanced design.
Donaldson, i in a resume of the need for plain sedimentation
prior to coagulation, states that in plants handling from 20 to 40
tons of suspended dry solids per million gallons, such as are found
in those waters met with in the ^Middle West and Southwest,
the advantages of preliminary sedimentation have been well
recognized for some time. He considers the use of grit chambers
for settling out the coarse material, even before plain sedimenta-
tion is begun, entirely justifiable in most cases. Mechanical
clarifiers have been employed in a few plants to permit of the
continuous removal of sediment which accumulates with great
rapidity in the handling of some very muddy waters.
' Wellington Donaldson: "The Trend of Purification Plant Design
and Operation." Eng. Contr., Aug. 12, 1925.
66
RESERVOIRS AND COAGULATION BASINS 67
Impounding Reservoirs. — Impounding reservoirs built pri-
marily for storing water are, of course, to be considered from a
somewhat different standpoint than those especially designed
for sedimentation purposes. The depositing of suspended sedi-
ment in storage reservoirs is an incident rather than the object of
their operation. However, considerable purification is effected
in them, and the influences which lead to such results will be
discussed in another section.
Settling Reservoirs. — Storage of turbid waters for purposes of
plain sedimentation, in reservoirs especially constructed for this
purpose, is undoubtedly good practice, but is not always provided
for. Usually such supplies are drawn from turbid streams in
which the water may at times be loaded with sediment. Pro-
\'ided the reservoirs are relatively large in proportion to the con-
sumption of water, quite a number of days of settlement may be
possible before the water' is drawn off. The relative positions of
the inlet and outlet of these reservoirs are obviously of great
importance in even approximating theoretical displacement of
the water if they are used continuously. The tendency of the
water currents to seek the shortest path between the inlet and
outlet, and thereby render more or less ineffective certain parts
of the reservoir, is a commonly observed condition. Baffling
undoubtedly has the effect of breaking up "short-circuiting
currents of water," but is not always employed in plain sedi-
mentation basins.
Cleaning out the sediment deposited in this class of reservoirs
is greatly facilitated by smooth and hard linings in the reservoirs,
by sufficient slope to the sides and bottom and by an adequate
system of gutters and drains. Proper facilities for flushing out
the mud by streams of water under pressure, or by scraping the
mud to the gutters assisted by a flow of water which is not under
pressure, are necessary in all well-designed basins.
In all settling basins the sand and heavier portions of the silt
will be found deposited close to the inlet. In some cases the
amount of sediment dropped near the inlet is very great, espe-
cially where the turbid stream supplying the water carries a good
deal of sand and silt, and where the pumping from the stream is
practically continuous.
Cincinnati Storage and Settling Reservoirs. — Combined stor-
age and settling reservoirs are in operation at Cincinnati, Ohio,
(Fig. 5) in which Ohio River water undergoes plain sedimentation
68
WA TEE F I 'RIFICA TION
before being coagulated with chemicals and filtered. These two
reservoirs hold approximately 392,000,000 gal. of water, and
were designed with the idea of their being operated on the fill-and-
i
Fig. 5. — Cincinnati settling reservoirs.
i
Fig. 6. — Cincinnati settling reservoirs, effluent float tubes.
draw plan. This method of operation, however, has never been
followed. The water flows continuously through them in parallel.
The inlets to the reservoirs are between 500 and 600 ft. from the
outlets. The latter consist of movable pipes (Figs. 6 and 7)
RESERVOIRS AND COAGULATION BASINS
69
with their mouths held about 4 ft. under the surface of the water
by means of floats. The water is thus continuously skimmed
5SSSS5JS^^^
Fig. 7. — Cincinnati settling reservoirs, profile showing float tubes.
PLAN
Slope 3-1 ^. ._, nigh Water Slope 10-1 Slope 6-1
SECTION ON LINE A-B
Fig. 8. — Cincinnati settling reservoirs, plan and cross section.
from the surface. The depth of water in the reservoirs varies
from 35 to 50 ft.
