Reductive dechlorination of carbon tetrachloride in iron- and sulfate-reducing microcosms

Groundwater contamination with chlorinated aliphatic hydrocarbons(CAHs) is a worldwide environmental issue. In recent years, monitored natural attenuation in anaerobic environments has been gaining more and more attention in the remediation of CAH-contaminated aquifers. To effectively apply this strategy, further understanding of the biogeochemical processes controlling the reductive transformation of these compounds is needed. In this research, we studied the biotic and abiotic reductive dechlorination of carbon tetrachloride (CT) in iron- and sulfate-reducing microcosms that were prepared with natural soils and sediments from different sources. CT reduction rates and product distribution as well as the concentrations of different iron and sulfur species were measured in sterilized/non-sterilized microcosms with single or sequential CT injections. Results showed that abiotic CT reduction occurred under all conditions and it was the predominant process in CT degradation. Biotic transformation was only observed under certain conditions studied and it was inhibited when the initial CT concentration was high. In sequential injection experiments, CT reduction rates decreased after each injection, which corresponded with the decrease of weakly bound Fe(II), while other species remained unchanged, suggesting that this species did play a role in the abiotic reductive dechlorination of CT.