project report on extended aeration and step aeration
TRANSCRIPT
Project Report on
Extended Aeration and
Step Aeration
Completed under the guidance of Dr.Jasmeet Kaur
(Professor of S.G.T.B Khalsa College)
Submitted by:
Hakim Asif Haider
Life Science
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ACKNOWLEDGEMENT
No significant achievement can be a solo performance
especially when starting a project from ground up. This
project on “Extended Aeration and Step Aeration” has by no
means been an exception. Apart from my effort, the success
of this project depends largely on the encouragement and
guidelines of many others. I take this opportunity to express
my gratitude to the people who have been instrumental in
the successful completion of this project.
I would like to show my greatest appreciation to Dr. Jasmeet
Kaur, Professor, S.G.T.B Khalsa College. I can’t thank you
enough for your tremendous support and help. I feel
motivated and encouraged every time we attend your class.
Without your encouragement and guidance this project
would not have materialized.
The guidance and support received from our parents for the
success of the project. We are grateful for their constant
support and help.
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Table of Contents
1. Acknowledgement………………………………… 22. Introduction………………………………………...43. Definition of Aeration……………………………...84. Purpose Of Aeration………………………………...95. Aeration in General………………………………..106. Aeration in History around the World……………..12
a) Dr. Hales...........................................................12 b) Montbruel and Ferrand's Project.....................13 c) Quai des Celestin, Paris....................................13 d) Britain...............................................................14 e) Scotland............................................................16 f) Russia................................................................16 g) Aeration in America .........................................18
1. Elmira, N.Y. Water Works Company (1861)...............18
2. Lawrence, Massachusetts (1875)..................................18
3. Utica, N.Y. Water Works Company (1890)..................19
4. Hayat Patents........................................................................21
5. Leed Patents..........................................................................22
6. Winchester Kentucky (1900)...........................................24
7. South Norwalk, Connecticut (1940)...............................24
7. Early Apparatus used for Aeration......................25
8. Methods of Aeration..............................................26
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9. Mechanical Equipment Used In Aeration...........27
10) Use of Aeration....................................................28
11) Conclusion............................................................30
12) Extended Aeration...............................................31
A. Comparison between Extended aeration and
Conventional Activated Sludge Process..............32
B. Application....................................................................33
13) Step Aeration..........................................................35
14) Bibliography...........................................................37
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II. Introduction
Water aerated naturally by flowing over sandy or
pebbly beds or rocky falls has been acclaimed by
writers of all ages and countries. Only a few of these
enthusiasts realized that the waters they so highly
praised were clear, bright, sparkling, tasteless and
odorless when they reached the streams. In the
eighteenth century, artificial aeration was directed at
making up the oxygen deficiencies of distilled water
and of rain water that had been stored up in household
cisterns. Toward the end of the eighteenth century and
early into the next century, aeration was applied to a
few public water supplies carrying decomposed
vegetable or animal matter. Not until the last half of the
nineteenth century did aeration become a marked
feature of municipal supplies. Even then, the number of
applications was small and pertained chiefly to stored
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surface waters subject to tastes and odors from algae
growths. In this period, aeration was applied here and
there, generally to ground waters, for the removal of
iron, and then of manganese, and also to eliminate
malodorous gases from sulfur bearing ground waters.
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1. DEFINITION OF AERATION
In its broadest sense, aeration is the process by which
the area of contact between water and air is increased,
either by natural methods or by mechanical devices.
Ordinary usage in water works practice has however,
been given the term in the more limited sense referring
specifically to use of mechanical devices or procedures.
In this limited sense aeration clearly defines itself as a
method of treatment rather than merely a modification
of natural conditions at the source of supply. The terms
'natural aeration` or 'reaeration` are used to represent no
mechanical procedures or slower aeration of large
bodies of water under natural conditions. In the
progress of water from source to consumer, aeration is
one of the most elemental techniques frequently
employed in the improvement of the physical and
chemical characteristics of water.
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2. PURPOSE OF AERATION
As suggested, the basic purpose of aeration is the
improvement of the physical and chemical
characteristics of waters for public supply. Primarily,
this improvement involves the reduction of
objectionable tastes and odours, but some additional
benefits of aeration, as a preliminary step to other
purification processes have also been noted.
