Prototyping Chain-Elongation-Mediated Dehalogenation for Groundwater Bioremediation

Chlorinated ethenes are widespread groundwater contaminants. Microbial reductive dehalogenation can detoxify chlorinated ethenes but requires sustained H2 delivery to organohalide-respiring bacteria. In enrichment cultures, microbial chain elongation was shown to reliably provide H2 for dehalogenation from the conversion of ethanol and acetate to butyrate and caproate and subsequent fermentation of these carboxylates. Supported by robust laboratory testing, here, we document the first field-scale application of chain elongation-mediated dehalogenation in chlorinated ethene-contaminated groundwater. Native groundwater communities produced mainly propionate from ethanol and acetate in microcosms and the field, whereas bioaugmentation with a chain-elongating enrichment culture redirected microbial metabolism toward butyrate production and supported dehalogenation to ethene. Dehalogenation was favored at a lower organic carbon loading (900 mg C L-1 either as ethanol + acetate, butyrate, or caproate). Chain elongation was more strongly stimulated at higher ethanol to acetate molar ratios and organic carbon loadings (3500 mg C L-1). Bioaugmentation with chain-elongating bacteria in groundwater produced detectable butyrate concentrations, increased the molar ratio of ethene and ethane from 0.20 to 0.51 during monitoring, and did not stimulate methanogenesis. This study positions chain elongation-mediated dehalogenation as an effective strategy for groundwater bioremediation of chlorinated ethenes.