Wastewater from a primary treatment tank is to undergo secondary treatment in an activated sludge unit. the following data and operational parameters are specified: hydraulic detention time= 6h mean cell residence time= 7days bod content at inlet of reactor = 150 mg/l food to microorganism ratio=0.3gm bod/gm vss-day two identical units are designed to operate in parallel and to process a combined wastewater flowrate of 0.7m3/s.

(a) how large must each reactor be (m3)?
(b) what is the rate at which cell mass must be discharged from the units in steady state operation (kg/day)?