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8ioovr - Page 2 <br /> multiple factors determining the overall rate of degra- <br /> dation. Factors such as favorable oxygen concentrations <br /> and a large surface area for microbial -contaminant <br /> interface could, for instance, be offset by low nutrient <br /> concentrations . Similarly, the favorable nutrient <br /> concentrations within certain soils may be offset by the <br /> presence of anoxic pockets of contamination within an <br /> improperly prepared or managed treatment cell . While <br /> rate-limiting factors are well known, their interactions <br /> with respect to determining rates at which hydrocarbons are <br /> biodegraded are not; therefore, it is of significant value <br /> to those now doing this work to have been given the <br /> opportunity to develop and implement improved treatment <br /> protocols . Actual experiences under field conditions <br /> have lead to a number of meaningful improvements that have <br /> resulted in the ability to bioremediate a wider range of <br /> contaminants more rapidly and less expensively than in the <br /> past . Much information has yet to be obtained, however, <br /> and efforts continue to acquire additional data on a number <br /> of subjects , including the following: <br /> Physical State of the Petroleum Contaminant <br /> The surface area available for microbial "attack" has a <br /> marked influence on the fate of the petroleum <br /> contaminant(s) . Contaminants may be present as a thin <br /> surface film, a stable oil-water emulsion, be entrained <br /> within sediments, or associated with suspended particles . <br /> Hydrocarbon utilizing organisms typically position <br /> themselves at the hydrocarbon-water interface, a location <br /> that assures the maximum access to both the hydrocarbon <br /> substrate and water soluble mineral nutrients . Many such <br /> microbes also produce surface active agents that emulsify <br /> oil , thereby, increasing surface area. This increased <br /> surface area also provides additional sites for microbial <br /> development and contaminant utilization. <br /> Temperature <br /> As with other microbial activities , the rate at which <br /> petroleum products are degraded is strongly temperature <br /> dependent. Mesophilic bacteria (those thriving at moderate <br /> temperatures) are generally considered the most prolific <br /> degraders . <br /> Oxygen <br /> In their initial attack on hydrocarbons such as petroleum <br />