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WATER PURIFICATION
PLANTS
AND
THEIR OPERATION
BV
MILTON F. STEIN
Mem. Am. Soc. d) E.
SECOND EDITION
NEW YORK
JOHN WILEY & SONS, Inc.
London: CHAPMAN & HALL, Limited
1919
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\
Copyright, 1915, 1910, by
MILTON F. STEIN
' <v
K
\
■h
Publishers Printing Coikpany
207-217 West Twenty-fifth Street. New York
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PREFACE
TO THE SECOND EDITION
The second edition has been made necessary because of the
advance and changes which have occurred in the technique of
water bacteriology since the book was first published, because of
the somewhat dififerent viewpoint as to interpretation of bac-
teriological tests now held, and in order to incorporate into the
instructions for the bacteriological tests certain new details and
explanations which it is hoped will lead to better results from
these tests in the hands of filtration plant operators.
With these ends in view Chapter IV and parts of Chapter V
have been entirely rewritten. It is difficult to adequately^ cover
the interpretation of tests in a limited space and in such a
manner as to be available for non-technical men. The treat-
ment may seem somewhat arbitrary, but it is believed that care-
ful reading of the articles on interpretation will convince the
trained bacteriologist that they are basically soimd and err on
the side of safety.
419564
ni
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PREFACE
In this book it has been the primary object of the writer to give
instructions for the operation of water-purification plants as
simply and concisely as is consistent with reasonable complete-
ness. In general, it has been the endeavor to treat the subject
with special regard to the requirements of the non-technical
operator of small plants, but certain portions have been treated
more elaborately, experience seeming to show that graduate
chemists have some difficulty in grasping certain phases of the
work on first assimiing charge of a purification plant. This seems
to be especially true as regards the relation of the laboratory
work to that of actual operation, the tendency being to neglect the
latter and lay xmdue stress on the former. For the benefit of the
non-technical operator it has been attempted to include in one
book all information and data required in the operation of the
plant, such as instructions for preparing standard solutions, mak-
ing bacterial and chemical tests of the water, handling coagulants',
washing filters, keeping records, etc. For his further aid, charts
embracing the computations necessary in determining the amoxmts
of coagulants to be used have been added.
To make the book more readable to those not intimately con-
nected with water-purification plants, a chapter has been added
giving detailed descriptions of the various types of plants and their
component parts, together with numerous examples. A chapter
on the natural chemistry of water has also been added, showing
the derivation of its chemical constituents from the geological
formations with which it comes in contact.
The writer recognizes that the treatment of water is a very
subtle and uncertain branch of applied chemistry, in which every
rule has nmnerous exceptions, and begs to be excused for the
rather arbitrary handling of some parts of the subject made
necessary to maintain simplicity and clearness to the non-technical
reader. For the same reason the products of chemical reactions
have been given as definite salts formed, instead of in the more
scientific ionic form.
In a book of this kind it is necessary to draw upon many
V
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Vi PREFACE
sources of information, and if the writer has failed to properly
acknowledge such source in any case, the omission has been in-
advertent. Special acknowledgment is due the United States
Geological Survey, from whose reports were obtained considerable
data for use in Chapter I, to The Engineering Record, to the
Transactions of the American Society of Civil Engineers, and to
the publications of the American Public Health Association.
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CONTENTS
CHAPTER I
PAGE
Water and Its Impurities 1
Common Constituents in Water 1
Suspended Matter 3
Acquisition of Chemical Constituents 4
Hardness 6
Gases contained in Water 8
I Mine Drainage 10
j Sewage Pollution 12
t Bacteria 13
{ Typical Streams .15
CHAPTER II
Ttpes of Purification Plants 19
Objects of Water Purification 19
Various Processes Used 21
Coagulation and Sedimentation 21
Slow Sand Filtration 22
Rate of Flow and Loss of Head 25
Theory of Filtration 26
Raking Filters 28
Scraping Filters 28
Mechanical Filtration .31
Settling Basins 33
Coagulating Apparatus .34
Filter Details 39
Washing Filters 46
Water Softening 51
Iron Removal 51
Slow Sand Filtration Plant at Washington, D.C 51
Torresdale Filters at Philadelphia, Pa 58
Mechanical Filtration Plant at Minneapolis, Minn. 62
Mechanical Filter Plant at Wilkinsburg, Pa 71
Filtration and Softening Plant at Columbus, Ohio 74
Iron Removal Plant at Iowa City, Iowa ........ 90
CHAPTER III
Physical and Chemical Tests 93
Tests Required 93
vii
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Viii CONTENTS
Physical and Chemical Tests — (CorUintied) page
Apparatus 94
General Instructions 96
Taste and Odor 100
Turbidity 101
Color 103
Alkalinity 104
Free Carbonic Acid 106
Examples of Tests 108
Alkalimetry and Indicators . 109
Iron 113
Free Aluminum or Iron Sulphate 115
Excess of Hypochlorite of Lime 116
CHAPTER IV
Bacteriological Testing of Water 117
Laboratory 118
Schedules for Bacterial Tests 118
Apparatus and Equipment 121
Hot Air Sterilizer 123
Autoclave 125
Arnold SterUizer 126
Incubators 126
Cleaning Apparatus 129
Preparing Apparatus * 129
Preparing Media 13Q
Testing Media 135
Collecting Samples 135
Plating 136
Incubation 139
Counting 139
Fermentation Tests 140
Control Tests 141
Boiling Out Old Cultures 141
CHAPTER V
Interpretation of Tests 142
Taste and Odor 142
Turbidity 143
Color 143
Alkalinity 144
Acidity 146
Free Carbonic Acid 146
Iron ^ 147
Free Alum 149
Free Ferrous Sulphate 150
bacteria 150
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CONTENTS IX
CHAPTER VI
PAGE
Coagulation and Sterilization 154
Description of the Process 154
Theory of Coagulation %• . • . 155
Aluminum Sulphate , . 156
Lime 162
Hydrated Lime 164
Soda Ash 166
Ferrous Sulphate 168
Natural Coagulation 174
Introduction of Coagulants 175
Comparison of Costs 176
Sterilization 176
Hypochlorite of Lime 177
Liquid Chlorine 182
Sodium Hypochlorite 183
Ultra-violet Rays 186
Copper Sulphate 186
Ozone 188
Automatic Regulation of Coagulants 188
CHAPTER VII
Water Softening 192
Hardening Constituents 193
Reactions of Water Softening 195
Special Tests in Water Softening 196
Total Magnesium 196
Incrustants 197
Treatment . 197
Introduction of Coagulants 200
CHAPTER VIII
Sedimentation 201
Types of Basins 202
Currents 203
Baffling 204
Cleaning Basins 204
CHAPTER IX
Filtration and General Operation 205
Routine of Operation 205
Making of Tests 205
Preparing Coagulant Solutions 206
Inspection 209
Operation of Filters 210
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X CONTENTS
Filtration and General Operation — (Continued) page
Washing Filters 213
Clear Water Basin 216
Laboratory 216
Calibration of Apparatus 216
Organization 218
Cost of Operation 220
Records and Statistics . 223
Automatic Recorders 225
Electric Alarms 226
Construction of Charts 226
Economy in Operation 229
General Remarks 232
Plate I. — Graphical Results for Tests of Alkalinity, Acidity, and Carbonic
Acid ' 233
Plate II. — Graphical Determination of Carbonates, Bicarbonates, and
Hydroxids 235
Plate III. — ^Amounts of Aluminum Sulphate Required for Various
Turbidities 237
Plate IV. — Coagulation with Aluminum Sulphate and Lime .... 239
Plate V. — Coagulation with Aluminum Sulphate and Soda Ash . . . 241
Plate VI. — Amounts of Ferrous Sulphate Required for Various Turbidities 243
Plate VII.— Coagulation with Ferrous Sulphate and Lime .... 245
Plate VIII. — Proportions of Iron and Acidity for Natural Coagulation . 247
Plate IX. — Cost of Coagulation by Various Methods 249
Plate X. — Chlorid of Lime Required for Various Strengths of Solution . 251
Plate XL — Ratio of Water to Amount of Chemicals for Various
Strengths of Solution 253
Appendix A. — ^Analysis of Coagulants . 255
Appendix B. — Standard Solutions 258
Appendix C. — Specifications for Coagulants 263
Appendix D.— Weir Table 265
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WATER PURIFICATION PLANTS
AND THEIR OPERATION
CHAPTER I
WATER AND ITS IMPURITIES
The water obtained from rivers, lakes, wells, and other sources
of supply usually contains a considerable quantity of foreign
matter in suspension and solution, not only as inert mineral sub-
stances, but also in the form" of living organisms and waste products
of organic origin. From the chemist's standpoint, all of these
foreign substances may be considei*ed to be impurities, but in
judging a water with regard to its fitness for domestic or industrial
use, only those substances which render it detrimental to health,
unfit for household and industrial purposes, or impleasant to the
sight, taste, or smell are so considered. In fact, a chemically pure
water is rather unpalatable, and experiment and observation seem
to show that the presence of certain common mineral substances
is desirable in water used for drinking purposes.
The foreign matter generally present in water may be listed as
follows:
Substances of Mineral Origin
In Suspension :
Clay and Inorganic Soil Wash.
In Psevda-SoliUion : *
Silica
Alumina
Iron Oxid
In Solution :
Bicarbonates
Carbonates
Sulphates \ of
Chlorids
Nitrates
Bicarbonate ;j
Sulphates [ of Iron
Hydroxid J
Mineral Acids
* Extremely fine particles in suspension.
1
Calcium
Magnesium
Sodium
Potassium
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• ••-•• •
• ••••• •
• • •
WATER PURIFICATION PLANTS
Dissolved Gases
' Carbon Dioxid
Oxygen
Nitrogen
Substances op Organic Origin
In Suspension :
Organic Soil Wash
Decomposing Organic Wastes
In Pseudo-Solution :
Colloidal Organic Wastes
Vegetable Color
Organic Acids
In Solution :
Vegetable Color
Organic Acids
Soluble Organic Wastes
Ammonia
Chlorids
Nitrites
Nitrates
Dissolved Gases
Carbon Dioxid
Hydrogen
Hydrogen Sulphid
Methane
Living Organisms :
Algae, Diatoms, and other plant forms
Bacteria
Minute animal forms
This list is neither complete nor rigid in its classification, but
presents only the most common substances present in one of a
number of possible groupings. The same substances may appear
in several groups, as often they may be of either organic or in-
organic origin.
To those engaged or interested in water purification, a knowl-
edge of how these impurities and constituents of water are ac-
quired, and of the properties imparted by them to the water, will
be of interest and value. It will assist them in better under-
standing the purposes of water purification, the difficulties and
limitations involved in interpreting the results of chemical and
bacterial tests, and in adjusting the processes of coagulation and
water-softening to the varying conditions of the waters being
ti^eated.
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WATER AND ITS IMPXTRITIES 3
Precipitation in the form of rain, snow, dew, etc., is the source
of all water supply. Initially this water is pure, being the product
of a natural process of distillation, but owing to the remarkable
solvent powers of water, it acquires impurities, such as carbonic
acid, oxygen, nitrogen, dust, bacteria, etc., even before reaching
the groimd. After its fall, it is disposed of in three ways. A
portion is evaporated from the upper soil and from water surfaces,
or, being taken up by plant roots, is transpired through the leaves,
and with this we are no further concerned. Of the remainder,
called the runoff, two dispositions may be made. Part of it flows
away over the ground surface to the nearest watercourse and
thence to the streams and rivers, constituting the flood flows
which follow heavy precipitation or n;ielting snows. The re-
mainder percolates through the soil and only reaches the streams
after a more or less lengthy and devious journey through disin-
tegrated, porous, and fissured rock and along impervious strata
thereof.
The rain, by the impact of its fall, loosens soil particles from
the surface, and carries them to the streams. If the groimd is
steep, so that the water rims off with high velocity, it will erode
the surface, thus adding to the sediment load of the water-
courses.
The sediment thus transported to the streams causes the turbid
appearance, or turbidity, of their waters. This is naturally greatest
during floods, when the surface runoflF to the streams is much
greater than the amount of ground water reaching them. Most of
the turbidity is derived from plowed fields, from which it follows
that in pastured, wooded, or rocky country the rivers are com-
paratively clear. If a region, however, is composed of steep hills
overlain with deep subsoil, this may contribute largely to the
turbidity of its streams. Rivers also erode and undercut their
banks, which is another contributory source, although most of the
sediment so derived is coarse and is deposited as a bar at first
opportunity. The first rush of a flood brings with it much coarse
sediment, but as the flood subsides the sediment carried becomes
finer, and is more difficult to remove in the process of purification.
In small streams the duration of floods is short, and while the
turbidity during high water may be very great, the average tur-
bidity is low. Many large rivers are always turbid, due to the
almost continuous occurrence of floods on some of their numerous
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4 WATER PURIFICATION PLANTS
I
tributaries, so that in addition to great turbidity during general
floods, they have a high average turbidity. The turbidity of a
water is measured by comparison with arbitrary standards, 'made
by adding definite amounts of especially prepared powdered silica
or fuller's earth to bottles of distilled water, as explained in
detail in Chapter III. The results are stated in parts per million.
Thus if one part by weight of the powdered silica is uniformly
mixed (by shaking in a bottle) with one million part's of perfectly
clear distilled water, the resulting turbidity of the standaid thus
prepared is said to be one part per million, and a sample of water
which on comparison with this standard presents a similar ap-
pearance, is said to have the same turbidity. Results obtained
with dififerem waters are not strictly comparable, being affected
by variations in the color, composition, and relative fineness of the
suspended matters. A turbidity of five parts per million is barely
discernible; a turbidity of 100 gives a water a very cloudy ap-
pearance; a water with a turbidity of 1,000 is practically opaque
in appearance. During floods the turbidity of a stream may rise
above 10,000 parts per million, and imder varying conditions
values may occur from this down to zero.
The portion of the nmpff which percolates through the soil
absorbs carbonic and traces of other acids from the decaying
vegetable matter contained therein, and from the excretion of
plant roots. The acidity thus obtained enhances its power of
solution, and enables it to attack mineral matters which would
otherwise prove insoluble. During the passage through the soil
much of the oxygen absorbed by the water from the air is removed
therefrom by the decaying organic matter. This enables the
water to hold in solution certain salts which would be oxidized to
an insoluble condition were oxygen present. After descending
through the soil and subsoil, the water enters the rock strata or
glacial drift composing the upper geological formation of the
regi(Hi. In the more ancient formations, the rocks consist of
granite, basalt, gneiss, etc., of which mixed silicates of aluminum
and potassium, sodium, calcium, or magnesium are the principal
constituents; the mineral felspar j a mixed silicate of sodium or
potassium and aluminum, being very prominent. The carbcHiic-
acid-charged water leaches the alkalies and alkaline earths from
these rocks and removes them in solution as bicarbonates, thereby
reducing the hard, resistent strata to soft, clay-like substances
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WATER AND ITS IMPURITIES 5
which can be dug with a spade. The action of the carbonic acid
and water on felspar (KAl Si808)2 is typical of this process:
(KAlSi808)2 + CO2 + 2H2O = K2CO8 + H2Al2(Si04)2H20 + 4 SiOg
Felspar + Carbonic Acid = Potassium Carbonate + Kaolin +
Silica. The potassium carbonate and siUca are carried off by
the water in solution, the latter in colloidal form. The kaolin re-
mains behind as clayey surface soil. The proportion of sodium
■and potassium silicates to those of calcium and magnesium in this
class of rocks is such that the resulting groimd water is high in
alkaline carbonates and low in the bicarbonates of the alkaline
earths.* It results that such ground waters are characterized as
«o/<, although of relatively high alkalinity. . The n^knce of these
alkaline carbonates makes possible the acquisiti<^Bnd retention
by the water of considerable quantities of silica (oi02), alumina
(AI2O3), and iron oxid (Fe208) as a suspension of extremely fine
particles, a state known as colloidal solution. In this colloidal
state, these substances do not readily enter into chemical reaction,
and are difficult to remove by filtration. While they cannot be
said to add to the turbidity of a water, they may give to it an
opaque appearance due to the reflection of Ught by the particles.
The waters from a region underlain by ancient formations of
igneous rock (or more recent formations in volcanic districts) of the
Tdnd above described are sometimes called primary waters, in
reference to the position of these rocks in geologic history. Such
waters are characterized by the proportion^ly (although not
necessarily quantitatively) large concentration of salts of the
alkalies (sodium and potassium) and the small amounts of salts of
calcium and magnesium present, and further by the presence of
silica and alumina (iron to a less extent) in the colloidal state.
Although it has been computed that silicates of the above
types constitute 98 per cent of the earth^s crust for the first 10-
mile depth, yet large areas are overlain with secondary or derivative
rocks. Often these take the shape of horizontal strata, evidently
deposited by sedimentation or biologic growths at a time when the
* Sodium, potassium, and certain less common chemical elements are
known as the metals of the alkalies. Calcium, magnesium, and certain less
common elements having similar properties are known as the metals of the
alkaline earths. The presence of both alkaline and alkaline earths compounds
contributes to the property of water called "alkalinity," while only the
alkaline earths compoimds contribute toward the property of " hardness."
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6 WATER PURIFICATION PLANTS
land was submerged beneath the sea. Such formations are the
limestones, dolomite (mixed calcium and magnesium carbonate),
sandstones, and shales, which form the great central valley of the
United States, as well as the more localized beds of salts (sodium,
calcium, and magnesium chlorids), gypsum (calcium sulphate), etc.
Again, large areas are deeply covered by till formed of finely
comminuted rock material interpersed with bowlders, which has
resulted from glacial action. In the northern United States a large
sheet of this material exists, covering roughly the Dakotas, Minne-
sota, Wisconsin, Michigan, Iowa, Illinois, Indiana, most of New
York, New England and part of Ohio, Nebraska, Kansas, and
Missouri. L^art it consists of gravels, sand, and clay, but con-
tains much ^^nd-up limestone and dolomite, so that it may be
said to act ^^ same as strata of these toward the percolating
water, the resulting ground water being high in bicarbonates of
calcium and magnesium.
The water passing through such secondary formations dissolves
the carbonates present by virtue of its contained carbonic acid,
and removes them as bicarbonates. Thus in the case of calcium
and magnesium carbonates the reaction is:
CaCOs + H2CO3 = CaC03,H2C03
MgCOs + H2CO3 = MgC03,H2C03
These bicarbonates give to a water the property of tem'porary
hardness, so called|^cause, by heating, the carbonic acid is driven
ofif, and the nomm carbonates are precipitated.
The existence of large deposits of salt and gypsum has been
mentioned. Water passing through such formations acquires
considerable amounts of these compounds as sodium and calcium
chlorids (NaCl and CaCl2), and as calcium sulphate (CaS04),
respectively. Magnesium sulphate (MgS04) is also acquired in
this way. These render the water permanently hardy i.e., the
hardness cannot be removed by ordinary boiling. A stream may
also have its chlorid content increased by the discharges from oil
and brine wells, and, if near the sea, by salt spray carried inland
on the winds. Decomposing organic matter is another source of
chlorids in water. Most limestones contain small amounts of
calcium sulphate, so that it is quite generally found in secondary
waters. *
If an alkaline stream mingles with one containing sulphates
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WATER AND ITS IMPURITIES 7
and chlorids of calcium and magnesium, a softening reaction
results quite similar to the artificial process, with the fonnation
of sulphates and chlorids of sodium and potassium, and the
precipitation of calcium and magnesium as carbonates or
their retention as bicarbbnates, according to the following
equations:
CaS04 1 , oxT r^n fCaCOs
MgS04
+ 2Na<sS04
CaCla 1 , oxT ni-. • fCaCOa 1 . .TVT oi
This accoimts for the large amounts of sodium sulphate sometimes
found in primary waters.
Traces of the nitrates of alkalies and alkaline earths exist in
various rocks, and these find their way into the water and enter
into reactions in a manner quite similar to the sulphates and
chlorids.
Iron is quite abundant and ahnost universally distributed,
occurring in most rock formations, and especially in gravels and
sands, which often have a distinct yellow or reddish discoloration
as a result. It occurs most commonly as hematite (Fe203).
As has been stated, water is often deprived of its oxygen by
decaying organic matter, in passing through the soil. In this
condition it will, if it comes in contact with iron oxid, remove
from the latter part of the oxygen, leaving it as ferrous oxid (FeO).
