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r� ��*�;��-� �_ .. ���.u.�''�' t _ }��b� .c-.,- as.ra � .y,�" .r_ _�� t�A.�t��saf �- �• � S�_ -� � �i <br /> k <br /> BIOREMEDIATION OVERVIEW AND WORK PLAN ALTERNATIVES <br /> As a result of considerable research and increased desire to <br /> employ alternative remedial technologies by government and <br /> industry, both here and abroad, the utilization of hydrocarbon <br /> degrading bacteria and fungi to detoxify soil and water has <br /> become quite popular. This popularity is certainly well deserved <br /> as virtually any anthropogenic compound, including f <br /> uel <br /> hydrocarbons, solvents, and pesticides may be thoroughly bio- <br /> degraded to form non--toxic end products such as carbon dioxide, <br /> minerals, and water. In addition to excellent treatment <br /> efficiency, biological detoxification processes are most <br /> affordable- frequently affording savings of 70%, or more, over <br /> conventional methods. <br /> The science upon which biological detoxification is based is <br /> itself founded upon knowledge of the chemical and physical <br /> changes which occur in petroleum and petroleum products which <br /> have entered the environment as pollutants. <br /> While changes in the composition of polluting hydrocarbon <br /> mixtures are both chemically and biologically induced, biological <br /> (microbial) degradation plays a major role in this process (known <br /> as weathering). Although the complete breakdown of hydrocarbon <br /> materials into carbon dioxide, water, and minerals is theoreti - <br /> cally possible under virtually all circumstances, petroleum <br /> hydrocarbons are very complex mixtures containing large numbers <br /> of alicyclic, aromatic, and other compounds. Gasoline, for <br /> example, may contain 200 suoh compounds and crude oil many <br /> + thousands. As each of these compounds possesses distinctive <br /> physical and chemical characteristics hydrocarbons differ in <br /> their capacity to service as microbial substrates (i.e. be <br /> utilized by bacterial and fungi as sources of carbon and <br /> energy) within a given environment. In addition, the physical <br /> state of the pollutants, environmental temperature, availability <br /> of oxygen and nutrients (particularly nitrogen, phosphorus, <br /> and iron) significantly impact the rate of pollutant degradation. <br /> Clearly, the fate of fuel hydrocarbon contaminants within a <br /> given habitat will depend on the set of abiotic parameters <br /> particular to that habitat; with the interactions of multiple <br /> factors determining the overall rate of biodegradation. Factors <br /> such as favorable oxygen concentrations and a large surface <br /> area for microbial/contaminant interface could, for instance, <br /> be off set by low nutrient concentrations. Similarly, the <br /> favorable nutrient concentrations within certain soils may be <br /> offset -by the_presence of anoxic pockets of contamination within <br /> an improperly prepared managed treatment cell. While rate- <br />