Cox, E.E., M. McMaster, and D. Major, 2002, "Successful Field Demonstrations of Bioaugmentation to Remediate Trichloroethene in Groundwater, "ATV Biologiske AFV
Pilot-scale field demonstrations were conducted in a chlorinated ethene-contaminated aquifer at Kelly Air Force Base, Texas, USA, to evaluate the applicability of accelerated anaerobic bioremediation using bioaugmentation with the microbial consortium KB-1. Results from laboratory microcosm studies and the field demonstrated that anaerobic bioremediation could be enhanced by the supply of organic nutrients but that complete reductive dechlorination of tetrachloroethene and trichloroethene to ethene only occurred after bioaugmentation.
At many contaminated sites, the most significant biodégradation mechanism for tetrachloroethene (PCE) and trichloroethene (TCE) in the subsurface is reductive dechlorination, which occurs under highly reducing anaerobic conditions. This degradative mechanism involves the sequential replacement of chlorine atoms on the solvent molecule with hydrogen atoms and can yield fully dechlorinated end products. Reductive dechlorination requires the presence of organic carbon and energy sources, either natural or anthropogenic. Although many anaerobic microorganisms can bring about reductive dechlorination by cometabolic reactions (probably due to the transfer of electrons from reduced co-factors involved in anaerobic metabolism), they do not derive energy or any other benefit from the reaction. In contrast, dehalorespiring microorganisms utilise chlorinated solvents as the terminal electron acceptors for respiration and thereby gain energy from the reductive dechlorination process. Known dehalorespiring bacteria include Dehalospirillium multivorans (ScholzMuramatsu et al, 1995), Dehalobacter restrictus (Schumacher & Holliger, 1996) and Dehalococcoides ethenogenes (Maymo-Gatell et al, 1997). To date, D. ethenogenes is 370 P. Morgan et al. the only organism known to completely and rapidly dechlorinate chlorinated ethenes to ethene by dehalorespiration. Several stable, natural microbial consortia containing D. ethenogenes strains have been isolated and have been shown to be capable of achieving the complete dechlorination of TCE to ethene. For example, Ellis et al. (2000) reported a field demonstration at Dover Air Force Base, Delaware, USA, where reductive dechlorination of TCE to cis-\,2-DCE took place following organic nutrient addition but further dechlorination did not occur until bioaugmentation was performed using a microbial consortium containing D. ethenogenes. In this paper, we report the laboratory and field demonstration of bioaugmentation using the KB-1 microbial consortium to achieve complete reductive dechlorination of PCE to ethene. A key component of this demonstration was the ability to assess before the field demonstration the absence of D. ethenogenes at the site and track the spread of the introduced D. ethenogenes.