Wastewater treatment is the process of removing impurities from wastewater and converting it into effluent that may be recycled back into the water cycle. Once returned to the water cycle, the effluent has a low environmental impact or can be reused for a variety of uses (called water reclamation). The activated sludge technique is a type of wastewater treatment that uses aeration and a biological floc made up of bacteria and protozoa to treat sewage or industrial wastewaters.