Sewage treatment or domestic wastewater treatment is the process of removing contaminants from wastewater and household sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is, to produce an environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse (usually as farm fertilizer).
We are using advanced technology it is now possible to re-use sewage effluent for drinking water, nevertheless Singapore is the only country to implement such technology on an invention scale in its production of new water.
Sewage treatment generally involves three stages, called primary, secondary and tertiary treatment.
Primary treatment
It consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface. The settled and floating materials are removed and the remaining liquid may be discharged or subjected to secondary treatment.