The U.S. Environmental Protection Agency's (EPA's) Office of Research and Development (ORD) has devoted considerable effort over the last two decades to advancing the understanding of appropriate applications of bioremediation. Over the years, research direction has transitioned from substantial emphasis on mechanistic studies to a greater emphasis on evaluation of bioprocesses in the field. The initial research impetus provided the background information necessary for successful field applications, and was accomplished collectively through in-house research studies and cooperative research projects with public and private research institutes. The field efforts are conducted through the Bioremediation in the Field Program, supported by EPA/ORD, EPA's Office of Solid Waste and Emergency Response (OSWER), and the EPA Regions through the Superfund Innovative Technology Evaluation (SITE) Program and Cooperative Research and Development Agreements (CRADAs) with companies. This two-phase program has resulted in the development of cost-effective technical approaches to site cleanup that have been validated in the field.
Remedial activities have been conducted on groundwater, soils, sediments, and landfills with a range of contaminants, including chlorinated solvents, polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons, oils, and many others. These activities range from catalyzing a shift in the nation's remedial approaches to groundwater cleanup using bioremediation to employing biotreatment technologies to remediate the Exxon Valdez oil spill, this country's largest cleanup effort.
As with other treatment strategies, the effectiveness and cost of biotreatment technologies are both site-and contaminant-specific. Because of the potential advantages offered by bioremediation, there remains a strong interest in the continued development of biotreatment processes. There are many cases where bioremediation can be employed with relative confidence. The aerobic degradation of petroleum hydrocarbons and low-molecular-weight aliphatic and aromatic hydrocarbons is well understood and has been applied at hundreds of sites using bioventing, biosparging, land treatment, biopile treatment, or composting. Bioslurry reactors also have been used historically, but tend to be less widely used than these other alternatives due to their higher capital costs and lower throughput rates. Regulatory approval for the aerobic biotreatment of these contaminants can be readily obtained, and the above processes can be applied with confidence to meet treatment goals. For such easily degraded contaminants, treatability tests can be minimized or even eliminated at most sites.
Whereas the biological treatment of easily degraded contaminants is relatively well understood and accepted, a large number of contaminants remain for which there are no readily available bioremediation technologies and for which biotreatment remains challenged. Reports of new and previously undocumented biotransformation pathways for recalcitrant contaminants continue to appear in the literature and suggest that new biodegradation pathways and mechanisms will continue to be discovered. Examples include recent reports of the anaerobic degradation of benzene and PAHs under sulfate-reducing conditions (Coates et al., 1996, 1997), anaerobic oxidation of dichloroethylene (DCE) and vinyl chloride (VC) (Bradley and Chapelle, 1996, 1997), the ability to stimulate anaerobic PCB dechlorination by the addition of surrogate polybrominated biphenyl compounds to soils or sediments (Bedard et al., 1998), and the complete dechlorination of polychlorinated biphenyl (PCBs) (Bedard and van Dort, 1998). These studies and others provide an optimistic future for the biodegradation of environmentally persistent contaminants, and reflect the need for further research for the development of new and innovative bioremediation strategies and technologies to address recalcitrant contaminants and increasingly challenging site conditions.Contact: