Synergistic Zerovalent Iron (Fe-0) And Microbiological Trichloroethene And Perchlorate Reductions Are Determined By The Concentration And Speciation Of Fe

Trichloroethene (TCE) and perchlorate (ClO4-) are cocontaminants at multiple Superfund sites. Fe-0 is often used during TCE bioremediation with Dehalococcoides mccartyi to establish anoxic conditions in the aquifer. However, the synergy between Fe-0 abiotic reactions and microbiological TCE and ClO4- reductions is poorly understood and seldom addressed in the literature. Here, we investigated the effects of Fe-0 and its oxidation product, Fe2+, at field-relevant concentrations in promoting microbial TCE and ClO4- reductions. Using semibatch microcosms with a Superfund site soil and groundwater, we showed that the high Fe-0 concentration (16.5 g L-1) expected during Fe-0 in situ injection mostly yielded TCE abiotic reduction to ethene/ethane. However, such concentrations obscured dechlorination by D. mccartyi, impeded ClO4- reduction, and enhanced SO42- reduction and methanogenesis. Fe2+ at 0.25 g L-1 substantially delayed conversion of TCE to ethene when compared to no-Fe controls. A low concentration of aged-Fe-0 synergistically promoted microbiological TCE dechlorination to ethene while achieving complete ClO4- reduction. Collectively, these results illustrate scenarios relevant at or downstream of Fe-0 injection zones when Fe-0 is used to facilitate microbial dechlorination. Results also underscore the potential detrimental effects of Fe-0 and bioaugmentation cultures coinjection for in situ treatment of chlorinated ethenes and ClO4-.