Explanation

Sewage treatment involves three stages: Primary treatment stage It removes most of the suspended wastes and includes fragmentation, sedimentation, floatation and filtration. Secondary treatment stage The sewage is accumulated in aerated tanks, where microorganism decompose the organic matter. Tertiary treatment stage To remove mineral loads, the sewage undergoes additional filtering and chemical treatment. Polluted water is purified by reverse osmosis technique which does not involve biological process.