Aquatic Pollution and Coastal Management

Unit 2 : Sewage and domestic wastes, treatment and reuse

2.5.Sewage Treatment Methods
Sewage treatment means removing organic and other oxygen demanding materials such as suspended solids, nutrients, fats, oil and grease and pathogens from the waste water so that the remaining waste water can be safely returned to the river or sea and become part of the natural cycle again.

Sewage pollution can be reduced and avoided by the application of various levels of treatment. In sewage treatment solids are separated from liquids by physical processes and then the liquid is purified by biological processes.
There are four possible stages in sewage treatment.

• Preliminary treatment
• Primary treatment
• Secondary treatment
• Tertiary treatment