Effect of Sorption on the Microbial Reductive Dechlorination of Soil-Bound Chloroalkenes

Abstract

The sequential, microbial reductive dechlorination of tetrachloroethylene and other chlorinated alkenes under methanogenic conditions was studied in liquid and soil slurry systems. A field contaminated soil was used and the effect of sorption on the reductive dechlorination rates was elucidated. As a result of microbial activity and enhanced reductive dechlorination, the extent of soil-bound contaminant release was five-fold more than in the soil slurry controls. The reductive dechlorination rates in the soil slurry system were between one and two orders of magnitude lower than those achieved in a soil-free culture. Therefore, the soil-bound contaminants exhibited lower bioavailability when compared to liquid-phase chloroalkenes. This study demonstrated the need for a continuous supply of electron donors to sustain an active primary metabolism (e.g., methanogenesis), as well as to supply the required electrons for the reductive dechlorination process. A very small fraction (less than 0.01%) of the total reducing power used for both the methanogenesis and dechlorination processes was actually channeled towards the latter process. The results of this study indicate tha development and/or enhancement of subsurface, methanogenic activity could effectively result in the biotransformation of soil-bound chloroalkenes.