70 WATER PURIFICATION
The irregular shape of these reservoirs (Fig. 8) is accounted for
by the desire in construction to make the excavations equal the
embankments as nearly as possible. As it was intended that
they should be operated by first filling with water, then allowing
the latter to stand and deposit its sediment for a day or so, and
finally drawing off the settled water, it was of no particular conse-
quence if the inlet was close to the outlet. Since they are not
vitilized in this manner, but are operated continuously, their
efficiency is undoubtedly somewhat reduced because of their
irregular outline, and the short distance between the inlet and
outlet. The apparently dead spaces in these reservoirs, however,
are by no means useless, since experience shows that diffusion of
the sediment causes a much more uniform deposition of the latter
than would be supposed. The depth of mud in the lobes of these
reservoirs will probably run from 35 to 40 per cent, of the average
depth in the portions of the reservoirs where more active sedimen-
tation is in progress.
Louisville Settling Reservoirs. — The two Crescent Hill reser-
voirs at Louisville, Ky., perform a similar service to those at
Cincinnati. They cover an area of 750,000 sq. ft., and hold, when
filled to a depth of 20 ft., a little over 100,000,000 gal. of water.
Originally the water as it was pumped from the Ohio River was
dehvered into the gate house at the end of the division wall sepa-
rating these two basins. It passed over a weir above the 20-ft.
level into the first basin, and was drawn off at a point diagonally
opposite at the bottom through a conduit 5 ft. in diameter.
Through this conduit, the water passed to the corresponding cor-
ner of the second basin, where it entered at the bottom. It was
drawn off at the diagonally opposite corner through the gate
house.
Delivering the muddy water at the surface of these reservoirs
and drawing off at the bottom has been changed, so that
the water now enters from the gate house at the bottom of the
first basin, and is withdrawn over a weir tower built to enclose the
inlet end of the conduit. After passing through the latter to
the bottom of the second basin, it is skimmed off at the top of this
basin at the gate house from which it flows to the coagulation
basins.
George W. Fuller observed, when these reservoirs as origi-
nally arranged, were drawn off to be cleaned, that with the
exception of the coarser material piled up near the inlet, the
RESERVOIRS AND COAGULATION BASINS 71
depth of sediment was substantially uniform over the entire
bottom. Allen Hazen has noted the same condition in other
reservoirs, and accounts for it by the mixing action by which
water in all parts of the reservoir is made substantially of the
same quality.
New Orleans Grit Reservoirs. — For removing the heavy silt
and sand of a normally turbid water, relatively small grit reser-
voirs have been used. In the New Orleans purification plant, two
such reservoirs are in service. Each reservoir is 75 by 150 ft. in
area, and has outer walls 20 ft. high. These reservoirs are pro-
vided with a center baffle which causes the water to travel up one
side of the reservoir and down the opposite side to the outlet. At
the normal capacity of the plant, a sedimentation period of about
1 hr. is obtained with one basin in service. The heaviest sedi-
ment settles nearest the inlet, and grows much lighter as the out-
let is approached (Fig. 9).
Kansas City, Mo. — In this city, four so-called clarifiers of the
Dorr type are used as presedimentation units. These clarifiers
are circular tanks, each 200 ft. in diameter, containing a slowly
rotating system of rake arms, and which in this case are driven
from the periphery of the tank. A 3-hour detention period
for a flow of 100 million gallons of water a day is provided. The
sludge may be removed continuously from the bottom of the
tank at the center by pumps. It is expected that these tanks
will be capable of removing from 80 to 90 per cent, of the sus-
pended matter in the raw Missouri River water.
COAGULATION BASINS
The bringing together of finely divided particles of suspended
sediment in natural waters by means of the action of certain
chemical compounds is termed coagulation. Basins, in which
this action may take place and the flocculated sediment settle out,
are commonly provided in connection with rapid sand filter
plants. They may also form a part of slow sand filter plants
where the sediment in the water settles out slowly and is liable to
clog the sand in the filters.
Mixing Channels.^ — The introduction and uniform distribution
in the water to be treated of chemical solutions of the strengths
usually employed in water purification offer some mechanical
difficulties. Since the efficiency of the coagulating compound
depends upon the formation of a large and well-defined floe, the
72
WATER PURIFICATION
RESERVOIRS AND COAGULATION BASINS 73
size and character of which is directly influenced by the tempera-
ture of the water and the nature of the salts and colloids in solu-
tion and suspension, a thorough mixing of the water with the
solution is of the utmost importance.
By sending the water through relatively narrow channels at a
velocity of 1.5 to 2.0 ft. per second, and allowing the travel
through these channels to take about 1 hr., a thorough mixing and
a complete coagulation is effected, which produces rapid sedimen-
tation in the coagulation basins into which the water discharges.
