Study on the denitrification performance and mechanism of high-Salinity wastewater treated by anaerobic ammonia oxidation driven by exogenous L-Proline

To address the inhibition of nitrogen removal performance in anaerobic ammonium oxidation systems under high salinity conditions, this study investigated the regulatory effects and mechanisms of exogenous L-proline through a 42-day salinity gradient shock experiment. Results indicate that at a total nitrogen load of 255 mg/L in influent, a salinity of 5 g/L enhances the system's nitrogen removal efficiency. However, prolonged exposure to high salinity (10 g/L) causes a gradual decline in denitrification performance. When salinity exceeded 15 g/L, system functionality deteriorated significantly, with average total nitrogen removal efficiency dropping to 43.14% and the stoichiometric ratio deviating from theoretical values (Rs value as low as 0.22). In contrast, adding 0.7 mM L-proline under 15 g/L salinity stress stabilized total nitrogen removal efficiency at approximately 92.96%, with stoichiometry aligning with normal anaerobic ammonium oxidation patterns. High-throughput monitoring revealed that exogenous L-proline maintained community diversity, increasing the abundance of the core bacterium Candidatus Brocadia from 1.18% to 5.99% and significantly boosting denitrifying bacteria like Thauera (from 0.1% to 24.20%). Analysis concluded that L-proline alleviates salinity inhibition in anaerobic ammonium oxidation treatment of saline wastewater.