[Effect of NO^--N Recycling Ratio on Denitrifying Phosphorus Removal Efficiency in the ABR-MBR Combined Process]

Based on the coupling of the ABR process and the MBR process, a novel combined ABR-MBR process, including biophase separation, liquid circulation, and functional linkage, was developed to achieve simultaneous carbon, nutrient, and phosphorus removal when treating domestic wastewater with low carbon/nitrogen ratio and to obtain the best combination of ABR, providing a quality carbon source, and MBR, achieving shortcut nitrification by optimizing hydraulic retention time (HRT). The influence of NO^--N recycling ratio on nitrogen and phosphorus removal was investigated at NO^--N recycling ratios of 100%, 200%, 300%, and 400%, respectively. The experimental results under different conditions showed that the efficiency of denitrifying phosphorus removal in the ABR was found to increase with increasing NO^--N recycling ratio from 100% to 300% but decreased when the NO^--N recycling ratio was 400%. Shortcut nitrification was achieved by controlling the low dissolved oxygen (DO) concentration ranges from 0.3 to 1.0 mg·L^-1 with the short HRT of 3 h in the MBR reactor. The nitrite accumulation ratio was above 60%, when the NO^--N recycling ratio was 300%. Meanwhile, shortcut denitrifying phosphorus removal (where NO₂^--N mainly acted as the electron acceptor for denitrifying phosphorus removal) was achieved and played the dominant role in phosphorus removal.