1. Determine the average biomass concentration in a conventional activated sludge reactor under the following conditions. Flow = 20 MLD Influent BOD = 200 mg/L Effluent BOD = 10 mg/L Cell yield coefficient Y = 0.5 Kg biomass/ Kg BOD utilized Endogenous decay coefficient=0.04 d' Tank volume = 6000 m Mean cell residence time = 10 d 2. A completely mixed activated-sludge plant is to treat 15 MLD of industrial waste water. The wastewater has a BOD of 1500 mg/L that must be reduced to 200 mg/L prior to discharge to a municipal sewer. Pilot-plant analysis indicates that a mean cell residence time of 7d maintaining MLSS concentration of 4000 mg/L produces the desired results. The value for Y is determined to be 0.6 kg/kg and the value of Kd is found to be 0.04d-. Determine (a) The volume of the reactor (b) The mass and volume of solids wasted each day (c) The sludge recirculation ratio 3. A municipal wastewater is to be treated and discharged into a stream that empties into a pristine mountain lake that is used for recreational purposes. Draw a schematic flow diagram to treatment plant to prepare the wastewater for discharge. 4. Treated municipal wastewater is to be injected into an aquifer to form hydrostatic barrier against saltwater intrusion. Withdrawal of the injected water for domestic use is not anticipated. Draw a schematic diagram of a treatment plant to prepare the wastewater for this purpose.