Disinfectants induce divergent metabolism mechanisms in different partial nitrification-anammox coupled denitrification systems: Energy transformation and microbial stress response

Optimizing nitrogen removal efficiency in partial nitrification anammox (PNA) system and elucidating its performance under disinfectants stress are crucial for advanced wastewater treatment. This study compared PNA/heterotrophic denitrification (PNA/HD) and PNA/sulfur autotrophic denitrification systems (PNA/SAD) to reveal their divergence mechanisms under disinfectants stress. Both systems achieved efficient nitrogen removal initially; however, under high disinfectant levels, with anammox activity declining in both systems, PNA/SAD maintained a total inorganic nitrogen removal efficiency of 93.97 %, significantly outperforming PNA/HD at 75.46 %. PNA/SAD enhanced extracellular polymeric substance (EPS) production, while PNA/HD exhibited lower EPS levels and insufficient antioxidant activity. The abundance of ammonia oxidation genes in PNA/SAD was 4.03–4.28 times higher than that in PNA/HD, with up-regulation of napA under aerobic condition confirming SAD’s advantage in disinfectant-containing environments. Down-regulation of genes encoding key dehydrogenases in the tricarboxylic acid cycle led to an insufficient energy supply in PNA/HD. In contrast, PNA/SAD maintained stable sulfur oxidation, providing a continuous electron supply. Quorum sensing in PNA/SAD synergistically regulated biofilm stability, resistance genes (RGs) and virulence factors expression, ensuring long-term stability. Conversely, PNA/HD lost environmental adaptability due to the down-regulation of RGs and virulence factors. This study highlighted the multifaceted stress resistance mechanisms of PNA/SAD, providing a theoretical basis for process optimization under disinfectants stress.