In the cool stagnant bottoms of lakes and reservoirs
during late summer and late winter, in deep wells and in
the dry-weather flow of some sluggish rivers are found
natural waters which are so deficient in oxygen that
they are objectionable in both taste and odour. Aeration
of such waters improves their taste by supplying the
deficient oxygen, rescuing the free carbon dioxide and
eliminating much of the hydrogen sulphide and other
odorous constituents present. Removal of iron and
manganese from such oxygen deficient waters also
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usually requires aeration as an initial step. This initial
step allows for the lower oxides of these minerals that
are dissolved in the water and combined with carbon
dioxide to be converted to higher insoluble oxides and
in turn removed by subsequent sedimentation, contact
or filtration.
3. AERATION IN GENERAL
The general idea behind aeration is to bring the water
into intimate contact with the air. Either the water may
be discharged into free air or the air may be forced into
a body of water. Apparatus used includes: low cascades,
multiple jet fountains throwing water to considerable
heights, multitudinous spray nozzles discharging not far
above the surface of a reservoir, superimposed trays or
shelves, submerged perforated pipes, and porous tubes
and plates. Motivation has been by gravity head for
water, pumping head for water and pumping head for
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air. Chronologically, working installations consisted,
first, of cascades and gravity operated multiple-jet
fountains, and then forced aeration for a few years of
commercial exploitation, followed by low-throwing
spray nozzles, and finally, diffusion of air through
porous tubes and plates in water.
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II. Aeration in History around the World
Obsessed by the notion that removal of organic matter
was the chief end and aim of aeration, many inventors
and promoters centered their energies there. Until near
the close of the nineteenth century, confidence in the
self purification of rivers continued widespread. After
two thousand years of recognition of the good effects
on water from natural aeration, experiments on artificial
aeration were reported. The first of these that has been
found was in a paper on blowing showers of air through
water being distilled, read by Dr. Stephen Hales on
December 18, 1755.
1) DR. HALES
For his experiments, Hales used a " Tin or Copper Air-
box" 6 inches in diameter and 1.5 inches apart. Rising
from this was an air supply pipe to which was attached
a leather hose connected with "the nose of Bellows"
used to force in air. Successful experiments with this
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device on milk and water were reported in another
paper read before the Royal Society.
2) MONTBRUEL AND FERRAND'S PROJECT
In contrast with the Hales method of blowing air
through water was the method of dropping water
through the air, put into use a little earlier. Post aeration
in a reservoir exposed to a current of air was included in
Montbruel and Ferrand's project of 1763-1764 to supply
Parisians with filtered water taken from the Seine above
sources of pollution.
3) QUAI DES CELESTINS, PARIS
At the Quai des Celestin water treatment plant, Paris,
put in use, by Happey in 1806, it is stated by
Dunglinson that after the water had been settled, and
then filtered twice; it was aerated by being dropped like
rain from the bottom of the second filters into
Clearwater tanks.
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4) BRITISH AERATION TECHNIQUES
Of the many British patents on aeration taken out in the
nineteenth century, the first was granted February 8,
1812, to Robert Dickinson and Henry Maudslay on “a
process for sweetening water and other liquids." The
process consisted of "simply of forcing a stream or
streams of air through the foul or tainted water." A
bellows or preferably a pump could be used. In this
setup, the air is being forced to the bottom of a water
cask through a tube or hose ending in a tube of iron or
copper, perforated with small holes "to divide the air
into numerous small streams, that the surface of water
brought into contact with the air may be greater." The
effect of the air is "that the offensive gas held in
solution will be expelled from the water in a short time;
after which the water should be left at rest for a short
time, to allow its insoluble purities to subside. Both the
apparatus and process are substantially the same in
principle as those described in 1755 by Dr. Hales and
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patented again and again in England and America
during the nineteenth century.
Four other British patents on aerating fresh water, two
of which were in general principle anticipations of
American patents or practices, included one by
Theodore Cotelle (December 1, 1838), and one by
Richard Johnson (on September 5, 1857). Cotelle's
paper covered details of admitting air to a filter through
tubes in the sides of the container. Johnson's paper
covered dropping water for some distance in "jets,
sheets or streams" upon a filter of broken slate, stone or
other material so contact with atmospheric oxygen
would cause "mineral particles held in solution by
carbonic gas" to precipitate on the surface of the bed.
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5) SCOTLAND'S AERATION TECHNIQUES
The earliest known of the cascade type of aerator,
working in series, was put into use in 1848 by the
Gorbals Gravitation Water Co. to supply water to a
district afterwards annexed to Glasgow, Scotland.
Water from a large settling reservoir cascaded into a
basin and from it into the first of three filters, arranged
in steps. Similarly there was a cascade between the first
and second filters, the second and third filters and the
third and last filter and a clear water reservoir.
