A modified Ludzack-Ettinger (MLE) process is used to remove nitrogen from 20MLd wastewater containing 40mg/L of TKN-N, 24mg/L of NH4+N, and 250mg/L of substrate (biodegradable organics). Assume 100% of organic nitrogen in the wastewater is oxidized. The effluent of this MLE process contains 2mg/L of NH4+N, and 20mg/L substrate, as well as 7 mg/L of NO3N. The daily wasted activated sludge is 1,000kg VSS. The return activated sludge (RAS) flow is 12ML/d. The wastewater temperature is 15C. (1) Calculate the internal recycle ratio to meet the effluent requirements (2) Calculate the net oxygen needed (in kg/hr of O2 ) for this MLE process (3) If the wastewater influent to the anoxic zone has BOD of 250mg/L. The MLVSS in the anoxic zone is 2,200mg/L. The fraction of rbCOD to bCOD is 40% (Table 82p.708 shows definition). What volume of the anoxic zone (in m3 ) is needed to achieve the required effluent quality