Treatment of wastewater is done in a sewage treatment plant to make it less polluting. Explain the following with reference to this treatment…

(a) Primary Sludge: All the solids that settle down, during the primary treatment of sewage water.

(b) Activated Sludge: Produced during the secondary treatment or biological treatment of sewage, primary effluent + aerobic microbes flocs (bacteria and fungus) - get converted to a sediment whose BOD has reduced significantly.

(c) Anaerobic sludge digesters: Large tanks where activated sludge is treated with anaerobic bacteria which digest the bacteria and fungi, and produce a mixture of \(\displaystyle \mathrm{CH}_{4}\), \(\displaystyle \mathrm{H}_{2} \mathrm{~S}\) and \(\displaystyle \mathrm{CO}_{2}\) / Biogas