6) RUSSIAN AERATION TECHNIQUES
In Russia, a dozen years later, an aerator was included
in a water treatment plant built to supply a government
mill on the River Neva at St. Petersburg. The contract to
build the plant included pumps, settling reservoirs, an
aerator and sand filters. The strainer was made up of
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four troughs arranged in the form of steps. Each of
these was divided longitudinally that did not reach the
bottom, into two compartments, the inner one of which
was covered by wire gauze, and received the water as it
fell from the steps above, and the outer of which
contained the horizontal tipped orifices through which
the water escaped as it flowed to the step below. Each
step was 2 feet high. The lowest step was superposed to
one of four sand and gravel filter tanks. After passing
downward through filter tanks, the filtered water flowed
to deep wells in which it was stored for use. The rated
capacity of the treatment plant was 100,000 cubic feet
in 10 hours or about 750,000 gallons. Observations on
that plant showed that water entered the first step in a
perfect lucid state, but before it has passed through two
sheets of gauze it became turbid, and deposited black
scum on the wire which required constant cleaning, so
great was the quanitity of the deposit. In the first filter
tank, the water was partially covered with black scum
or froth, sometimes more than an inch in thickness, and
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thin scum, having a metallic lustre, appeared on the
second reservoir.
7) Aeration In America
1) ELMIRA, N.Y WATER WORKS CO. (1861)
The first known aerator on an American water supply
was a part of works built between 1860 and 1861 by the
Elmira, N.Y. Water Works Company. In this process,
water from an impounding reservoir was admitted to a
distributing reservoir through a fountain discharging
trough which contained a cluster of holes for aerating
and purifying.
2) LAWRENCE, MASSACHUSETTS (1875)
The next American aerator of record was of the single
cascade type. It was part of the water works of
Lawrence Massachusetts, completed in 1875. Water
from the Merrimac River or an adjacent filter gallery
was discharged from the force main through a bell-
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shaped mouth onto a stone platform from which it fell
over six granite steps, each 10 feet wide into the
reservoir.
3) UTICA, N.Y. WATER WORKS CO. (1890)
The most elaborate of the early American fountain
aerators was one put into use October 26, 1890, by the
Utica, NY, Water Works Company. Seventy-six
vertical pipes, 1 foot above high water level, discharged
into a distributing reservoir. This reservoir was fed from
another, under a 44 foot head when the upper reservoir
was full. The risers were fed from 12 inch pipe laid in a
quadrangle formed on each side by three 12 foot lengths
of cast iron pipe joined by quarter bends. This square
was laid on the bottom of the reservoir in water 10 feet
deep. Attached directly to this quadrangular manifold
were 71, 2 inch vertical pipes about 2 feet apart. Five
branch pipes led to risers. Of these, four had diameters
of 2 inches and led one from each corner of the square.
The caps of the 76 risers were perforated to give
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orifices of the following diameters: 16, 1 inch; 16, 3/4
inch; 16, 5/8 inch; 56, 1/2 inch; 80, 1/4 inch; and 52,1/8
inch. The jets converged toward the centre of the
fountain. Their total discharge capacity was 4000
gallons per minute. By means of screw joints the upper
part of each riser could be removed to avoid ice
damage.
When the Utica aerator was installed, it was designed to
eliminate objectionable tastes and odours. When
installed, the water supply was impounded in three
reservoirs from which it passes by gravity to the
distribution system. With the growth of the city the
capacity of the aerator became inadequate, reservoirs
were build at a higher level and the aerator was
dismantled approximately 1902.
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4) HYATT PATENT
Nearly all the aerators thus described worked under
gravity heads and discharged water into the air. In the
last two decades of the nineteenth century, Professor
Albert R. Leeds and John W. Hyatt patented forced
aeration by means of which air or oxygen was
discharged into water. In Hyatt's first patent he said by
passing the combined water and air through a filter the
particles of filtering material would finely subdivide the
air and enhance the action. When the air and water were
thus combined, the water would absorb the oxygen of
the air and the impurities in the water would be
consumed or rendered inert. In one of his devices, water
was to be passed down through an inverted cone-shaped
vessel pierced with holes articulated above with a group
of Sprengel air pumps. Water falling through these
induction tubes was to suck in air and mingle it with the
water. To mix the air and water still more, the combined
fluid was to be passed over one or more such devices as
small stones, horizontal perforated plates or baffles
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attached to the inside of the left arm of the U-tube
containing the Sprengel pumps. The water was then to
be passed up through the right arm of the U-tube, which
might also be circumvented into the top of the filter.
