What is the role of microbes in sewage treatment plant?

Explanation

(iv) Role of microbes in sewage treatment:
1) Waste water generated in large quantities is called sewage.
2) Sewage contains organic matter, human excreta, domestic waste and microbes.
3) It can not be drained directly in water bodies like rivers without prior treatment in sewage treatment plant.
4) Primary treatment is a physical process using filteration and sedimentation.
5) Secondary treatment is also known as biological treatment . Effluent and Priamry treatment is passed in aeration tanks along with air. Aerobic organisms grow in this process and decomposes organic matter. It reduces biological oxygen demand of effluent.
(6) Tertiary treatment occurs after Secondary treatment. In this process anaerobic microbes grow and digest bacteria and fungi. After tertiary treatment effluent is released in water bodies.