A sewage treatment plant is an industrial facility for the treatment of urban wastewater, largely from toilets and bathrooms, to produce a non-polluting effluent that can be used as part of another process or directly discharged into the environment (for example, rivers). They may also be known as "wastewater treatment works" or "wastewater treatment facilities", treated water as well as sludge are recycled. A WWTP is designed in accordance with the waste composition of the metropolitan area served.