Innovative sandwich electrode-assembled bioelectrochemical system for efficient organic pollutants removal in...

Rapid industrialization has caused widespread global groundwater contamination. Bioelectrochemical systems (BES), as a promising in-situ groundwater remediation technology, are limited by the low conductivity of natural groundwater (< 1000 μS cm^-1). To address this constraint, this study developed a sandwich electrode-assembled BES (SEA-BES), evaluated its pollutant removal performance with nitrobenzene (NB) as an example, and conducted pilot-scale tests. A non-woven cloth separator reduced SEA-BES electrode spacing to the μm-scale. The SEA-BES significantly reduced solution resistance in low-conductivity groundwater (from 66.5 Ω in conventional BES to 1.0 Ω at 250 μS cm^-1) and achieved low energy demand (0.086 kWh mg^-1 COD). Pseudo-first-order kinetic analysis of NB removal (initial NB concentration: 40 mg L^-1; treatment time: 24 h) revealed significantly higher rate constants for the SEA-BES (0.1149 h^-1, R²=0.9985), which was 1.39-fold higher than that of the conventional BES (0.0827 h^-1, R²=0.9991). This enhancement is mainly attributed to optimized electron transfer (especially enhanced direct electron transfer), enriched targeted functional genera (e.g., Methanobacterium), and reduced dependence on EPS-mediated stress compensation. This study further developed an intermittent electrical stimulation mode to boost applicability and reduce energy use, achieving 74.23 % TOC mineralization, which was 18.32 % higher than that of the continuous stimulation mode. A 46-day pilot test confirmed stable pollutant removal. In summary, the SEA-BES with an intermittent electrical stimulation mode provides an efficient, low-energy solution for remediating organic pollutant-contaminated low-conductivity groundwater.