Bioremediation
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CHAPTER 3.8 no i t a i demero iB
Bioremediation RONALD L. CRAWFORD
Introduction As a result of human ignorance in the safe use of chemicals, carelessness in manufacture of synthetic compounds, occasional accidents, and improper disposal of chemical wastes, toxic anthropogenic chemicals have become ubiquitous contaminants of soils and waters worldwide. These compounds include thousands of individual molecules. They are found in the environment sometimes individually but more often as complex mixtures. Many are overtly toxic (e.g., the metal mercury or the herbicide dinoseb). Many more are chronic toxins, some of them carcinogens (e.g., organic polynuclear aromatic hydrocarbons or metals such as arsenic). They are derived from sources such as petroleum, synthetic organic chemicals, mining activities, and natural or man-made radionuclides. Governments now regulate the use and disposal of toxic chemicals more rigorously than in the past. However, the legacy of environmental damage from previous decades of improper practice now requires cleanup to mitigate, insofar as possible, hazards to human health and the environment. Traditional environmental cleanup methods include approaches such as excavation and incineration of contaminated soil or pumping and aboveground treatment of groundwater. These techniques are both expensive and politically unpopular. Affordable, innovative technologies are needed by the environmental restoration industry. Bioremediation is such a technology.
In situ approaches treat contaminants in place without moving them to a treatment facility. Bioremediation sometimes can be speeded or, in very difficult circumstances, even made possible by augmenting natural systems with exogenous biological materials. This process is called bioaugmentation. Bioaugmentation usually involves the use of natural microorganisms or plants grown to large numbers in fermenters or greenhouses and can include the use of genetically engineered microorganisms (GEMs) or plants developed specifically for the purpose. More often bioremediation can be accomplished most efficiently by simply stimulating natural, indigenous, contaminant-transforming microbial or plant populations by providing them the necessary nutrients, environmental conditions, or both needed for growth and metabolism. This process is called biostimulation. Yet another bioremedial option is called intrinsic bioremediation. This encompasses natural microbial processes that occur without human intervention (selfrestoration). Finally, abiotic processes sometimes can be used in combination with biotic processes to degrade particularly recalcitrant molecules. Examples of abiotic catalysts that may enhance biodegradative processes include ultraviolet light, inorganic reductants, and Fenton reagent (iron and hydrogen peroxide). The bioremediation industry has developed many novel approaches for biostimulation, bioaugmentation, combined abiotic/biotic processes, and for monitoring and quantifying intrinsic bioremediation.
Bioremediation Bioremediation employs living
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