A complete mix activated sludge plant operates at design Q with the reactor tank volume set by a nominal residence time of 6 hours.
a) It was predictable that it would operate at 25% RAS for an expected Xr= 2,000 mg/l. Explain what would the actual residence time be?
b) Explain the secondary clarifier only produces Xr= 1,000 mg/l, as a result RAS is increased to 50% Q. Explain what is the actual residence time then? Does the F/M the MLVSS concentration as well as SRT change?
c) The secondary clarifier essentially produces 3,000 mg/l Xr, however RAS stays at 25% as originally planned. Do F/M, MLVSS as well as SRT change from what was planned?