| Trichloroethylene (TCE) is one of the most prevalent groundwater contaminants in the U.S., and is classified as a Group 1 carcinogen by the International Agency for Research on Cancer. Anaerobic reductive dechlorination is an effective bioremediation technique when biogeochemical and energy requirements are met. In this study, the impacts of applying of a simple versus complex substrate (lactate versus whey) during biostimulation and bioaugmentation of aquifer material, were compared in order to determine which form of carbon would support the biogeochemistry and energy production necessary to achieve dechlorination of TCE.;Glass columns were packed with aquifer material collected from Hill Air Force Base Operable Unit 5, Utah, received a continuous flow of groundwater containing TCE and carbon in the form of whey, lactate, or no carbon (control), and were inoculated with a culture containing Dehalococcoides mccartyi (Dhc). Changes in carbon metabolites, redox conditions, and TCE degradation byproducts were measured weekly. Soils were analyzed at the point of iron reduction, and TCE reduction to each sequential degradation byproduct; cis-dichloroethene (DCE), vinyl chloride (VC), and ethene for iron mineralogy, sulfides, and microbiology.;Sulfate reducing conditions were met in both carbon treatments. With both carbon sources, TCE was being reduced to ethene by the end of the study, although there was a significantly greater amount of VC accumulation in the lactate treatment than in the whey. Concentrations of butyrate, hydrogen, and reduced iron (aqueous) were significantly greater in the whey than the lactate treatment, which may have facilitated the high rates of VC reduction. Propionate concentrations were greater in the lactate treatment than in the whey, along with acetate during ethene production. During DCE and VC reduction, the difference in metabolites among the lactate and whey treatments did not lead to a difference in the concentration of the genes vcrA, tceA, or Dhc. The addition of whey supported the biogeochemical conditions and energy production required to achieve full dechlorination of TCE with high rates of VC reduction. When compared to lactate, the use of whey during TCE bioremediation could reduce the risk of human exposure to VC, a carcinogenic TCE degradation byproduct. |
