Hua Wang
Published: 2013
Total Pages: 70
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Trichloroethylene (TCE) is a volatile, chlorinated aliphatic organic compound. It has been used ubiquitously as an ingredient in industrial cleaning agents and as a degreasing agent, which has resulted in widespread contamination of groundwater. Since TCE is a highly oxidized compound, reduction reactions are considered a promising way to treat it. Permeable reactive barriers (PRB) containing highly-reducing reactive media [e.g., zero-valent iron (Fe° or ZVI)] have been successfully used in situ to remediate TCE in groundwater. There have been more than 200 ZVI PRBs installed worldwide since the mid-1990s. Despite their promise, ZVI PRBs are susceptible to passivation over time, largely due to oxidation of the Fe° by dissolved oxygen or nitrate. Several recent studies have suggested that electrically-induced reduction (EIR) is a promising approach to restore reductive activity in passivated ZVI PRBs. The overall objectives of this study were to simulate in the laboratory a ZVI PRB to remediate TCE-contaminated groundwater and systematically evaluate the effect of applying direct current. Results suggest that: (1) any enhancements in the rate or extent of TCE removal in `fresh' ZVI that may be the result of application of direct current are indistinguishable from those due to TCE reduction by ZVI alone; (2) upon application of direct current (6V and 12V) to partially passivated ZVI, a significant improvement in TCE reduction was observed; (3) the longevity of ZVI de-passivated by EIR was not determined, but preliminary results suggest the observed effect may be short-lived and be due to direct reduction of TCE by electrons; and (4) experiments in a partially passivated ZVI-sand column suggest that observed enhancements in TCE removal are correlated with voltage, with higher current densities resulting in faster rates of TCE reduction.