Biodegradation refers to the degradation of organic contaminants in soil and/or groundwater by indigenous or transplanted/acclimated microorganisms, primarily bacteria and fungi. Organic contaminants are converted into carbon dioxide, water, and microbial cell mass under aerobic conditions (in the presence of oxygen). Under anaerobic conditions (in the absence of oxygen), methane, small quantities of carbon dioxide and hydrogen, and occasionally intermediate species, which may be less, equally, or more hazardous that the metabolized compound, are produced.
Biodegradation can be used to degrade environmental pollutants such as pentachlorophenal (PCP), lindane (hexachlorocyclohexane), dichloro-diphenyl trichloroethane (DDT), and 2,4-dichlorophenol. Fungi, such as Fusarium oxysporium and Phanerochaete Chyrysosoporium, as well as bacteria, such as P. cepacia and Pseudomonas putida, are used to degrade these pollutants .
The effective treatment of contaminated sites may be limited by several factors. Certain characteristics in the soil matrix or preferential flow paths of injected fluids may result in poor contact between microbes and contaminants. High concentrations of chlorinated compounds, inorganic salts, heavy metals, or long chain hydrocarbons may be toxic to microbes. In addition, the circulation of liquid solutions in the soil may increase contaminant mobility.
A test done by the Department of Bioscience and Biotechnology at the University of Roorkee showed that the biodegradation of Baygon in soil had a half life of 15 days at 30 deg.C. After 15 days of incubation in the soil, Baygon was fully dissipated and a new metabolite was formed whose biological activity is unknown .
Both soil and contaminant characteristics must be known prior to field testing and evaluation. The depth of contamination, contaminant concentrations, permeability, pH, organic content, moisture content, nutrient level, and texture are some of the soil characteristics that need to be measured. The specific contaminants in the soil need to be identified, and their biodegradability, chemical reactivity, and water solubility need to be quantified .
The cost of in situ biodegradation can range between $20 and $80 per cubic yard of soil, depending on the type and depth of the contaminants, groundwater pumping rates, and whether non-indigenous microbes and/or hydrogen peroxide is used .
Status of Technology
Biodegradation is being used for military applications. The molecular processes involved in microbial and enzymatic degradation are being exploited by agencies of the U.S. Department of Defense in diverse ways. The military is using this method to restore contaminated soils or ground water on battlefields. This method also is used in commercial applications and is being tested in laboratories .
1 Kumar, R. and C.B. Sharma, 1992, Biodegradation of Carbamate Pesticide Propoxur in Soil, in Environment and Biodegradation, V.P. Agrawal and S.V.S. RanaIndia eds., Society of Biosciences, India, pp. 137-148.
2. Ward, F.P., Military Applications of Biodegradation, in Biotechnology and Biodegradation, Advances in Applied Biotechnology Series, Vol. 4, A. Chakrabarty, D. Kamely, and G. Omenn eds., Gulf Publishing, Houston, TX, pp. 147-154.
3. The EPA Office of Research and Development, 1999, Alternative Treatment Technology Information Center (ATTIC), 4.1 - Biodegradation.
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