A Potential Difference-Driven Cascade Effect of Cathode Biofilm–Plant Physiology Governs the Efficiency-Energy-Risk Trade-Off in Constructed Wetland–Microbial Electrolysis Cells

Abstract

Conventional potential difference optimization in microbial electrolysis cell-integrated constructed wetlands (ECWs) treating antibiotic-laden wastewater frequently prioritizes single-dimensional removal efficiency, critically overlooking trade-offs with energy consumption and ecological risks. By evaluating four ECWs operated under varying potential differences treating chloramphenicol (CAP) wastewater via physicochemical metrics, multiomics, structural equation modeling, and comprehensive risk assessment, we identified a potential difference-driven “cathode biofilm–plant physiology” cascade effect governing this “efficiency-energy-risk” trade-off. Specifically, moderate potential differences (0.5 and 0.8 V) achieved superior total nitrogen (79.5–80.1%) and substantial CAP (90.9–92.5%) removal, driven by the selectively enriched electroactive, dissimilatory nitrate reduction to ammonium and CAP-degrading bacteria (e.g., Geobacter sp., Ectobacillus sp., Defluviilinea sp016789025). These microbiomes provided continuous ammonium supply, activating diverse plant nitrogen pathways and stimulating robust root radial oxygen loss to engineer a microoxic-anoxic microenvironment for comprehensive risk mitigation. Concurrently, relative to the 0.2 V control group, the 0.5 V condition minimized greenhouse gas emissions (a 49.2% reduction), lowered effluent ecotoxicity by 47.4%, and suppressed AMR risk by 56.0%, without incurring excess energy input. Ultimately, the optimal 0.5 V potential difference establishes a sustainable efficiency-energy-risk equilibrium, empowering ECWs as robust biogeochemical barriers under a unified “One Health” perspective.