This ferrous oxid combines with the carbonic acid in the^ water to
form the soluble ferrous bicarbonate (Fe(HC03)2), which is
carried off in solution. Many waters contain a trace of iron in
this form. When a badly polluted stream devoid of oxygen
flows over or percolates through a gravel bed, or when the under-
flow of such a stream is tapped by means of wells, the water be-
comes so highly charged with iron as to become unusable. Simi-
larly a subterranean supply drawn from a gravel bed is usually
high in iron. On standing, exposed to the air, an iron-containing
water will become turbid, due to the oxidation of the iron, which
is changed to the insoluble ferric hydroxid (Fe(0H)3). The iron
bacterium, Crenothrix, subsists on the soluble ferrous carbonate
and changes it into an insoluble ferric state, leaving it in the water
as a stringy, gelatinous precipitate. This bacterium grows with-
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8 WATER PURIFICATION PLANTS
out light, consequently thrives in covered reservoirs, water mains,
and the like. Iron sulphate occurs in mine waters and will be dis-
cussed later.
Of the gases contained in water, the most common are carbonic
acid (CO2), oxygen, and nitrogen. The former is derived from the
air, from decaying vegetation and plant excretion in the soil, and
from decaying organic matter in lakes, swamps, and quiescent
bodies of water generally. Oxygen is derived mainly from the
air. These gases are acquired from the air quite rapidly, so that
if the water is for any reason depleted, a fresh supply is soon ob-
tained. There is some question as to how this repletion takes
place. In event of wave action, rapids, or cascades, the method
is, plainly enough, one of mechanical mixture, followed by the
solution of the gases in the water. In the case of quiet bodies of
water, the process is less plain. It is contended by some that the
gases are dissolved in the surface water by contact, and pass into
the interior of the water by diffusiony which is the tendency of
soluble bodies in solution so to distribute through the solvent that
the concentration will be uniform throughout. Thus, a gas
dissolved in the surface of a liquid would distribute itself through-
out the body thereof so as to bring about a uniform distribution of
the gas particles. This theory is opposed with much validity by
the contention that the rate of diffusion is too slow to account for
the rapid replenishment which actually occurs. The opponents
advance the theory of " streaming action," according to which
evaporation from the surface layer concentrates the impurities in
it, causing it to become of higher specific gravity than the water
below, and to sink, carrying down the occluded gases obtained by
contact with the air. In lakes and swamps abounding in plant
life a balanced relation between carbonic acid and oxygen has
been foimd to exist. During the growing season, carbonic acid is
absorbed by the plants, and oxygen is given off, causing the water
to be Jiigh in oxygen and deficient in carbonic acid. During the
dormant period of plant, life the reverse is true. Plants will first
use up the free carbonic acid in the water, and thereafter the half-
bound carbonic acid, which is in loose combination as the bicar-
bonates of calcium and magnesium, causing these to precipitate
as normal carbonates. It follows that during the growing season,
the alkalinity and temporary hardness of the water are reduced.
The presence of a trace of carbonic-acid gas seems to render water
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WATER AND ITS iM^tJRlTlES
9
more palatable, probably because it is a natural content of normal
waters.
All normal waters contain oxygen in considerable concentra-
tion, usually over 50 per cent of the saturation value, and it is
only deficient in waters polluted by putrescible organic matter, or
containing oxidizable mineral matter (such as mine drainage).
Waters not charged with sufficient oxygen give off disagreeable
odors and will not support fish life, and are shimned as water
supplies.
Nitrogen is absorbed from the air in the same manner as oxygen,
but is an inert gas chemically. Methane (marsh gas) is found in
swamp water, due to decayed vegetation. Hydrogen sulphid is
found in presence of decaying organic matter and in some deep
well waters. The last two gases are conspicuous because of the
unpleasant taste and odor which they impart to the water. They
can be removed to a large extent by aeration.
The saturation value of all gases in water varies with the
temperature. Table I shows these variations for oxygen, from
which it is seen that the concentration increases with lower
temperatures.
TABLET*
Quantities op Dissolved Oxygen in Parts per Million by Weight in
Water Saturated with Air at the Temperature Given
Temp. C.
Oxygen
Temp. C.
Oxygen
Temp. C.
Oxygen
14.70
11
11.05
21
9.01
1 .
14.28
12
10.80
22
8.84
2
13.88
13
10.57
23
8.67
3
13.50
. 14
10.35
24
8.51
4
13.14
15
10.14
25
8.35
5
12.80
16
9.94
26
8.19
6
12.47
17
9.75
27
8.03
7
12.16
18
9.56
28
7.88
8
11.86
19
9.37
29
7.74
9
11.58
20
9.19
30
7.60
10 .
11.31
* standard Methods of Water Analysis — American Public Health Association.
As has been said, the water in a stream is of two components
the surface runoff and the ground-water supply. The first com-
ponent furnishes the flood flows and the turbidity, the second
feeds the stream uniformly with a mineralized water, consequently
supplies the low-water flow of the stream almost entirely. It
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10 WATER PURIFICATION PLANTS
results that during high water the mineral content of the water is
low while during low water it is high. Furthermore, the under-
flow of a stream generally carries more dissolved mineral matter
than the surface flow. During floods the carbonic acid and organic
matter in the water may increase, due to flushing out of back-
channels, stagnant pools, and swamps.
Water from streams draining areas of primary rock, sand, or
other resistant material are very often colored. This is not due to
turbidity, which gives to water an apparent color depending on the
kind of sediment carried, but to coloring matter in solution, which
cannot be removed by ordinary filtration. This coloring matter is
derived from decaying vegetable matter in swamps, or from muck
and peat beds. It consists generally of tannates, gallates, and
organic acids from the leaves and bark of shrubs and plants.
Turbid waters are not generally colored, since the clay carried as
sediment is partly in the colloidal state and has the power of re-
moving color by the process of adsorption, by which the colloidal
particles draw the color into themselves, as a sponge does water.
The efficacy of this process depends upon the type of clay con-
stituting the turbidity, impure clays being best.
Thus far, only the properties of normal or natural waters have
been considered. In some cases industrial wastes modify or
completely change the character of streams. Most notably is this
the case with streams receiving mine drainage, especially from coal
mines. Coal contains sulphur in the form of calcium sulphate,
as iron pyrites (FeS2), and probably in organic form. This is
discharged in the mine drainage as sulphuric acid (H2SO4) and
ferrous sulphate (FeS04).
On reaching the stream, the ferrous sulphate is oxidized by the
oxygen contained in the water, forming ferric hydroxid, which
settles out, and ferric sulphate, which remains in solution:
6FeS04 + 30 + 3H2O = 2Fe2(S04)3 + Fe2(OH)6
Fe2(OH)6 = FesOs + SHaO
The rate of oxidation is partly dependent on the replenishment of
the air supply in the water. Under the most favorable conditions
of oxygen supply the process consumes several days, so that water
in mining regions may contain sulphuric acid and both ferrous
and ferric sulphates. As limestones are present in coal-bearing
formations, the normal streams of such regions would contain
bicarbonates of calcium and magnesium, but the iron sulphates
Digitized by LjOOQ IC
WATER AND ITS IMPURITIES 11
and sulphuric acid react with these, and calcium and magnesium
sulphates result, together with iron carbonate, which, if sufficient
oxygen is present, is precipitated as hydroxid. Thus a mine water
will contain the constituents of permanent hardness, and, with in-
creasing mine-drainage factor, ferrous and ferric sulphate and
finally sulphuric acid. Where the mine drainage is of recent
addition paucity of oxygen and the presence of ferroiLS carbonate
will be noticeable.
The most objectionable property of water containing mine
drainage is its corrosiveness. The iron sulphates and acid will
actively attack metals. A limited quantity of ferric sulphate,
once admitted into a boiler or other closed metallic water con-
tainer, will attack the same unintermittently. The ferric sulphate
will dissolve sufficient iron to reduce itself to the ferrous condition,
and being oxidized by the air admitted with fresh water, will again
attack the boiler, and by continuous repetitions of this process
will accomplish its early ruin. Brass piping, plumbing fixtures,
etc., are eaten away, and even ''acid-proof " bronze is not immime.
Other objectionable qualities are the taste imparted and dis-
coloration in laundry work. In the stream itself the lack of dis-
solved oxygen is harmful and often prohibitive to fish life, but no
bad odors are caused by decomposing organic matter, as should
be expected in deoxidized water, because the iron sulphates pre-
cipitate organic matter as non-putrefactive compounds. Such
waters are comparatively free from bacteria, which cannot live
imder very acid conditions. If, however, the exposure to acid
water is short, they may form spores. It thus sometimes happens
during the purification of acid water that the raw water seems
sterile, but when treated with lime and settled, numerous colonies
of bacteria appear, due to development of the spores imder favor-
able alkaline conditions. Acid water will cause sediment in sus-
pension to coagulate, so that in a turbid stream, on entering a
mining region, the suspended matter will collect in clots, and later
settle out, leaving the water clear. Should a stream containing
ferrous sulphate mingle with one high in color, due to vegetable
tannates and gallates, the water will become black, due to the
formation of natural ink.*
While mine drainage is the most important industrial waste in
♦ Proc. Eng. Soc. Western Penna., Vol. XXVII, No. 8.
Digitized by LjOOQ IC
12 WATER PURIFICATION PLANTS
changing the character of streams, other wastes may have a
marked but more localized effect. Drainage from salt and oil
wells may so pollute a stream, especially if small, as to render it
unfit for use, and even large rivers may acquire a briny taste from
this source. About 250 parts per million of chlorine will give
water a salty taste. The salt further deposits in boilers, forming
scale. Tannery waste imparts a color to the water, and, due to
acids present, has a germicidal effect, although not generally
strong enough to kill the spores. Paper-mill waste consists
partly of vegetable organic matter and of spent acid and bleach
hquors. Other sources of pollution are dye works, steel mills
(pickling acids), slaughter-houses, and breweries. The last two
may have an important influence where a water supply is obtained
from wells in alluvial drift. They impart much organic matter
to the water, whose putrefaction deprives it of oxygen, so that the
water in percolating through the alluvial gravel becomes very
highly charged with iron, and unfit for use.
Sewage from towns and cities is an important source of pollu-
tion, particularly because through it such diseases as typhoid fever,
cholera, etc., are disseminated. The sewage contains much nitrog-
enous organic matter in solid (finely divided) and colloidal states
and in solution, as well as large numbers of sewage bacteria
(which may average 3,000,000 per cubic centimeter and more).
Through the agency of some of these bacteria, the organic matter
absorbs the dissolved oxygen from the water of the stream into
which the sewage discharges, and is oxidized, with the production
of carbonic acid, water, and salts of nitrogen. Other bacteria
attack the solid and colloidal organic matter, reducing it to
solution, and by a process of fermentation break it up into ammonia,
hydrogen and hydrogen sulphid, nitrogen, and marsh gas. By
further oxidation, the ammonia is changed to nitrites and, finally,
to stable nitrates. Physically, sewage pollution may impart to the
water a turbid appearance varying with large amounts from milky
white to almost black, according to the amount of putrescible
matter; strong odors, due to putrefaction; and innumerable bac-
teria. Chemically, it is evidenced by the scarcity of dissolved
oxygen and by the presence of ammonia, carbonic acid, nitrites
and nitrates. The indicative tests are those for albuminoid
ammonia (due to very recent pollution and the presence of im-
oxidized nitrogenous matter), free ammonia (evidence of partially
Digitized by LjOOQ IC
WATER AND ITS IMPURITIES 13
decomposed sewage, and, consequently, more remote pollution),
nitrites, and nitrates, the final decomposition products in stable
inorganic form. Sewage is high in chlorine, but this passes vm-
changed through the various stages of putrefaction and affords no
reliable evidence of the time of pollution.
The living world is largely represented in natural water. Of
plant forms, besides such higher plants as water lilies, water ferns,
etc., there is a large representation of free floating types, the
group Thallophytes being most prominent. This group has two
great divisions Algce and Fungi. In the first division are in-
cluded the masses of green floating filaments, blue-green algae
(Cyanophycese), so commonly seen in ponds and reservoirs, which
impart grassy odors to the water, and the pond scum, or green
algae (Chlorophyceae). Also the minute, one-celled plant forms
(diatoms), which may be either free-swimming (having the power
of motion) or attached by gelatinous stalks, and which give off
strong odors, especially in the spring and fall. The peculiarity of
the Algse is their ability to subsist on inorganic matter, being
true plants. The Fungi, however, are parasitic, and can only live
on organic matter. Such are water molds and bacteria (Schizo-
mycetes).
Bacteria are microscopic, one-celled fungi, which generally have
the power of motion. They are very numerous in water, and de-
rived from several sources. Many species are indigenous to water;
others arie soil bacteria which have been washed into the stream,
and these predominate during floods and in turbid waters. Sewage
contributes others, each cubic centimeter containing many mil-
lions. Most bacteria in the water are harmless or beneficial,
assisting in the decomposition of organic matter, but some species
contained in sewage are very harmful, being capable of producing
disease, if the water is used for drinking purposes. These diseases
are mainly intestinal in character, and are transmitted by the dis-
charges of patients entering streams as part of the sewage, the
bacteria being disseminated through the water, which is drunk
by other persons further down stream. The most common are
typhoid fever, cholera, dysentery, diarrhoea, and other intestinal dis-
turbances. The bacteria of these diseases do not grow or multiply
in the water, which acts simply as a carrier. They are, in fact,
very difficult to discover or isolate in a water supply, but there
exists a group of bacteria, the Coli bacilli, which flourish only in the
Digitized by LjOOQIC
14
WATEB PUBinCATION PLANTS
\
'.•^L-^
/;"!
/
Bacillus Trphosos
XIOOO
OageOated Form onkffc
/
B. Coli Commonlfl
XIOOO
Cholera
X2000
Blae-OrccD Algae
XlOO
£t-Liii; Spores
Piatoms (Top View)
X30
Paramaecla
X30
Fig. 1. — Microscopic Life in Water. The number below each
group indicates the degree of magnification.
Digitized by LjOOQ IC
WATER AND ITS IMPURITtBS
15
intestines of man and higher animals,* are readily detected and
identified, and are therefore considered indicative of human or
animal pollution. Their evidence has great sanitary value, as a
water receiving hiunan excreta may at any time receive that of a
sufferer from typhoid or other intestinal diseases.
As to the representatives of animal life, besides fish and the
higher forms there are, among others, fresh-water sponges (Spon-
gidae), minute, free-swimming shrimp-Uke forms (Crustacea), and
Protozoa. The last are microscopic unicelled animalcules, which
seem quite closely related to bacteria in form and habits. Both
sponges and protozoa may cause tastes and odors in water.
As this discussion of the properties of water has been, in the
main, qualitativey it may be well in closing to give a few quantita-
tive examples of water types, so that the reader may form an idea
of the proportions in which the various constituents exist:
TABLE II
Typical Waters: Analyses in Part per Million
Compounds
A
^
C
D
E
Sodium Sulphate
6
2
9
"5
"4
"i
'l30'
49
15
6
" 57
"*8
"V
. . .^.
iVd
135
17
4
68
....
* '51
23
6
"i
ivi
96
17
16
Potassium Sulphate
3
Calcium Sulphate
78
Magnesium oulphate
33
Iron Sulphate
Sulphuric Acid
12
40
Soc ium and Potassium Chlorid
4
7
Calcium Chlorid
Sodium and Potassium Nitrate
1
6
2
15
25
n
28
2
Sodium and Pot-assium Carbonate
Bicarbonate of Iron
Sodium and Potassium Bicarbonate
Calcium Bicarbonate
Magnesium Bicarbonate
Silica
9
Alumina
8
A, Stream flowing through primary formation. The car-
bonates and bicarbonates of the alkalies are high, those of the
alkaline earths low. The water received some calcium and
magnesium sulphate, which reacted with the alkaline carbonates
to form alkaline sulphates, with a corresponding increase in the
* For a modification of this statement, see page 141.
Digitized by LjOOQ IC
16 WATER PURIFICATION PLANTS
bicarbonates of the alkaline earths. Note the high silica content
(in colloidal state).
B. Typical secondary stream, from limestone formation.
The principal constituents are alkaline earth bicarbonates. A
small amoimt of alkaline carbonates was present, as well as some
calcium or magnesium sulphate, which by interaction formed
sodium sulphate and alkaline earth bicarbonates. In this water
all hardness is temporary and equals the total alkalinity.
C Stream high in calcium sulphate {permanent hardness).
This water is characterized by permanent hardness and a high
magnesium content.
Z). Stream high in chlorids. Polluted by salt wells or mines.
E, A stream badly polluted by mine water. This was normally
a water of type C, although lower in bicarbonates, but has been
entirely changed in character by the action of iron sulphate and
sulphuric acid from mine drainage, almost all constituents being
converted into sulphates. An extension of the analysis to dis-
solved gases would probably show much carbonic acid and a de-
ficiency of oxygen. The alumina in solution is characteristic of
such waters.
Note in all the analyses: (a) the imiformity of the chlorids
(except, of course, in D); (6) the imiformity of nitrates, iron
(except in E), and silica (except in A), suggesting that these
constituents are more or less equally distributed through all
geological formations and are sluggish chemically in the form
present.
Fig. 2 shows a map of the United States on which the geological
formations are very broadly indicated. The principal primary
formations are in the Appalachians, the northern part of Wis-
consin and Minnesota, and the great mountain region of the West.
A large area of central and northern United States, roughly that
portion north of the Missouri and Ohio Rivers, is deeply covered
with glacial drift, which in some cases consists of ground-up local
rock, and in others of materials transported hundreds of miles
from their original locations. Some of this material has also been
carried south of the area of glaciation by prehistoric torrents, and
by the rivers and winds. Streams in this glaciated region derive
many of their mineral qualities from the leaching of this drift.
The limestone formation occuring in Missouri, Kentucky, southern
Ohio, Tennessee, Alabama, and Georgia is also indicated. The
Digitized by LjOOQ IC
WATER AND ITS IMPURITIES
17
Fig. 2. — Map to Illustrate how Geologic Formations Influence the
Properties of Water.
Digitized by LjOOQ IC
18 WATER PURIFICATION PLANTS
streams of this formation are notoriously hard, and require soften-
ing for economical use. Areas polluted by mine drainage are
shown in black. The map illustrates the heterogeneous chemical
contents to be expected in large rivers. Thus the Missouri
originates in an area of primary rocks, later flows through a region
of secondary or derivative formation, receiving also its quota of
hard water from limestone beds. This map is submitted to illus-
trate broadly the principles involved and makes no pretense at
great accuracy or detail.
Digitized by LjOOQIC
CHAPTER n
TYPES OF PURIFICATION PLANTS
The objects of water purification may be briefly stated as
follows:
1. To render the water safe and harmless for drinking and
domestic use. This involves the almost complete removal of
bacteria, in order to be sure that all nathogenic (disease-producing)
species are eliminated.
2. To make the water inviting and pleasing in appearance and
taste. This requires:
(a) The removal of suspended matter.
(6) The removal of odors and tastes.
(c) The elimination of dissolved color.
(d) The removal or oxidation of organic matter.
(e) The removal of iron.
3. Improving the water for industrial and household use by:
(a) Reducing the hardness (temporary and permanent).
(6) Eliminating iron in solution.
(c) Neutralizing acids (such as sulphuric and carbonic).
Any or all of these objects are attainable by means of a proper-
ly designed and operated purification plant to a degree sufficient
to meet all requirements. It is possible to remove over 99 per cent
of the bacteria regularly, and by sterilization the removal may be
made practically complete. It is hardly necessary to say that
this has a marked effect on the reduction of water-borne diseases,
but it may be well to call attention to Fig. 3, showing the death-
rate from typhoid fever in Columbus, Ohio,* for the last ten years,
during five of which the water was filtered. Filtering has reduced
the death-rate from an average of about 75 per 100,000 to about 17
per 100,000 per year. The reduction in typhoid fever is further
shown by the following table, compiled by Mr. Allen Hazen:
♦Compiled by Charles P. Hoover, Chemist in Charge of Filtration Plant,
Columbus, O.
19
Digitized by LjOOQIC ^
20
WATER PURIFICATION PLANTS
TABLE III
Annual Average Death-Rates from Typhoid Fever Before and After
Filtration
City
Extent of Record
Years Before Years After
Typhoid Death-Rates
PER 100,000 •
Before
After
Binghamton, N. Y.
Cincinnati, O
Columbus, O
Hoboken, N. J
Paterson, N. J
Watertown, N. Y. .
York, Pa
Albany, N.Y.*....
Lawrence, Mass.*..
Washington, D. C*
5
4
11
7
5
5
2
9
7
5
5
4
4
6
9
7
12
9
15
6
47
50
78
19
32
100
76
74
114
57
15
12
11
14
10
32
21
22
25
33
* Slow sand filters.
