KCET 2018 Biology Solved Paper

An activated sludge is generated by aeration of sewage which consists of organic material containing large number of microorganisms consisting of bacteria (coliforms Clostridium, Pseudomonas, etc.) and fungi that form a filamentous mesh-like filter and are called floc. This floc is then added to wastewater coming in after primary treatment. The mixture is aerated and agitated. The microorganisms feed on the organic matter in the wastewater and degrade it. After a sufficient period of time, the water is taken to a settling tank and allowed to settle. The supernatant is used for the next treatment as effluent.