Saturday, January 01, 2005

Aeration and aerators

What is aeration?

Aeration is the process by which the area of contact between water and air is increased, either by natural or mechanical means, resulting in air being suspended in water.

Purpose of aeration

One of the pollutants of water are organic matters. The reason why organic matters are considered water pollutants is that microorganism feed on them, and in the process used up the dissolved oxygen needed for aquatic life. If the organic matters are in sufficient quantity, this can lead to nearly all the dissolved oxygen being used up, aquatic life killed, and to anaerobic conditions in which anaerobic microorganism produces hydrogen sulfite and other odorous constitutents are produced.

The purpose of aeration of water is the improvement of their physical and chemical characteristics, the removal or reduction of objectioanl taste and odor and precipitation of inorganic contaminants such as iron and manganese. In water treatment, the purpose of aeration to to ensure continued aerobic conditions for the microorganism to degrade the organic matters.

Types of aerators

Waterfall aerators which uses spray nozzles, cascades or multiple trays

Mechanical aerators which employ motor driven impellers or combination air-injection devices

Surface spray or vertical pump aerator which have a submersible motor which rotates an impeller to pump surface water into the air as a spray. A vertical pump aerator consists of a motor with an impeller (propeller) attached to its shaft. The motor is suspended below a float with a center opening and the impeller jets water into the air at low velocity.

A pump-sprayer aerator employs a centrifugal pump to spray water at high velocity through holes in a manifold and into the air.

Paddle wheel aerator uses paddles mounted on a rotating shaft. A paddle wheel aerator splashes water into the air as the paddle wheel rotates

Propeller aspirator pump. The propeller-aspirator-pump aerator has a high velocity, uncased impeller at the end of a hollow shaft and housing. In operation, air flows down the shaft by the venturi principle and is released into the water in fine bubbles

Diffusion or bubble aerators which bubble compressed air through water. They may be divided into fine pore and coarse bubble aerator. Fine bubble aerators have high OTR (Oxygen Transfer Rate) and high efficiency (oxygen transfered per unit energy per unit time).

Membrane diffuser, a fairly recent technology, operate with low maintenance.

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