Long-Term Nitrogen Removal Performance and Microbial Analysis in a SNAD-Based MBBR at Room Temperature

In recent years, the simultaneous partial nitrification, anammox, and denitrification (SNAD) process has attracted considerable attention due to its advantages such as low energy consumption and low sludge production. This study investigated the long-term performance and microbial mechanisms of a single-stage moving bed biofilm reactor (MBBR) employing the SNAD process for treating real domestic sewage at room temperature. A pre-carbon adsorption unit (reactor A) reduced the influent C/N ratio from 5.68:1 to 3.13:1, enabling efficient nitrogen removal in reactor B. Results demonstrated that dissolved oxygen (DO) and C/N ratio critically influenced system performance. At DO ~0.3 mg/L, stable SNAD operation achieved 65% total nitrogen (TN) removal, with synergistic contributions from partial nitrification, anammox, and heterotrophic denitrification. Elevated C/N ratios (4.71:1) reduced TN removal by ~30%, linked to decreased abundances of anammox bacteria. Microbial analysis revealed Candidatus Brocadia as key anammox bacteria, Nitrospirae as dominant ammonia-oxidizing bacteria and Denitratisoma as main denitrifying bacteria to drive nitrogen conversion. This study confirms the feasibility of SNAD-MBBR for real domestic sewage under ambient conditions, highlighting optimal DO and C/N control for microbial synergy and process stability.