Simultaneous denitrification and phosphorus removal by organic/inorganic media: performance evaluation and microbial community analysis

While previous research often focused on individual electron donors, the comparative performance, potential synergistic or antagonistic effects, and underlying mechanisms of hybrid organic/inorganic systems for simultaneous nitrogen and phosphorus removal remain unclear. This study investigated the efficacy of media, including zero-valent iron (ZVI), pyrite (Py), zero-valent sulfur (ZVS), and orange leaf (OL), over 90 days using laboratory-scale columns (14.4 cm × 120 cm). The hybrid OFS system (comprising OL, ZVI, and ZVS) achieved a peak TP removal efficiency of 97.31%, a performance attributed to ZVS promoting ZVI dissolution, while the coupled oxidation of ZVI and ZVS stabilized pH and optimized FePO4 precipitation. However, OL compromised TP removal by increasing the P load and inhibiting chemical precipitation. Effluent P levels were also increased by acidification-induced cell lysis. For NO3−−N removal, the OS system (comprising OL and ZVS) outperformed the S system (only ZVS), achieving a maximum NO3−−N removal efficiency of 77.56%, primarily due to a synergistic effect between OL and ZVS, supported by a higher abundance of sulfur-oxidizing and denitrification genes and a more balanced microbial community. In contrast, weak iron oxidation in ZVI and Py systems and limited sulfur dissolution from Py restricted NO3−−N removal.