[Operating Characteristics of a DPR-SNED System Treating Low C/N Municipal Wastewater and Nitrate-containing Sewage]

In order to realize the simultaneous treatment of low C/N municipal wastewater and high nitrate wastewater, a sequencing batch reactor (SBR), inoculated with activated sludge, was used to initiate the denitrifying phosphorus removal coupled with simultaneous nitrification and endogenous denitrification (DPR-SNED). The anaerobic/anoxic/hypoxic durations and dissolved oxygen (DO) concentration were appropriately controlled, and the nitrogen and phosphorus removal characteristics were examined. The experimental results demonstrated that, in the anaerobic/hypoxia operation mode, with an anaerobic duration of 3 h and DO concentration of 0.5-1.0 mg·L^-1, the simultaneous nitrification of phosphorus removal (SNEDPR) system successfully began in 60 d. The effluent PO₄^3--P concentration was below 0.5 mg·L^-1, the nutrient and COD removal efficiencies were stably maintained above 90% and 80%, respectively, and the SNED efficiency and COD_ins efficiency reached 70% and 95%, respectively. When the operation mode was anaerobic/anoxic/hypoxic and nitrate-containing sewage was added at the beginning of the anoxic stage, DPR-SNED was achieved with the effluent PO₄^3--P concentration<0.5 mg·L^-1, nutrient and COD removal efficiencies above 88% and 90%, respectively, and SNED efficiency and COD_ins efficiency maintained at 62% and 90%, respectively. After the successful initiation of DPR-SNED, enhanced intracellular carbons storage was achieved by phosphorus-and glycogen-accumulating organisms using the limited carbons in raw municipal wastewater to provide sufficient carbon sources for subsequent nutrient removal. In addition, the endogenous partial denitrification ensured the efficient nitrogen removal performance of the DPR-SNED system at low C/N conditions (average 4).