Oxygenated gasoline biodeterioration and its control in laboratory microcosms

An array of microcosms containing California Air Resources Board (CARB)-compliant, oxygenated 87-octane gasoline over nutrient-amended water was monitored over a 7-month period. The array included triplicate microcosms of each of four conditions: unchallenged control, challenged control and challenged with two different antimicrobial agent treatments. After 7 months, significant fuel chemistry and physical changes occurred in all the microcosms that were challenged with an uncharacterized microbial inoculum drawn from a contaminated fuel system. Most noteworthy was the average 67% loss of oxygenates and the marked shift from isoparaffins and normal paraffins to alkyl isoparaffins, coupled with a shift to higher carbon numbered compounds. Moreover, in the untreated, challenged control microcosms, mild-steel corrosion rates were approximately double, and filter-plugging rates were greater than four times those observed in the unchallenged control microcosms. Both antimicrobial agent treatments attenuated the physical and chemical changes. There were no significant physical or chemical changes in the unchallenged control microcosms, indicating that physical weathering during the test period played only a minor role in the changes.