Explain the Activitated Sludge (Aeration Tank)?

The activated sludge treatment process is a biochemical oxidation process. Organic solids are stabilized through the oxidation process in the activated sludge basin. This basin is also referred as aeration tank and the process is known as suspended growth process. The incoming waste to the activated sludge basin is composed of inorganic and organic solids. The organic portion of the incoming waste is responsible for the BOD and it represents the Food (F) for the microorganisms in the activated sludge basin.

The solids in the activated sludge basin are called mixed liquor suspended solids (MLSS). These solids are composed of an organic (MLVSS) and an inorganic part (MLFSS). The MLVSS is often considered to represent the microorganisms in the activated sludge basin. The stabilized organic solids are removed in the secondary sedimentation basin. Most of stabilized solids are returned or recycled to the activated sludge basin. Part of the stabilized solids is wasted each day. The wastewater from the aeration tank then flows over the secondary sedimentation basin (where the solids have been removed) and to the disinfection basin and then discharged to the receiving stream.