Can we Speed up the Rate of Biodegradation
Methyl tertiary butyl ether (MTBE), a widely used fuel oxygenate, has been added to gasoline over the past decades to increase the octane index, prevent engine knocking and reduce air pollution from vehicle emissions. Although its application is banned or restricted by now, the frequent release of MTBE-blended gasoline from leaking underground storage tanks, pipelines, surface spills etc. have already resulted in a huge number of polluted sites, and MTBE became one of the most commonly detected groundwater contaminants worldwide. Considering that the US EPA currently lists this compound as a possible human carcinogen, 20 ppb of which can make drinking water supplies undrinkable due to its offensive taste and odor, the urgent need for its remediation is obvious.
Although many physical, chemical and biological remediation methods have been tested for MTBE clean-up, based on our experiences the in situ bioremediation offers the best hope for addressing the extent of MTBE contamination. Nevertheless, natural attenuation processes unequivocally have to be accelerated using on-site biostimulation and bioaugmentation techniques. In order to sustain the desired rate of biodegradation in the aquifer, sufficient quantities of nutrients such as inorganic nitrogen and phosphate have to be supplemented.
Along with the available nutrients, oxygen is the primary growth-limiting factor for gasoline degrading bacteria. The slurry of the oxygen releasing compound, magnesium peroxide was successfully applied in field studies when it was injected into direct-push borings using pressure activated probes. Nutrients and magnesium peroxide placed in the saturated zone had positive effect on the indigenous flora, which manifested in quick depletion of gasoline-range alkanes and BTEXs, but the same cannot be definitely said for MTBE.
When exogenous bacteria, nutrients and magnesium peroxide were applied in situ, significantly higher biodegradation rates were achieved, which were in good correlation with the values observed in laboratory microcosm tests. Furthermore, the analytical and PCR-DGGE data could reveal that the proliferation of the suitable exogenous strain coexisted with rapid MTBE degradation, which occurred in line with the depletion of other gasoline compounds.
Journal of Bioremediation & Biodegradation
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