Wastewater treatment is a process used to convert wastewater – which is water that is no longer needed or suitable for its most recent use – into an effluent that can be either returned to the water cycle with minimal environmental issues or reused. The latter is called water reclamation: instead of disposing of treated wastewater it is reused for various purposes. During the treatment process, pollutants are removed or broken down. The infrastructure used for wastewater treatment is called a wastewater treatment plant (WWTP), or a sewage treatment plant in the case of municipal wastewater households and small industries.
The treatment of wastewater belongs to the overarching field of sanitation, which also includes the management of human waste, solid waste and stormwater (drainage) management.By-products from wastewater treatment plants, such as screenings, grit and sewage sludge may also be treated in a wastewater treatment plant.