MICROBIAL BIOTECHNOLOGY: SCOPE, TECHNIQUES CONTD
2) BIO REMEDIATION: Bioremediation depends on the activities of living organisms to clean up pollutants dispersed in the environment. Physical or chemical treatments, such
as vaporization, extraction, or adsorption, relocate rather than remove pollutants. In contrast, there are many instances in which biodegradation converts organic pollutants to harmless inorganic products, including carbon dioxide, water, and halide ions. Other advantages are that bioremediation
is generally inexpensive and causes little disturbance to the environment. Naturally occurring consortia, frequently dominated by bacteria, have the capacity to degrade a wide spectrum of environmental pollutants.
Notably, such consortia are responsible for the cleanup of massive oil spills. There is a long list of oil spills with serious environmental impact. Following are three of many examples of this type of widely dispersed pollution. In March 1989, some 41 million liters (>10.5 million gallons) of crude oil
escaped from the tanker Exxon Valdez and contaminated more than 2000 km (∼1250 miles) of rocky intertidal coastline in Alaska. In 1991, during the Gulf War, huge amounts of oil were released into the marine environment, with devastating impact on marine life. In 1997, more than 5000 tons of heavy oil leaked from the Russian tanker Nakhodka, which ran aground and sank in the Sea of Japan. The oil contaminated more than 500 km (∼310 miles) of the coastline. Over time, in all of these cases, the endogenous microbial community largely degraded the oil. In the case of the Exxon Valdez, the activity of the naturally occurring hydrocarbon-degrading bacteria at the spill site
was enhanced by the addition of fertilizer containing organic nitrogen compounds and inorganic phosphorus compounds.
Many thousands of organic and inorganic compounds are used daily
around the world in hundreds of thousands of products. These compounds
are introduced either accidentally or on purpose into the soil and groundwater. The seriousness of the problem posed by the introduction of human made contaminants into the environment is highlighted by the following pronouncement by the Danish government in 2003: The government’s most important goal with regard to chemicals is that by 2020 there should no longer be any products or goods on the market containing chemicals with particularly problematic health or environmental impacts.
Among such pollutants, highly chlorinated compounds have received particular attention because of their known and potential adverse environmental and health impacts. One class of such compounds includes highly chlorinated aliphatics such as tetrachloroethene, trichloroethene, 1,1,1-trichloroethane, and carbon tetrachloride, which are used as dry cleaning
fluids and degreasing solvents. Another class is represented by highly chlorinated aromatics such as pentachlorophenol (wood preservative), polychlorobiphenyls (insulators, heat exchangers), and dioxins (combustion byproducts). These compounds are either fully or partially degraded by the
combined activities of various endogenous microorganisms under aerobic
or anaerobic conditions. By and large, the natural attenuation of chlorinated
organic compounds at many different sites by the action of endogenous
microbial populations, whether under aerobic or anaerobic conditions, is
slow, is incomplete, and, in some cases, has resulted in the formation of
toxic products up of sites contaminated by radionuclides poses an exceptionally
challenging problem of great importance. A U.S. Department of Energy
(DOE) report summarizes the situation succinctly.
With the end of the Cold War threat in the early ’90s and the subsequent shutdown of all nuclear weapons production reactors in the United
States, DOE has shifted its emphasis to remediation, decommissioning,
and decontamination of the immense volumes of contaminated water and
soils, and the over 7,000 structures spread over 120 sites (7,280 square kilometers) in 36 states and territories. DOE’s environmental legacy includes
1.7 trillion gallons of contaminated ground water in 5,700 distinct plumes,
40 million cubic meters of contaminated soil and debris, and 3 million
cubic meters of waste buried in landfills, trenches, and spill areas.” Source:
U.S. Department of Energy. (2003).Bioremediation of Metals and Radionuclides. What Is It and How It Works, LBNL-42595, 2nd Edition, p. 5, Washington, D.C.: Office of Biological and Environmental Research, Office of Science, U.S. Department of Energy.
Subsurface bioremediation of such sites has attracted much attention. A
key objective is to stabilize the buried wastes in place to prevent leaching and
widespread contamination of groundwater. The most common radioactive
components inthese wastes are uranium(U),strontium(Sr),plutonium(Pu),
cesium (Cs), and technetium (Tc).
CITED BY KAMAL SINGH KHADKA/ SHAILENDRA PARAJULI
Msc Microbiology, TU.
Assistant Professor Of Pokhara University, PBTPC, PNC,LA, NA.
www.cee.ucr.edu › Department of Chemical Engineering
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