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,%vow, "Awl BIOREMEDIATION OVERVIEW As a result of considerable research and increased desire to *-• employ alternative remedial technologies by government and industry, both here and abroad, the utilization of hydrocarbon degrading bacteria and fungi to detoxify soil and water has become quite popular. This popularity is certainly well deserved as virtually any anthropogenic compound, including fuel hydrocarbons, solvents, and pesticides may be thoroughly bio- degraded to form non-toxic end products such as carbon dioxide, minerals, and water. In addition to excellent treatment efficiency, biological detoxification processes are most affordable- frequently affording savings of 708, or more, over conventional methods. The science upon which biological detoxification is based is itself founded upon knowledge of the chemical and physical changes which occur in petroleum and petroleum products which have entered the environment as pollutants. While changes in the composition of polluting hydrocarbon mixtures are both chemically and biologically induced, biological (microbial) degradation plays a major role in this process (known as weathering) . Although the complete breakdown of hydrocarbon -' materials into carbon dioxide, water, and minerals is theoreti- cally possible under virtually all circumstances, petroleum hydrocarbons are very complex mixtures containing large numbers of alicyclic, aromatic, and other compounds. Gasoline, for example, may contain 200 such compounds and crude oil many thousands. As each of these compounds possesses distinctive physical and chemical characteristics hydrocarbons differ in their capacity to service as microbial substrates (i.e. be utilized by bacterial and fungi as sources of energy and electrons) within a given environment. In addition, the physical state of the pollutants, environmental temperature, availability of oxygen and nutrients (particularly nitrogen, phosphorus, and iron) significantly impact the rate of pollutant degradation. V Clearly, the fate of fuel hydrocarbon contaminants within a given habitat will depend on the set of abiotic parameters particular to that habitat; with the interactions of multiple factors determining the overall rate of biodegradation. Factors such as favorable oxygen concentrations and a large surface area for microbial/contaminant interface could, for instance, be off set by low nutrient concentrations. Similarly, the favorable nutrient concentrations within certain soils may be offset by the presence of anoxic pockets of contamination within an improperly prepared/managed treatment cell. While rate- limiting factors are well known, their interactions with respect to determining rates of hydrocarbon biodegradation are not; .r ..r