A 500-bed hospital has a small activated sludge wastewater treatment device. The average wastewater flow is 1200 L/day per bed. The average soluble BOD5 after primary settling is 500mg/L. The aeration tank has a liquid dimension of 10 m wide * 10m long 4.5m deep. The parameters are as follows: MLVSS-2000 mg /L MLSS = 2400 mg /L .Return sludge concentration 12000 mg VSS /L Wastage sludge concentration is same with return sludge Suspended solids in effluent 30 mg /L Bacterial decay rate 0.06/d Yield coefficient 0.42 inert fraction of suspended solids :-67% · .Allowable BOD in effluent 30 mg/L Determine

a) Aeration period in hrs
b) Solid retention time required (in days)
c) Sludge wastage flow rate