From Hazen, in International Congress of Demography and Hygiene, 1912.
TYPHOID FEVER DEATH RATE
PER 100.000 POPULATION
COLUMBUS. OHIO
150 19t
M 1905
1906
1907
1908
1909
1910
1911
1912
1913
150
125
125
'
100
100
75
75
50
50
25
^
■
25
1
1
1
1
1
1
__
■
■
1
1
1
■
■
I
I
1
H
1
I
1
I
1
I
1
I
I
I
I
I
U
NFILTERED WATER
FILTERED WATER
Fig. 3. — ^An Example of the Decrease in Typhoid Fever Death-Rate Fol-
lowing Filtration of the Water Supply.
Digitized by LjOOQ IC
TYPES OF PURIFICATION PLANTS 21
Suspended matter can be completely removed; odors, tastes,
and color can be greatly reduced. Hardness can be reduced to
the residuum due to dissolved carbonates, and the same may be
said of acids, if the treatment is carried fa,r enough. Iron and
organic matter can be brought down to negligible quantities.
The processes of water purification finding practical applica-
tion for municipal purposes are:
(a) Coagulation and sedimentation.
(6) Slow sand filtration.
(c) Rapid sand or mechanical filtration.
To these might be added filtration through natural sand beds,
possible only under exceptional geological conditions, and various
experimental methods of improven value.
Coagulation and Sedimentation. Coagulation and sedimen-
tation is used to some extent in purifying the turbid river waters
of the Middle West, and has found its most successful application
at St. Louis, Mo.,* and a number of other municipalities situated
on the Missouri River. It requires coagulating apparatus and
facilities of the kind described in connection with mechanical
filtration, and large settling basins, of from one to three days'
capacity.
The coagulants used are generally ferrous sulphate and lime,
owing to their comparative cheapness and the high specific gravity
of the coagulum formed. As the waters thus treated are very
turbid, large amounts of coagulants are required, and for the same
reason the question of organic coloring matter, a delicate subject
in connection with the iron-lime treatment, is eliminated.! Alum
and lime as coagulants have also been used in this process.
The settling basins are similar to those described in connection
with mechanical filtration, except in respect to size. Needless to
say, the study of proper baflBling in order to prevent short-circuit-
ing or currents is of utmost importance in this case. It is not
likely that this process will find extensive use in the future, as
mechanical filtration has proven to be more effective and eco-
nomical. The general tendency is toward supplementing with
filtration such plants as are now in operation.
* The process at, St. Louis has been supplemented by mechanical filtration,
t See page 243.
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22 WATER PURIFICATION PLANTS
The (lata and charts in this book apply with equal force to this
process, as does also much of the matter in the last chapter, despite
the title thereof.
Slow Sand Filtration. This process is of English origin, and
dates from about 1830. From England it was disseminated
throughout the Continent, where it is now widely used. In
America it has found extended use in the older installations and
in the purification of the Supplies of large cities, although of
recent years the mechanical process has become an important
competitor in plants of large size, and has far outstripped it in the
case of supplies for smaller towns.
Description of Plant. A general view of a typical slow sand
filtration plant is shown by Fig. 4. It consists of duplicate sedi-
mentation basins d-d, the filter units g-g-gj the office and labora-
tory e, and various auxiliaries.
The water is drawn from the river through the intake a, and
pumped to the sedimentation basins by low-service pumps in the
station b, entering the basins through a distributing grid of pipe
which may termma^e in the aerating risers c-c-Cj to remove ob-
noxious gases from the water, and distribute it uniformly across
the basins. It is sometimes desirable with turbid waters to use
coagulants to assist in clarification, in which case the necessary
apparatus, similar to that used in mechanical filtration, is in-
stalled in the building e, which is enlarged for that purpose and
for coagulant storage. The size of the basins is dependent on the
amoimt and fineness of sediment in the raw ^yater, the period of
sedimentation being generally from four to twelve hours. In
filtering clear lake water, where the removal of bacteria is the main
object, the sedimentation basins may be omitted entirely.
After passing through the basins the water is collected by the
inlets of the pipe manifold at the lower end, which is connected
with the settled water main extending through the court between
the two rows of filters. Branches from this main lead to each
filter, terminating within the filter in a float valve which maintains
a uniform depth of water over the sand.
Each filter consists of a water-tight basin of masonry or rein-
forced concrete, generally roofed over with a groined arch con-
struction supported on columns, the whole being covered with
several feet of soil and sodded, as an additional protection against
freezing of the water, which materially affects the efficiency of
Digitized by LjOOQ IC
TYPES OF PURIFICATION PLANTS
23
Digitized by LjOOQ IC
24 WATER PURIFICATION PLANTS
filtration. Covering the filter also prevents the formation of
algae, by excluding the light necessary for their growth. Access
to the uiterioE is provided by an inclined runway and by numerous
double-covered manholes in the roof, which also furnish the
necessary light and ventilation for carrying on work in the filter.
The area of these filter units is from one-fourth to one acre or more,
depending on the total capacity of the plant.
The filtering medium consists of a bed of clean quartz sand ft,
of a size of grain approximating that of granulated sugar. In
technical terms it has an effective size * of about 0.3 to 0.4 milli-
meters and a uniformity^ coefficient of about 1.5. The depth of
sand bed is generally from 3 to 4 feet in a new filter, decreasing as
the dirty sand is scraped off with continued use. This sand is
imderlain with a foot of gravel i, so graded as to increase in coarse-
ness toward the bottom. The function of this gravel is to prevent
the sand from being washed into the collector system with the
filtered water, and to allow ample water passages through which
the filtrate can flow to the collecting pipes. Open-jointed tile
pipes jj from 4 to 8 inches in size, rest on the filter bottom, buried
in and surroimded by the gravel. Generally one such collector
pipe serves the area between two adjacent rows of columns, and
carries the filtered water to the main collector A;, which is placed
through the center of the filter unit.
It is most important that the filtration proceed at a uniform
rate, and to this end each filter imit is provided with a regulator
house If the lower portion of which forms a water-tight well con-
taining the regulation mechanism. The arrangement shown, used
in the Albany plant by Mr. Allen Hazen, will illustrate the general
principle of regulation, although not of the most recent type. It
does not profess to operate automatically, and therefore will better
serve to emphasize the attention required to maintain a uniform
rate of filtration, even by more recent " automatic " types. The
well is divided into two parts by a concrete diaphragm m, and by
tight wooden stop planks above the diaphragm. The filtrate,
collected by the main k, flows into the first compartment of the
well through the valve o, rising therein to a height lower than the
* The effective size of a sand is that size of sand grain than which 90 per
cent of the grains are larger.
t The uniformity coefficient is the ratio of the size of sand grain than which
60 per cent is finer, to the effective size.
Digitized by LjOOQ IC
TYPES OF PURIFICATION PLANTS 25
water level over the sand by a distance r, representing the friction
of the water through the sand, gravel, and under-drain system or
'* loss of head " through the filter. The water flows through the
^ orifice n into the second compartment of the well, and thence
through a valved branch pipe to the main s, which carries the
effluent of all the units to the filtered or " clear '' water basin,
ready for delivery into the distribution system. The rate of flow
through the orifice n is a function of the difference in water level
between the two compartments of the well when the orifice is
submerged, and a fimction of the water level in the first compart-
ment when that in the second is below the bottom of the orifice.
By arranging a float in each compartment so as to indicate this
difference in water level on a dial, the rate of filtration may be
determined from the reading of the dial, and can be regulated to
the desired amoimt by means of the graduated valve o. Two
other floats, similarly arranged, indicate the loss of head through
the filter. A valve and drain pipe are provided, leading to a
main drain for emptying the filter.
Rate and Loss of Head. The rate of filtration varies from
2,000,000 to 6,000,000 gallons per acre per day, 3,000,000
gallons being very commonly used. The rate used at any plant
should be varied as experience dictates, the controlling elements
being the quality of effluent, which will deteriorate with too high
rates, and the period between cleaning the filters, which will
shorten imder the same conditions, and may become so frequent
as to prove uneconomical. The head of water required to force
the water through the filter at the determined rate is measured by
the loss-of-head gage. For any given rate of filtration the loss
of head increases with the length of time the filter is in operation,
due to the deposits of silt formed on and in the filter sand, which
greatly augment the friction through same, until finally the head of
water would become sufficient to break down the resistance of the
sand, causing unfiltered water to find its way into the collector
mains. At a safe interval before this occurs, the filter must be
shut down and either raked or cleaned by scraping. This maxi-
mum loss of head may be conservatively placed at from 5 to 6
feet. The required head should be furnished by the water above
the sand, that is, the water level in the first compartment of the
regulator well should never fall below the level of the top of the
sand. Should this occur, a " negative head " or partial vacuum
Digitized by LjOOQ IC
26 WATER PURIFICATION PLANTS
will form in the upper portion of the sand bed, resulting in the
liberation of some of the dissolved air from the water, thereby
causing disturbances in the filtering process. This is especially
prone to happen in cold weather, as the dissolved air carried by the
water is then at a maximum.
The Theory of Filtration. Filtration is a combination of
several processes. The most obvious of these, although not the
most important, is the straining out of particles too large to pass
the interstices between the sand grains. However, as most of the
particles of suspended matter are so small as to readily pass
through these spaces, it is obvious that other processes must be
acting to remove them from the water. The small pockets formed
by adjacent sand grains act as minute sedimentation basins in
which the suspended matter may settle. Bacterial action plays
a most important r61e. After a filter is in operation for a time a
slimy gelatinous film forms on the surface and explorations into
the sand will show similar jelly-like matter forming between or
coating the sand grains. Examination will show this jelly to be
of bacterial origin, as is also shown by the fact that it forms when
filtering clear waters. The surface coating has been named the
Schmuizdecke (dirt cover) by the Germans, who attribute
most of the efficacy of the filter to its action, and place so much
confidence in it that they consider a sand bed a foot thick sufficient,
if properly coated, to yield a satisfactory eflBluent. The Schmuiz-
decke probably retards much of the suspended and colloidal matter,
but the bacterial jelly within the sand is also important both be-
cause of its straining effect and because it entraps and holds
particles of silt and bacteria on the " sticky-fly-paper " principle.
The efficiency of a filter increases with age, due to continued bac-
terial growth and the resulting formation of slime and jelly in the
interior. This jelly-like matter is capable of absorbing color
from the raw water and may effect a reduction up to 25 per cent.
There is also a small amoimt of chemical action within the filter,
in the way of oxidation of the dissolved organic matter contained
in the water.
While a properly working filter bars the passage of practically
all the bacteria in the raw water, a considerable number may
sometimes be foimd in the effluent. It has been proven by experi-
ment that these result from growths in the sand and imderdrains,
and also that they are harmless varieties.
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a
6
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28 WATER PURIFICATION PLANTS
Raking the Filters. When the loss of head becomes excessive,
due to clogging of the filter sand, conditions may be relieved by
loosening the surface by means of ordinary rakes. It is found that,
after raking, the filter clogs more rapidly than before, so that re-
peated raking more than twice in succession is impracticable
and scraping must be resorted to.
Scraping the Filters. In the lower left comer of Fig. 4 a filter
is shown, as it would appear with the roof removed, undergoing
the process of cleaning by scraping. The filter is shut down and
drained, and the surface of the sand is removed to a depth of one-
half to one inch with broad flat shovels, and gathered into con-
venient piles. The piles of dirty sand are removed by means of a
portable sand ejector <, shown in detail by Fig. 5.* This consists
of a tight metal box containing a large ejector, operating under
water pressure furnished by a three or four inch pipe. The sand
is shoveled into this box, where it is kept in a fluid condition by
water jets from several perforated *' irrigating pipes " in the
bottom of the box. In this fluid or suspended condition it is
drawn into the ejector and discharged through a " sand pipe ''
(generally 4 inches in diameter) leading to the sand washers Vr-u.
Pressure and sand pipes are located, with convenient outlets, along
the filter walls, so that the ejector can be attached at any desired
point by means of hose connections. The sand washer is shown in
detail by Fig. 6.t It consists of a conical metal hopper, in the
throat of which are located an ejector and an auxiliary jet, the pur-
pose of which is to supply sufficient water to maintain a con-
tinual upward current which escapes by means of the overflow
notch at the top of the hopper. The mixture of dirty sand and
water from the filter enters the hopper from above and settles
toward the bottom against the continual upward current from
the auxiliary jet. The dirt and silt are thus removed and carried
up and out of the hopper via the overflow. The sand settles to the
bottom, where it is seized by the ejector and carried through
piping to the sand storage bins x-x. Two washers are generally
operated in series, washing the sand twice, and the dirty overflow
water passes through several concrete boxes w on its way to the
sewer, so that any fine sand carried over may be trapped therein.
* Trans. Am. Soc. C. E., 1904, 1. Ill, p. 227.
t Trans. Am. Soc. C. E., 1906, 1. VII, p. 586.
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TYPES OF PURIFICATION PLANTS
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30 WATER PURIFICATION PLANTS
preventing the clogging of the sewer. The sand bins x-x have
conical bottoms provided with drains, so that the water may be
removed from the sand. '
In winter it is difficult to wash sand, owing to trouble with
freezing pipes, ice, etc., and it is therefore customary to scrape the
sand into piles, to await the advent of warmer weather for washing.
If these piles tend to grow so large as to seriously cut down the
efifective area of the filter, open-bottomed boxes or frames are
placed in the filter and the sand shoveled into these, being thereby
more closely confined.
The frequency of scraping is a factor of the turbidity of the
settled water and the rate of filtration. In the worst cases it may
be required at intervals of a few days; under favorable conditions
the period between scrapings may be from four to six weeks. The
advantage of preliminary sedimentation in this connection is
obvious.
After scraping, the sand surface is smoothed and the filter is
slowly filled with purified water from below, and when this has risen
well above the sand, raw water is introduced and filtration slowly
started, with frequent examinations as to the quality of the
effluent.
Replacing Sand. When, by several scrapings, about a foot of
sand has been removed, the filter is resanded to its original level.
To do this, it is first scraped to a greater depth than usual, to make
sure of removing all the dirty sand, and is then filled with water
to the level at which it is desired the sand surface should come.
Ejectors placed in the sand bins discharge clean sand through
sand return pipes terminating in lines of hose which are floated on
small rafts over the surface of the filter to be resanded, and which
are guided so as to distribute the sand evenly. When the desired
level is reached, the water is drawn down, the surface smoothed
over, and the filter started.
General Operation. The general remarks on operation given
hereafter apply to slow sand as well as to rapid sand filtration. If
coagulants are used, the tests and methods given apply; if not, the
chemical tests, in the main, may be omitted, and much stress
placed on the bacterial tests. The interpretation of tests as re-
gards bacteria and coli holds also. Much attention should be
given to bacterial tests of the effluents of individual filters.
Sterilization. It has become customary of late years to treat
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TYPES OF PURIFICATION PLANTS 31
the filtrate with hypochlorite of lime, as an additional precaution.
This is explained in detail in Chapter VI. . Needless to say, the
hypochlorite cannot in this case be applied to the settled water,
as this would interfere with the bacterial action within the filter.
Modem Tendencies in Slow Sand Filtration. There is a
tendency toward increased rates of filtration, in the most recent
plant 6,000,000 gallons per acre per day being used. With turbid
waters adequate coagulation and sedimentation have been intro-
duced, as an adjunct to higher rates, and to relieve the filters of
part of the load. Extensive experiments have been made with
apparatus for washing the sand in place, but as yet have not been
entirely successful. Centralization of control by leading all
piping to one common regulator house has also been attempted.
It will be seen that all these improvements tend toward a quasi-
mechanical type of filtration.
Mechanical Filtration. The primary difference between rapid
or mechanical and slow sand filtration is in the higher rate used in
the former process— 100 to 150,000,000 as against 3,000,000 gallons
per acre per day, or about 50 to 1. This high rate necessitates
reheving the filters of the burden of removing coarse suspended
matter, which is accomplished by coagulation and sedimentation.
It also follows that, as the rate of clogging the sand varies directly
with the rate of filtration, the filter beds must be cleaned daily, and
of necessity this must be done in dtu, to avoid a laborious removal
and replacing of the sand. Since there is no time for the forma-
tion of a Schmutzdecke by natural biological processes, a substitute
must be supplied in the shape of a jelly-like film, or " mat," of
coagulum, which forms with great rapidity on starting the filter
after cleaning.
Description of Plant. Fig. 7 shows a typical rapid sand
filtration plant. The general similarity, in parts and arrangement,
to the slow sand plant is readily grasped. The most striking feature
is the contraction or concentration of the whole plant as compared
with the slow sand type. The settling basin is present as before,
but is often deeper and of a different type of construction and more
thoroughly baffled. The office and laboratory building remains,
containing also the coagulant apparatus and storage, for which
reason it is frequently called the '^ coagulant house or building."
The court between the filters assumes a different shape, though
maintaining its functions, by being divided into a lower story or
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32
WATER PUMFICATION PLANTS
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TYPES OF PURIFICATION PLANTS 33
pipe gallery, containing the piping, valves, and regulating devices,
and an upper operating platform. We may imagine the individual
regulator houses as expanding and merging into one continuous
structure over both the former court and the greatly contracted
filter units, their former locations being indicated only by the re-
maining characteristic groups of valve stands on the operating
platform.
The advantages of this new arrangement as regards ease of
operation and access to all parts are easily seen. The whole
filtering area is under the eye of the operator; he may examine the
distribution of the raw water and its quality at all points. By
. manipulating a few valves, he may drain any unit sufiiciently to
examine the sand surface and mat, in a very short time. The
tendency toward vertical stratification of the sand is nullified by
the small area, and a uniform horizontal hydraulic grading of the
sand bed is maintained by frequent washing. The capacity of the
units is generally less than those used in slow sand filtration, so that
the effluent may be more closely controlled by individual samples,
and any defective imit can be shut down immediately, with small
loss of pimiped and coagulated water, and the fault can be found
and corrected with a minimum of labor. The formation of the
mat, or artificial Schmutzdecke, can be controlled as to consistency
and thickness by applying coagulants directly to the raw water in
the filter after washing.
Two important differences in the theory and operation are
these: bacterial growths in the filter bed are not required, owing to
the artificial mat formation; therefore the beds may be sterilized
by adding hypochlorite to the settled water, and the presence of
"after-growth '' bacteria in the effluent done away with. Negative
head in the sand bed, so scrupulously avoided in slow sand filtra-
tion, is featured in the rapid process, as decreasing the necessary
depth of filter tubs and tending toward a uniform distribution of
rate over the bed. This is possible because the filters are washed
so frequently as to minimize the chance of sufficient air being
liberated within the bed to affect the operation.
Settling Basins. The settling basin shown in Fig. 7 is con-
structed of reinforced concrete, of a type frequently adopted where
land is limited or expensive, as the vertical side walls give a maxi-
mum capacity with the least area. A basin similar to that shown
in Fig. 4 with earth embankments is less frequently used for me-
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34 WATER PURIFICATION PLANTS
chanical filter plants. The water enters through the inlet manifold,
terminating in the risers 6-ft-6-6, which may extend above the
water, acting as aerators as shown, or not, according to the condi-
tions to be met. The basin is provided with baffles, C1-C2-C3,
whose function it is to prevent undercurrents and to maintain
a uniform flow throughout the basin. After passing through
the basin the water is collected by the risers d-d-d-d of the outlet
manifold and carried to the filters through the settled water
main e.
The floor of the basin is of smooth concrete with a decided pitch
from all sides toward the center, where a sump / is located. In
this sump is a drain valve operated by a handwheel h^ by means of
which the basin may be emptied for cleaning through the drain g.
After being emptied, the remaining mud is washed out through the
drain by means of a hose. Fig. 7 shows a single basin, which
necessitates either shutting down while cleaning, or by-passing the
water directly to the filters by closing valves i and j and opening
valve k. Many plants have duplicate basins, one of which may be
cleaned at a time without interference with the operation of the
plant.
Coagulating Apparatus. The coagulant house shown is three
stories high. The first floor forms the main entrance to the filter
house, contains the wash water pumps, air compressor, receiving
room and storage for coagulants, stairway to upper floors, etc.
The second floor contains the combined office and laboratory, the
solution tanks i-i-Z and orifice boxes m-m-m, from which pipes
n-n-n carry the coagulant solution and discharge it into the raw
water main a at 0. Sometimes additional coagulant pipes are
provided, so that the coagulants may be introduced at the center
baffle of the settling basin, C2, or into the settled water main e.
