Differential impacts of rain event and continuous rainfall on biological phosphorus removal of a full-scale wastewater treatment plant: performance analysis and optimization strategies

This study classified wet weather into rain event and continuous rainfall, focusing on the impact of continuous rainfall on enhanced biological phosphorus removal (EBPR) efficiency in a full-scale wastewater treatment plant. During rain event and continuous rainfall, influent COD concentrations was reduced by 7.9 % and 11.4 %, but effluent COD, ammonium nitrogen and total nitrogen remained below discharge limits. Compared to rain event, continuous rainfall significantly deteriorated EBPR performance and disturbed phosphorus metabolism. Continuous rainfall resulted in a negative difference between phosphorus uptake and release, depletion of poly-β-hydroxyalkanoates pools under aerobic conditions, and decreased relative abundance of phosphorus-accumulating organisms, norank_f__PHOS-HE36 and norank_f__Caldilineaceae. Simulation results indicated that new strategy of shortening aerobic hydraulic retention time and decreasing sludge recirculation ratios improved EBPR efficiency by 76.0 % and reduced treatment cost by 28.1 % during continuous rainfall. Overall, this study highlights that continuous rainfall has more severe impairment to EBPR than rain event, and provides effective strategy to alleviate it.