Design of Activated Sludge Process
1. The aeration tank volume in an activated sludge plant was calculated to be 5184 m3, to be provided in four parallel units. The depth of the tanks will be 3 m. Aerators are available with power of 1, 2, 5, 10, 25, 50 KW and their areas of influence are 25 m2 for 1, 2, and 5 KW, and 36 m2 for 10, 25 and 50 KW aerators respectively. The expected maximum oxygen requirement for the process was calculated to be 13700 Kg/d. Manufacturers specify that the oxygen transfer capacity of these aerators is 2.0 Kg O2/kW-h under standard conditions. Based on this information, design an adequate aerator arrangement for each aeration tank. The operating temperature of the aeration tank is expected to be 30oC. The steady state dissolved oxygen concentration in the aeration tank should be 1 mg/L. Saturation concentration of oxygen in water at 20oC is 9.1 mg/L and at 30oC is 7.5 mg/L.
2. 1 MLD of 400mg/L Glucose solution (C6H12O6) is to be treated by a completely-mixed activated sludge process (ASP). Hydraulic detention time in the aeration tank is 4 hours. The effluent from the process should have 20mg/L glucose. Biological solids retention time (BSRT) of the ASP is 6 days. Based on this information, calculate the oxygen requirement in the aeration tank in Kg/d. Assume all necessary nutrients that are required for bio-mass growth are present in excess. Also assume that BODu = 1.5 x BOD5. YT and Kd values for microbial degradation of glucose are 0.5 mg/mg and 0.05 /d respectively (calculated based on BOD5 values).
3. The volume of an aeration tank in an activated sludge plant is 4700 m3. The oxygen requirement for the process was calculated to be 5400 Kg/d. It was decided that 50 kW surface aerators should be used for aeration purposes. Manufacturers of such aerators specify that the oxygen transfer capacity of these aerators is 2.0 Kg O2/kW-h under standard conditions. Based on this information, calculate the total power requirement for satisfying oxygen requirements in the aeration tank, and hence calculate the number of aerators required. The operating temperature of the aeration tank is expected to be 30oC. The steady state dissolved oxygen concentration in the aeration tank should be 1 mg/L. Saturation concentration of oxygen in water at 20oC is 9.1 mg/L and at 30oC is 7.5 mg/L.
4. Activated sludge plant is to be designed to treat 5 mld of city sewage having BOD5 of 300 mg/l to achieve effluent BOD5 of 20 mg/l. Consider MLVSS as 3500mg/l and mean cell residence time as 10 days. Determine sludge wasting rate, aeration tank volume and oxygen requirement. Assume all necessary data.
5. Calculate oxygen requirement of a complete - mix activated sludge process treating domestic wastewater having flowrate of 20 mld. BOD5 concentration of settled wastewater is 250 mg/L. The effluent soluble BOD5 is 6.2 mg/L. Excess sludge produced is 1500 kg/day. Assume that the temperature is 20 °C and the conversion factor, BOD5 / BODL is 0.68
