The enhancement of autotrophic denitrification by manganese carbonate on sulfur-pyrite composite filler and its biochemical mechanism

A novel manganese carbonate-pyrite (MnCO 3 -S-FeS 2 ) composite filler was developed to enhance the autotrophic denitrification efficiency of the sulfur-pyrite system(S-FeS 2 ) composite filler in the treatment of low-carbon‑nitrogen (C/N) wastewater. The average removal efficiency of nitrate was 83.85 % and 79.81 %, respectively, in the MnCO 3 -S-FeS 2 system with a hydraulic retention time (HRT) of 24 h and 12 h. They were significantly higher than S-FeS 2 system (75.50, 65.48 %) and the unfilled system (53.29 %, 45.83 %). Research on the physiological response of microbial cells showed that, the MnCO 3 -S-FeS 2 system, co -metabolic substrates led to a substantial rise in microbial extracellular polymeric substances (EPS) secretion, particularly extracellular proteins. When the system reached the end of its operation, The contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were 98.74 mg/g-SS and 122.31 mg/g-SS, respectively. High-throughput sequencing confirmed that Thiobacillus , Chlorobium , and Desulfobacterota were significantly enriched in the MnCO 3 -S-FeS 2 system, facilitating manganese, sulfur, and nitrogen cycling. The research shows that the introduction of manganese carbonate significantly improved denitrification performance by serving as an electron donor, pH buffer, and metabolic enhancer, providing a new strategy for low C/N ratio domestic sewage treatment . • The MnCO 3 -S-FeS 2 filler system is an efficient autotrophic denitrification system. • MnCO 3 serves as an alkalinity buffer, providing an inorganic carbon source. • The synergistic effect of S, Fe and Mn elements enhances the denitrification effect. • Elucidated the metabolic characteristics of nitrates. • The synergistic denitrification mechanism between various elements was expounded.