Electron Transfer Regulation and Nitrogen Removal Pathways in Constructed Wetland with Manganese Ore and Activated Carbon Coupling Microbial Fuel Cell
Manganese-rich constructed wetlands (CWs) have emerged as an effective strategy for enhanced nitrogen removal, yet current understanding of their denitrification mechanisms remains limited to speculative interpretations of microbial community structures. This study developed a novel CW-MFC system integrating manganese ore (MO) and activated carbon (AC) substrates with microbial fuel cell (MFC) technology to investigate the manganese-nitrogen coupling biochemical metabolism. It was systematically evaluated the effects of influent organic carbon concentrations on nitrogen removal performance and elucidated the mechanisms of electron transfer and their coupling with nitrogen removal pathways through multi-dimensional analyses, including functional enzymes, extracellular polymeric substances (EPS) characterization, intra-/extracellular electron transfer-related gene expression, and electron transport activity. Results showed that the synergistic integration of MO, AC, and MFC configuration significantly enhanced nitrogen removal efficiency, with ammonium removal reaching up to 5.5 times that of the control group. The functional substrates notably upregulated enzyme activities of nitrogen transformation in biofilms while stimulating nitrification and anammox processes at the anode. EPS analysis revealed that Mn2+ derived from manganese reduction was captured by EPS, thereby facilitating the manganese cycling. Concurrently, the increased abundance of electron transport chain (ETC) and extracellular electron transfer (EET) genes, coupled with increased cytochrome C (Cyt-C) concentration and activity, confirmed enhanced EET performance. It indicated that the coordinated EET network among electrodes, microorganisms, MO, and AC serves as critical electron mediators for nitrogen transformation. This study provides mechanistic insights into manganese-carbon coupled CW-MFC systems regarding nutrient removal, biogeochemical cycling, and electron transfer dynamics, advancing fundamental knowledge for the development and application of manganese-rich constructed wetland technology.