Gasoline is able to pollute the environment through leaks in underground storage tanks and spills at refineries, tank farms, terminals and commercial filling stations. BTEX compounds (Benzene, Toluene, Ethylbenzene, and Xylene) are common components of gasoline, and are used as raw
materials in the production of pesticides, plastics, and synthetic fibers. With the potential for these toxics to enter and disrupt anaerobic treatment plant operations, it is important that their effect on methanogenic bacteria be evaluated. The objective of this research was to assess the
effects of gasoline and BTEX compounds at high concentration levels on methanogenic bacteria. Another objective was to assess the effects of the BTEX combinations as they compare to gasoline. The following toxicant combinations were studied: Unleaded gasoline (100%); BTEX (25%
of each); Ethylbenzene/Xylene (50% each), Benzene/Xylene (50% each). This experiment showed that there was negligible difference between toxicant exposure at 2000 mg/L and 4000 mg/L for a given toxicant. The results also showed that the different BTEX combinations
had essentially the same effect on the methanogens regardless of the concentration. In acclimation studies, it was observed that there was negligible acclimation to the toxicants. The gas production recovery period was much slower and not as consistent between the various toxicant combinations
as in the first exposure. The toxic effect of gasoline was less than that of the BTEX combinations. This experiment revealed that methanogens could withstand an initial high concentration toxic slug dose of BTEX and gasoline, and recover their normal gas production. However, the second toxic
exposure indicated that there might be latent physiological damage to the methanogens from high toxic exposure that was not readily apparent from the first exposure data.
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