Total emission load reduction of COD, NH4-N, TN, and TP is the key measure in controlling water pollution and eutrophication. Municipal wastewater treatment plants (MWWTPs) are major contributors in lowering energy consumption and reducing pollutant discharge. The flow-based operating costs have not been directly established to relate to costs of pollutant reduction based on an investigation of 11 MWWTPs in China. However, energy consumption to eliminate one kilogram of COD or NH4-N was observed to decrease when the total reduced pollutants is increased. Additional energy consumption required to remove nitrogen and phosphorus is allotted for mixers and internal return pumps. Major factors for operating costs include influent and effluent concentration, design capacity, and flow loading rate. Therefore, an operating cost model for the total emission load reduction of COD, NH4-N, TN, and TP was developed based on energy consumption and the above mentioned major factors. Using this model to calculate the operating costs for MWWTPs would facilitate more reduction of key pollutants than the flow-based method.

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