Aquatic Pollution and Coastal Zone Managememnt (2+1)

Unit 2 : Sewage and domestic wastes, treatment and reuse

b) Activated Sludge Process
In this process, the waste is subjected to mechanical aeration in specially designed tanks, which may be rectangular to oval or circular in shape. Aeration makes the particles of suspended matter to flocculate into small gelatinous masses swarming with aerobic microorganisms capable of oxidizing the organic matter readily. This gelatinous mass is called “activated sludge” which is heavily laden with bacteria followed by protozoans.

The flocculate, which develops during aeration is permitted to settle in a secondary sedimentation tank. The added flocculant particles will absorb more suspended and colloidal matter from the waste, increase in size and break into smaller units that repeat the same process until all the organic matter is incorporated in the floccules.

The activated sludge treatment is a batch process which usually employs aeration for a period of 4-10hours before the treated waste can be subjected to secondary settling.