Biotransformation of toxic wastes to harmless products
The rapid expansion and increasing sophistication of the chemical industries in the past century and particularly over the last thirty years has meant that there has been an increasing amount and complexity of toxic waste effluents. At the same time, fortunately, regulatory authorities have been paying more attention to problems of contamination of the environment. Industrial companies are therefore becoming increasingly aware of the political, social, environmental and regulatory pressures to prevent escape of effluents into the environment. The occurrence of major incidents (such as the Exxon Valdez oil spill, the Union-Carbide (Dow) Bhopal disaster, large-scale contamination of the Rhine River, the progressive deterioration of the aquatic habitats and conifer forests in the Northeastern US, Canada, and parts of Europe, or the release of radioactive material in the Chernobyl accident, etc.) and the subsequent massive publicity due to the resulting environmental problems has highlighted the potential for imminent and long-term disasters in the public's conscience.
Even though policies and environmental efforts should continue to be directed towards applying pressure to industry to reduce toxic waste production, biotechnology presents opportunities to detoxify industrial effluents. Bacteria can be altered to produce certain enzymes that metabolize industrial waste components that are toxic to other life, and also new pathways can be designed for the biodegradation of various wastes. Since waste management itself is a well-established industry, genetics and enzymology can be simply "bolted-on" to existing engineering expertise.
Examination of effluents from the chemical and petrochemical industries shows that such effluents typically contain either one or a limited range of major toxic components. In some cases other considerations (such as aesthetic ones) can be important for removal of certain components (such as dyes). This means that in general one industry may apply one or a few genetically modified bacterial strains to get rid of its major toxic waste. However, it may be important to contain the "waste-eating" bacteria within the manufacturing plant, and not release these with the waste water. In such cases, filter installations will have to be built to separate the bacteria from the effluent.
Of course, the bioprocesses for treating toxic effluents must compete with existing methods in terms of efficiency and economy. However, the biotechnological solution to the problem requires only moderate capital investment, a low energy input, are environmentally safe, do not generate waste (hopefully), and are self-sustaining. Biotechnological methods of toxic waste treatment are likely to play an increasingly key role both as a displacement for existing disposal methods and for the detoxification of novel xenobiotic compounds. On the other hand, however, it is important to limit the generation of both hazardous and non-hazardous waste as much as possible, and utilize recycling methods wherever possible.
Over the last few years, a number of companies have been established already to develop and commercialize biodegradation technologies. Existence of such companies now has become economically justifiable, because of burgeoning costs of traditional treatment technologies, increasing public resistance to such traditional technologies (ranging from Love Canal to the ENSCO incinerator plans in Mobile AZ years ago), accompanied by increasingly stringent regulatory requirements. The interest of commercial businesses in utilizing microorganisms to detoxify effluents, soils, etc. is reflected in "bioremediation" having become a common buzzword in waste management. Companies specializing in bioremediation (or, as it was known several years ago, in biodegradation technologies) will need to develop a viable integration of microbiology and systems engineering. As an example of a bioremediation company, Envirogen (NJ) has developed recombinant PCB (polychlorinated biphenyl)-degrading microorganisms with improved stability and survivability in mixed populations of soil organisms. The same company also has developed a naturally occurring bacterium that degrades trichloroethylene (TCE) in the presence of toluene, a toxic organic solvent killing many other microorganisms. A large number of similar companies can be found using a web search engine and an appropriate keyword (such as "bioremediation").
Microorganisms have also been successfully applied during the removal of the Exxon Valdez oil spill. A number of microorganisms can utilize oil as a source of food, and many of them produce potent surface-active compounds that can emulsify oil in water and facilitate the removal of the oil. Unlike chemical surfactants, the microbial emulsifier is non-toxic and biodegradable. Also, "fertilizers" have been utilized to increase the growth rate of the indigenous population of bacteria that are able to degrade oil.
Use of microbes for bioremediation is not limited to detoxification of organic compounds. In many cases, selected microbes can also reduce the toxic cations of heavy metals (such as selenium) to the much less toxic and much less soluble elemental form. Thus, bioremediation of surface water with significant contamination by heavy metals can now be attempted.
A web address with links to sites related to bioremediation: http://www.nal.usda.gov/bic/Biorem/biorem.htm. As is apparent from this site, the US government (in particular the US Department of Energy; DOE) has a keen interest in bioremediation (for example, see the NABIR (Natural and Accelerated Bioremediation Research) Program at http://www.lbl.gov/NABIR/index.html. Part of this interest stems from the commitment to clean up heavily polluted sites (such as the Hanford site in Washington state) that once were nuclear weapons facilities and that contain large, buried metal buckets of radioactive waste that now are starting to leak. A DOE website on Hanford cleanup (involving both traditional technologies and bioremediation) can be found at http://www.hanford.gov/rl/index.asp.
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Center for Bioenergy & Photosynthesis
Arizona State University
Room PSD 209
Tempe, AZ 85287-1604
13 February 2006
phone: (480) 965-1963
fax: (480) 965-2747