The third floor is on a level with the tops of the solution tanks and
is used for charging these and for coagulant storage. It also con-
tains a scale for weighing chemicals and the stirring apparatus of
the tanks. An elevator or hoist is installed, serving all floors, but
primarily for carrying up barrels and sacks of coagulant to the
third floor.
Fig. 8 shows in section a typical solution tank and orifice box.
Except when used for lime, these tanks are generally built of re-
inforced concrete. On top of the tank is a dissolving box with a
perforated bottom, into which the weighed coagulant is dumped
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TYPES OF PURIFICATION PLANTS
35
Water Motor
Tm l:;i\v WdlL'i'
Fig. 8. — Section of a Coagulant Tank and Orifice Box.
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36 WATER PURIFICATION PLANTS
and dissolved by a spray of hot water, the solution flowing through
the perforations into the tank. An automatic float shuts off the
hot water when the tank is full, to prevent overflowing. Before
starting to use the solution the operator closes the hot-water
valve by hand. In the tank are mixing paddles attached to a
vertical shaft, rotated by bevel gearing, belt-driven from a water
or electric motor. These paddles keep the solution thoroughly
mixed and of uniform strength throughout.
From the bottom of the tank, a short valved pipe connection
leads to the orifice box. It is the function of this device to feed the
solution into the coagulant pipe at a constant rate, regardless of the
amount in the solution tank. To this end a float valve on the inlet
maintains a constant head on an orifice or opening in a thin
metal plate in the bottom of the box, under which conditions, by
the laws of hydraulics, the flow through the orifice will be constant
and proportional to its area of opening. A sliding or rotating disk
allows this area, and consequently the rate, to be varied, and a
graduated handwheel is provided, so that the size of opening may
be known to the operator. A screen across the box prevents
large particles from obstructing the orifice, and the glass front
allows the operator a view of the interior, and, by a mark etched
upon it, tells him at a glance whether the water in the box is at the
correct level, a most important point, as the rate of flow varies
with the water level over the orifice. This is but one of a very
diverse variety of orifice boxes, which differ in detail, but not in
principle. Some are arranged to automatically vary the orifice
opening with variations in the rate of the raw water, a desirable
point if it does not lead to neglect by the operator, for automatic
devices act as such only when given the necessary attention, which
is increased over that required by simple non-automatic, in pro-
portion to their degree of complexity.
The solution tank should be provided with a float gage for
indicating the depth of solution and having in conjunction a lov)-
water alarm, consisting of an electric bell which will ring when the
solution tank is about to become empty. The dial of the float
gage is conveniently graduated as in Fig. 9, where it is seen that,
besides the depth scale, concentric scales are added corresponding
to the opening of the orifice box, these being graduated in hours,
so that in charging the tank, knowing the opening of the orifice box
and length of run, the operator can fill the tank to the required
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TYPES OF PURIFICATION PLANTS
37
Fig. 9. — Dial for a Solution Tank Depth Gage.
m:^
Hjpo Solution Tank ^Si^
Fig. 10. — Dissolving Device for Hypochlorite of Lime.
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38
WATER PURIFICATION PLANTS
cij
t-
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TYPES OF PURIFICATION PLANTS 39
depth, or if the opening of the orifice is changed during a nm, he
can tell at a glance how long the tank will last at the new rate.
Each solution tank is provided with a drain and valve for clean-
ing purposes.
Lime cannot be dissolved directly in the manner described,
but before being poured into the solution tank must be slaked, as
described in Chapter IX. This requires the use of iron slaking
boxes.
Hypochlorite of lime presents some difficulties owing to its
comparative insolubility and its lightness, causing it to float on the
water like flour. The home-made device shown in Fig. 10 is very
handy for dissolving hypo in small plants. It consists pi an ice-
cream freezer, with the can perforated with numerous small holes
(say one-eighth inch). The freezer pail is bolted solidly to the top
of the solution tank. A valved drain is provided from the freezer
to the tank, as well as a supply of warm water to keep the pail
filled. The weighed hypo is placed in the perforated can, and the
pail filled with water. On turning the freezer the paddles force
the hypo toward the periphery of the can by centrifugal force, and
the scrapers squeeze it through the perforations in the can. The
freezer should be large compared to the amount of hypo used, and
all possible parts should be well coated with asphalt paint, to
prevent corrosion.
Fig. 11 shows a hypochlorite plant suitable for treating the
unfiltered water supply of a city. It consists of dissolving ap-
paratus, two orifice boxes, two solution tanks, stirring devices,
hypo storage, and laboratory. To dissolve the hypo, which is
received in sheet-metal canisters, a canister is suspended from
the traveling scale and run over the dissolving box. The at-
tendant cuts two holes in the end of the canister, one at the top
and one at the bottom. By directing a stream of water under
pressure into the upper hole, the hypo is washed out through the
lower hole into the dissolving box. Thence it flows into one of the
solution storage tanks and passes through the orifice box into the
water. In dissolving the hypo, the attendant wears a mask and
goggles and receives fresh air under slight pressure through a
hose. Thus annoyance from fumes and dust are obviated. A
similarly designed apparatus can be used in connection with
filtration plants.
The Filters. Figs. 12 and 13 show respectively the part plan
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40 WATER PURIFICATION PLANTS
and section of a modem concrete filter house. Referring to Fig.
13, it will be seen that the filters are in two rows, with the pipe
gallery and operating platform between them, and a subbasement
for filtered water storage below, making a very compact and eco-
nomical arrangement. The water from the settling basin enters the
pipe gallery through the settled water main e, extending the length
of the gallery with a valved branch to each filter. The level of the
water on the filters may be regulated by float valves attached to
the ends of the settled water inlets, as shown in the right-hand
filter of Fig. 13, or the level for all the filters may be fixed by an
overflow pipe in the settling basins.
The nature of the filtering material through which the water
passes is shown in the section, Fig. 13. It consists of a 30-inch
layer of sand similar to that used in slow sand filters in quality, but
slightly coarser (effective size 0.4 to 0.6 mm.). In operation it is
covered with a mat or film of coagulum. The sand rests on about
a foot of graded grayel, generally increasing in size from one-
eighth inch at the top to three-quarters inch at the bottom. The
gravel in turn is supported by perforated brass strainers, through
which the water passes to the collector pipes below. Fig. 14
shows several types of strainer systems. The upper type is ex-
tensively used in plants using a high rate of wash. The bottom of
the filter is molded into a series of parallel ridges and grooves, ap-
proximately of the dimensions shown, all leading to a central
collecting gutter. The grooves or valleys have ledges on- which
rest perforated brass plates supporting the gravel. The portion
of the groove below the strainer plate serves as a collecting channel
for the filtered water. The gravel is confined between the ridges
and is held down against the upward pressure while washing by a
brass wire screen. A somewhat similar strainer system is in use
at the Columbus, Ohio, plant and is shown by Fig. 42. The lower
types are in general use at plants where both air and water are
used in washing, and are similar to that shown in Fig. 13. There
is a main collector through the center of the filter with lateral
pipes (generally 2-inch diameter and spaced six inches on centers).
Into these lateral pipes brass strainers are screwed. The left-hand
side of the cut shows the arrangement for separate air and wash-
water manifolds. In this case the perforated brass air laterals are
placed just above the gravel. The strainer heads shown are of the
slotted type, the wash water being distributed laterally through
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41
Fig. 12. — Plan of a Small Filter- Building, Showing Filter Units and Piping.
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42
WATER PURIJ'ICATION PLANTS
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TYPES OF PURIFICATION PLANTS
43
the slots. The right-hand strainers are of the patented combined
air and wash-water type (Williamson strainers). It will be noted
that the strainer shanks extend almost to the bottom of the
lateral pipes. To wash with air, the air is admitted to the upper
half of the lateral pipes, which contain sufficient water to seal the
Perforated Braa$ Plate
Mfas Id. hoics |»er Uu.ft.
ii..
Omded Omrel
Collector I^atemt
^^mm^
V Co1[nbiD(^d
/Air and Wash
Fig. 14. — ^Typical Strainer Systems Used in Mechanical Filters.
extended ends of the strainer shanks. The air escapes through
the strainers via small holes drilled in the shanks of the strain-
ers. There are many types of strainers in use other than those
described.
As in the case of slow sand filters, the laterals discharge into a
main collector, bisecting the filter, which carries the filtered water
to an effluent or rate controller, situated in the pipe gallery, one
being provided for each filter unit. Owing to the rapid increase in
loss of head, automatic control is here imperative. If the filters
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WATER PURIFICATION PLANTS
operate under negative head, the controllers are set some distance
below the filters, which requires them to regulate equally well
with their outlets under back pressure from the clear-water basin.
Fio. 16.— Rate of Flow Controller for Mechanical Filters. Orifice Box Type»
It is also desirable that they should operate with a minimum dif-
ference of head. The conditions practically eliminate the fixed-
Fia. 16.— Rate of Flow Controller for Mechanical Filters. Velocity Type.
head-over-orifice type, Fig. 15 (such as described for the slow sand
plant, or an enlarged orifice box), and require a device wherein the
velocity head or an artificially created difference of head in the
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effluent pipe regulates the area of a valve pro rata. A typical con-
troller of the velocity type is shown diagrammatically in Fig. 16.*
Fig. 17.— Rate of Flow Controller for Mechanical Filters. Venturi Type.
Courtesy Simplex Valve and Meter Company.
Fig. 17a. — ^Venturi Type Rate Controller.
The water flows downward through the draft tube a and striking
the plate b has its direction reversed so that it impinges on the
inverted hollow cylinder c, the sides of which form the gates over
* Made by the Norwood Engineering Co. for the Charleroi, Pa., plant.
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46 WATER PURIFICATION PLANTS
the apertures d-d-d. The impact of the water raises the cylinder
in proportion to the velocity in the draft tube, thereby throttling
the apertures d-d-d, and allowing the water to escape as indicated
by arrows. By means of a cone valve e regulated from a valve
stand on the operating floor, the controller can be set to any de-
sired rate. Fig. 17 is a schematic sketch of a controller of the dif-
ference-in-head type. An obstruction, such as a Venturi tube,
orifice plate, etc., is placed in the effluent pipe at a, followed by a
valve 6 whose opening is regulated by the position of the piston c.
The position of this piston is determined by the difference between
the direct upward pressure from below the obstruction and the
downward pressure transmitted to the top of the piston from above
the obstruction by means of the pipe d. The controller can be
set to deliver at any desired rate by the position of the weight w
on the lever arm.
Clear- Water Basin. The clear-water basin, into which the
effluent discharges from the controllers, is simply a reinforced con-
crete tank beneath the fflters, for equalizing the load on the high-
pressure pumps and furnishing a reserve for washing filters, etc.
It is provided with a sump and valve for drainage and cleaning.
Washing Filters. In washing a fflter it is first shut down by
closing the settled-water and effluent valves p and q and draining it
to the top of troughs by opening the sewer valve s. Fig. 13. As-
suming the filter to be piped for air, the compressor is then started
and the air valve t opened, admitting compressed air to a grid
placed just below the surface of the filter gravel which distributes
the air uniformly through the sand bed by means of minute per-
forations in the pipes of the grid. The purpose of the air is to
loosen the sand, mix it, and remove dirt by the abrasion of the sand
particles. After three to five minutes of air washing the air valve
is closed and the wash valve u, Fig. 13, is slowly opened. Filtered
water flows from the wash-water pipe v through the collector sys-
tem and upward through the strainer openings, which are propor-
tioned to give a uniform upward flow over the area of the filter.
The wash water flowing upward through the sand thoroughly
cleanses it and grades it hydraulically, the dirty water escaping
by means of the wash troughs w-Wy Figs. 12 and 13, and sewer
outlet to the sewer Xj Fig. 13. After the sand is clean the filter is
again put into operation. Washing requires about 12 to 15
minutes per filter.
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TYPES OB^ PUKIFICATION PLANTS 47
In some plants the air is omitted, in which case a higher wash
velocity is used, and it becomes necessary to tie down the gravel
with brass sfcreen or it will be impelled upward into the sand by the
wash water. In old plants where the filter units consist of circular
wood or steel tanks, mechanical rakes are used for agitation during
washing. Such a unit is shown in Fig. 18. A central shaft
carries two radial arms with vertical raking bars reaching nearly
through the sand and revolved during washing by suitable gearing,
generally belt-driven. The other details are readily understood
from the figure and correspond to those already described.
Wash water may be obtained by tapping the wash-water pipe
into a pressure main, obtaining the required pressure by means of a
reducing valve. This involves a waste of pressure and there is
also danger from water hammer in the high-pressure mains due to
chattering of the reducing valve. A better way is to have dupli-
cate centrifugal wash pumps drawing from the clear-water basin
and discharging into the wash-water main at the proper pressure,
or, better yet, to have the pumps discharge into an elevated tank
of proper height and dimensions to insure a uniform pressure.
ValveSy Gages, etc. The valves required per filter are the
Influent (settled water). Effluent j Wash Watery Sewer j Air, and
Filter Drain; the last being used to completely empty the filter
or when it is desired to waste the effluent. These are arranged
with valve stands on the operating floor, so as to form a convenient
^oup in front of each fflter. In the case of large filters, hy-
draulically operated valves are used, and the handles for these are
^ouped together on a table in front of each filter. The con-
troller also has an adjustment by which its rate can be changed
from the operating floor. Here, too, are placed the loss-of-head
gages, one for each fflter, which indicate the friction through the
fflter, as already explained for slow sand fflters, and often gages
showing the rate of flow. Each unit should be equipped with an
effluent sampling pump, by means of which samples may be ob-
tained at any time for analysis. There should be gages to show
the wash and air pressures and floats to indicate the levels of water
in the settling and clear-water basins.
Laboratory. The requirements of the laboratory are quite
simple. The necessary apparatus is given in the chapters on
Bacterial and Chemical Tests. As to the room, it should be dry,
well lighted and ventilated, and provided with heat and artificial
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X
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TYPES OF PURIFICATION PLANTS 49
List of Parts in Wooden Tank. Filter (Fig. 18):
1. — Loss-of-Head Gage.
2.— Filtered Water Effluent Valve.
3. — Waah Water Supply Valve.
4.— First Filtered Water Valve.
5.— Float Tube.
6.— Float Tank.
7.— Float.
8.— Unfiltered Water Influent
(Automatic Control).
9.— Orifice Filter Control.
10.— Butterfly Valve.
11.— Float.
12. — ^Agitator Gears.
13.— Clutch Pulleys.
14. — Shifting Lever.
15.— Waste Wash Water Valve.
16. — Agitator Rake Bars.
17.— Filtering Sand.
18.— Filtering Gravel.
19. — Strainers.
20.— Concrete Fill.
21.— Filtered Water Collecting System.
22. — Supply and Wash Trough.
23. — Operating Platform.
24.— Filtered Water Effluent Pipe.
25.— First Filtered Water Pipe to Drain.
26.— Wash Water Supply.
27. — ^Waste Water Pipe to Drain.
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WATER PURIFICATION PLANTS
light, preferably steam and electricity. It should be provided
with gas for use in Bunsen burners, autoclave, sterilizers, etc.
The incubators are preferably heated with electricity, as being
least troublesome. The principal work table should be located
in front of a large window, preferably facing north, and should
Courtesy Pittsburgh Filter Manufacturing Co.
Fig. 18a. — Typical Operating Table Showing Levers for Operating
Hydraulic Valves, Recording Loss-of-Head Gage (on Left), and Effluent
Sample Pump (on Right).
have a slate top, or one of heavy wood, painted a dull black.
The reagents should be handily placed on shelves above the table,
and drawers should be provided for filters, test tubes, etc. There
should be a sink provided with hot and cold water, an ice-box, and
a water still.
Much can be done by a small expenditure for extra apparatus
to expedite the tests. Thus by using self-filling burettes and a
complete set of apparatus for each test, kept ready for use and set
up in definite places in the order in which the tests are made,
much needless walking about to get apparatus is done away with.
There should be a desk and chair for the chemist and a filing
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GENERAL PUN OF
WASHINGTON FILTRATION PUNT
SHOWING FINISHED SURFACES
From Tran*. Amtrtean SaeUtg of Cittl Enfineer*, Vol. LVII.
FiQ. 19.— General Plan of W^j,^
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N0.3
.£Bt^lil5 l ^^'«^M COURT Wa.f43 7
JIJ2B__: NcUae : No.m i N0.U28 •
.shington Filtration Plant Showing Finished Surfaces.
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TYPES OF PUKIFICATION PLANTS 61
system for the records, but superfluous chairs and furniture are to
be avoided as tending to make the laboratory too comfortable a
place for visitors.
Mechanical Filtration and Water Softening. The mechani-
cal filter plant is adapted, with a few slight alterations, to do
efficient work in water softening. The principal requirements to
fit it for this work are an ample settling basin and larger facilities
for storing and handling coagulants, especially lime. This matter
is more fully taken up in Chapter VII, on Water Softening.
Mechanical Filtration and Iron Remoyal. The removal of
iron in conjunction with mechanical filtration is accomplished by
aeration followed by treatment with lime and some aluminimi
sulphate, as the precipitate formed by lime alone is too fine to be
readily filtered out. This is treated fully in Chapter VI, Coagula-
tion and Sterilization.
The Slow Sand Filtration Plant at Washington, D. C* The
water supply of the City of Washington is obtained from
the Potomac River by a diversion dam above the Great Falls,
being conducted thence to the city through an aqueduct and tunnel
of an aggregate length of 90,000 feet. Two large reservoirs, each
of 150,000,000 gallons nominal capacity, are located along the
aqueduct, and this terminates in a third reservoir of 300,000,000
gallons capacity situated within the city proper, at a sufficient ele-
vation to supply most parts thereof by gravity, a few excep-
tionally high points being supplied by means of booster pumps.
The capacities given are nominal, about 300,000,000 gallons being
actually available from the three reservoirs. The aqueduct has a
capacity of 75,000,000 gallons per day.
As considerable sedimentation is secured in the reservoirs, no
additional basins were built, the water being pumped directly
from the last (Washington City) reservoir to the filters which are
adjacent thereto. The pumping equipment consists of three
engine-driven centrifugal pumps, each of 40,000,000 gallons per
day capacity, located in a pumping station built as part of the
filtration project. The lift from the reservoir to the water level on
the filters varies from 21 to 35 feet as the reservoir is drawn down.
* " Works for the Purification of the Water Supply of Washington, D. C."
By Allen Hazen and E. D. Hardy, Trans. American Society of Civil En-
gineers. Vol. LVII, p. 307.
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WATER PURIFICATION PLANTS
As the close regulation of centrifugal pumps under varying head is
difficult, allowance was made for a fluctuation of 6 inches in depth
of water on the filters, which gives an aggregate margin of 4,000,000
gallons. The filtered water is collected in a pure-water reservoir,
All Pipee Spaced 9^'apart in Laterals
DETAIL OF
INTERIOR DRAINS
15 SpUt Tito CoTor-
^SpUtTUe Utenl
CLAN OF UNDEflDRAihAOE Sir STEM > SHOWmo WA^J^O^.E&, LATfRAtS AND CONNECT ION B
Scale of Feet
SECTION ON A-B
From Trana. American Society of Civil Engineers, Vol. LVII.
Fig. 20.— Details of Filters, Washington, D. C.
roofed with a concrete groined-arch construction, of 14,000,000
gallons capacity, whence it is supplied to the city through a set of
equalizing float valves.
The arrangement of the plant is shown by Fig. 19. It is ir-
regular, as the available ground was limited and had to be iised
most economically. There are twenty-nine filters, each having one
acre of sand area, so that at the customary rate (3,000,000 gallons
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TYPES OF PURIFICATION PLANTS
53
per acre per day) the plant has a daily capacity of 87,000,000
gallons. Allowance must be made, however, for filters out of use
due to sand scraping and repairs. It will be noted that the filters
So TTIn Pn!n
SECTION ON D-D ^ifaUhilum*?, .^fcLL (Ufi)
Fnm TraiM, American Society of Cvril Engineers, Vol, LVII.
Fig. 21.
are grouped on each side of " courts " which contain the piping,
sand-washing apparatus, etc.
The filters are essentially of the type already described, the
principal features being shown by Fig. 20. The walls, floor, and
groined-arch roof construction are of concrete masonry, the type of
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Engineering Record, April 7, 1906,
Fig. 22. — Sand Storage Bins, Washington, D. C, Filtration Plant.
Engineering Record, April 7, I90ti,
Fig. 23. — Sand Washers, Washington Filtration Plant.