The eddies formed in the channels by reversing the direction of
flow or by baffles or by projecting portions of the concrete con-
struction in the channels, assist materially in bringing about a
thorough mixing.
In New Orleans, mixing channels are provided for applying a
5 per cent, milk of lime in the manner described above. In this
plant dupHcate reservoirs, 75 by 320 ft. each with outer walls 19
ft. high, are divided into 16 rectangular double-decked passages
with a cross-sectional area of over 60 sq. ft. each, and an aggre-
gate length of about 5,120 ft. When passing 40,000,000 gal. of
water in 24 hrs., the flow of the water through the channels
requires about 1 hr.
Iron sulphate for coagulation purposes, and soda ash for
reducing the permanent hardness of the water may be both intro-
duced in these channels, but provision is also made for applying
a coagulant at various points in the flow of the water through the
coagulation basins proper.
Obviously, mixing channels may become settUng chambers
unless the velocity of flow is sufficient to retain the flocculated
sediment in suspension. This does take place^ but corrects itself
by reducing the cross-section of the channel by deposition of
sediment until the velocity is sufficient to maintain a scouring
action through the passage. On the other hand, too great a
velocity may break up the floe and thereby diminish its ability to
settle rapidly, as well as failing to entrap the very fine suspended
sediment for which the coagulating chemical was added. Pro-
vided a very thorough mixing action is obtained in the channels,
it is evident that the coagulation basins themselves may be made
smaller than they otherwise could be.
A more recent design is found in the Grand Rapids, Mich.,
plant, where the water after passing through a grit chamber hold-
ing about a 26.5-min. supply at a normal rating of 20,000,000 gal.
74 WATER PURIFICATION
per day, enters a mixing chamber 44 ft. wide bj' 160 ft. long. The
chamber holds 732,000 gal., or about a o3-min. supply at normal
rating. The basin is provided with wooden baffles of "around the
end type," spaced 3 ft. apart for the full length of the chamber.
J. W. Armstrong who designed this plant, as well as the plant
at New Orleans, states this type of baffle permits the operation
of the plant with varying heads of water, and offers reasonably
good facilities for cleaning and inspection.
Baffled mixing chambers of either the "over and under,"
"around the end," or combinations of these two types are,
according to Donaldson, "admittedh' lacking in flexibility to
meet variations in w^ater flows. The}^ have never been very
popular in the western country on account of the large amount of
suspended solids carried by the water, which tends to deposit and
break down the baffles. There seems to be a tendency to get
away from this type of mixing device."
Mixing by Means of the Hydraulic Jump.^ — Experiments by
the author at Cleveland, Ohio, resulted in the development of a
flume in which a hj-draulic jump could be produced. The
application of the chemical to be mixed with the water to be
treated is made just prior to the entrance of the water to the
flume. The water acquires a velocity of 10 to 12 ft. per second
in passing down the sloping floor of the flume before it strikes
the pool of slowly moving water on or near the bottom of the
slope. As a result, there is an abrupt rise in the surface of the
moving stream in the region of impact, and is accompanied by
a great deal of turbulence in the moving mass of water (Fig. 9a).
The hydraulic jump, may be scientifically defined as that
phenomenon in which a part of the kinetic energy of a stream of
water flowing in an open channel, at less than the critical depth,
is converted into potential energy in the attempted turbulent
passage from the lower to the alternative flow level. These
alternative levels are the only two possible levels for steady flow
under given energy conditions; and the critical depth is that
depth at which alternative flow levels coincide.
The hydraulic jump, while a common phenomenon in nature,
has been, so far as is known, only utilized for the dissipation of
energy in flowing water. In the mixing apparatus devised by
the author, this energy has been utilized to mix a small volume
of chemical solution with the large volume of water to be treated.
1 United States Patent 1362611.
RESERVOIRS AND COAGULATION BASINS 75
One method by which the effect may be produced is by causing
the water to flow through an open flume, which widens uni-
formly from the throat, and which slopes downward from the
end of the throat to the end of the flume. The hydrauhc jump
will occur, if the flume is correctly designed, on the slope of the
expanding section of the flume.
Since a comparatively simple relation exists between the
critical depth and the known cross-section of the throat of the
flume, it is possible to develop a meter to measure the flow, and
Avhich could take the place of a Venturi tube and register.
