From the aeration basin, the mixture of treated wastewater and microorganisms, called "activated sludge," flows to two covered 55 ft. diameter clarifiers. The clarifiers provide the detention time and a quiescent atmosphere necessary for separation of the treated water and the cell mass. Clear water flows over the weirs located at the surface of the clarifiers. A rotating suction header located at the bottom of each clarifier collects the settled sludge. Return activated sludge (RAS) pumps, located in the basement of the Secondary Treatment Building, pump sludge from the bottom of each clarifier back to the aeration basin where it is used further for wastewater treatment.