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TYPES OF PURIFICATION PLANTS
55
structure being such as to require little reinforcement. The roof
is covered with earth and sodded. The central collecting pipe is •
located below the floor level, and the filtered water is led to it by
SAND BINS
REINFORCING IN BOTTOM
OF CONE
Trans. American Society of Civil Engineers, Vol. LVII.
Fig. 24. — Details of Sand Bins, Washington Filtration Plant.
lateral drains of 12-inch half-tile and 6-inch tile, the latter
being used near the extremities of the laterals. A peculiarity of
construction consists in the interposition of a brass orifice plate at
the junction of laterals and main collector for the purpose of com-
pensating for variations in loss of head between those laterals
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Trans. American Society of Civil Engineers, VoL LVII.
Fig. 25. — Interior View of Filter, Washington Filtration Plant (Showing
Filter Sand and Gravel Removed). Note Lateral Drains.
Trana, American Society of Civil Engineers^ Vol, LVII.
Fig. 26.— General View of Washington, D. C, Filtration Plant.
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TYPES OF PURIFICATION PLANTS 57
remote from and those adjacent to the filter outlet. The drain-
age system is covered with 12 inches of graded gravel supporting
40 inches of filter sand (effective size, 0.32 mm. ; uniformity coef-
ficient, 1.77). The working head of water on the filters is 4 feet.
The effluent pipes from the filter units are carried to centrally
located regulator houses, of which there are seven, generally ar-
ranged to serve five filters each. Fig. 21 gives the details of one
such house. The substructure contains six water-tight concrete
compartments, five serving as receiving basins for the effluent of
the filters, the sixth containing recording mechanism. The filter
effluents enter the respective compartments through Venturi
meters and valves with graduated handwheels. The Venturi
meters indicate and record the rates of filtration for each filter,. and
adjustments of rate are made by means of the graduated valves.
The effluents discharge into a central collecting flume through
valved apertures and are carried to the filtered-water reservoir via
a main effluent pipe. Facilities for draining any compartment are
provided. The superstructure is of brick with stone trimming and
tile roof.
The method of handling and washing sand is that already de-
scribed, and the reader is referred to Figs. 5 and 6 for details of the
portable sand ejectors and sand washers used. Fig. 22 illustrates
one of the sand storage bins, of which there are twenty-nine. In
the left background is the superstructure of one of the regulator
houses, and to the right is the entrance to one of the " ramps " or
inclined walkways leading into the filters. Fig. 24 shows the de-
tails of a sand bin. It is built so that a wagon can drive under-
neath, be filled with clean sand, which is then delivered into the
filters through manholes in the roof.
An administration building contains general offices, chemical
and bacterial laboratories, lockers, toilets, storerooms, etc.
While no provision was made for coagulation, because of popular
prejudice against the use of chemicals, the advantages to be
gained therefrom were fully appreciated by the designing en-
gineers and recent experimental work at the plant has more than
fulfilled anticipations as to the value of coagulation. Improve-
ments in sand washing have also been made, notably in sub-
stituting the ejector method for the use of carts in replacing sand
in the filters.
The plant was built under the direction of Colonel A. M.
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WATER PURIFICATION PLANTS
Miller, assisted by Capt. W. P. Wooten and R. D. Chase. Mr.
Allen Hazen was consulting engineer and Mr. E. D. Hardy has
had charge of the plant since its completion.
The Torresdale Preliminary Filters at Philadelphia, Penn.*
The City of Philadelphia has installed a number of rapid sand-
filter plants, with the object of removing the coarse suspended
Engineering Record, November H, 1908.
Fig. 27.— Torresdale Filtration Plant.
Plan and Part Section.
matter from the water preliminary to final filtration. Of these
the installation at Torresdale is typical. The original plant was of
the slow sand type, similar to that at Washington, already de-
scribed, and, filtering at a rate of 3,000,000 gallons per acre per day,
* Engineering Record, November 14, 1908.
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TYPES OF PURIFICATION PLANTS 59
had a daily capacity of 120,000,000 gallons. While the quality
of effluent was satisfactory, it was desired to increase the capacity
of the filters. By means of the preliminary filter plant here de-
scribed, it became possible to double the rate of filtration of the slow
sand filters, enabling an output of 240,000,000 gallons per day to
be obtained.
The preliminary filters are adjacent the original slow sand
plant, are of 240,000,000 gallons capacity, and essentially of the
mechanical type, although somewhat simplified and operated
without coagulation. As shown by Fig. 27, the plant consists of
120 beds, arranged in 8 rows of 15 beds each. Each bed measures
20 "feet 3 inches by 60 feet, has a capacity of 2,000,000 gallons per
day when operated at the rate of 80,000,000 gallons per acre per
day, and has a complete system of control valves and piping,
manipulated by levers on an individual operating table. There
are four filter houses, one between each double row of filters. The
raw water is admitted to the filters by means of channels or
gullets between the rows of filters, entering at the center of the rear
wall, and after filtration is collected in effluent gullets imder the
filter houses.
The filters, flumes, floors, roofs, etc., are of concrete, reinforced
or supported by structural shapes. The superstructure is of face
brick trimmed with gray granite.
The raw water is pumped to the preliminary filters from the
river through an 11-foot riveted steel conduit encased in concrete.
This conduit runs the full length of the filter plant and has three
7-foot and two 53^-foot steel branch connections, leading to the
five influent gullets already mentioned. These influent gullets
extend the full width of the plant, between adjacent rows of
filters, being formed by the back walls of the filter rniits, except
the two outside gullets, where an additional wall had to be added.
The raw water enters the filter beds by means of cast-iron pipes
in the rear wall, each controlled by a 16-inch hydraulic valve
located in the central wash gutter. This is formed in the cus-
tomary way by two reinforced concrete walls extending longi-
tudinally through the center of the filter and 12 inches apart,
dividing the filter bed proper into two equal portions. Steel wash-
water troughs extend laterally across the filters at right angles to
and level with the tops of the central gutter walls, and serve to
convey the wash water to the central gutter, whence it finds its
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WATER PURIFICATION PLANTS
way to the sewer through a hydraulically operated sluice gate
at the front end of the filter. There are twelve such wash-water
troughs per filter, being spaced equally, six on each side of the
central gutter. The general arrangement of central gutter
troughs, etc., is shown in Fig. 28.
The filtering material consists of gravel and sand of graded
sizes, decreasing in size upward, viz., at the bottom, 15 inches of
gravel, varying in size from 2 to 3 inches; 4 inches of gravel from
Engineering Record, November H, 1908,
Fig. 28.— Torresdale Filtration Plant. View of Filter Bed.
% to 13^ inches; 3 inches of gravel from M *o 3^ inch; 8 inches
from M to 3^ inch, and a top coating of 12 inches of sand from
0.8 to 1 mm. size. Under the gravel, and running longitudinally
through the center of each of the two equal filter beds into which
the unit is divided by the cross walls, is an effluent collector formed
by half tile of concrete, with slotted openings for admission of the
filtered water. The two lines of tile unite for each filter, allowing
the filtered water to flow through a short length of 16-inch pipe and
via an automatic rate controller into the effluent gullet situated
between each two rows of filters. Each filter outlet is equipped
with an hydraulically operated valve. The main effluent gullets
terminate in 7-foot steel conduits leading to an 11-foot steel, con-
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TYPES OF PURIFICATION PLANTS 61
crete-cased head conduit, through which the water passes on to the
slow sand filters.
For washing the filters, water and air are used, and a separate
system of piping is provided. Filtered water is pumped into an
elevated wash-water tank, built of reinforced concrete, from which
a 48-inch wash-water line leads to the plant, a 30-inch branch
line from which extends through the pipe gallery between each two
rows of filters. At the center of each filter there is a 20-inch wash-
water take-oflf controlled by a hydraulic valve. This 20-inch
line extends longitudinally through the filter, being himg from the
roof above the central gutter, and divides at the center of the bed
into four 12-inch distributing pipes, from each of which two 8-inch
down pipes take oflf, leading to 8-inch manifold headers placed
above the filtered water collectors (below the sand and gravel).
The manifold proper consists of 13^-inch lateral pipes, spaced 5^
inches on centers and drilled with /{e-ii^ch holes on the bottom.
This effects an essentially equal distribution of the wash water
under the gravel, which, rising upward through the sand, cleanses
the same of its collected impurities, the dirty wash water over-
flowing into the collecting troughs, thence to the central gutter,
and out into the wash-water drain, which consists simply of the
space between the filter walls and the effluent gullet. Air agita-
tion is used during washing, being suppHed by an air main in each
gallery, with branches to the individual filters connected into the
wash-water header, the same manifold being used for distributing
wash water and air. A 6-inch valve is provided for draining each
filter.
Fig. 29 shows a section through one of the filter galleries. At
each side are the front walls of opposite filter units. The filter
floor is carried through as the gallery floor. In the center, ex-
tending longitudinally through the gallery, is the effluent gullet or
flume, 6 by 6 feet in area, into which the filtered water discharges
through an effluent controller. The top of this flume supports the
30-inch wash header and above that the operating platform.
The air pipe is suspended from the ceiling, and at each filter a
12-inch branch is taken off connecting into the 20-inch wash-
water pipe. The air supply is controlled by a 12-inch hydraulic
valve. The spaces between the filter walls and effluent gullet
Iform the wash-water drains, and the central gutters and drain
pipes discharge directly into these.
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WATER PURIFICATION PLANTS
This plant is of special type, designed for a definite purpose,
namely, to prefilter the water only, and the design is not adapted
for more general use. The plant was designed and constructed
^O , __^ ¥^
CROSS SECTION THROUGH FILTER HOUSE
Engineering Record^ November IJ^, 1908.
Fig. 29.— Torresdale Filtration Plant.
under the direction of Mr. Fred C. Dunlap, chief of the Bureau
of Water, Philadelphia, Perm.
The Mechanical Filtration Plant at Minneapolis, Minn.* This
plant is of interest as being typical of the modem installation of
larger size, because of its flexibility of operation, made necessary
by the rapid variations of the Mississippi River, from which the
* Engineering Record, November 18, 1911.
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TYPES OF PURIFICATION PLANTS
63
raw-water supply is derived, and because of its method of
handling and mixing chemicals.
The filtration plant is built near two old service reservoirs,
each of 47,000,000 gallons capacity. One of these was built up 10
feet and adapted as a preliminary settling basin, to which the raw
water is pumped and allowed to settle (approximately 24 hours)
Settling Reservoir
Engineering Record, November 18,1911.
Fig. 30. — Minneapolis Filtration Plant. General Plan.
before reaching the filtration plant. The other reservoir was
roofed over with a groined arch construction of reinforced concrete,
and serves as a clear-water reservoir, receiving the efliuent of the
filter plant and equaUzing the load on the filters, a very desirable
feature. The normal rating of the plant is 39,000,000 gallons per
day.
The general layout of the plant is shown in Fig. 30. After
passing through the preliminary settling basin, the water flows
through a 60-inch cast-iron Une to a controlling chamber, entering
the same through a Venturi meter, which measures and records
the volume and actuates the chemical feed controls, causing an
automatic adjustment of the amount of coagulant to the raw water
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64 WATER PURIFICATION PLANTS
to be treated. The controlling chamber is provided with sluice
gates, so that the raw water may pass from it either into the mixing
chamber or directly into the coagulating basins; other sluice gates
provide for passing it directly to the filters or allowing some of it
to waste through a 20-inch cast-iron pipe line intended for flushing
sediment from the floor of the coagulating basins.
Normally the water passes from the controlling to the mixing
chamber, the coagulant solutions, aluminum sulphate and lime
(when required) being introduced at this point. The mixing
chamber is a covered structure of reinforced concrete, 34 feet
8 inches wide by 173 feet long inside, with wooden baffles of the
vertical type, 3 feet center to center. The water passes back and
forth between the baffles in its journey through the mixing cham-
ber, traveling a total distance of about 2,000 feet. This insures a
thorough mixing of the coagulants with the water and allows time
for the chemical reactions to take place. The mixing chamber is
built across the ends of the coagulating basins, with a space of
about 73^ feet between the two, this space being denoted on the
drawing. Fig. 30, as the center passage. This center passage is
divided by horizontal diaphragms of concrete into two flumes or
conduits, the side wall of the mixing chamber and the end walls of
the coagulating basins forming the vertical sides of the flumes.
The lower flume receives the water from the mixing chamber and
introduces it into the coagulating basins. As it may not always be
desirable to run. the water through the full length of the mixing
chamber, four sluice gates are located in the west wall of same,
communicating directly with the lower flume and thence with the
coagulating basins, As already stated, the water may enter the
lower flume at the north end, directly from the controlling chamber,
thus by-passing the mixing chamber. The upper flume receives
the water after its passage through the basins and conducts it to
the filters. It may also receive the water directly from the con-
trol chamber or after its passage through the mixing chamber.
Further gates provide for by-passing either basin, or operating the
basuis both in series or parallel. The extreme flexibility and
absence of complicated pipe work in this arrangement are commend-
able. Below the central passage is a 12-inch sewer into which
both the mixing and controlling chambers and the coagulating
basins may be drained.
After passing through the mixing chamber, the treated water
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TYPES OF PURIFICATION PLANTS 65
enters the coagulating basins. These are in duplicate, each mea-
suring 95 feet 8 inches by 119 feet 4 inches inside, and have a com-
bined capacity of about 2,800,000 gallons. Each basin has three
vertical concrete baffles with water passages aroimd the ends, so
that the water makes four passes in traversing the basin. The
basins can be flushed by by-passing raw water from the controlling
chamber through the 20-inch flushing line already mentioned,
being drained off through sumps leading to the 12-inch cast-iron
drain under the central passage. Additional fire-hose connections
are provided for hosing out the heavy sludge.
The water, after passing through the coagulating basins, enters
the upper flume over a skimming weir, through which it passes
into a 60-inch influent pipe, leading to the filters. These are twelve
in number, six on either side of the operating gallery, and have
each a capacity of 3,250,000 gallons at a rate of 125,000,000 gallons
per acre per day. Each bed is divided into* two parts by central
wash-water gutter of the usual type, which, in conjunction with
eight lateral gutters, serves to distribute the settled and treated
water entering the filter through a twenty-inch valved branch con-
nection from the 60-inch influent header in the gallery.
The filtering medium consists of 30 inches of sand having an
effective size from 0.35 to 0.44 mm. and a uniformity coefficient
of 1.65. The strainer system consists of concrete ridges cast on
the bottom of the filter at right angles to the central gutter. The
grooves between the ridges are filled with graded gravel and a
brass screen is bolted over the gravel to prevent displacement
while washing. The gravel rests on perforated brass strainer
plates, below which are water passages for collecting the effluent
and distributing the wash water. The filtered water collected by
the 'Strainer system flows into a manifold of collector pipes, and
through these and a rate controller into the clear-water basin
beneath the filters.
The filters are washed by forcing filtered water under pressure
upward through the strainer system. No air is used, the wash
pressure being sufficient to thoroughly agitate and cleanse the
sand. The rate of wash is 15 gallons per square foot per minute.
The dirty wash water is collected by the cross troughs and flows
into the central gutter, thence through a valved coimection into a
reinforced concrete sewer beneath the filter gallery. As no large
sewer was available, the dirty wash water is collected in a receiving
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WATER PURIFICATION PLANTS
basin, and slowly drained away through a 12-inch sewer. Water
for washing is obtained from an elevated tank of reinforced con-
crete, located above the receiving basin just mentioned. The
capacity of this tank eliminates the necessity for large wash pumps,
as it can be filled between washings by relatively small pumps, in
SECTION THROUGH CHEMICAL STORAGE BINS AND DETAIL OF AGITATOR.
Engineering Record, November 18, 1911.
Fig. 31. — Minneapolis Filtration Plant.
the present case by two centrifugals of 1,600 gallons per minute
capacity.
Special interest attaches to the arrangements for handling and
mixing chemicals. The necessary apparatus is contained in a
head house located across one end of the filter building. The
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TYPES OF PURIFICATION PLANTS
67
E^Trrq
Engineering Record, November 18, 1911.
Fig. 32. — Minneapolis Filtration Plant. Plan of Head House.
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68 WATER PURIFICATION PLANTS
floor elevations axe such that the chemicals caa be handled and
stored by gravity, but the solutions must be pumped to the orifice
boxes which feed them into the mixing chamber.
The lime and alum are purchased in carload lots and carted to
the plant by wagons. The wagons discharge upon a dumping
platform shown on the left-hand side of Fig. 31, at elevation 328.0.
The lime and alum pass from this platform through separate
chutes to the boot of a bucket elevator, the lime passing en route
through a small crusher, which breaks it into lumps of a size readily
handled by the elevator. The material is raised by the elevator
into a hopper at the top of the building and discharges through a
grain chute equipped with a revolving spout capable of discharging
into any one of 12 reinforced concrete storage bins. In event of a
breakdown in the bucket elevator, a freight elevator of standard
design may be used to raise the chemicals from the unloading
platform to the top of the storage bins, into which they are then
shoveled by hand labor. Below the bins a traveling bucket
operates on a suspended rail and serves to convey the coagulant to
the solution tanks. The arrangement of the tracks is shown in
Fig. 32. The traveling bucket is balanced on a scale beam,
enabling the operator to measure out the required amount of
chemical directlj'' from the bins.
The lime-slaking apparatus is rather unique, consisting of two
concrete mixers, each of 1)^ yards capacity, into which the lime
is dumped directly from the traveling bucket. Water is added
and the mixture revolved in the drum of the machine. The milk
of lime discharges into a trough having valved outlets into each of
the three lime solution tanks. These are circular steel tanks,
12 feet 5 inches in diameter and 13 feet deep. Steel is used, be-
cause calcium hydroxid has a destructive action on concrete. The
alum and hypo tanks, however, are of concrete and rectangular in
plan. The agitating device employed in each of the several tanks
consists of a helicoidal bronze impeller mounted on a vertical shaft
driven by a motor at the top of the tank. The direction of rota-
tion is such as to create a downward current at the center of each
tank, driving the solution along the floor of the tank and up the
sides. This course of the solution is further aided by a conical
baffle placed over the impeller.
The aluminum sulphate is dissolved previous to discharge into
the solution tanks in concrete dissolving boxes, 6 by 3 feet in plan
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TYPES OF PURIFICATION PLANTS 69
and 4 feet deep, which are provided in duplicate. Agitation in
these boxes is provided for by a manifold of 1-inch galvanized pipe
At the bottom drilled with /ig-inch holes 3 inches on centers.
Water flowing upward through this grid dissolves the alum more
readily than the Usual downward stream. The dissolved alum
overflows from these boxes and passes into the solution tanks
through a screened opening.
An attempt is made in this plant to overcome the hardship
which usually attaches to the handling of the hypochlorite of lime
used for disinfection of the filtrate. The device used is shown in
Fig. 31. The hypo is received in drums weighing about 750
pounds. The drums are lowered to the operating floor by means
of the freight elevator and rolled under an I-beam traveler,
running across the hypo dissolving boxes. The drum is lifted
into the dissolving box by means of a set of chain blocks, coming
to rest on a false bottom of perforated grate bars. The dis-
solving box is then filled with water so as to submerge the drum
-completely. While the drum rests on the grate bars, holes are
driven in both ends by steel pins; a single pin embedded in one end
of the dissolving box is driven into the exact center of one end of
the drum, while the other end is perforated by four pins mounted
on a chuck rotating on a steel shaft passing through the end
of the dissolving box by means of a stuffing gland. Besides its
rotary motion, the shaft can move longitudinally through the
^and and the can is perforated by striking the end of the shaft
lyith a sledge, causing the four pointed pins in the chuck to per-
forate one end of the drum, and driving the drum bodily against
the center pin at the other end. The drum can now be rotated
by tinning the shaft through agency of a ratchet and is cut in
two under water by a large can opener. The hypo is then dis-
solved out by the same type of manifold device used in the alum
dissolving boxes and flows into the hypo solution tanks.
As the coagulant leaves the solution tanks at a level much
below that of the water in the mixing chamber, it is pumped to
<;hemical control devices by small bronze centrifugal pumps.
The chemical feed tanks are located on the ground floor. The
solutions are pumped into them at a constant rate, a uniform head
being maintained by overflows in the tanks which carry the sur-
plus back into the respective solution tanks. The chemical feed
controllers consist of adjustable orifices automatically regulated
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WATER PURIFICATION PLANTS
by the difference in head of the Venturi meter in the controlling
chamber, so that the amomit of coagulant is always proportional
to the rate of raw-water pumpage. The lime is applied as the
Engineering Record, November 18, 1911,
Fig. 33. — Minneapolis Filtration Plant. Solution Tanks, Overhead
Conveyor, and Controllers.
water enters the mixing chamber, the alum a little later at some
point in the central passage. The hypo is added as the water
enters the clear-water reservoir.
