Enhancement of magnetic biochar on nitrogen removal performance of Anammox granular sludge under acute polystyrene nanoplastics stress

BACKGROUND Nanoplastics pose a significant threat to the efficiency and stability of anaerobic ammonium oxidation (Anammox). This study investigated the nitrogen removal efficiency, extracellular polymeric substance (EPS) secretion, microbial community, and enhancement mechanisms of Anammox with magnetic biochar (MBC) under sudden exposure to high‐concentration polystyrene nanoplastics (PS‐NPs). RESULTS Results demonstrated that sudden exposure to PS‐NPs at 300 mg L −1 distinctly reduced the nitrogen removal efficiency of Anammox, while the addition of MBC could significantly alleviate the inhibition. Fourier transform infrared analysis manifested that MBC could adsorb the PS‐NPs by electrostatic attraction, surface complexation and π – π interactions. MBC could stimulate anaerobic ammonium‐oxidizing bacteria to secrete a large amount of EPS (including protein, humic acids, and cytochrome c). Microbial community analysis showed that the addition of MBC could maintain the stability of microbial community structure. KEGG pathway analysis indicated that addition of MBC significantly enhanced the nitrogen metabolism pathway and glycan biosynthesis and metabolism pathway of Anammox granular sludge (AnGS) under acute PS‐NPs stress, thereby improving its nitrogen removal efficiency and structural stability. CONCLUSION This study provided valuable insights into the response characteristics and enhancement mechanism of MBC for AnGS exposed to PS‐NPs, which may be helpful for the application of Anammox in actual wastewater treatment.