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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