Iron-based anodes facilitate concurrent mercury removal and bioenergy generation in constructed wetland-microbial...

Constructed wetland-microbial fuel cell (CW-MFC) is a promising technology for wastewater treatment with concurrent resource and energy recovery. However, its power generation capacity and mercury (Hg) removal efficiency are significantly limited by the insufficient electron transfer of anode materials. In this study, CW-MFCs were developed using zero-valent iron and siderite as anode materials. The incorporation of iron-based substrates significantly enhanced Hg removal, with total Hg removal efficiencies increasing by 22.9 % and 18.4 %, respectively, compared to conventional CW-MFCs. The integration of iron-based materials increased the availability of organic/inorganic electron donors by 9.1-350.0 %, thereby enhancing power generation performance by 17.9-34.9 %. This enhancement promoted the reduction of Hg(II) and inhibited the formation of methylmercury. Additionally, the electricity generated by the MFC facilitated Fe(III)/ Fe(II) redox cycling, which supported continuous corrosion and electron release from the iron anode. Metagenomic and electrochemical analyses demonstrated that the use of iron-based materials in CW-MFCs improved both extracellular and intracellular electron transfer efficiencies, and strengthened the synergistic interaction between the iron-based anode and electroactive bacteria. The genes that related to Hg(II) reduction, including merA, were also improved. Generally, this study highlights the potential of iron-based anodes to enhance Hg removal and power generation in CW-MFCs, providing a sustainable and energy-recovering strategy for wastewater treatment.