Question

Describe the various stages in the treatment of sewage.

Answer 1

Treatment of sewage involves three stages:
(a) Primary treatment: This stage is a mechanical process that involves screening and settling of large particles from sewage using vertical bars and grit chambers. After screening, water is passed through sedimentation tanks.

(b) Secondary treatment: This stage is a biological process. It involves breaking down of organic matters obtained from primary treatment with the help of bacteria to produce biogas. Water is sent to aeration tanks and air is blown through them to speed up the treatment of water.

(c) Tertiary treatment: This stage is a chemical process. It is the last stage in the treatment of sewage. Chemicals are added to remove phosphorous and nitrogen from sewage. Bacteria and other germs are killed by the addition of chlorine.