Can we Speed up the Rate of Biodegradation in MTBE-Contaminated Aquifers?

Zoltán Bihari

doi:10.4172/2155-6199.1000e105

ISSN: 2155-6199

Journal of Bioremediation & Biodegradation

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Can we Speed up the Rate of Biodegradation in MTBE-Contaminated Aquifers?

Zoltán Bihari^*
Institute for Biotechnology, Bay Zoltán Foundation for Applied Research, Derkovits fasor 2, H-6726 Szeged, Hungary
Corresponding Author :	Zoltán Bihari Institute for Biotechnology Bay Zoltán Foundation for Applied Research Derkovits fasor 2 H-6726 Szeged, Hungary E-mail: bihari@baybio.hu
Received: November 09, 2011; Accepted: November 11, 2011; Published: November 16, 2011
Citation: Bihari Z (2011) Can we Speed up the Rate of Biodegradation in MTBEContaminated Aquifers? J Bioremed Biodegrad 2:e105. doi:10.4172/2155-6199.1000e105
Copyright: © 2011 Bihari Z. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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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.

However, the challenge of remediating MTBE in groundwater is one of the most difficult subsurface contamination problems. In comparison with other major gasoline components, BTEXs and alkanes, MTBE stands out for its high solubility in water and hydrophilic behavior. These properties facilitate rapid transfer of MTBE into the aqueous phase, fast plume migration, and limit the significance of sorption or volatilization. Thus, a relatively small amount of spilled gasoline can lead to the contamination of an extensive portion of the aquifer. Moreover, MTBE has an apparent resistance to biodegradation. Its estimated half-life in the environment is at least two years, whereas the typical half-life for BTEX compounds is two to three months.

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. Considering that not all sites have proper MTBE-degrading microflora, and the fuel oxygenates are insufficient carbon and energy sources for bacteria, bioaugmentation with a pre-selected, fermented suite, e.g. Methylibium isolates, seems to be necessary.

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. Our findings suggest that the biodegradation can be sped up with a sufficient treatment setup indeed, and a consecutive, slow decomposition of these contaminants may be anticipated. However, the reader is advised to consider our approach as a guideline, not as the Holy Grail, since the site-specific geophysical, geochemical, hydrological and microbiological conditions also have a major impact on bioremediation effectiveness.