This plant was designed by Hering & Fuller, consulting en-
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TYPES OF PURIFICATION PLAINTS
71
gineers, New York. Mr. Andrew Rinker, city engineer, had
supervision of the construction with Mr. W. N. Jones in direct
charge, assisted by Mr. J. A. Jensen, waterworks engineer. Mr.
J. W. Armstrong had immediate charge of plans and specifications
for the consulting engineers.
The Mechanical FUter Plant at Wilkinsburg, Penn.* This
is a type of plant peculiarly adapted to very hilly or semi-
mountainous regions where the location is adjacent to a high pres-
sure reservoir and rather difficult of access. In this instance the
plant is located on a hill top about one mile from the Allegheny
River (the source of supply) and about 600 feet above same. The
water is pumped directly from the river to the sedimentation
basins against a total pressure of 250 pounds per square inch.
PLAN OF MECHANICAL FILTRATION PLANT, WILKINSBURG, PA.
Engineering Record, October 1,1910.
Fig. 34.
The plant comprises two uncovered sedimentation basins of re-
inforced concrete, each 150 feet long, 60 feet wide, and 223^ feet
deep, and 10 filter beds, each having a capacity of 1,250,000 gallons
per day, making the total plant capacity 12,500,000 gallons daily.
The water enters the sedimentation basins through cast-iron
manifolds terminating in 6-inch aerating pipes, and is collected
at the outlet end of the basins by a reinforced concrete flume con-
necting with a cast-iron pipe which delivers the coagulated and
* Engineering Record, October, 1910.
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72 WATER PURIFICATION PLANTS
settled water to the filters. The general arrangement of plant is
shown by Fig. 34.
The filters are housed in a long brick building, being arranged
five on each side of a central pipe gallery. The equipment is
of standard design. The eflfluent and wash-water manifold is
entirely of cast iron with cast-iron laterals and brass strainers,
and above this are placed 8 inches of gravel and 36 inches of sand.
Air agitation is used, the air manifold being below the gravel and
consisting of small perforated brass tubes supplied through a
central header pipe. The wash-water troughs are of cast iron, ex-
tending laterally from a central gutter of the usual type and are
designed to handle 10 gallons of wash water per minute per square
foot of sand area. The eflfluent controllers are of the velocity
type, similar in principle to the one previously described. All
valves are hydraulically operated, the handles for each filter being
grouped on an enclosed marble operating table. This table also
contains the loss-of-head gage, which is of the registering type, two
pens recording the head on the filter and the draft on the eflfluent
pipe upon a moving chart, clock-driven. Fig. 35 shows a general
view of the operating gallery and tables. The interior walls are
of buff fire-flashed brick and the whole presents a very neat and
sanitary appearance. In the general ofl&ce, a marble sample
table is located on which are mounted glass tubes and spigots, one
for each filter, and one each for the raw and treated water. Sample
streams from the respective sources are kept constantly circulating
through these by individual 3^-inch centrifugal pumps, so that the
operator has constantly on view and on tap water from all the
units of the plant. The eflfluent discharges through the controller
into a reinforced concrete conduit leading to Reservoir No. 1.
At the east end of the filter building and integral therewith
is the head house, having three floors: a basement, level with the
pipe gallery, a main floor at the operating platform level, and a
second floor. The basement contains piping; air, wash, and pres-
sure pumps, sampling pumps, electric generating and heating
plants. The main floor contains the solution tanks and orifice
boxes, the main entrance or lobby, general office, and laboratories.
The office and laboratories are floored and wainscoted with white
tile and have a steel ceiling. The lobby contains the stair well,
leading to the basement and second floor, the main switchboard,
and the more important gages.
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74 WATER PURIFICATION PLANTS
The second floor is devoted to storing, handling, and mixing
the coagulants. The upper ends of the solution. tanks, located on
the floor below, project through to this level for charging purposes.
Lime, alum, and hypo tanks are provided in duplicate, each being
equipped with a concrete solution box having a screened outlet into
the tank. Owing to the isolated location of the plant, the chemicals
must be bro.ught up by wagons, which deliver at one end of the
head house. The barrels or sacks of coagulant are handled by
means of a trolley or I-beam traveler, the track for which is sus-
pended from the ceiling of the second floor and extends through an
opening in the end wall similar to a hay-trolley on a bam. The
hoisting is done by an electric motor which is mounted directly on
the trolley traveler.
A novel method is used for handling the air and water for
washing. Small motor-driven centrifugal wash pumps and rotary
air pumps in duplicate are located in the basement ^ and these
deliver into the combined air and wash-water tanks shown in
Fig. 36. This is really a gasometer, the lower tank holding the
wash water and serving to seal the upper inverted air tank, which
rises and falls as the volume of air contained varies. This enables
small wash and air pumps to be used, running about 50 per cent
of the time, and allows the electric generating plant to be kept
down to a reasonable size. These pumps shut off automatically
when the tank fills up, and start after the water and air levels drop
a certain amount.
As it is expensive to pump water up to the plant, the dirty wash
water is collected in a settlii^ basin, and after the silt settles out is
repumped into the sedimentation basins, by automatically con-
trolled centrifugal pumps.
The generating plant is of 30 kilowatt capacity, gas-engine
driven. The heating plant is of the usual steam-boiler type.
This plant was installed by the Pennsylvania Water Co.,
W. C, Hawley, chief engineer and superintendent. Mr. J. N.
Chester, of Chester & Fleming, Pittsburgh, was consulting en-
gineer. The Pittsburgh Filter Manufacturing Co. furnished and
installed the equipment.
The Filtration and Scrftening Plant at Columbus, Ohio.* The
Columbus filtration plant is an excellent example of an in-
* Engineering Record, February 24, 1906.
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TYPES OF PURIFICATION PLANTS
75
stallation designed to soften as well as to filter the water. The
source of supply is the Scioto River, which drains a region under-
lain with dolomite (mixed calcium and magnesium carbonate), and
consequently the water is quite hard, the total hardness being
Courtesy Pittsburgh Filter Manufacturing Company,
Fig. 36. — Wilkinsburg Filtration Plant, Combined Air and Wash-Water
Tank.
about 250 parts per million, and the incrustants averaging about
100 parts per million. The treatment given the water reduces
the total hardness to 80 and the incrustants to about 40 parts per
million. The capacity of the plant is 30,000,000 gallons per day.
The water is treated with lime to precipitate the bicarbonates of
calcium and magnesium, then with soda ash to remove the in-
crustants, and finally alum is added as a coagulant, although
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76 WATER PURIFICATION PLANTS
an cfTort is mado to utilize the gelatinous magnesium hj'^droxid
formed in the softening process for this purpose.
The general layout of the plant is shown in Fig. 37, referring
to which it will be seen that the water enters a weir basin (which
forms the first floor of the head house), through a 48-inch cast-iron
main, passing through a Venturi meter immediately before entering
this basin. Besides recording the rate of pumpage of the raw
water, this meter also controls the rate of discharge of the coagulant
solutions, varying this in proper ratio to the raw-water pumpage.
Along the sides of the weir basin are adjustable weirs, of which
there are three sets of two each, for diverting certain proportions
of the raw water to lime saturators, soda trough, and mixing tanks.
The plant was designed so that a maximum of 25 per cent of the
raw water passed over the weirs to the Ume saturators, a similar
amount over the soda weir, and the remaining 50 per cent passed
over the weirs into the mixing tanks. An additional weir was
provided for feeding untreated water to the effluent of the settling
basins, to eliminate any caustic alkalinity of the settled water due
to overtreatment with lime; and an overflow weir, slightly higher
than the rest and leading to the settling basins, takes care of undue
fluctuations in the raw-water pumpage.
To the portion passing over the lime weirs, milk of lime is
supplied by means of a perforated pipe, after which the water
passes into the six lime saturators by means of a central flume
with a branch pipe into each saturator. Within the saturator
tank each pipe divides into four branches, which distribute the lime
and water evenly over the bottom of the tank. The water rises
slowly in the tank, being constantly stirred by revolving paddles
(four sets per saturator), and overflows into a central flume be-
tween the two rows of saturators and above the entrance flume.
Thus the water and lime are intimately mixed, giving a saturated
solution of lime water (about 60 grains per gallon). The lime-
saturated water flows through the flume and a cast-iron pipe be-
neath the weir basin and enters the mixing tanks together with the
main body of water.
The purpose of the mixing tanks is to bring about a thorough
mixture of the water with the softening reagents, thereby
greatly facilitating the reactions. These tanks have a total
capacity of nearly 1,000,000 gallons, so that the water requires
almost an hour to pass through them. They are two in number,
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i 7IbriflAdDnklQ
Bnginmifig Rteard, Fitruam f4t 1909.
FiQ. 37.— Columbus Filt
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f*i]imtioQ Plant, General Flan.
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TYPES OF PURIFICATION PLANTS
77
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WATER PURIFICATION PLANTS
arranged on either side of a central gallery, which contains the con-
duit for carrying the mixed water to the settling basins, the flume
for introducing the soda ash (as will be explained presently), and
the mixing tank blowoffs for drainage and cleaning. The mixing
tanks are fitted with vertical baffles spaced 3 feet on centers,
causing the water to take a circuitous course, passing over one
DIVIDING MAIN WALL OF SETTLING BASIN
Bngineeri'ng H^ord, Fdmiary 2Ut 1906,
Fig. 39. — Columbus Filtration Plant.
baffle and under the next. Sluice gates into the receiving conduit
are provided at intermediate points, so that a shorter period of
mixture can be obtained if desired.
The soda ash is introduced into its quota of water as this is
passing over the soda weirs, and travels through a flume at the top
of the gallery between the mixing tanks, entering these at a point
60 feet from the weir basin, via an overflow weir extending across
both tanks. The construction of the mixing tanks is shown by
Fig. 38.
The treated and thoroughly mixed water passes on to the
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TYPES OP PURIFICATION PLANTS 79
settling basins, which have a capacity of 15,000,000 gallons, or a
period (nominally) of 12 hours. Through the settling basins ex-
tends a dividing wall, which is cored out as shown by Fig. 39 to
form three flumes or gullets, the upper carrying the softened water
to the basins, the middle carrying the settled water from the
basins to the filters, and the lower being used to drain the basins
and containing the blowofif valves. The upper level of this
wall serves as a gate-house, containing the sluices controlling the
admittance of water to and withdrawal from the basins, and is
enclosed in a brick superstructure. Laterally the basins are
further subdivided by walls so as to form, in all, six compartments.
Each compartment has a vertical baffle through the middle, ex-
tending from the main dividing wall to within 60 feet of opposite
end, compelling the water to make a complete circuit of the com-
partment, i.e., leaving the softened-water flume it would travel
outward from the main dividing wall laterally in both directions
to the far end of the baflfles, around these, and then back to the
dividing wall, repeating the process for each compartment. The
water in each half of the basin would, therefore, make six complete
passes across the basin before reaching the settled-water conduit at
the outer end of the dividing wall. It is also possible to distribute
the water so that each compartment of the basin takes its quota
of the water, making essentially six smaller settling basins, each
receiving one-sixth of the water. This would reduce the velocity
through the basins to one-third of the normal. Any compart-
ment can be shut down, drained, and flushed by pressure hoses.
After passing through the settling basins, the water is carried
to the filters through the settled-water flume. There are ten
filter units, each of 3,000,000 gallons per day capacity. They
offer no novel points not already described. Fig. 40 gives sections
through one of the filters and the pipe gallery. The settled water
enters the gallery by means of a 48-inch " raw-water " pipe, with
20-inch branches entering the units at the central gutter. The
water is filtered through 30 inches of sand (effective size, 0.4 mm.,
uniformity coefficient,. 1.5), and through a layer of graded gravel
(from 716 to 1 inch in size). A detail of the strainer system is
shown by Fig. 42. The ridges shown are 8^ inches on centers,
and the brass strainer plates in the valleys are similarly spaced.
The filtered water is collected by a pipe manifold and passes via
a rate controller and effluent pipe to the clear-water reservoir.
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WATER PURIFICATION PLANTS
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Enginmifig Btcord, F^manf »A. im. Fig, 41.-Columbus Fatration Plant
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il Btterwl Water
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SECTION C-D
SECTION E-F
Details of Piping in Filters and Pipe Gallery,
I PrfMiTLrf
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TYPES OF PURIFICATION PLANTS
81
Wash water is supplied from a reinforced concrete tank and
delivered to the filters by a 24-inch line passing through the pipe
gallery with 20-inch branches into each unit. It is distributed
throughout the filter unit by means of the strainer system. After
rising upward through and cleansing the sand, it is removed by
DETAILS OF STRAINER
Engineering Record, February 2 A, 1906,
Fig. 42. — Columbus Filtration Plant.
six lateral gutters in each half of the filter, leading into the central
gutter, and is thence carried away by a 30-inch drain in the filter
gallery. The plant is designed to give a rate of wash of 8 gallons
per square foot per minute.
In addition to water, air is used for agitation before or during
washing, and for this purpose a system of air pipes and manifold is
provided. There is a 12-inch air-supply line in the gallery, with 10-
inch branches to each filter. These branches are hung along the
central gutter, and outlets in the bottom connect with lateral
pipes supported on the concrete ridges which hold down the
gravel. These laterals are 1 inch in diameter, made of brass and
spaced 8^ inches apart. They are drilled on the bottom with
J/^inch holes, 8^ inches center to center. The air system is de-
signed for a maximum rate of 3 cubic feet of air per square foot per
minute.
All valves in the operating gallery are hydraulically controlled,
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WATER PURIFICATION PLANTS
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TYPES OF PURIFICATION PLANTS
83
the levers for each unit being grouped on a marble table, which
also contains the loss-of-head gage. Each filter is further equipped
with a small pump and motor, which draws water from the ef-
CoHTtesy Charles P. Hoover, Chemist in Charge,
Fig. 44. — Columbus Filtration Plant. Raising Lime Bags by Continuous
Elevator.
fluent pipe and discharges it into a small bowl on the operating
table, so that a sample of filtered water from any unit can be
readily obtained.
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84 . WATER PURIFICATION PLANTS
A one-story superstructure entirely covers the top of the
mixing tanks and serves as a storage house for lime, soda ash, and
alum. The chemicals are received in carload lots, generally in
bags, there being a railroad siding on each side of the storage
house, which has unloading platforms and side doors similar to a
freight station. The capacity of the storage house is 900 tons,
or about 20 carloads. An apron conveyor, running centrally the
entire length of the storage house, and driven by an 18-horse-power
motor, serves for carrying the bags of chemicals to the third floor of
the head house, where the solutions are made up.
The second floor of the head house is almost completely filled
by the chemical-solution tanks, of which there are nine, three each
for soda, coagulant (alum or ferrous sulphate), and lime. The
tanks are of reinforced concrete, circular, 12 feet 6 inches in dia-
meter and 11 feet 5 inches deep. The coagulant and soda solu-
tions are kept uniform by agitation with compressed air, an air
grid of brass piping in each tank distributing the air uniformly.
In the lime tanks, revolving paddles on a centrally mounted ver-
tical shaft serve the same purpose. The tanks are provided with
the customary piping for carrying the solutions to the orifice boxes,
and for draining, and each tank is equipped with a float gage for
recording the depth of solution.
The tops of the solution tanks support the third floor of the
head house. Here are located the devices for making up the
chemical solutions. The apron conveyor enters through the wall
of this building adjacent to the storage house and traverses it
centrally for about two-thirds the length, at which point the head
pulley of the conveyor is located. Bags of chemicals, if not
removed previously, are therefore dumped automatically at this
point. As the amount of lime used exceeds that of alum and
soda, it is delivered in this way, and the slaking tanks are located
conveniently to the end of the conveyor. ,They are three in num-
ber, 6 feet in diameter and 2 feet 8 inches deep, built of rein-
forced concrete. Hot water is used in slaking, and the lime and
water are stirred during the process by motor-driven vertical
rakes. The slaked lime is discharged into the lime-solution tanks
already described. There are two dissolving tanks each, for
coagulant and soda ash, conveniently located along the sides of the
conveyor. These tanks are of concrete, rectangular in plan,
5 feet long, 3 feet wide, and 2 feet 8 inches deep. The material
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TYPES OF PURIFICATION PLANTS 85
to be dissolved is placed on a screen about 3 inches above the
bottom of the tank, and water (which may be heated) is passed
upward through it, overflowing a weir and passing into the solu-
tion tanks. Scales for weighing are provided, and a chute is
located at one end of the building by means of which empty
sacks are returned to the storage room, where they are packed for
shipment to the chemical-supply company.
The chemical solutions are fed to the raw water automatically
in proportion to its amount by orifice boxes controlled through
the Venturi meter in the raw-water main.
The plant contains the usual offices, bacteriological and chem-
ical laboratories, a locker room, lavatory, and storeroom.
Soon after commencing operation the method of handling lime
was found to be unsatisfactory. The bags of lime varied as much
as 15 pounds from the standard weight, and on storage they air-
slaked and broke open. Thereafter the lime was bought in bulk
and sacked at the plant, which proved a disagreeable and un-
satisfactory method. To overcome these difficulties, a system of
conveyors and automatic scales was installed and put into service
in 1913.*
Referring to Fig. 45, it will be seen that a large overhead
storage bin, having a capacity of 220 tons, was built over one of the
sidings adjacent to the head house. The lime, being received in
bulk, in carload lots, is fed into a hopper by means of a power
shovel operated by a man in the car. From this hopper the lime
is fed to a bucket elevator by a screw feeder and lifted into the
bin. To supply the solution tanks, the lime in the storage bin is
fed to the elevator through a chute from the bin bottom and is
lifted to an overhead screw conveyor, which carries it to any of
three smaller hoppers suspended over the three Hme-slaking tanks.
Each of these hoppers feeds into an automatic weighing device,
electrically controlled, which weighs out a predetermined quantity
of lime at regular intervals into the slaking tanks, whence the
lime solution travels through the solution tank and orifice box
to the raw water as already described.
The weighing device consists of an equal-armed scale (like
a chemical balance in principle), to one arm of which the desired
weight is attached, while the other suspends a receptacle to receive
* Annual Report, Division of Water, Columbus, O., 1913.
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86
WATER PURIFICATION PLANTS
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TYPES OF PURIFICATION PLANTS
87
the lime from the hopper above. The tilting of the beam, when the
proper amount is weighed out, automatically closes a gate in the
bottom of the hopper. The charge is dumped into the slaking
tank through an opening in the bottom of the receptacle, the
gate to which is opened at the proper time by an electromagnet.
Fig. 46. — Columbus Filtration Plant. Titning Device for Automatic Scales.
The electric circuit controlling the dumping is closed by the clock
device shown in Fig. 46. A clockwork gives a uniform rotative
movement to a circular disk with contact points on its periphery.
Every time a contact is made, the electric circuit actuating the
magnet in the weighing device is closed, and a charge of lime is
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WATER PURIFICATION PLANTS
dumped. Different disks are used to give any desired interval
between contacts. A number of these are shown in the right and
left hand comers of the case containing the apparatus. Switches
are provided to throw any of the three weighing devices into
■U©^ £ji9lXBQ ©X
Engineering Record, July «5, 1910.
Fig. 47. — Iowa City Iron Removal Plant.
Works.
General Plan of Purification
operation and electric lights in series with the circuits indicate
that these are unbroken by lighting up with each discharge.
The original design and construction was carried on under
direction of Messrs. Julian Griggs and Henry Maetzel, succes-
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90 WATER PURIFICATION PLANTS
sively chief engineers of the Board of Public Service. Mr. John
H. Gregory was engineer in charge and Messrs. Rudolph Hering
and George W. Fuller were consulting engineers. The later im-
provements were carried out by Messrs. Charles P. Hoover,
<;hemist in charge, and C. J. Clarke, engineer of the water-works
department.
The Iron-Remoyal Plant at Iowa City, la.* The mechanical
filter plant requires no especial adaptation in order to remove iron
successfully. If in the bicarbonate form, the addition of lime,
followed by sedimentation of sufficient duration to allow of com-
plete reaction between the lime and bicarbonates, and filtration
to remove the precipitate, will eliminate the iron very readily.
Sometimes a coagulant is added to hasten precipitation. Such a
plant is in successful operation at Iowa City, la. The water
supply is obtained from galleries in the bed of the Iowa River,
-and contains from 3.5 to 4.3 parts per million of iron.
The mechanical filter plant consists of lime-dosing apparatus,
settling basins, and filters of 2,000,000 gallons per day capacity.
