Define return activated sludge (RAS) and waste activated sludge (WAS) in an activated sludge system.

• A. RAS is settled solids pumped back to the aeration basin to maintain biomass; WAS is sludge removed from the system to control MLSS and maintain treatment efficiency.
• B. RAS is sludge wasted to digestion; WAS is returned to aeration.
• C. RAS and WAS are both solids removed to digestion.
• D. RAS is the effluent; WAS is the influent.

Answer: (B)