Description
The activated sludge flocks are separated from the treated water by directing a portion of the water in the aeration basin to a separate sedimentation basin, the so-called clarifier. The activated sludge enters the clarifier in the center and flows to the circumference. Due to the almost total absence of turbulence in the clarifier, the activated sludge flocks will start to settle causing a separation of activated sludge from the water.
The supernatant water layer will become increasingly thicker towards the circumference, where it will pass over an overflow weir and leave the system as treated effluent. The overflow weir has a V-nodge shaped profile to make it harder for the wind to create preferential flows in the clarifier (preferential flows cause turbulence resulting in a worse separation result).The settled activated sludge is moved by a bottom scraper to the sediment cone in the centre of the clarifier from where it is removed most of the time to be recycled back to the process.
Periodically the excess activated sludge that grew in the basin is discharged from the process by directing a part of the activated sludge for instance to sludge drying beds or to a sludge dewatering system, etc.