Types of Aerators

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Presented By

SAJI SIMON C

P12EN006

M.TECH 1ST YEARENVIRONMENTAL ENGG

SVNIT


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Aeration is the process of bringing water andair into close contact in order to removedissolved gases, such as carbon dioxide, and tooxidize dissolved metals such as iron. It canalso be used to remove volatile organicchemicals (VOC) in the water.

Aeration is often the first major process at thetreatment plant. During aeration, constituentsare removed or modified before they caninterfere with the treatment processes.


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Aerators fall into two general categories

WATER INTO AIR

AIR INTO WATER


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Cascade Aerators

A cascade aerator consists of a series of steps thatthe water flows over. In all cascade aerators,

aeration is accomplished in the splash zones. Theaeration action is similar to a flowing stream.Splash areas are created by placing blocks acrossthe incline. Cascade aerators can be used to oxidize

iron and to partially reduce dissolved gases. Theyare the oldest and most common type of aerators.


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CASCADE AERATORS


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Cone aerators are used primarily to oxidizeiron and manganese from the ferrous state tothe ferric state prior to filtration. The design of

the aerator is similar to the cascade type, withthe water being pumped to the top of the conesand then being allowed to cascade downthrough the aerator.


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CONE AERATORS


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This type of aerator has one or more spraynozzles connected to a pipe manifold. Movingthrough the pipe under pressure, the water

leaves each nozzle in a fine spray and fallsthrough the surrounding air, creating afountain affect. In general, spray aeration issuccessful in oxidizing iron and manganese

and is successful in increasing the dissolvedoxygen of the water.


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SPRAY AERATORS


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The slat and coke trays are similar to thecascade and cone types. They usually consist ofthree-to-five stacked trays, which have spaced

wooden slats in them. The trays are filled withfist-sized pieces of coke, rock, ceramic balls,limestone, or other materials. The primarypurpose of the materials is provide additional

surface contact area between the air and water.


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SLAT AND COKE AERATORS


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A draft aerator is similar to the others exceptthat the air is induced by a blower. There aretwo basic type of draft aerators. One hasexternal blowers mounted at the bottom of thetower to induce air from the bottom of thetower. Water is pumped to the top and allowedto cascade down through the rising air. Theother, an induced-draft aerator, has a top-

mounted blower forcing air from bottom ventsup through the unit to the top. Both types areeffective in oxidizing iron and manganesebefore filtration.


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DRAFT AERATORS


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These are not common types used in watertreatment. The air is injected into the waterthrough a series of nozzles submerged in the

water. It is more commonly used in wastewatertreatment for the aeration of activated sludge


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There are two basic types of pressure aerators.One uses a pressure vessel. The water to betreated is sprayed into the high-pressure air,

allowing the water to quickly pick up dissolvedoxygen.


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A pressure aerator commonly used inpressure filtration is a porous stone installed in a

pipeline before filtration. The air is injected intothe stone and allowed to stream into the water asa fine bubble, causing the iron to be readily

oxidized. The higher the pressure, the morereadily the transfer of the oxygen to the water.The more oxygen that is available, the morereadily the oxidation of the iron or manganese


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PRESSURE AERATORS


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If operated properly, a process called air

stripping can be quite effective inremoving volatile organic chemicals(VOCs) from water. The presence of VOCs,many of which are man-made or formed

during industrial processes, is increasinglybecoming a problem for public watersuppliers. US EPA has set MaximumContaminant Levels for many VOCs (see

the Public Water Supply Regulationchapter). A major concern is that VOCsmay be carcinogens. Example of VOCs arebenzene from gasoline andtrichloroethylene from dry cleaningestablishments.


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Air stripping has been shown to becapable of removing up to 90 percent of the

most highly volatile VOCs. It can beaccomplished by letting the water flow overcascade aerators or in specially designed air-

stripping towers. In these, water is allowed toflow down over a support medium orpacking contained in the tower, while air isbeing pumped into the bottom of the tower


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Types of Aerators

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