Question

A conventional activated sludge plant treating a domestic flow of 150 ML/d is operated at a SRT of 10 d with a MLVSS of 3500 ppm. The activated sludge plant is required to reduce the influent BOD from 200 ppm to less than 10 ppm prior to discharge. The discharge from the aeration basin is clarified, such that the clarifier overflow contains no particulate material and the MLVSS of the recycle stream is 8000 ppm. You are required to determine

1. the hydraulic residence time, the aeration basin volume, and the effluent BOD concentration.

2. the flowrate of the sludge waste stream and the flowrate of the clarified effluent, if sludge is wasted from the recycle stream,

3. the recycle ratio of the sludge with respect to the clarified effluent, and

4. the percentage of water recovered as secondary effluent.

[data: μmax = 6 mg VSS/mg VSS.d; Ks = 75 mg/L as BOD; Y = 0.6 mg VSS/mg BOD]

Answer 1