In Conventional Activated Sludge Process wastewater is sent to an aeration tank where bacteria (activated sludge) feeds upon the organic matter in the water and breaks it down into smaller substances. The water from the aeration tank then moves to the secondary clarifier where the sludge settles down. A part of the sludge from the clarifier is then sent back to the aeration tank to maintain the mixed liquor suspended solids (MLSS or bacterial) concentration in the tank.