Abstract:The study investigates the optimization of nitrogen removal efficiency in an enhanced anaerobic membrane bioreactor coupled with a partial nitrification/anammox (eAnMBR-PN/A) integrated process. Simulation results demonstrate that the surface oxygen loading rate significantly influences system performance. When maintained between 0.12 and 0.14 g/(m3·d), the system achieves a peak total nitrogen (TN) removal efficiency of 64.45%, which corresponds to the highest relative abundance of anaerobic ammonium-oxidizing bacteria (AnAOB) in the biofilm. However, at rates exceeding 0.16 g/(m3·d), elevated dissolved oxygen concentrations inhibit AnAOB activity while promoting the growth of nitrite-oxidizing bacteria (NOB), resulting in nitrate accumulation and reduced TN removal efficiency. The carbon-to-nitrogen (C/N) ratio also plays a crucial role in regulating system performance. At low influent -N concentrations (<35 g/m3), increasing the C/N ratio enhances TN removal by stimulating the denitrification activity of heterotrophic bacteria (HB). In contrast, at high -N concentrations (≥35 g/m3), maintaining a low C/N ratio (<2.0) is essential to prevent HB from competitively competitively inhibiting AnAOB functionality. The findings indicate that the eAnMBR-PN/A process can effectively remove nitrogen from municipal wastewater with low C/N ratios by optimizing oxygen transfer and substrate distribution. This provides valuable theoretical insights and a technical pathway for the low-carbon transformation of wastewater treatment plants. The study highlights the importance of balancing the surface oxygen loading rate to avoid suppression of ammonia-oxidizing bacteria (AOB) activity at low oxygen levels and inhibition of AnAOB at high oxygen levels. Additionally, when the influent -N concentration is low,increasing the influent chemical oxygen demand (COD) can enhance TN removal, albeit at the cost of higher operational expenses. Conversely, under high -N concentrations, maintaining a lower influent COD facilitates AnAOB activity, thereby reduce costs. Microbial community analysis reveals that at oxygen loading rate of 0.12 g/(m3·d), a stable symbiotic biofilm community of AnAOB, AOB, and HB is established. As the oxygen loading rate increases to 0.16 g/(m3·d) and above, AnAOB abundance initially increases and subsequently decreases due to high dissolved oxygen inhibition. In conclusion, the eAnMBR-PN/A integrated process offers an effective solution for nitrogen removal from municipal wastewater with low C/N ratios. By optimizing the oxygen loading rate and C/N ratio, the system can achieve high nitrogen removal efficiency while reducing operational costs. This study advances the understanding of nitrogen removal mechanisms and underscores the potential of the eAnMBR-PN/A process in promoting the enrichment of functional microbial communities for efficient treatment. Close-