A pre-anoxic MLE activated sludge process has the following influent wastewater characteristics and is operated with an anoxic volume of 500 m3 and MLVSS of 2000 mg/L at 20 oC. Given that influent flow rate = 12,000 m3/d, influent soluble BOD (rbCOD) is 60 mg/L, and the nitrate production based on the influent flow rate (i.e., NOx) is 30 mg/L. a) For an return activated sludge (RAS) of 0.9, determine the IR that should be used to meet an effluent NO3-N concentration limit of 5 mg/L, assuming that the nitrate removal is limited only by the anoxic tank capacity.