Effluent from the primary treatment of the sewage is passed through large aeration tanks for biological treatment. Explain the complete process that follows till the water is ready to be released into the natural water bodies.

• During treatment (after adding small amount of inoculum) primary effluent is constantly agitated mechanically and air is pumped into it.

• This allows the vigorous growth of useful microbes into flocs.

• The microbes consume the major part of the organic matter in the effluent

• It reduces the BOD of the effluent.

• The effluent is then passed into settling tank where the bacterial flocs are allowed to sediment.

• Major part of the activated sludge is pumped into aerobic sludge digester (and remaining water is released into natural water bodies.)