Here the growth settles to the bottom of the tank. It is raked to the center of the tank by rotating arms and flows to the return activated sludge pump station. The clarifier effluent flows by gravity to the infiltration basins where it seeps into the ground. The sludge from the return activated sludge pump station is pumped back into the aeration basin on the anoxic zone side. The return sludge seeds the incoming waste water and increases the BOD removal capacity.
Excess sludge is removed from the clarifier of aeration basin by the waste activated sludge pump.
The excess sludge is disposed by spraying on adjacent forest land with a permanent spray irrigation system.