Natural bioremediation, the use of indigenous microorganisms to degrade hazardous substances within aquifers without engineered stimulation, shows great promise as a cost-effective approach to hydrocarbon plume management. This technique requires thorough site characterization and monitoring to verify that the natural attenuation processes continue to provide adequate risk protection. Significant progress has been made towards understanding the hydrogeochemical and microbiological factors that influence the feasibility of natural bioremediation of fuel-contaminated aquifers in North America and Europe. Nevertheless, this experience should be extrapolated with care to contaminated sites in Brazil, where gasoline contains about 22% of ethanol. Preliminary laboratory studies show that ethanol can enhance the solubilization of BTX in water, and it might exert diauxic effects during BTX biodegradation. A better understanding of the biochemical, physical, and ecological effects of ethanol is needed to develop a rational basis for the selection, mathematical modeling, and monitoring of appropriate natural bioremediation systems in Brazil.

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