Enhanced natural attenuation - Determining the potential for reductive dechlorination in an oxic aquifer

The aim of the study was to demonstrate the stimulation of reductive dehalogenation of chlorinated ethenes in an oxic aquifer. Microcosms with aquifer material were amended with different organic substrates as electron donors in order to stimulate microbial reductive dechlorination. Next to molasses and lactate a commercial product was applied, which has been described as controlled-release carbon zero valent iron particles (EHC™). In addition, vitamins and bicarbonate buffer were added to the microcosms to further stimulate growth of halorespiring microorganisms. Reductive dechlorination was followed by measuring chlorinated ethene concentrations and their stable carbon isotope fractionation. The microbiological community was monitored by terminal restriction fragment length polymorphism (T-RFLP). The EHC™ amended microcosms showed only incomplete conversion of PCE, resulting in an accumulation of cis-DCE after incubation for 103 days. In the microcosms amended with molasses, complete reductive dechlorination of PCE to ethene was observed within 56 days. The degradation of the less chlorinated ethenes correlated with the appearance of Dehalococcoides microorganisms and carbon isotope fractionation. Also one of the parallel set-ups amended with lactate showed complete dechlorination. In this microcosm an isotopic overtaking of VC was observed, proving complete microbiological degradation to ethene. Control microcosms without substrate addition showed no dechlorination during the whole experiment. Our study demonstrates that the potential for microbial reductive dechlorination was present and can be stimulated in an oxic aquifer by establishing reducing conditions and supplementing fermentable substrates.