Question

Is the sewage treated before being transported to the nearest river and mixed with it?

Answer 1

Part 1: Sewage treatment
The sewage is treated before disposal to rivers. The sewage treatment involves:

• Primary treatment where sand, grit, pebbles and bigger substances (mostly insoluble ones) are removed using large sedimentation tanks. This forms a supernatant called the effluent and the deposition is called primary sludge.
• In secondary treatment, organic matter is removed and the BOD is reduced. This is done by using aerobes that help in oxidation of organic matter.