Electrically enhanced, Nature-Driven microbial attenuation of chromate and dichloromethane in groundwater

Natural attenuation is a nature-based approach that relies on intrinsic biogeochemical and microbial processes to mitigate mixed heavy metals and organic pollutants in aquifer, yet its efficiency is limited by electron donor scarcity and suppressed microbial activity. Here, a low-energy bioelectrochemical strategy that uses a mild electric field (0.6 V) was introduced to sustainably stimulate the attenuation of chromate [Cr(VI)] and dichloromethane (DCM) co-contamination in groundwater. With minimal electrical input, Cr(VI) and DCM removal reached 95.0 ± 2.6% and 95.2 ± 0.5%, substantially outperforming the no-voltage and single-pollutant systems. The electric field alleviated electron-donor limitations and metabolic inhibition, enabling efficient and energy-conserving bioremediation. Mineralogical and spectroscopic analyses (SEM-EDS, XPS, XRD) confirmed the reduction of Cr(VI) to Cr(III) precipitates (e.g., Cr₂O₃) and the progressive dechlorination and mineralization of DCM. Integrated metagenomic and metatranscriptomic profiling revealed active functional guilds (e.g., Sphingopyxis, Pseudomonas, Hyphomicrobium) expressing key genes for chromate reduction (yieF, chrA), dehalogenation (dhlA, dcmA), and electron-shuttling metabolism (ribE). This work demonstrates an applicable remediation technology that can be powered by renewable electricity and integrated into secure groundwater management systems. It offers a pathway for environmentally safe pollutant mitigation by harnessing nature-based microbial processes, supporting the transition toward enhanced natural attenuation.