In a trade catalogue of 1886 Hyatt stated that his
aerating system combined 25 percent or more of
atmospheric air with water under static pressure,
oxidizing the impurities, destroying the conditions
favourable to germ propagation, and so regenerating the
water that it will keep sweet much longer in pipes and
reservoirs than water not so treated.
5) LEEDS PATENT
A plant for aeration by compressed air in accordance
with the Leeds patent was put into operation on the
water works of Norfolk, Virginia in July of 1888. It was
installed by the National Water Purifying Company in
place of filters that had been recommended. The water
supply was from impounding reservoirs, the bottoms of
which were not stripped before flooded. When the
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reservoirs were drawn down, vegetable growths
occurred, followed by tastes and odours. Aeration
helped to eliminate the odours in the water. As first
operated compressed air was delivered through outlets
from a pipe paralleling the inside of the reservoir. The
installation consisted of an air pressure and perforated
pipe system which aerated the water in the pump
suction and basin. It was operated intermittently until
1896 when a connection was made from the compressor
to the delivery main.
Writing in 1895, Professor Leeds stated that on his
recommendation combined aeration and filtration was
adopted in 1887 for the 2 million gallon per day water
supply in Long Branch. The object of aeration there was
to charge the water itself with oxygen to maximum then
allow this oxygenated water to purify the filter bed. The
Hyatt filters of 1888 were operated by gravity up until
the year 1929, when a clear water basin was installed.
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6) WINCHESTER, KENTUCKY (1900)
Alternate sprays and cascades produced by discharging
water over the edge of plain pans and through
perforated pans, superimposed, were produced by an
aerator put into use at Winchester, Kentucky. late in
1900. It was equipped with a ball float and cone
adjustor.
7) SOUTH NORWALK, CONNECTICUT (1940)
At South Norwalk, Connecticut, double aeration and
double filtration were put into use to treat impounded
surface water subject to organic growths and tastes and
odours. Water was aerated before and after filtration.
Both aerators and first filters were still being used in
early 1940 but the final filter had been converted into a
clear water basin.
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III. Early Apparatus Used For Aeration
1) Aer-O-Mix
The apparatus known as the Aer-O-Mix was first used
in January 1929. The water flows into the tank
surrounding the Aer-o-mix head, enters the head
through the apertures in the perimeter, then passes
downward through the annular throat and past the lower
ends of the multiple tubes in the head, drawing bubbles
of air down through these tubes, by aspiration. The
mixture of water and bubbles passes downward through
the retention pipe, through the U turn and up again and
through a discharge plate where the air is released. A
modification of this design is used where there is not
sufficient head for the water to flow through the aerator
by gravity. In that case a vertical motor is mounted
above the head, its shaft extending downward through
the centre of the head, being connected to an impeller in
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the top of the retention tube. The action of the impeller
forces the water down through the tube.
IV) Methods of Aeration
From the examples of various aeration plants provided
above, we can conclude that there are several different
ways in which aeration can proceed. By causing the
water to flow by gravity down an arrangement of
steps, thus splashing and breaking up into films and
drops; by causing it to flow downward through a
vertically arranged series of trays containing beds of
coke or gravel, it being pumped to the utmost tray; by
throwing it into the air in a spray; and by blowing or
drawing air bubbles through it, is some of the ways to
bring the water into contact with the air. Pumping by
air lift also has a partial aerating effect.
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V) Mechanical Equipment Used in Aeration
After discussing several accomplishments in the history
of aeration, we can address the topic of present day
mechanical equipment for aeration. It can be classified,
for convenience into two basic categories, the diffusion
type and the waterfall type. In the choice between
waterfall and diffusion types of aerator units, theory
strongly favours the latter. A diffusion unit wherein
finely divided air bubbles are introduced over the
bottom of a basin, through which water is flowing,
provides most adequately for all the factors that
control the efficiency of aeration. Some authorities feel
that the principal advantage arises from the fact that
the velocity of bubbles ascending through the water is
much lower than the velocity of free falling drops of
water, thus affording a longer period of contact for an
equal expenditure of energy.
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VI) Use Of Aeration
1) IRON REMOVAL
Trays filled with coke or stones are used for aeration at
a number of installations, chiefly in connection with
iron removal, where aeration and contact action are
combined, or where compactness is desirable.
Experimental work is desirable to determine the number
of trays, depth, etc.
2) ORGANICS REMOVAL
Ultimately, since the removal of organic matter was the
chief end and aim of aeration, many inventors and
promoters concentrated their interests there. In the four
decades of the present century the proper objectives of
aeration have been defined and various means of
adapting apparatus to those objectives have been
devised.
