Triiron Tetraoxide (Fe₃O₄) Triggers Aerobic Denitrification Performance in Low C/N Water: Novel Insights into the Electron Transport System and Bacterial Community Model

Denitrification performance is significantly influenced by electron donors, mainly organic electron donors. Inorganic electron donors (e.g., Fe3O4) have shown potential for enhancing the nitrate removal efficiency. However, the mechanism of Fe3O4 on denitrification under aerobic conditions remains poorly understood. This study investigated the synergistic mechanisms of electron transfer and microbial interactions facilitated by Fe3O4 in an aerobic denitrifying bacterial community isolated from a micropolluted reservoir. The results revealed that the aerobic denitrifying bacterial (ADB) reactor achieved over 50% efficiency in both denitrification and organic carbon removal. When Fe3O4 was added, the removal efficiencies for nitrate (NO3–-N) and organic carbon increased to 82.38 and 66.84%, respectively. The adenosine triphosphate (ATP) activity and electron transport system activity (ETSA) increased by 1.3- and 1.7-fold, respectively, with the upregulation of denitrification-related enzymes. High-throughput sequencing analysis demonstrated that the bacterial community structure in the water column, biofilm, and sediment was enriched with Proteobacteria and Actinobacteria phyla in the biofilm. Additionally, statistical modeling further highlighted the stabilizing effects of Fe3O4 on the reaction system and the microbial community’s adaptive responses to environmental factors. In summary, this study provides a novel approach for leveraging Fe3O4 and aerobic denitrifying bacterial communities to achieve efficient nitrogen removal in micropolluted waters.