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 that is safe enough for release into the environment. Effluent Treatment Plant or ETP is one type of wastewater treatment method which is particularly designed to purify industrial wastewater for its reuse and its aim is to release safe water to environment from the harmful effect caused by the effluent. Wastewater treatment. The major aim of wastewater treatment is to remove as much of the suspended solids as possible before the remaining water, called effluent, is discharged back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the water.