1: Consider a biologic treatment activated sludge (AS) system that is modeled as a CSTR aeration basin, and settling clarifier with return activated (RAS) from the clarifier to the CSTR, and waste activated sludge (WAS) removed from the clarifier. The influent BOD is 1000 mg/L, the flow rate is 100,000 m3/day. The biorefinery permit requires a discharge concentration to be 10 mg/L BOD.

a) If 10% of the flow is wasted, what is the required aeration basin volume? Hint: start by calculating the solid retention time.

b) What is the sludge production rate (mass per time)?