Synergistic Zerovalent Iron (Fe) and Microbiological Trichloroethene and Perchlorate Reductions Are Determined by the Concentration and Speciation of Fe.

Trichloroethene (TCE) and perchlorate (ClO) are cocontaminants at multiple Superfund sites. Fe is often used during TCE bioremediation with to establish anoxic conditions in the aquifer. However, the synergy between Fe abiotic reactions and microbiological TCE and ClO reductions is poorly understood and seldom addressed in the literature. Here, we investigated the effects of Fe and its oxidation product, Fe, at field-relevant concentrations in promoting microbial TCE and ClO reductions. Using semibatch microcosms with a Superfund site soil and groundwater, we showed that the high Fe concentration (16.5 g L) expected during Fe injection mostly yielded TCE abiotic reduction to ethene/ethane. However, such concentrations obscured dechlorination by , impeded ClO reduction, and enhanced SO reduction and methanogenesis. Fe at 0.25 g L substantially delayed conversion of TCE to ethene when compared to no-Fe controls. A low concentration of aged-Fe synergistically promoted microbiological TCE dechlorination to ethene while achieving complete ClO reduction. Collectively, these results illustrate scenarios relevant at or downstream of Fe injection zones when Fe is used to facilitate microbial dechlorination. Results also underscore the potential detrimental effects of Fe and bioaugmentation cultures coinjection for treatment of chlorinated ethenes and ClO.