Fig. 9a. — Hydraulic jump in one of the three mixing flumes at the Baldwin
filter plant at Cleveland, Ohio.
Doubtless a mechanism could also be devised by which the feed-
ing of a chemical solution would automatically be proportioned
to the flow of the main body of water through the flume.
The advantages of this apparatus for mixing may be sum-
marized as follows:
1. The mixing effect is produced with great rapidity and with
remarkable thoroughness.
2. The chemical reactions cannot take place until the chemical
or chemicals are in solution and are diffused throughout the
water to be treated, which latter is so many times larger in volume
76
WATER PURIFICATION
than the reagent solutions being applied, that the value of a
rapid and thorough method of mixing is obvious.
3. The energy relations of the hydraulic jump have been
studied by several investigators, and the principles involved are
fx/ra Si rang 8 'threaded f/an^e
jl riveted io bofh>m of Tank ' '^
II _ /_ //
5 ExiraSfrong Pipe 2-0'' Ig.
thread one end 5. 563 "O. D.
' 8 ioS C.I. Screw Reducer
'- 8 Nipple, 6' Ig. fhrd.boih ends, Ex. Sirong Pipe__
' - - 'A
Scale: ^'=3-0
Fig. 9&. — Section through mixing tank showing motor-driven agitators for
mi.xing chemical solutions with water.
sufficiently well understood so that it is possible to design and
construct a flume in which the "jump" may be produced and
controlled within comparatively narrow limits.
4. The loss of head through such a "jump'' may be made as
low, if not lower, than is produced in any of the conventional,
RESERVOIRS AND COAGULATION BASINS 77
baffled mixing chambers; hence its practicability and economy
from the hydraiiHc standpoint.
5. The structure in which the "jump" may be produced is
simple, requiring comparatively Uttle space and a small amount of
material for its construction.
6. The hydraulic jump flume conveniently lends itself, from
the structural standpoint, to being placed at the end of raw
water influent pipe lines or conduits, and preceding conduits
leading to the coagulation and sedimentation basins.
This method of mixing has been employed at quite a number
of plants with very satisfactory results. The largest plant using
this method of mixing is the Baldwin Filtration Plant of Cleve-
land, Ohio. This plant has a capacity of 165 m.g.d. Three
flumes side by side are provided at this plant for mixing the alum
solution with the raw water.
Other Methods of Mixing. — Mechanical stirring devices
located in a mixing tank have also been utilized for diffusing the
chemicals in the water to be treated. These devices have
usually taken the form of paddles slowly rotated in a tank by
motors, whereby the chemical solution and water to be treated
are thoroughly mixed. This is the type of mixer used in the
Sacramento, Calif., filter plant, and also in some water-softening
plants like those at Newark, Ohio, and So. Pittsburgh, Pa. The
Topeka, Kan., plant utihzes a combination of "around the end
baffles" and mechanical agitators; while the Kansas City, Mo.,
plant employs circular mixing and reaction tanks without
mechanical agitators.
In rotating paddle mixing, H. N. Jenks concludes that in order
to obtain a uniform velocity of 0.6 ft. per second for the water
being treated, as recommended by C. P. Hoover,^ it was necessary
to have the area of the paddles 25 per cent, of the area of the
vertical cross-section of the mixing tank.
Settlement After Coagulation. — The deposition of coagulated
sediment should take place rapidly if the proper amount of
chemicals have been added to the water, a thorough mixing of the
water with the chemicals has been effected, and temperature con-
ditions are favorable. The same general principles governing the
deposition of sediment in plain sedimentation basins, as previously
discussed, apply here, except that the suspended particles are
1 Charles P. Hoover: "Mixing Devices and Reaction Times." Jour.
Am. Water Works Assoc, May, 1924.
78 WATER Pl'lUFICAriON
larger and should gravitate toward the bottom more rapidly.
A velocity of flow of 1.0 to 1.5 ft. per minute can probably be
safely maintained in most cases without carrying too much of
the finest material forward to the outlets of the basins. Baffles
will probably be found advantageous in most basins of this type.
A uniform and even distribution of flow across the entire cross-
section of the basin is desirable between the inlets and outlets.
Skimming from the surface at the outlets is the proper method
for the withdrawal of the settled water. Provision for secondary
application of the coagulating chemicals as the water flows
through the basins for the purpose of correcting the original
treatment, should never be omitted in any well-designed plant.
