The Activated Sludge Process has been employed for waste water treatment for over one hundred years. Many variations of the process have been employed to optimize it for the specific applications. Regardless of the specific configuration of the process, the Activated Sludge Process employs microorganisms to assimilate and digest organic carbon compounds in the wastewater. The microorganisms can range from simple single cell bacteria to more complex life forms such as protozoa.

Aeration Process: Aeration is the process by which air is circulated through, mixed with or dissolved in a liquid or substance. Aeration is the process by which the area of contact between water and air is increased, either by natural methods or by mechanical devices. Aeration is one of the most elemental techniques frequently employed in the improvement of the physical and chemical characteristics of water.
The role of aeration in the activated sludge process is to provide oxygen to the microorganisms as they assimilate the organic carbon compounds and digest a portion of them to carbon dioxide and water, Sulfate and Nitrate compounds. The remaining waste solids are changed to a form that can be settled and removed as sludge by sedimentation.

Diffused Aeration: Diffused Aeration is defined as the injection of air at bottom of the aeration tank for transfer of oxygen into the waste water.

Diffused Aeration can be generally classified into:

• Fine bubble Diffused Aeration
• Coarse bubble Diffused Aeration

 Though there is no specific industry / government standards for differentiation between the two, but one can generally say that a system which delivers a bubble size of < 2mm is a fine bubble aeration system and one which delivers a bubble size of > 2mm is a coarse bubble aeration system

Some advantages Fine bubble Diffused Aeration is listed below:

1. Delivers high Oxygen Transfer Efficiencies.
2. Delivers high Aeration Efficiencies (mass oxygen transferred per unit power per unit time).
3. Suitable for high Oxygen Demands.
4. Easily adaptable to existing setups or for plant upgrades.
5. Flexibility of application to various Tank Geometries (rectangular, circular, L-shape etc).
6. Result in lower Volatile Organic Compound Emissions than coarse bubble diffusers or mechanical aeration devices (surface aerators).