Key Takeaways & Executive Findings
- •• • Ammonium removal efficiency in the MO-AC-MFC system reached up to 5.5 times that of the control, demonstrating a significant enhancement in nitrogen removal performance. • • The integration of MO and AC with MFC configuration upregulated nitrogen transformation enzyme activities in biofilms, stimulating nitrification and anammox processes at the anode. • • EPS analysis confirmed that Mn2+ from manganese reduction was captured by EPS, facilitating manganese cycling and contributing to sustained electron transfer. • • Increased abundance of ETC and EET genes, along with elevated Cyt-C concentration and activity, confirmed enhanced extracellular electron transfer, which is critical for nitrogen transformation.
Abstract
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.
1. Introduction
Constructed wetlands (CWs) are widely used for wastewater nitrogen removal, but conventional systems often suffer from limited electron transfer efficiency, leading to incomplete denitrification and low nitrogen removal rates. Manganese-rich substrates have been proposed to enhance nitrogen removal via redox cycling, yet the underlying mechanisms remain poorly understood, often relying on indirect microbial community analyses. The lack of direct evidence on electron transfer pathways and their coupling with nitrogen metabolism has hindered the optimization of such systems for practical applications.
This study addresses this bottleneck by integrating manganese ore (MO) and activated carbon (AC) with microbial fuel cell (MFC) technology in a CW-MFC system. The conductive AC network bridges the biofilm-electrode interface, while MO provides redox-active sites for manganese cycling. By systematically evaluating nitrogen removal performance under varying influent organic carbon concentrations and employing multi-dimensional analyses—including functional enzyme activities, EPS characterization, and gene expression profiling—the research elucidates the electron transfer regulation mechanisms and their coupling with nitrogen removal pathways. These findings provide a mechanistic foundation for designing more efficient manganese-rich CW systems for enhanced nitrogen removal.
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WANG Yifei, ZHAO Donghua, SONG Xinshan (2026). Electron Transfer Regulation and Nitrogen Removal Pathways in Constructed Wetland with Manganese Ore and Activated Carbon Coupling Microbial Fuel Cell. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025031202
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Frequently Asked Questions
What is the maximum ammonium removal enhancement observed in the MO-AC-MFC system compared to the control?
The ammonium removal rate reached up to 5.5 times that of the control group, indicating a substantial improvement in nitrogen removal performance.
How does the presence of manganese ore and activated carbon influence the microbial electron transfer processes?
The integration of MO and AC enhances extracellular electron transfer (EET) by increasing the abundance of ETC and EET genes, as well as Cyt-C concentration and activity. The conductive AC network bridges the biofilm-electrode interface, while Mn2+ captured by EPS facilitates manganese cycling, collectively improving electron transfer rates.
What specific nitrogen removal pathways are stimulated in the MO-AC-MFC system?
The system promotes nitrification, heterotrophic/autotrophic denitrification, and anaerobic ammonium oxidation (anammox) at the anode, as evidenced by upregulated functional enzyme activities and gene expression.
What is the role of extracellular polymeric substances (EPS) in the system?
EPS captures Mn2+ derived from manganese reduction, which facilitates manganese cycling and helps coordinate electron distribution, thereby optimizing the denitrification process.
What are the implications of this study for scaling up manganese-rich constructed wetland systems?
The study provides mechanistic insights into electron transfer regulation and nitrogen removal pathways, offering a basis for optimizing substrate composition and operational parameters to enhance nitrogen removal efficiency in full-scale systems.
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