Insight into the potentiality of nano zero-valent iron on enhancing the nitrite accumulation and phosphorus removal performance of endogenous partial denitrification systems

Endogenous partial denitrification (EPD) has drawn a lot of interest due to its abundant nitrite (NO₂^--N) accumulation capacity. However, the poor phosphate (PO₄^3--P) removal rate of EPD restricts its promotion and application. In this study, the potentiality of various nano zero-valent iron (nZVI) concentrations (0, 20, 40, and 80 mg/L) on NO₂^--N accumulation and PO₄^3--P removal in EPD systems had been investigated. Results showed that nZVI improved NO₂^--N accumulation and PO₄^3--P removal, with the greatest nitrate-to-nitrite transformation ratio (NTR) and PO₄^3--P removal rate of 97.74 % and 64.76 % respectively at the optimum nZVI level (80 mg/L). Microbial community analysis also proved that nZVI had a remarkable influence on the microbial community of EPD. Candidatus_Competibacter was contribute to NO₂^--N accumulation which was enriched from 24.74 % to 40.02 %. The enrichment of Thauera, Rhodobacteraceae, Pseudomonas were contributed to PO₄^3--P removal. The chemistry of nZVI not only compensated for the deficiency of biological PO₄^3--P removal, but also enhanced NO₂^--N enrichment. Therefore, nZVI had the huge potentiality to improve the operational performance of the EPD system.