Enhancement of nutrient removal in a novel simultaneous nitrification, denitrification and phosphorus removal system via phosphorus recovery regulation under carbon limited condition

A key challenge in traditional biological nutrient removal is the competition for limited organic carbon, which compromises the efficiency of both denitrification and phosphorus removal when carbon is scarce. To overcome this limitation, this study focused on low C/N ratio wastewater, and sequencing batch biofilm phosphorus recovery reactors (SBBPRs) were developed and constructed. This approach integrates simultaneous nitrification, denitrification and phosphorus removal (SNDPR) with phosphorus recovery (PR), reducing carbon source competition while achieving phosphorus resource recycling. Compared with the control groups (without PR), the nitrogen and phosphorus removal efficiencies of SBBPRs were remarkably enhanced. At C/N ratios of 5.0 and 3.0, the nitrogen removal efficiencies reached 87.7% and 69.7%, respectively, and the phosphorus recovery efficiencies were 53.7% and 57.0%, respectively. Based on the analysis of carbon source distribution within the SBBPRs, it can be observed that the phosphorus recovery process enhanced the storage of carbon sources in glycogen accumulating organisms (GAOs), thereby strengthening the endogenous denitrification process and ensuring the denitrification efficiency of the system. Electron transfer capacity and enzyme activity were also enhanced. The analysis of microbial community structure revealed that Candidatus_Competibacter, a denitrifying glycogen-accumulating organism (DGAO) was enriched in 31.0% and 21.5% at C/N ratios of 5 and 3, respectively, which provided a guarantee for endogenous denitrification. Meanwhile, the prediction of microbial Bugbase function reflected the system's excellent metabolic ability. This study provided new insights into low-carbon, high-efficiency nitrogen and phosphorus removal from wastewater.