Electrode-Triggered niche differentiation and endogenous electron cycling boost bioremediation of mixed aromatic contaminants in oligotrophic groundwater

Chlorinated and non-chlorinated aromatic contaminants frequently co-occur in groundwater, but their synergistic bioremediation is often hindered by conflicting redox requirements, microbial niche competition, and the need for external organic carbon sources. Here, we present an electro-stimulated bio-circulation well (ES-BCW) that couples electrode-mediated redox regulation with internal hydraulic recirculation, enabling the simultaneous continuous reductive dechlorination and oxidative aromatic degradation without exogenous organic carbon supplementation. Under continuous operation (120 d), the ES-BCW system achieved average removal rates of 53.2 µmol L −1 d −1 for 1,2,4-trichlorobenzene (1,2,4-TCB) and 169.5 µmol L −1 d −1 for toluene, respectively, demonstrating competitive performance for anaerobic co-treatment of mixed aromatic contaminants. Optimal weak electrical stimulation (1.2 V) with a controlled reflux (50%) promoted spatial niche differentiation between cathodic reductive and anodic oxidative zones. Microbial analysis revealed selective enrichment of dechlorinating ( Dechloromonas and Sphingobium ), toluene-degrading ( Azoarcus and Thauera ), and electroactive ( Geobacter and Sulfurospirillum ) genera. Integrated metagenomic and metabolomic analyses revealed coordinated enrichment of dechlorination ( pcpB, pcpC ) and toluene oxidation ( bssABC, bbsG ) genes, coupled with increased abundances of energy carriers and key electron transfer components (i.e. cytochromes). These shifts collectively supported enhanced electron flux redistribution, metabolic synergy, and sustained acetate cycling, establishing a self-amplifying loop of endogenous carbon reuse that enabled redox partitioning between cathodic reductive and anodic oxidative niches. The ES-BCW system offers an endogenous carbon-driven strategy for synergistic bioremediation of mixed aromatic contaminated oligotrophic groundwater.