The water is raised from the galleries to the settUng basins by
centrifugal pumps, steam driven. Lime solution is applied near
the point of entrance into the basins. The basins, two in number,
are of 250,000 gallons capacity. The water takes a circuitous
route through these and enters a fiume extending along the rear of
the filters, as shown by Fig. 47. In this case, as in the Torresdale
plant, the settled water enters the filters at the rear through
valved branches from the flume. While this simplifies con-
struction, it has the opposite effect on operation. Each filter
contains one cast-iron wash trough through the center, by way of
which the settled water is also introduced and distributed. The
filtering material consists of 28 inches of sand of the' usual size,
supported on 12 inches of graded gravel. The collector manifold
consists of a single 6-inch cast-iron header extending longitudinally
through the center of the filter with I3^inch wrought-iron laterals
on either side, spaced 6 inches center to center. Brass strainer
heads are tapped into these laterals, b/is inches on centers.
The filters are washed in the usual way, both air and water
being used. Wash water is supplied by an 8-inch centrifugal
pump at the rate of 7.5 gallons per square foot per minute, the
dirty wash water overflowing into the central trough and being
* Engineenng Record^ July 23, 1910
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TYPES OF PURIFICATION PLANTS
91
led into a sewer. Air is used in the customary manner, being dis-
tributed through the same manifold as the wash water.
Two Ume-solution tanks, 12 feet in diameter and 10 feet &
inches deep, are located along one end of the settling basins. The
lime is slaked in a concrete box, 3 feet wide, 9 feet long, and 2 feet
deep, placed on the floor above the solution tanks, and is discharged
^ y^ Index Wheel
Engineering Record, July 2S, 1910.
Fig. 49. — Iowa City Iron-Removal Plant.
Lime-Solution Orifice.
into the latter through sluice gates at both ends of the box. The
lime solution is kept uniform in strength by means of revolving
paddles in the solution tanks. Pipes from these tanks lead to two
IJ/^inch bronze centrifugal pumps, which raise the solution to an
elevated orifice box, through which it is discharged into the raw-
water main. Fig. 49 shows a detail of the orifice box. The orifice
consists of an annular slot in a rubber disk, the opening of which
can be varied by means of a revolving sector turned by a vertical
shaft. An index wheel at the top of the shaft indicates the rel-
ative size of the orifice. A constant head is maintained by means
of an overflow weir discharging back into the solution tanks. A
clear-water basin is located below the filters.
The plant is of reinforced concrete construction with brick
superstructure. As it was built for a special purpose and at a
minimum cost, it does not possess the flexibility and ease of opera-
tion desirable in the average plant. This plant was designed and
built by the New York Continental Jewell Filtration Company.
Digitized by LjOOQ IC
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Digitized by LjOOQ IC
CHAPTER III
PHYSICAL AND CHEMICAL TESTS
Tests must be made in connection with water purification in
order to ascertain those qualities of the raw water affecting its
treatment, to measure the improvement effected by purification,
and to make sure that the filtrate is up to the standard of purity.
It is not necessary to make a complete analysis of the water,
in fact, it is not desirable, as to do so would occupy much valuable
time, which could be better employed outside of the laboratory.
It is of greater importance tha't the determinations herein out-
lined be made with sufficient frequency to include all possible
variations in the condition of the raw water, in general not less
than once a day.
The usual tests to be made are as follows:
In the Raw Water: In the Filtrate:
Taste, and odor Taste and odor
Turbidity Turbidity
Color Color
Alkalinity or acidity Alkalinity
Free carbonic acid (CO2) CO2
Iron Free alum or ferrous sulphate
Bacterial count at 20° Cent. Iron
Bacterial count at 37° Cent. Bacterial count at 20° Cent.
Coli determinations Bacterial count at 37° Cent.
Coli determinations
Of these, color may be omitted in waters where this quality is of
small moment, and iron except in the case of waters containing an
appreciable amount. The remaining tests are necessary in order
to keep well informed on the condition of the raw and filtered
water.
In carrying but the following tests, great care should be ob-
served, in order to insure accurate results. The apparatus used
should be clean, and immediately before use should be wiped out
with a clean cloth and then rinsed out with distilled water of
93
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94
WATER PURIFICATION PLANTS
Mouth Piece
known purity. This is best accomplished by means of a wash
bottle, Fig. 50. This consists of a liter flask, with rubber stopper
perforated for two glass tubes as shown. By blowing into the
mouthpiece, a fine stream of distilled water can be directed on
apparatus requiring to be rinsed. Glass tubing for making this
and other apparatus can be cheaply bought and bent to the de-
sired shape by heating to redness in an ordinary gas flame. The
tubing can be cut with a small tri-
angular file, by nicking and then
breaking it, the cut ends being
rounded in the gas flame. Ap-
paratus should be thoroughly
rinsed and dried after use. Oc-
casionally it should be cleaned
with the solution described in
Chapter IV, being thoroughly
rinsed afterward to remove all traces
of fluid.
Care must be used in measur-
ing samples to obtain the exact
amount required, as well as in read-
ing the burettes and observing the
end point in tests involving indi-
cators. Needless to say, samples
should be collected in clean bottles,
and before testing it is well to rinse
the mouth of the sample bottle by
pouring out and wasting some of
the water contained. If distilled
water is not available, the apparatus should be washed out be-
fore use with some of the water to be tested.
A supply of distilled water is very desirable for laboratory use.
The bottled " distilled " water on the market is often untrust-
worthy and should not be accepted as reliable until proved by the
tests given in this chapter, especially those for CO2, alkaUnity, and
iron, which should all give negative results. More thorough tests
are given in Appendix B. If possible the water should be distilled
in the laboratory. The apparatus required is shown in Fig. 51.
The water to be distilled is placed in the boiler (a) , generally made
of copper, tin-lined, and is evaporated by means of a Bunsen burner
Fig. 50.— Wash Bottle.
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PHYSICAL AND CHEMICAL TESTS
95
iiiaiiiitltiuiiM
Condenser
tro Waat-L'
Oolloutinij
taat-L' / U \ From
»
Bottle ._^^Jr._^.
Fsam Till?
Fig. 51.— Water Still.
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96
WATER PURIFICATION PLANTS
Glass Tube
Loose Stopper
Hose
Pinch Cock aU o.
-^ : 7£>^ ■^~ Carboy
placed below the boiler. The steam passes off through the block
tin tube into a " worm " or condenser of the same material, im-
mersed in a tank of cold water, causing it to condense. The
distilled water is collected in the bottle (6). A constant supply of
cool water is kept circulating about the worm by means of a hose
connection from the tap, and
a waste overflow, generally
carried by a hose to the sink.
The first portion of the dis-
tillate caught by the bottle
(6) should be used to rinse
out same and then be wasted.
Distilled water greedily ab-
sorbs CO2 and oxygen from
the air, and, if desired to
be free of these, should be
freshly boiled. The labora-
tory supply of distilled water
is conveniently kept in the
container shown by Fig. 52.
It consists of a large glass
carboy, loosely corked, with
a siphon made of glass and rubber tubing. The water can be
pulled over into the siphon by suction and will then continue
to flow whenever the pinch-cock is opened until the carboy is
empty.
It is suggested that those inexperienced in making chemical
preparations obtain the reagents and standard solutions required
in the following tests from a competent chemist or chemical
supply house. Those wishing to prepare their own standard
solutions will find directions in Appendix B.
Extreme care should be used in handling and preserving
standard solutions. They should be kept in hard glass, glass-
stoppered bottles, except sodium carbonate, the container for
which is preferably rubber-stoppered. The bottles should be kept
closed at all times to prevent the entrance of impurities or evapora-
tion of the solution. The stoppers when removed should never
be laid on their sides, nor should the mouth of the bottle be
carelessly handled. Before opening, the mouth and neck of the
bottle should be wiped free of du3t with a clean dry cloth. In
Fig. 62. — Distilled-Water Container.
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PHYSICAL AND CHEMICAL TESTS 97
transferring solutions to bottles or burettes, the latter should be
perfectly clean and dry. A small amount of the solution should
then be poured into the bottle or burette, and used to rinse the
same thoroughly, being then poured out. After this preliminary
rinsing the bottle or burette may be l&lled with the solution.
Burettes should be fitted with a small glass cap, or else corked,
when not in use, to prevent evaporation. It is not advisable to
keep a large stock of standard solutions on hand, as these de-
teriorate, it being preferable to make or have made new solutions
at intervals of a few months. Where large amounts of solutions
are used, a standard may be prepared with especial care, and kept
for comparative purposes, the solutions used being made up to the
required strength by titration with this standard. A ^ solution
of sulphuric acid is well adapted for this purpose and will keep a
long time. Then to prepare a ^ solution of sodium carbonate
dissolve the approximate amount required (see Appendix B) in a
liter of double-distilled water and titrate 10 cc. of this solution
with the standard acid, using erythrosin or methyl orange as an
indicator. The sodium carbonate solution should be made a
little strong, and then diluted down with distilled water until
10 cc. of the standard acid will exactly neutralize 10 cc. of the
sodium carbonate solution. An acid solution for general use can
now be made, using the sodium carbonate just prepared as a
standard of comparison. (In preparing acid solutions, or in
diluting strong acids, the acid should always be poured into the
water; if this operation is reversed the acid will sputter and fly
about and may cause painful and dangerous burns.) To prepare
solutions of other concentrations, it is only necessary to vary the
ratio of standard solution used in titration. Thus for a j^ solu-
tion of sodium carbonate, a sample of 10 cc. should require 50 cc.
of the ^ sulphuric acid to neutralize it; for a f-^ solution |^ X 10
or 22.7 cc. of the sulphuric acid would be required.
The metric system of measurement is used in chemical and
bacterial work. Lengths are measured in meters, decimeters
(1/10 meter), centimeters (1/100 meter), and miUimeters (1/1000
meter). The symbols for these units are " m.," " cm.," and " mm.''
respectively. Volumes are measured in cubes of the linear units,
thus cubic centimeters (abbreviation " cc.''), and cubic decimeters
are commonly used, the latter being the unit of liquid measure
and being called the "liter" (abbreviation "1."). It follows
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98 WATER PURIFICATION PLANTS
that a liter equals 1000 cc. Units of weight are the gram, which is
the weight of 1 cc. of water under standard conditions, the multiples
being the " kilogram " (1000 grams) and the milligram (1/1000
gram). The abbreviations used are respectively, " gm.," " kgm.,"
" mgm." The following table shows the relation between units
of the English and metric systems.
Table
1 inch =
2.54
centimeters
1 foot
30.48
centimeters
1 yard =
0.9144 meters
1 pound =
0.454
kilograms
1 ounce =
28.35
grams
1 grain =
64.80
milligrams
1 pint =
0.568
liters
The strength of standard solutions is given as normal (abbre-
viated " N.'O? or fractions thereof, thus one-l&ftieth normal (fX
one-tenth normal (j^). The meaning of these terms is beyond
the scope of this book, but can be found in any work on general
chemistry.
The apparatus used in the following tests may be obtained from
any scientific or chemist's supply house. For measuring out
samples a measuring glass or graduate is generally used (Fig. 53).
Greater accuracy can be obtained by using a measuring bottle
(Fig. 54). This is a long-necked Tbottle of a size to hold a definite
quantity of liquid (50 cc, 100 cc, etc.), when filled to a mark in the
glass of the neck. In use, the bottle is filled slightly above the
mark and the surplus is removed by smartly jerking the bottle.
Where the test involves colorimetric determinations a Nessler tube
(Fig. 55) is used, the sample being made up to the mark. For
measuring out small quantities of Uquid (for instance, the eryth-
rosin in the alkahnity test) pipettes (Fig. 56) are used. These '
are made to hold 1 cc, 5 cc, 10 cc, etc., up to 100 cc. or more. The
pointed end is inserted into the solution and the mouth is applied
to the other end, the solution being sucked into the pipette to a
little above the mark on the stem. The mouth is then removed
and a finger quickly substituted over the upper end. By slightly
releasing the pressure of tlie finger the solution is allowed to run
out until it stands just at the mark, after which the finger is
tightly pressed over the end and the measured quantity of solution
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PHYSICAL AND CHEMICAL TESTS
99
is removed and discharged into the sample. Needless to say it is
inadvisable to use a pipette in drawing off strong acids or poisons,
owing to the danger of getting some in the mouth.
Standard solutions are measured out from burettes (Fig. 57).
These consist of glass tubes graduated (generally to 1/10 cc), so
t
^
Fig. 53
Fig. 64
10
oc
u
Fig. 58
V
Fig. 56
Fig. 57
Fig. 55
3z
^
Folded
Fig. 59
that the amount of solution run into the sample can be read off.
The initial reading (to 1/10 cc.) is taken before the test and after
sufficient solution has been run into the sample to produce the re-
quired change in color of the indicator the burette is again read,
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100 WATER PURIFICATION PLANTS
the difference between the two readings giving the number of
cc. of solution used. The glass pet cock at the lower end allows
the stream from the burette to be regulated. The small glass bell
cap on top prevents evaporation.
The sample during the test may be contained in a glass bottle,
a porcelain casserole (Fig. 58), or dish (any white porcelain dish or
cup may be used), or in a glass beaker. The latter is simply a
container of thin glass (see Figs. 73 and 75 of coagulation, which
show typical beakers). Generally a clear drinking glass or bpttle
may be substituted for a beaker, unless it is required to heat the
solution contained.
For special tests of water, other than those given here, the
reader is referred to " Standard Methods of Water Analysis,"
published by the American Public Health Association, or to any
standard work on volumetric analysis.
Taste and Odor. Many waters contain mineral constituents
or organic matter giving off tastes and odors. The odor of the
raw water should be determined cold, that of the l<rate both hot
and cold. It is not necessary to taste the water, as the senses of
taste and smell are very closely allied.
The cold odor is determined by half j&lling a large bottle with
the water and inserting the stopper. Then shake the bottle
vigorously, remove the stopper, and smell the odor at the mouth
of the bottle.
The hot odor is determined by heating about 200 cc. of the
sample, in a beaker covered with a watch glass, to almost boiling.
Allow the beaker and contents to cool for several minutes, remove
the watch glass, and smell the odor.
. The odor may be described in the report by the following
abbreviations:*
V — vegetable m — moldy
a — aromatic M — ^musty
g — grassy d — disagreeable
^ f — fishy p — peaty
e — earthy s — sweetish
Turbidity. The generally accepted standard for turbidity is
that as measured by the turbidity rod of the United States Geo-
logical Survey. This, as generally constructed (Fig. 59), is a hard-
*" Standard Methods of Water Analysis." American Public Health
Association.
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••• •
PHYSICAL AND CbmfiCAL.iSslJ^: ••.• [v •/.; 101
wood rod, half inch by half inch in section, about four feet long,
having a platinum wire of 1 millimeter (0.04 inch) diameter in-
serted at right angles to its length near one end, and an open sight
(such as a screw eye) at the other end, 1.2 meters (4734 inches)
from the wire. The wire should project beyond the rod at least
one inch. The user places his eye at the sight and submerges the
wire end of the rod into the water to be tested at right angles to the
surface. The rod is pushed into the water until the wire just dis-
appears, as seen by the observer. The turbidity is measured by
the submergence of the rod. A turbidity which causes the wire
to disappear with a submergence of 100 millimeters is called 100,
other turbidities are marked on the rod as per the following table :
Graduation oj
^ Turbidity Rod*
Turbidity
Deothof
Wire,
Hazen
Reciprocal
Turbidity
Depth of
wire.
Hasen
Reciprocal
min.
Scale
mm.
Scale
10
794
0.032 •
160
69
.37
15
551
.046
180
62
.41
20
426
.060
200
57
.44
25
350
.073
250
49
.52
30
296
.086
300
43
.59
40
228
.111
350
39
.65
50
187
.136
400
35
.72
60
158
.160
500
31
.82
70
138
.184
600
28
.92
80
122
.208
800
23
1.09
90
110
.230
1,000
21
1.21
100
100
.254
1,500
17
1.49
120
86
.295
2,000
15
1.72
140
76
.334
3,000
12
2.10
* From the papers of the U. S. Geological Survey.
In this table the corresponding values for the Hazen Reciprocal
Turbidity Rod have been given, as this standard was used in
making some of the older records and may be convenient in re-
ferring back to these.
Turbidity measurements should be made in the open, pref-
erably during the middle of the day and not in direct sunlight.
For high turbiditie? a glass jar about 6 inches in diameter and
8 to 10 inches deep can be used. For low turbidities a tank 3 feet
in diameter and 4 feet deep or a barrel is required. Very high
turbidities must be diluted in order to obtain accurate results, that
is, the sample is mixed with one or more times its volume of clear
Digitized by LjOOQ IC
102 ;.\J ;/; V- ^JST-^i^^yiiuFjCATION PLANTS
water, and the turbidity obtained multiplied by a corre^wnding
factor.
For convenience in laboratory use, " bottle standards '' are
often prepared* (Fig. 60). Take diatomaceous earth, wash with
water to remove soluble salts, and ignite to remove organic matter;
treat and warm with dilute hydrochloric acid; wash with dis-
FlG. 60.— Turbidity Standards.
tilled water to remove acid, and dry. Grind and sift through a
200-mesh sieve. Fill a number of clear glass half-gallon bottles
with distilled water, and add the prepared diatomaceous earth,
testing with the turbidity rod until the desired turbidity is ob-
tained. Or one gram of this powder can be mixed with 1000
grams of distilled water to give a stock suspension having a
turbidity of 1000, and the bottle standards prepared from this by
dilution. Low turbidities can be obtained by dilution with dis-
tilled water. Standards having turbidities of 3, 5, 10, 15, 20, 30^
40, 50, 60, 70, 80, 90, and 100 are generally prepared in this way.
The bottles should be kept tightly corked and sealed. The water
to be tested is put in a bottle similar to those used for the standards
and compared with these, both sample and standard being well
shaken before comparison.
* " Standard Methods of Water Analysis." American Public Health
Association.
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PHYSICAL AND CHEMICAL TESTS
103
Color. The standard solution for color determination is pre-
pared as follows: "Dissolve 1.246 grams of potassium pla-
tinic chlorid (PtCl42KCl), containing 0.5 gram platinum, and one
gram crystallized cobalt chlorid (COCI26H2O), containing 0.25
gram of cobalt, in water, with 100 cc. concentrated hydrochloric
acid, and make up to one liter with distilled water."* This
Fig. 61. — Color Standards and Rack.
standard solution has a color of 500 parts per million. Slight
variations may be made in the amount of cobalt chlorid to more
nearly match the color of any particular water. From the stand-
ard solution, dilutions are made with distilled water having colors
of 0, 5, 10, 15, 20, etc., up to 70, and these are put into 100 cc.
Nessler tubes of such dimensions that the 100 cc. mark comes
about 25 cm. above the bottom and is uniform in all the tubes.
The solution must be up to the 100 cc. mark and the tubes should
be corked when not in use to prevent evaporation and the entrance
of dust. The tubes are placed in a vertical position in a " color
rack " (which can be obtained from any dealer in chemical ap-
paratus), resting on a white porcelain plate or slab.
The water to be tested is first filtered to remove the turbidity
♦''Standard Methods of Water Analysis."
Association.
American Public Health
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104
WATER PURIFICATION PLANTS
and then poured into a 100 ec. Nessler tube similar to those in the
rack. For comparison it is placed next to those in the rack, the
color being determined by looking downward into the upper ends
of the tubes against the white porcelain slab beneath. It is thus
compared successively with the various standard tubes, the results
Fig. 62. — ^Apparatus for Alkalinity Test.
being recorded as that of the standard to which the color of the
sample most nearly agrees.
Alkalinity. Apparatus: 1-100 cc. burette, graduated to 1/10 cc.
for ^ sulphuric acid (H2SO4); 1-100 cc. burette, graduated to
1/10 cc. for f-Q sodium carbonate (Na2C03); 1-250 cc. clear glass,
wide-mouthed, glass-stoppered bottle; 1-100 cc. measuring glass
or flask.
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PHYSICAL AND CHEMICAL TESTS
105
Reagents: ^ sulphuric acid; ^ sodium carbonate; eiythrosin
solution (0.1 gram of the sodium salt in one liter distilled water);
chloroform, neutral to erythrosin.
Procedure: With a graduated glass or flask measure 100 cc.
of the sample to be tested into the 250 cc. glass-stoppered bottle,
Fig. 63. — Apparatus for Free Carbonic-Acid Test.
add 1 cc. of erythrosin with a pipette and 5 cc. of chloroform.
