4. (Grade II) At an activated sludge wastewater treatment plant receiving 3.25 MGD, the final effluent suspended solids concentration averages 21.2 mg/L. What would the calculated MCRT value be when the aeration basin carries 2,050 mg/L MLSS and wastes 0.0550 MGD.The waste activated sludge has a concentration of 7,980 mg/L. The aeration tank has a volume of 1.00 MG and the secondary clarifier has an operational volume of 0.250 MG.

Fig: 1