Extracted text: A wastewater flow with the following characteristics is to be treated in a completely mixed activated-sludge system. This system is operated at the sludge age of 10d and treats wastewater flowing at 18,000 m3/d. Average influent BOD is 200 mg/L and 92% BOD removal has been achieved. Yield is 0.4 kg biomass/kg BOD and decay coefficient is kd = 0.06 d1. The reactor is designed to operate at a biomass concentration of 2,500 mg/L and the biomass concentration in return sludge is 15,000 mg/L. The mass of solids wasted each day? () tonne/d (*No unit)