Electrochemically enhanced reduction of trichloroethene by passivated zero-valent iron

• Electrochemical reduction of TCE is verified in a dynamic flow-through system.
• Electrochemical reduction of TCE does not result in accumulation of metabolic intermediates.
• Low voltage appears to help recover reductive activity of passivated ZVI.
• The recovery of passivated ZVI may be partially due to reduction of iron oxides.

Zero-valent iron (ZVI) is commonly used for the in situ remediation of groundwater aquifers contaminated with trichloroethylene (TCE); however, ZVI is susceptible to passivation over time, which can significantly reduce its treatment efficiency. Recent studies have suggested that electrically-induced reduction (EIR) or "E-Redox" technology, which applies a low-level direct current (DC), can restore the reactivity of passivated ZVI in situ. In this study, a continuous-flow column reactor was used to assess the effects of low-voltage DC on the abiotic reduction of TCE in groundwater and on the performance of passivated ZVI. In experiments with partially passivated ZVI, the application of DC increased the rate and the extent of TCE reduction; both were correlated with the level of applied voltage (0–12 V). The results provide evidence that EIR may partially recover the reduction potential of passivated ZVI and shows promise as a technique to extend the longevity of zero-valent iron. Several mechanisms, including the reduction of ferric iron minerals to ferrous iron at the ZVI surface, likely results in the enhanced TCE reduction.