Enhanced denitrification and acetochlor degradation in biochar-microelectric field constructed wetlands treating agricultural runoff: Performance, carbon release and microbial response.

To address the challenge of nitrate (NO3--N) and herbicide acetochlor (ACT) co-contamination in intensive agricultural runoff, this study developed a biochar-coupled micro-electric field constructed wetland system (BC-MEF-CWs). The aim was to enhance the electrochemical activity of the biochar medium via a micro-electric field (MEF), thereby synergistically improving simultaneous removal of NO3--N and ACT, while characterizing substrate-extractable organic matter (SEOM) and microbial community responses. Results showed that, at influent concentrations of 30.6 mg L-1 NO3--N and 97.9 μg L-1 ACT, the BC-MEF-CWs achieved removal efficiencies of 85.1% for NO3--N and 83.7% for ACT at a current density of 0.06 mA cm-2, significantly higher than those of conventional CWs (48.5% and 27.7%, respectively). The MEF accelerated biochar-derived organic carbon release, reshaped the microbial community toward Proteobacteria and denitrifying genera enrichment, and promoted lipid- and lignin-like substances in SEOM alongside enhanced biofilm stability and electron transfer potential. Furthermore, the system effectively alleviated oxidative stress caused by ACT on plants. This study demonstrates that BC-MEF-CWs can efficiently remove multiple pollutants in agricultural runoff through coupled electrochemistry and biochar-mediated mechanisms, offering a novel technological pathway for non-point source water pollution control.