Stimulation of reductive dechlorination for in situ bioremediation of a soil contaminated with chlorinated ethenes

A soil from a former chemical redistribution company, contaminated with mainly chlorinated aliphatics, was studied for bioremediation purposes. Groundwater analyses revealed that the original pollutants, i.e. tetrachloroethene (PCE) and trichloroethene (TCE), were present at levels ranging from 2.3 to 122 mg/L. Dichloroethene (DCE), vinylchloride (VC), ethene and ethane were also detected at significant concentrations although they had never been introduced to the soil. Relatively high concentrations of cis-DCE as compared to trans-DCE and 1,1-DCE indicated that a slow in situ biodegradation had taken place by reductive dechlorination. Laboratory experiments with flow-through soil columns were performed to determine the optimal conditions for the enhancement of reductive dechlorination by the indigenous dechlorinating population. The addition of single electron donors to artificial groundwater resulted in the dechlorination of PCE to TCE and cis-DCE, whereas complete dechlorination to ethene was solely achieved with compost extract added to native groundwater.