A complete-mix activated sludge process (CMAS) is to be designed to treat 5.0 million gallons per day (MGD) of primary effluent having a BOD5 of 180 mg/L. The NPDES permit requires that the effluent BOD5 and TSS concentrations should be 20 mg/L or less on an annual average basis. The following biokinetic coefficients obtained at 20∘C will be used in designing the process: Y = 0.6 mg VSS/mg BOD5, k = 4 d−1, Ks = 70 mg/L BOD5, and kd = 0.05 d−1. Assume that the MLVSS concentration in the aeration basin is maintained at 2,500 mg/L and the VSS : TSS ratio is 0.75. The temperature of the wastewater during the winter months is expected to remain at 15∘C for extended periods. During the summer, the wastewater temperature may reach 30∘C for several weeks. Determine the following:

a. Effluent soluble BOD5 (SBOD5) concentration in mg/L necessary to meet the effluent total BOD5 (TBOD5) requirement of 20 mg/L.

b. Mean cell residence time (d) necessary to meet the NPDES permit during the winter months.

c. Volume of the aeration basin in cubic feet.

d. Mean cell residence time (d) necessary to meet the NPDES permit during the summer months.

e. Oxygen requirements (lb/d) assuming complete nitrification during the summer months and a TKN0 = 35 mg/L.

f. The quantity of excess biomass produced (lb/d), in terms of TSS, at the shortest MCRT that the facility will be operated.

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