Monitoring Bioaugmenation with Single-Well Push−Pull Tests in Sediment Systems Contaminated with Trichloroethene

Abstract

Bioaugmentation to enhance the rate and extent of reductive dechlorination of chlorinated ethenes was investigated in intermediate ( approximately 1 m) scale physical aquifer models (PAMs) designed to simulate the groundwater flow field near an injection well. Push-pull tests were used to quantify the reductive dechlorination of injected trichloroethene (TCE) and trichlorofluoroethene (TCFE) in prepared sediment packs with and without an added dechlorinating culture containing Dehalococcoides spp. Distribution of the added culture throughout the sediment pack was confirmed by microscopic observation. Repeated additions of TCE (100-350 microM) were completely transformed to ethene in 14 days and a subsequent TCFE addition (114 microM) was completely transformed to fluoroethene (FE) in 24 days. Similar transformation rates, product distributions, and time courses for TCE and TCFE transformation were observed when these compounds were added together at similar initial concentrations. In the control PAM (nonbioaugmented), TCE and TCFE were transformed to only cis-DCE and cis-DCFE, respectively, and transformation rates were 6-12 times slower than those in the bioaugmented PAM. The use of TCFE for push-pull tests is shown to be an effective tool for detecting and quantifying the effects of bioaugmentation on TCE transformation.