Water & Wastewater

RAS and WAS

Return and Waste Activated Sludge

Definition

Return activated sludge is recycled from the clarifier back to the aeration basin to maintain the biological population; waste activated sludge is removed to control it.

RAS and WAS rates are the primary levers an operator has over the biological process, which makes their flow measurement and control genuinely consequential.

RAS and WAS ControlReturn and waste activated sludge: what each flow does for the process, RAS control by influent flow ratio or by blanket level, WAS control to a target sludge age or a target mixed liquor concentration, the flow and solids measurements each needs, and the pump and valve arrangements that make the setpoints achievable.

RAS and WAS

Definition

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