Question

Have you ever wondered where this huge quantity of sewage or urban waste water is disposed of daily?

Answer 1

Part 1: Disposal of sewage
Wastewater or sewage is disposed of in certain water bodies after it passes through sewage treatment plants (STP). Sewage needs to be treated to prevent the contamination and pollution of water bodies.

Part 2: Sewage treatment
Sewage treatment involves primary and secondary treatment:

• Primary treatment

1. Physical removal of debri and solid particles present.
2.Done by using large sedimentation tanks.

• Secondary treatment

1. Biological treatment where the primary effluent is aerated allowing the growth of flocs.
2. BOD is reduced as the organic matter is oxidised by the flocs.
3. The effluent is passed to the settling tank where the flocs settle (activated sludge).
4. The activated sludge formed is fed into anaerobic sludge digesters and can be used for biogas production.
5. The treated effluent is then discharged into rivers.