Sewage treatment is the process of removing contaminants from municipal wastewater, containing mainly household sewage plus some industrial wastewater. Physical, chemical, and biological processes are used to remove contaminants and produce treated wastewater (or treated effluent) that is safe enough for release into the environment. The sludge has to undergo further treatment before being suitable for disposal or application to land. Sewage treatment may also be referred to as wastewater treatment. Reuse is often for agricultural purposes, but more recently, sludge is being used as a fuel source.

Sewage treatment plant processes fall into two main categories: electrically operated and non-electric sewage treatment systems.