If possible, an auxiliary basin for getting the benefit of this
secondary treatment ought to be installed, otherwise too much
coagulated material is liable to be carried through the outlets to
the filters.
The primary coagulation basins are usually constructed in
duplicate in order to be able to clean one of them at a time
without interrupting the operation of the whole plant. An ade-
quate number of sumps and drains ought to be provided, so
that the deposit when ready to be cleaned out does not have to
be mov'ed too far. The size of the drains should be ample to
prevent clogging, and plenty of water should be available for
flushing purposes.
St. Louis Settling Basins. — The six original settling basins of
this water-works plant (Fig. 10) were constructed as plain sedi-
mentation basins. For a number of years since the chemical
coagulants sulphate of iron and caustic lime have been used to
clarify the water, they have become coagulation basins. They
originally consisted of six rectangular masonry tanks 670 by 400
ft. in plan, and placed side by side. The walls are of masonry but
the bottoms are of concrete. They were intended to be operated
in parallel, but since coagulants have been used the walls dividing
adjoining basins have been cut down, so that the water now
passes through them in series, entering through four 3-ft. by 3-ft.
openings at the end of one of the basins. The water is withdrawn
through a masonry conduit at the end of the sixth basin after
having passed through the preceding five basins. Sluice gates in
each basin, connected with both the inlet and outlet conduits,
make it possible to withdraw basins from service for cleaning,
and to provide for emergency conditions.
RESERVOIRS AND COAGULATION BASINS 79
Two additional basins, covering together an area 400 ft. wide
by 1,660 ft. long have been constructed of concrete. The two
basins are separated by a division wall, and are each 400 by 800
ft. in plan, and have an average depth of about 21 ft. Their
combined capacity is 75,000,000 gal. This makes the total
Fig. 10. — St. Louis settling basins.
capacity of the eight basins 255,000,000 gal. These are the
largest coagulation basins known to the author, and they handle
effectively a very turbid water. The effluent from these basins
is now filtered.
Fiu. 10a. — St. Louis filtration plant.
Cincinnati Coagulation Basins. — A good example of coagulation
basins which are effective, but which are unprovided with baffles,
are the three basins of the Cincinnati plant (Figs. 11 and 12). A
lined basin or reservoir 400 by 400 ft. in plan is divided by a con-
crete wall into two basins, each of which may be operated inde-
pendently, but which are usually operated together in parallel.
The depth of these basins is about 21 ft. The water enters the
80
WA TER P URIFICA TION
two basins through sluice gates at the bottom of a gate house at
one end of the division wall. It flows into the bottom of the
basins through two reinforced-concrete conduits on either side of
the above-mentioned gate house. These conduits are 7 ft. in
i
Fig. 11. — -Cincinnati coagulation basins.
h_
\
X
Coai^ulation
Basia.No.1
J—
\
/
/
\
-B
Coagulation
Basin Xo.2
)
Coag-ulation
(
Basin No.3
E I
Filter House
PLAN
Slope lX-1
SECTION ON LINE A-B
Fig. 12. — Cincinnati coagulation basins, plan and cross section.
diameter and have set in the top of each of them twenty-one 20-in.
tees. Each of these tees discharges through the two openings in
line with each other, and in parallel with the line of flow through
the body of the conduit. In this manner the velocity of the
RESERVOIRS AND COAGULATION BASINS 81
counter-currents of water tend to oppose each other, and to
produce a uniform and quiet inflow. The water then passes
across to the opposite side of the basins, and is skimmed off at
the surface by openings into a steel conduit which conveys the
settled water to either a third basin for secondary treatment,
or directly to the filters. Two mud valves hydraulically oper-
ated are placed in the bottom of each basin. The slope of the
bottom toward the sumps of these valves is approximately 2 per
cent. The sides have a slope of 1.75 to 1. These basins have a
concrete lining covered with hard-burned brick which are grouted
in place so as to form a smooth hard surface for flushing out the
deposited mud.
Fig. 12a. — Cincinnati filtered water reservoir.
The third basin is 400 by 80 ft. and about 16 ft. deep. It is
used in series with the two larger basins, and although operated
continuously to obtain the maximum period of sedimentation, was
originally intended for settling the water after a secondary appli-
cation of chemicals, when the first application had been found
insufficient. Whenever it is necessary to make a second applica-
tion of chemicals, which is rarely the case, the third basin is used
as originalh' intended.
The two large
…[truncated]