A New Strategy of Electron Injection for Contaminant Reduction in Groundwater.

In situ chemical reduction (ISCR) is an efficient process for groundwater remediation, whereas the injection of reductants poses secondary contamination risks. Here, we propose a new strategy of electron injection for contaminant reduction in groundwater without the injection of reductants. The reductants are physically separated from the contaminants in aquifers, and electron transfer from reductants to contaminants was achieved by two connected electrodes due to the potential difference. Results showed that 0.1 mM Cr(VI) (pH 2.5) was removed by 98% within 2 h in a laboratory batch system using 10 mM sodium dithionite (pH 11.8) as the electron source. Electrochemically stable electrodes, such as graphite and mixed metal oxides, exhibited high performance in Cr(VI) removal. Over 85% of Cr(VI) removal was maintained in 10 cycles of consecutive treatments. This electron injection system could remove 81% of Cr(VI) within 60 h in a simulated aquifer. By leveraging electron injection, this approach provides a feasible pathway for aquifer redox regulation, thereby reducing the reliance on massive chemical inputs and minimizing secondary environmental disturbances caused by traditional ISCR.