Effects of arsenic stress on a simultaneous nitrification and denitrification system: Nitrogen removal and microbial community dynamics

Simultaneous nitrification and denitrification (SND) is a promising technology for nitrogen removal. However, its response to heavy metal stress in actual wastewater systems is still not well understood. This study systematically investigated the long-term performance and adaptation mechanisms of a membrane bioreactor (MBR) treating high-ammonia wastewater under arsenic stress (As(III), 0.00–20.00 mg·L −1 ). The system demonstrated strong operational stability and shock resistance, achieving average removal efficiencies of 95.83% for chemical oxygen demand (COD) and 97.33% for ammonia nitrogen (NH 4 + -N). To counteract arsenic toxicity, the system enhanced arsenic adsorption and barrier functions by increasing extracellular polymeric substance (EPS) polysaccharide secretion and reducing the protein-to-polysaccharide ratio. Phaeodactylibacter , SM1A02 , mle1–27 , and Nitrospira , which are arsenic-tolerant functional genera, were significantly enriched, enabling the dynamic regulation of nitrogen removal and arsenic efflux gene expression in response to arsenic concentrations. This study reveals a coordinated adaptive mechanism in MBR systems under arsenic stress, offer important theoretical insights for bioremediating heavy metal laden refractory wastewater.