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3) VOLATILES REMOVAL
Aeration is a procedure of air stripping that is being
thoroughly investigated for the removal of volatile
organic compounds from contaminated groundwater
supplies. The effectiveness of removal of these
compounds is both a function of their solubility and
their volatility. Data from EPA field tests and
laboratory experiments shows that aeration is an
extremely effective method of removing chlorinated
organic from water.
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VII) Concluding Statements on Aeration
Aeration by spraying into the air takes too much
energy. Other methods call for jets, pans showers
through small, closely spaced perforations, coke trays
and compressed air admitted to the water at the
bottom of the basins. In no case reported is high
pressure air used nor is there a single instance of
compressed air admitted to a main tank.
We thus conclude our study of aeration. Outlined
above is the theory, history and practice behind this
intimate mixing of air and water. As Theophrastus, an
early Greek philosopher once explained, "running
waters are generally better than standing water, and
when aerated are still softer, or less harsh."
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VIII) Extended Aeration.
Extended aeration is a method of sewage treatment
using modified activated sludge procedures. It is
preferred for relatively small waste loads, where lower
operating efficiency is offset by mechanical simplicity.
This Process, also referred to as total oxidation, is a
modification of the ASP (Activated Sludge Process).
The fundamental idea in extended aeration as compared
to the Conventional Activated Sludge Process is to
minimize the excess amount of excess sludge and this is
achieved by increasing residence time; thus the reactor
volume is comparatively larger than that required in
conventional activated sludge process. As a result
essentially, all degradable sludge formed is consumed
by endogenous respiration.
In extended aeration process the raw sewage goes
straight to the aeration tank for treatment. The whole
process is aerobic. This simplification implies longer
aeration time which has earned for the process the name
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"extended aeration". The BOD removal efficiency of
the extended aeration process is higher than activated
sludge process which makes it especially desirable to
use where it is to be followed by tertiary treatment for
reuse.
a) Comparison between Extended Aeration and
Conventional Activated Sludge Process.
1) Longer Detention Time in Aerator.
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2) Lower Organic Loadings.
3) Higher concentration of biological agents in Aerator
4) Higher Consumption of Oxygen In Extended
Aeration Process.
b) Applications
Extended aeration is typically used in prefabricated
"package plants" intended to minimize design costs
for waste disposal from small communities, tourist
facilities, or schools. In comparison to traditional
activated sludge, longer mixing time with aged sludge
offers a stable biological ecosystem better adapted for
effectively treating waste load fluctuations from
variable occupancy situations. Sludge may be
periodically removed by septic tank pumping trucks
when solids concentrations become high.
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Extended Aeration
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IX) Step Aeration
Step Aeration Is a Modification of the Conventional
Activated sludge process in which fresh feed is
introduced at several points along the aeration tanks.
This arrangement provides for the equalization of the
F/M ratios along the tank.
The Aeration tank is divided by baffles into several
parallel channels. Each channel constitutes one step of
the process and the steps are linked together in series.
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X) Bibliography
a) References
1) Hammer, Mark J. (1975). Water and Waste-Water
Technology. John Wiley & Sons. ISBN 0-471-
34726-4.
2) Metcalf & Eddy, Inc. (1972). Wastewater
Engineering. McGraw-Hill Book Company. ISBN 0-
07-041675-3.
3) Steel, E.W. and McGhee, Terrence J. (1979). Water
Supply and Sewerage, 5th Edition. McGraw-Hill
Book Company. ISBN 0-07-060929-2.
4) Baylis, John R., Elimination of Taste and Odor in
Water, McGraw Hill Book Company, 1935.
5) Baker, M. N., The Quest for Pure Water, The
American Water Works Association, 1949.
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6) Hazen, Allen., Clean Water and How to Get It.
John Wiley & Sons, Inc., 1914.
7) Isacoff, Eric W., & Neely, James W.,
Carbonaceous Adsorbents for the Treatment of
Ground and Surface Waters. Marcel Dekker Inc.,
1982.
8) Nordell, Eskel., Water Treatment for Industrial and
Other Uses. Reinhold Publishing Corporation,
1951.
9) Ramalho, R.S., Introduction to Wastewater
Treatment Processes. Academic Press, 1977.
10) Ryan, William J., Water Treatment and
Purification. McGraw Hill Book Company, 1937.
11) Manual of Water Quality and Treatment, American
Water Works Association, New York, 1940.
12) Water Quality and Treatment, 2nd Edition, The
American Water Works Association, Inc. 1950.
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