Engineering anaerobic dechlorination for bioremediation

Contaminated sediments are a larger source of toxic exposure for Great Lakes basin residents than any other pollution source. Sediment toxins such as chlorinated aromatic compounds can be re-introduced into water through any kind of disturbance and enter the food chain through bottom-dwelling organisms. Contaminants often become highly bioconcentrated by the time they get to the top predators in the food chain - such as trout, bald eagles and humans. Recently, it has been demonstrated that anaerobic bacteria can perform reductive dechlorination and mineralization of toxic chlorinated organic compounds including polychlorinated biphenyls (PCBs), tetrachloroethylene (PCE), and chlorinated biphenols. These compounds are found widely distributed in Great Lakes sediments and are aerobically recalcitrant but can be reductively dechlorinated to less chlorinated compounds which can be further mineralized by CO, by aerobic organisms. Unfortunately, direct applications of anaerobic dechlorination have been difficult because the organism(s) responsible for this reaction and their exact mode of action have not been identified. We now advocate the use of a microenvironmental approach in designing and utilizing consortia of microbes and enzymes for actual decontamination of sediments. Basically, self-immobilized and/or co-immobilized microbial consortia are developed to overcome the incompatibility between the microbial consortia and the hostile environment. For example, anaerobic granules which are self-immobilized methanogenic consortia with a matrix structure with diameters ranging from 0.1 to 5.0 mm have been adapted for anaerobic dechlorination and used for in situ treatment of various chlorinated compounds in sediments. In this communication, we will describe the performance of several anaerobic granules for direct dechlorination of pentachlorophenol (PCP), PCE and PCBs.