What is the purpose of Return Activated Sludge (RAS) in wastewater treatment?

Return Activated Sludge (RAS) plays a critical role in the activated sludge process of wastewater treatment. The main purpose of RAS is to return a portion of the settled activated sludge from the secondary clarifier back to the aeration tank. This action helps maintain a sufficient concentration of microorganisms, which are essential for effectively breaking down organic matter in the influent wastewater.

By reseeding the aeration tank with RAS, the biological treatment process is optimized, as it ensures a healthy population of microorganisms that can efficiently consume the organic pollutants present in the wastewater. Additionally, this practice aids in managing the accumulation of sludge, as the microorganisms can become overly concentrated if not adequately removed. Thus, the return of activated sludge helps maintain an optimal sludge age and promotes effective treatment performance.