Using the Food-to-Microorganism Ratio to Inform Design. (+2.5 total) Wastewater with a flow rate of 9 MGD exits a primary settling basin with a BOD5 = 140 mg/L before being transferred to an activated sludge tank. If the activated sludge tank is optimized for an MLSS concentration of 2,150 mg/Land a food-to-microorganism ratio (F/M) of 0.2 day¹, what must be the volume and aeration period (i.e.,hydraulic retention time, e) of the tank?V=2.9 x 106 gal; e = 7.8 hours.