ETBE as an additive in gasoline: advantages and disadvantages
The most widely used gasoline additive methyl tert-butyl ether (MTBE) has been questioned recently, since frequent detection of this compound in groundwater indicates that it could be a risk to our environment. Consequently, legislative efforts have been made by some local governments to phase out the use of MTBE. Among a number of alternative substitutes, ethyl tert-butyl (ETBE) seems to be the more promised one due to its lower water solubility, suggesting that it could pose less impact to our water supply. However, a thorough understanding of its environmental fate is needed before ETBE is widely accepted as a more environmentally friendly gasoline additive. As a part of this effort, the degradation of MTBE and ETBE as well as their effects on the fate of aromatic gasoline components, i.e. BTEX (benzene, toluene, ethyl-benzene and xylenes) were studied on two soils contaminated with MTBE-blended or ETBE-blended gasoline. During a period of 5 months, the general aerobic degradation of the gasoline and its different additives were monitored by gas chromatography – thermal conductivity detection (GC-TCD) and concentration changes of MTBE and ETBE were monitored with the help of gas chromatography - mass spectrometry (GC-MS). The results of this study showed that the degradation of MTBE, ETBE and BTEX occurred in all the systems, nevertheless MTBE and ETBE degraded far more slowly in contrast with the degradation of BTEX, indicating that MTBE and ETBE are more persistent. When the degradation of MTBE and ETBE were compared, ETBE decreased a little faster than MTBE, implying that ETBE advantages slightly in degradation over MTBE. Concerning the effects of MTBE and ETBE on the fate of BTEX, the results showed that MTBE might enhance whereas ETBE might inhibit the degradation of BTEX though at a lower level. In addition, less degradation of MTBE and ETBE was observed in organic-rich soil in all the cases, probably because that there are more other substrates available for the microorganisms in organic-rich soil.
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