Performance enhancement of simultaneous nitrification-endogenous denitrification and phosphorus removal process:...

Achieving stable partial nitrification remains challenging, making it necessary to improve the flexibility of simultaneous nitrification-endogenous denitrification and phosphorus removal (SNEDPR) sludge for NO_x^- reduction. The contributions of denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs), the main denitrifying bacteria in SNEDPR, to NO₃^- and NO₂^- reduction remain unclear due to their metabolic similarities. By adjusting influent NH₄⁺-N levels or the anaerobic phase duration, DGAOs or DPAOs were selectively favored, allowing their roles to be distinguished. The balanced collaboration between DGAOs, which mainly reduced NO₃^-, and DPAOs, which mainly reduced NO₂^-, resulted in largely balanced NO₃^- and NO₂^- reduction rates, leading to more stable and efficient nitrogen removal. Glycogen-accumulating organisms promoted unexpected sludge granulation, which contributed to the formation of anoxic zones within the sludge and thereby enhanced simultaneous nitrification-denitrification. Additionally, continuous aeration was found to be more effective than intermittent aeration in maintaining the maximum phosphate uptake rate. The removal efficiencies of nitrogen and phosphate ultimately reached 92.49 ± 0.66 % and 96.58 ± 2.34 %, respectively, under continuous aeration conditions.