Cork the bottle and shake well. If the sample has a pink color it
is alkaline. In that case titrate with ^ sulphuric acid, adding a
little at a time, and shaking well after each addition. Continue
to add the, acid until the pink color disappears. The number of
cubic centimeters of sulphuric acid added, multiplied by 10, gives
the alkalinity in parts per million.
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106 WATER PURIFICATION PLANTS
In case the sample remains white after adding the erythrosin,
it is acid, and should be titrated in a similar manner, using the ^
sodium carbonate. The number of cubic centimeters of sodium
carbonate used, multiplied by 10, gives the acidit'" in parts per
million as H^&Oa-
Remarks: For strict accuracy, a correction should be applied
for the alkalinity of the erythrosin. This correction can be
obtained by running a test as above with distilled water, when
the alkalinity obtained will be that due to the erythrosin. In gen-
eral, this correction is about 1 part per million, to be subtracted
for alkaline samples and added for acid samples.
The chloroform used can be recovered by emptying the samples
into a wide-mouthed bottle after the test. The chloroform col-
lects in the bottom of the bottle, the water above can be decanted
from time to time, and when sufficient chloroform has collected it
can be recovered by redistillation.
If the sample is very turbid, it should be filtered before the test,
so that the action of the indicator will not be obscured.
Free Carbonic Acid. Apparatus: 1-100 cc. burette, graduated
to 1/10 cc. for f-Q sodium carbonate* 1-250 cc. porcelain dish or
casserole; glass stirring rod.
Reagents: ^ sodium carbonate (Na2C03) and phenolphthalein
solution (1 gram in 200 cc. of 50-per-cent alcohol).
Procedure: Pour 100 cc. of the sample into the procelain dish
and add a few drops of phenolphthalein. If the water remains
colorless it contains carbonic acid. In that case, add sodium car-
bonate from the burette slowly, gently stirring the water mean-
while. Continue adding sodium carbonate until a faint, per-
manent pink color appears in the water. The niunber of cubic
centimeters of sodium carbonate added, multiplied by 4.4, gives
the amount of free carbonic acid (as CO2) in parts per million.
Remarks: To obtain accurate results, it is very important
that in collecting the sample, carrying it to the laboratory, and in
conducting the test, it be as little agitated as possible, since the
free CO2 readily escapes. The stirring rod should be used gently,
merely to mix the reagent through the sample. A rubber-tipped
stirring rod can be used to advantage.
As in the alkalinity test, a very turbid water can be filtered
before the test, but this must be accomplished with the least
possible agitation.
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PHYSICAL AND CHEMICAL TESTS 107
In acid waters erroneous results will be obtained, due to the
phenolphthalein indicating the acids as well as the CO2. In such
a case, run the test as above outlined, then subtract from the
reading in cubic centimeters of sodium carbonate required to
obtain a pink coloration with phenolphthalein, two times the
number of cubic centimeters required for the acid test with
erythrosin, and multiply the remainder by 4.4 to obtain the
parts per million of CO2.
Example: Acidity test with erythrosin required 10 cc. of ^
Na^COs
CO2 test with phenolphthalein required 25 cc.
2 X 10 cc. = 20 cc.
Subtracting 5 cc.
Multiplying by 4.4
Parts per million CO2 22.0
The same result can be obtained by determining the amount
of sodium carbonate required with phenolphthalein, then taking
a second sample, boiling off the free carbonic acid, and repeating
the test. The difference between the two tests, in cubic centi-
meters, multiplied by 4.4, will give the CO2 in parts per million.
Swamp waters and others containing weak organic acids may
give slightly erroneous results in the above test, but this error is
generally relatively unimportant.
By means of Plate I, the results of alkalinity, acidity, and CO2
tests can be determined graphically from the burette readings.
In this chart the necessary corrections for the effect of reagents
and the presence of acids in the free carbonic-acid test are made.
The chart is ruled with a series of horizontal lines corresponding to
the number of cubic centimeters of reagent required in making the
test. There is also a series of vertical lines corresponding to the
results required in parts per million, as indicated by the figures
along the lower margin. Three heavy diagonal lines are drawn
across the chart, representing respectively the relation of the de-
sired result in parts per million to the cubic centimeters of reagent
used, for the free carbonic-acid test, titrating with one-fiftieth
normal sodium carbonate and phenolphthalein indicator, for the
alkalinity test and for the acidity test, with (in both cases) eryth-
Digitized by LjOOQIC
108 WATER PURIFICATION PLANTS
rosin as indicator, and one-fiftieth normal sulphuric acid and sodi-
um carbonate respectively. The fine diagonal lines in the lower left
corner are for use in correcting the carbonic-acid results in acid
water. The uses of this chart are best illustrated by examples:
Example No. 1. Alkalinity Test with Erythrosin. In test-
ing a water for alkalinity according to instructions given on page
104, 12.60 cubic centimeters of ^ sulphuric acid are required to
discharge the pink color of the erythrosin. Look along the left-
hand margin of the chart for the horizontal line corresponding to
12.6. As each horizontal line represents two-tenths of a cubic
centimeter of reagent, the required line is the third above the
heavy line marked 12. Follow this horizontal line toward the
right until it crosses the diagonal line marked ^^ Alkalinity with
1 cc. Erythrosin." This intersection occurs midway between
two vertical lines. Following downward between these lines to
the lower margin, this is intersected two and one-half spaces be-
yond the 120 line. As each space on the lower margin corresponds
to two parts per million, the result of the test, in parts per million,
is 125.
Example No. 2. Acidity Test with Erythrosin. In a test
made according to instructions on page 104, 6 cubic centimeters
were required before the pink color of the erythrosin appeared.
Look along the left-hand margin of the chart, below the zero line,
and find 6 on the scale marked " ^ Sodium Carbonate in CC."
Follow this line horizontally toward the right until the diagonal
Une marked ^' H2SO4 Acidity with 1 cc. Erythrosin " is intersected.
This occurs midway between two vertical lines. Following down-
ward between these to the lower margin, this is intersected one-half
space beyond the heavy vertical line marked 60. As each space
on the lower margin corresponds to two parts per million, the
result of the test, in parts per million, is 61.
Example No. 3. Test for Free CO2 with Phenolphthalein. In
making a test for free CO2 in accordance with instructions on page
106, 7 cubic centimeters of reagent were used to produce a pink
color. In the left-hand margin of the chart find 7 in the column
marked ^' Reagent Required in Cubic Centimeters." Tracing to
the right along the horizontal line through this point, until the
diagonal marked " Free CO2 with Phenolphthalein " is reached,
follow downward along the vertical line through this intersection,
and at the lower margin find 30.8 as the result in parts per million.
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PHYSICAL AND CHEMICAL TESTS 109
Example No. 4. Test for Free CO2 in an Acid Water. As-
suming that it is desired to test for free CO2 a sample of water
which has an acidity with erythrosin of 24 parts per million
(requiring 2.4 cubic centimeters of ^ Na2C03 to neutralize). It
is found to require 7.1 cubic centimeters of ^ Na2C03 to produce
a pink color phenolphthalein. In the scale on the left-hand margin
estimate the point corresponding to 7.1 (7 is the line midway be-
tween 6 and 8; 7.1 would be 1/20 of a space, a very small distance,
above this). Follow this line horizontally toward the right until
the " Free CO2 " diagonal is reached. This occurs about midway
between two vertical lines. Follow downward between these until
the horizontal line under " O " in the left-hand scale is reached.
From this point continue downward* and toward the left, parallel
to the light diagonals until the horizontal line through 2.4 cc. on the
" ^ Sodium Carbonate " scale is reached. (This horizontal is the
second line below " 2 " on this scale, as each space represents
0.2 cc. of reagent.) From this intersection follow vertically down-
ward to the lower margin, where the result in parts per million is
found to be 10.
Alkalimetry and Indicators. The tests for alkalinity and CO2
involve the use of alkalimetry (or acidimetry) and indicators.
The bases (as sodium hydroxid (NaOH) and calcium hydroxid
(Ca(0H)2) and certain salts cause alkaline reaction in water due to
the presence of hydroxyl (OHO ions. The salts give this reaction
by interaction with the water, a phenomenon known as hydrolysis.
As an example of this interaction take a solution of sodium car-
bonate in water; the salt is ionized as Na* and CO3'', the water
slightly as H* and OH'. The two possible products are sodium
hydroxid (NaOH) and carbonic acid (H2CO3). The latter is a
weak acid — ^very slightly ionized — which does not affect the prop-
erties of the solution. The sodium hydroxid is ionized to a much
greater extent, giving the water an alkaline reaction. This inter-
action may be represented schematically:
Na2C03<=±2Na- + CO3"
2H2O ?z>2H- +20H'
i2NaOH
Other salts, which by hydrolytic action with water produce a
highly ionized acid, give the water an acid reaction. Thus the
hydrolysis of aluminum sulphate is as follows:
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110
WATER PURIFICATION PLANTS
Al2(S04)8^
6H2O
^2A1*-+3S04"
±6H' +60H'
^3H2S04
The indicators used, phenolphthalein and erythrosin, have the
faculty of indicating the presence of a small excess of either
hydroxyl ions (OH') or hydrions (H) by changes of color. The
phenolphthalein (C14H10O4), a colorless substance and very feebly
acid, is not perceptibly dissociated in solution:
C14H10O4 (colorless) ?=iCi4H904' (red) + H*
In the presence of an alkaUne salt the H ion combines with the
OH' ion present and the above equilibrium is displaced forward,
and a visible amount of the red negative ion is formed.
The action of these two indicators with substances commonly
met with in the above tests is as follows:
Substance
Colof
with
Color
with
Phenolphthalein
Sulphuric acid, HgSO ^ . .
Colorless
Colorless
Colorless
Not indicated
Pink
Pmk
Pink
Pink
Pink
Pink
Not indicated
Not indicated
Not indicated
Colorless
Ferrous sulphate, FeS04
Colorless
Aliinniniinn milphf^tp, Al2(SOj3 ..,,.,
Colorless
Carbonic acid, H2CO3
Colorless
Sodium bicaruonate, NaHCO,
Not indicated
Calcium bicarbonate, CaH,(C03),
Not indicated
Sodium carbonate, Na^COo. . . . 7"
Calcium carbonate. CaCO^.
Pink
PiTik
Sodium hydroxid, NaOH
Pink
Calcium hydroxid, Ca(OH),,
Sodium chlorid. NaCl. .
Pink
Not indicated
Sodium sulphate, Na2S04
Not indicated
Calcium sulphate, CaS04
Not indicated
From this tabulation it is seen that phenolphthalein is a most
deUcate indicator with acids, indicating even carbonic acid. Its
use in determining the acidity of a water would be confusing, as
it would be afifected by carbonic and weak organic acids present.
ErytHrosin indicates both sulphuric acid and the acid sulphates
of aluminum and iron. If it is desired to determine the free sul-
phuric acid only, a less delicate indicator — ^methyl orange* —
* Methyl-orange indicator is made by dissolving 1/10 gram of the com-
pound (also known as Orange III) in a few cubic centimeters of alcohol and
diluting to 100 cc. with distilled water. The 100 cc. sample to be tested for
acidity is titrated in the cold with sodium carbonate solution (^) using a few
drops of methyl orange as an indicator. The methyl orange gives a red color
with acid water, which changes to yellow when the acid is neutrahzed.
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PHYSICAL AND CHEMICAL T|JSTS 111
must be used instead of erjrthrosin and chloroform, in the test for
acidity.
The table also shows that alkalinity may be due to the bicar-
• bonates, carbonates, and hydroxids of the alkalies and alkaline
earth metals. Bicarbonates in an untreated water are generally
attributed to calcimn (Ca) and magnesimn (Mg), while car-
bonates are attributed to sodium (Na) and potassium (K), as the
carbonates of these metals are soluble in water, whereas those of
calcium and magnesium are only very sparingly soluble. If there
is a sufficiency or surplus of carbonic acid present, all the alkalinity
will exist as bicarbonates. Bicarbonates and hydroxids cannot
exist together, as they react chemically, forming carbonates and
water. It will be noted that erythrosin indicates all three kinds
of alkalinity, whereas phenolphthalein indicates only carbonates
and hydroxids. Another peculiarity of the alkalinity with phenol-
phthalein arises from the fact that it does not indicate bicarbonates.
The reaction in neutralizing alkalinity with standard sulphuric
acid may be represented by the equations:
CaCOs + H2SO4 = CaS04 + H2CO3
CaCOs + H2CO3 = CaH2 (€03)2
Thus one unit of sulphuric acid neutralizes two units of carbonates
as indicated by phenolphthalein. The following rules for de-
termining the three types of alkalinity may be given:
1. When an alkaline water is neutral or acid with phenolphtha-
lein the alkalinity is due to bicarbonates.
2. When the phenolphthalein alkalinity is less than half of the
erythrosin alkalinity, twice the phenolphthalein alkalinity gives
the carbonates, the difference between these and the erythrosin
alkalinity gives the bicarbonates.
3. When the phenolphthalein alkalinity is one-half the eryth-
rosin alkalinity, carbonates only are present.
4. When the phenolphthalein alkalinity is more than half
the erythrosin alkalinity, hydroxids are present. To find the
amount, multiply the difference between the two alkalinities by
two and subtract this from the erythrosin alkalinity. The re-
maining alkalinity is due to carbonates.
5. When the phenolphthalein and erythrosin alkalinities are
equal, only hydroxids are present.
Knowing the alkalinity of a water with phenolphthalein and
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112 WATER PURIFICATION PLANTS
with erythrosin, the bicarbonates, carbonates, and hydroxids can
be determined graphically from Plate II. The horizontal lines re-
present phenolphthalein alkalinity, as indicated by the scale on
the left-hand margin, each space being equivalent to one part per
million. The diagonal lines represent erythrosin alkalinity, each
space being equivalent to 5 parts per million. The vertical lines
represent the components of these alkalinities as bicarbonates
(lower margin, toward the left), hydroxids (lower margin toward
the right), and carbonates (upper right margin). The following
examples will illustrate the use of this chart:
Example No. 1. Given a water of the following
characteristics:
Phenolphthalein alkalinity — 25
Erythrosin alkalinity — 100
Find 25 on the scale along the left-hand margin (the heavy line
midway between 20 and 30), and follow the line through this point
horizontally to the right until the erythrosin diagonal marked
100 is reached. By following the vertical through this point
downward to the lower margin, the bicarbonate alkalinity is found
to be 50 (midway between 40 and 60). If the horizontal line
through 25 is followed further to the right, it will be found to take
a sharp upward turn, and continuing along this to the upper mar-
gin the carbonate alkalinity of the water is found to be 50
also.
Example No. 2. Given a water of the following
characteristics:
Phenolphth^ein alkalinity — 40
Erythrosin alkalinity — 60
Find 40 on the scale along the left-hand margin, and follow this
line horizontally to the right until it intersects the erythrosin
diagonal marked 60. Following the vertical line through this
point downward to the lower margin, the water is found to have a
hydroodd or caustic alkalinity of 20 parts per million. Following
the heavy diagonal line through this same point of intersection
upward to the upper margin, the carbonate alkalinity is found to
be 40 parts per million.
The above determinations are in terms of calcium carbonate.
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PHYSICAL AND CHEMICAL TESTS
113
More properly they should be multiplied by the following
factors:
Substance as
CaCOs
Multiply By
Gives Result As
Bicarbonates. . .
Carbonates ....
Hydroxids
1.62
1.06
0.74
Calcium bicarbonate (CaH2(C03)2)
Sodium carbonate (NagCOa)
Calcium hydroxid (CaCOH)^)
Sometimes it is desirable to determine the " half -bound " and
"bound " carbonic acid (CO2). To obtain these data, multiply the
bicarbonates and carbonates respectively (in terms of calcium
carbonate) by 0.44. It is not correct to record bicarbonates and
half-bound C02,or carbonates and bound CO2, in an analysis, as the
one includes the other in both cases. Free CO2, however, is an
independent substance, as its name implies.
Iron. Apparatus: 1-100 cc. measuring glass; 1-250 cc. porcelain
evaporating dish; 100 cc. Nessler tubes, IJ/g ii^ch diameter by 534
inches high to 100 cc. mark (at least twelve are required for per-
manent standards); 1-100 cc. burette, graduated to 1/10 cc. for
standard iron solution.
Reagents: Hydrochloric acid (1:1); nitric acid (1:2); potas-
sium permanganate solution (5 gm. per liter); potassium sulpho-
cyanid solution (20 gm. per liter); standard iron solution ("dissolve
0.7 gram of crystallized ferrous ammonium sulphate in 50 cc. of
distilled water and add 20 cc. of dilute sulphuric acid. Warm
the solution slightly and add potassium permanganate until the
iron is completely oxidized. Dilute the solution to one liter."*
One cc. of this standard solution in 100 cc. of distilled water is
equal to one part per million of iron).
Procedure: Boil 100 cc. of the sample several minutes in an
evaporating dish with 5 cc. nitric acid. Add two or three drops
of the potassium permanganate solution and allow to stand a few
minutes. If the red color disappears, add more permanganate, drop
by drop, until a faint pink color persists. Add 10 cc. of the potas-
sium sulphocyanid solution, mix thoroughly, and pour into a 100 cc.
Nessler tube. Pour 100 cc. of distilled water into a second
Nessler tube, add 5 cc. of nitric acid and 10 cc. of potassium
♦"Standard Methods of Water Analysis."
Association.
American Public Health
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114
WATER PURIFICATION PLANTS
sulphocyanid. Add standard iron solution to the second Nessler
tube until the color of its contents matches that of the sample.
The number of cc. of iron standard added gives the dissolved iron
in parts per million.
If the sample contains organic matter, it must be treated as
follows: after filtering, evaporate to dryness and ignite to destroy
Fig. 64. — Apparatus for Iron Test.
organic matter; cool and add 5 cc. of hydrochloric acid (1:1) to
residue, and if this is not dissolved immediately, heat gently; wash
the liquid into a 100 cc. Nessler tube, and make up to 100 cc.
with distilled water; then add potassium permanganate and sul-
phocyanid and proceed as before, using hydrochloric acid in the
second Nessler tube also.
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PHYSICAL AND CHEMICAL TESTS
115
If desired, permanent iron standards, similar to the color
standards herein before described, can be made up. The follow-
ing solutions are required:*
Platinum solution: 12 grams of potassium platinic chlorid
(PtCl4,2KCl), dissolved in distilled water, with the addition of
100 cc. strong hydrochloric acid, and made up to one liter with
distilled water.
Cobalt solution: 24 grams of cobaltous chlorid crystals
(CoCl2,6H20), dissolved in distilled water, with the addition of
100 cc. strong hydrochloric acid, and made up to one liter with
distilled water. The standards are made up by the addition of
various amounts of these solutions to distilled water in the 100 cc.
Nessler tubes described under " Apparatus," as follows:
standard
Standard
Iron
No. of CC.
No. of CC.
Iron
No. of CC.
No. of CC.
Solution,
Platinum
Cobalt
Solution,
Platinum
Cobalt
Parts per
Solution
Solution
Parts per
Solution
Solution
MiUion
MUlion
0.0
.0
1.5
28
17.0
0.1
2
1.0
2.0
35
24.0
0.3
6
3.0
2.5
39
32.0
0.5
10
5.0
3.0
40
43.0
0.7
14
7.5
3.5
40
55.0
1.0
20
11.0
4.0
40
67.0
In each case the platinum and cobalt solutions are poured into the
Nessler tube first and enough distilled water is added to make up
the solution to the 100 cc. mark. The water to be tested is treated
as before, and after adding the potassium sulphocyanid is im-
mediately compared with the permanent standards.
Logwood Test for Free Alum and Iroii. Apparatus: Two
250 cc. porcelain dishes or casseroles.
Reagents: Solution of logwood in distilled water; acetic acid
(glacial).
Procedure: Pour 100 cc. of water to be tested into each of
two porcelain dishes. To the second dish add a small piece of
alum or iron sulphate, and run this dish as a control, to check the*
color changes in the sample being tested. Add a few drops of log-
wood solution to each dish, stir gently, and observe the colors.
Then add a few drops of acetic acid to each dish, stir, and note the
* Jackson, Tech. Quar., 13, p. 320.
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116 WATER PURIFICATION PLANTS
color changes. The colors obtained vary slightly with different
waters, thence the need for running the check sample containing
alum or iron along with the water being tested. Approximately
the following color changes occur: If alum is present: when log-
wood is added, the water turns blue, when acetic acid is added the
blue changes to red, fading gradually to yellow. If no alum is
present: when logwood
…[truncated]