Question

List various stages of sewage treatment.

Answer 1

Sewage treatment generally involves three main stages:

1. Primary treatment.
2. Secondary treatment.
3. Tertiary treatment.

Primary treatment involves the temporary holding of the sewage in a quiescent basin so that the solid material should settle down and the remaining supernatant such as oil, grease and other aqueous pollutants will remain at the upper layer.

Secondary treatment involves the removal of dissolved suspended matter. It is done by treating it with the water-borne micro-organisms in a controlled and managed habitat.

Tertiary treatment is carried out in a sensitive or fragile ecosystem. In this stage, the treated water is disinfected physically or chemically prior to release into the river stream or sea.