The method depends on establishing and maintaining a population of degrading micro-organisms and providing close contact with the degrading microorganisms and supply of dissolved oxygen. The microorganisms feed & grow upon the oxidizable material in the wastewater and form a suspended floc of “activated sludge” in the water. Air bubbled through the water by means of diffused or mechanical aeration that replenishes the oxygen needed for the biological oxidation. After a period of time the mixture of wastewater and activated sludge, known as “mixed liquor”, flows to a clarifier where it is allowed to settle. Part of the settled activated sludge is usually mechanically returned (by pump) to the aeration tank or vessel to start the process again.

ASP advantages

• Clear sparkling effluent of high quality is obtained.
• There is freedom from fly and odour nuisance due to high degree of treatment given to the sewage in this process.
• The process is highly efficient. Removal of SS, BOD, and bacteria are around 90% each.
• Low cost of installation as compared to that of trickling filters.
• There is a comparatively very small loss of head through the treatment plant
• The excess sludge has higher fertilizing values as compared to sludge obtained from other treatment methods.
• The degree of stabilization or nitrification is controllable within limits, so as to match with the quantity and character of receiving sewage. The treatment may be partial or full as desired or required.