Metagenomic analysis of denitrifying phosphorus removal in SBR system: Comparison of nitrate and nitrite as electron acceptors

Denitrifying phosphorus removal (DPR) is a novel technology for removing phosphorus and nitrogen with low energy requirements. Still, the metagenomic analysis comparing the effect of different electron acceptors on DPR has not been studied clearly. In this study, Nitrate-DPR and Nitrite-DPR were established using different concentrations of nitrate and nitrite as electron acceptors. The results showed that the nitrogen and phosphorus removal efficiency of Nitrite-DPR could reach 99%, which was significantly higher than that of Nitrate-DPR. The sludge settling ability of Nitrite-DPR was also enhanced. The high-throughput sequencing analysis indicated that unclassified_g_Thauera, Chloroflexi_bacterium, Betaproteobacteria_bacterium, and Gammaproteobacteria_bacterium were the main functional bacteria in Nitrate-DPR, while in the Nitrite-DPR, Candidatus_Contendobacter_sp., unclassified_g_Thauera, Candidatus_Competibacteraceae_bacterium, Rhodocyclaceae_bacterium, and Xanthomonadaceae_bacterium were the main ones. Metagenome sequencing analysis further revealed the superior performance of Nitrite-DPR. A series of functional genes, for example, ActP, ACK, PTA and ACS (dominated the synthesis and decomposition of intracellular carbon source), Nir, Nor and Nos (dominated nitrogen metabolism), along with ppk, adk and ppx (dominated phosphorus cycle), were all significantly increased in nitrite-electron acceptor system. It is noted that T6SS functional genes, related to the resistance of microorganisms to environmental stress, were also increased in Nitrite-DPR significantly, which accounted for the significant increase in tightly bound extracellular polymeric substances (TB-EPS) protein in Nitrite-DPR to some extent. The DPR mechanism was deeply explored in this study, and a theoretical basis for the practical application was established.