Bioremediation of cis‐DCE at a Sulfidogenic Site by Amendment with Propionate

Abstract

AbstractThe technical feasibility of in situ reductive dechlorination of cis‐dichloroethene (cDCE) and vinyl chloride (VC) was demonstrated at a sulfidogenic ground water site. Preceding laboratory studies had indicated that dechlorination at the site was limited by the supply of electron donors, that dechlorinating activity was sparsely and heterogeneously distributed, and that dechlorination was strongly enhanced by mixing sediments from multiple locations at the site. Based on these observations, the remediation strategy consisted of amending the ground water with sodium propionate solution using a pair of recirculation wells as a mixing device. This strategy was able to overcome the sparse initial distribution of biological activity by creating a treatment zone. Dechlorination and sulfate reduction commenced within 10 and 4 d, respectively, after propionate amendment began. Dechlorination efficiency increased during the 2 months of continuous operation. By the end of the 2 months, treatment converted ∼1000 μg/L cDCE nearly stoichiometrically into ethene, with only low concentrations of VC remaining. More than 90% of chlorinated ethenes were removed as the ground water traveled from one well to the other (travel time of ∼1 to 2 weeks). Near‐complete removal of ∼250 mg/L sulfate accompanied the rapid dechlorination, but no methanogenesis was observed. Aquifer clogging in the vicinity of the propionate injection wells became evident after ∼40 d of propionate amendment and was attributed to the growth of sulfate‐reducing bacteria and/or the formation of insoluble metal sulfides. Clogging was mitigated by pulsed amendment of the propionate solution.