Micro-nano biochar interfaces promote adsorption-reduction coupling to accelerate bioelectrodechlorination in groundwater

Chlorinated aliphatic hydrocarbons (CAHs), such as trichloroethylene (TCE), are frequently detected high-toxicity contaminants in groundwater. Bioelectrodechlorination provides a sustainable alternative for CAHs remediation, but its practical application is hindered by limited interfacial reactivity due to low CAHs bioavailability and inefficient electron supply. Herein, we propose the construction of biochar-based functional electrodes featuring micro-nano interfacial architectures with hierarchical porosity, excellent biocompatibility, and enhanced interfacial extracellular electron transfer (EET) relative to carbon felt, which strengthened the coupling among local contaminant enrichment, cathode-associated biofilm development, and interfacial electron transfer, thereby accelerating TCE reductive dechlorination. The biochar-modified electrode increased the TCE dechlorination rate by 3.67-fold and reduced the interfacial charge-transfer resistance by 1.79-fold. Cathodic polarization at −0.5 V (vs. SCE) achieved the optimal balance between performance and energy efficiency, delivering 98.7% removal within 48 h at a low energy consumption of 4.1 Wh kg−1 TCE, whereas less negative or more negative potentials decreased dechlorination efficiency by 4.3–11.0%. Under optimized conditions, TCE was efficiently removed and predominantly converted to cis-1,2-DCE. Biochar functionalization promoted biofilm development and selectively enriched electroactive and dechlorinating populations. Metagenomic analysis revealed marked upregulation of reductive dehalogenase genes (tceA, rdhA) and EET-related genes (cytc-c, e-pilin, and riboflavin). Environmental-economic benchmarking further demonstrated that biochar-based bioelectrodechlorination outperforms organic carbon-driven bioreduction and conventional electroreduction in removal efficiency, electron utilization, process controllability, and material sustainability.