Fenton sludge-derived biochar for enhancing constructed wetland-microbial fuel cell system performance: Mechanisms and comprehensive evaluation.

Iron-rich Fenton sludge generated from wastewater treatment was pyrolyzed to prepare biochar, which was then applied as an electrode substrate in a constructed wetland-microbial fuel cell (CW-MFC) to simultaneously enhance wastewater treatment efficiency and recover bioenergy. By comparing the performance of three groups (pure gravel system: CW-MFC I; 400°C biochar-amended system: CW-MFC II; 600°C biochar-amended system: CW-MFC III) under varying influent concentrations, the enhancement mechanism of sludge-derived biochar was systematically investigated. Results show CW-MFC III with 600°C biochar achieved optimal performance, and the average removal efficiencies of COD, TP, NH4+-N and TN reached 91.3%, 91.4%, 81.3% and 79.5% respectively, all significantly higher than the control. It also obtained the highest output voltage (545.3 mV) and maximum power density (39.2 mW/m2). Material characterization proved 600°C pyrolysis endows biochar with developed pore structure, high graphitization and stable crystalline Fe2O3, bringing excellent adsorption, electrical conductivity and phosphorus removal potential. Microbial analysis confirmed 600°C biochar anode enriched more electroactive genera (e.g. Geobacter) and nitrogen/phosphorus removal functional bacteria. This study clarifies the "adsorption-chemical precipitation-bioelectrochemistry" synergistic mechanism, and verifies the great feasibility and application potential of this strategy for simultaneous pollutant removal and power generation.