Sewage treatment effect of MPSRs under different influent NH4+-N concentrations and its mechanism of nitrogen removal

To meet total nitrogen (TN) standards in the effluent owing to increased influent NH4+-N concentrations during the dry season, three sets of micro-pressure swirl reactors (MPSRs) were used for wastewater treatment experiments with different NH4+-N concentrations (31.57, 50.89, and 72.44 mg/L). At the stable operating stage, the average effluent chemical oxygen demand and PO4 3--P concentrations were 35.41 and 0.27 mg/L, respectively; the TN removal efficiency was 75.67 %, and the simultaneous nitrification and denitrification efficiency reached 52.11 %. The influent NH4+-N concentration was positively correlated with the duration of the hypoxic zone. As the NH4+-N concentration increased, the storage efficiency of the carbon sources increased from 77.08 % to 83.25 %. Microbial community analysis demonstrated that as the dissolved oxygen environment changed, the dominant bacterial community transitioned from glycogen-accumulating organisms to endogenous denitrifying bacteria. Denitratisoma, with its endogenous denitrification ability, increased by five times after nitrite stress. Functional genes indicated that carbon storage shifted from exogenous polyhydroxyalkanoate (PHB) synthesis to endogenous denitrification-mediated PHB synthesis with increasing NH4+-N concentrations. These results demonstrate the denitrification mechanism of the MPSR under high NH4+-N concentrations and provide a new solution for the denitrification of high NH4+-N urban wastewater.