After that, the wastewater that is settled is transferred to aeration tanks were blowing of the air is done into the water. The main objective of this step is to promote the growth of microorganisms by providing them with oxygen. These particular microorganisms play a very important role in the purification of wastewater as they consume the organic pollutants that are present in it.
After that, this mixture of microorganisms and wastewater is taken to a secondary sedimentation tank for further treatment. At the secondary sedimentation tank, the biomass settles down to the tank bottom. It is the place where it is concentrated as sludge.