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Fuel oxygenates such as methyl -butyl ether (MTBE), ethyl -butyl ether (ETBE) and -amyl methyl ether (TAME) today are among the most frequently detected volatile organic compounds in groundwater and, thus, they have become priority groundwater pollutants over the last decade. Thus, their quantitative determination at very low concentrations is routinely required. Methods for this purpose and for compound-specific isotope analysis (CSIA), especially of MTBE and its key degradation intermediate -butyl alcohol (TBA) in ground and surface water are reviewed in this work. For quantitative determination, fuel oxygenates are almost exclusively analyzed by gas chromatography, mainly with mass spectrometric detection due to selectivity and sensitivity requirements. Sample introduction/enrichment based on membrane introduction mass spectrometry, direct aqueous injection, headspace analysis, purge trap, solid-phase microextraction (direct immersion or headspace) and other microextraction approaches such as solid phase dynamic extraction and liquid-phase microextraction are discussed. Furthermore, the use of ion mobility spectrometry for the determination of fuel oxygenates and related compounds is reviewed. Specific advantages and disadvantages of these techniques are compared and criteria for the choice of an appropriate method are given. The application of CSIA nowadays can be used to determine the isotopic composition of MTBE and related compounds in the low μgL range and thus will become an invaluable tool in the characterization of the environmental fate of such pollutants. Therefore, an overview of analytical aspects of this technique is included here.

In the last decade, it became increasingly evident that the fuel oxygenate methyl tertiary butyl ether (MTBE) is nearly ubiquitous in the worldwide environment. The detection frequency of MTBE rivals other volatile organic compounds (VOCs) that have been produced and used for a much longer period of time. Its mere presence in water bodies used as drinking water reservoirs (rivers, lakes, or groundwater tables) has aroused concern about its potential sources, persistence, or possible adverse effects (aesthetic or toxic implications) for end-users and aquatic life. The purpose of this chapter is to provide an updated overview of the current environmental concentrations, the occurrence of the pollutant in the different aquatic compartments, the relevance of diffuse and point sources, and the different alternatives for remediation of MTBE contaminated sites.

The National Water-Quality Assessment Program of the United States (US) Geological Survey conducted surveys of the occurrence of methyl tert-butyl ether (MTBE) and other fuel oxygenates in ground water used as a source of drinking water and in drinking water in the United States (USA) from 1993 to 2001. MTBE was detected in about 4% of samples of source water collected from private and public supply wells located throughout the USA and in about 9% of samples of drinking water from 12 Northeastern states. Other fuel oxygenates were detected very infrequently. Few samples of source water or drinking water had concentrations of MTBE greater than the US Environmental Protection Agency drinking-water advisory or state-level benchmarks.

As many as five million people in the USA may potentially be exposed to MTBE through source water derived from ground water. Public wells appear to be more vulnerable to contamination by MTBE than private wells, and more people in the USA rely on drinking water from public wells than private wells. Because of the uncertainty in the long-term health effects of MTBE in drinking water, it is important to monitor for MTBE in ground water used as a source of drinking water, especially ground water from public wells. Better understanding of the sources of MTBE to ground water, the intrinsic susceptibility of aquifers to contamination, and the behavior and fate of MTBE in ground water would aid in adequately protecting ground-water resources from contamination by MTBE.

Ethers, such as methyl -butyl ether (MTBE) and ethyl -butyl ether (ETBE) are added to gasoline to enhance the octane index and to improve the air emission quality. MTBE, especially, has been found in several aquifers as a contaminant after accidental releases of ether-supplemented gasoline. The presence of these ethers in groundwater is considered to be the consequence of their persistence in the environment, due to their high water solubility and poor biodegradability. Herein, we will summarize the results of studies that have been carried out to investigate the actual capacity of indigenous microflora sampled from a variety of contaminated sites under different conditions (oxic and anoxic), and present the results of a survey to evaluate both the biodegradation capacity of ethers and -butyl alcohol (TBA) and the presence of catabolic genes that have been shown to be involved in fuel-ether degradation pathways. The aim of this study was to assess the correlation between the indigenous biodegradation capacity and the presence of these specific genes, so as to provide a basis for the use of genetic tools, such as microarrays, for the management of this environmental issue.

Isotope fractionation of fuel oxygenates has been employed as an indicator for monitoring in-situ degradation in the field. For quantification of in-situ degradation, the Rayleigh concept can be applied. The selection of an appropriate isotope enrichment factor (ε) that is representative of the biogeochemical conditions governing the microbial degradation process in the field is crucial for quantification. Therefore, the biogeochemistry of contaminated aquifers has to be taken into account in the development of isotope strategies in assessment and monitoring operations. In addition, controlled microcosms studies are needed to determine the extent of isotope fractionation under different conditions. The simultaneous analysis of carbon and hydrogen isotope composition of fuel oxygenates in a two-dimensional isotope approach opens opportunities for analysis of the predominant degradation process in the field and can be used to select an appropriate fractionation factor. In this contribution we summarise the concept of isotope fractionation of fuel oxygenates to assess in-situ degradation with respect to analytical techniques, recent progress on isotope fractionation in laboratory studies, the concept of two-dimensional isotope analysis, and experience from field studies.

Based on a physical-chemical-biological database, the behavior of MTBE and CAH (chlorinated aliphatic hydrocarbons) in the subsoil is described and compared. In contrast to MTBE, CAH can form independent phase bodies that can infiltrate deep into aquifers. Due to its striking higher solubility, MTBE spreads much faster in groundwater. The longest CAH plume recorded in literature so far amounts to 10 000 km. The longest reported MTBE plume reaches 1900m. Interpreting the available worldwide data, spreading of MTBE groundwater contaminations leads plume lengths that fall rather into the category of the BTEX as into the class of CAH. A substantial reason for comparison with the lower CAH plume expansions might consist of the fact that MTBE plumes—due to high water solubility and thereby the connected fast development of the MTBE source transfer—progress comparatively fast into the stable and/or regressive status of the plume development. Beyond this, MTBE infiltrates as subordinated portion of gasolines (predominantly 1–3 wt% in regular grade fuel and/or premium fuel), in comparatively low quantities into the subsoil, so that these comparatively low quantities do not possess large source strengths over longer periods. Only spills with very large gasoline quantities may longer MTBE plumes develop under certain conditions.

MTBE contamination in groundwater is an increasing environmental problem and treatment costs using conventional remediation technologies will increase if water is contaminated by MTBE. Generally, natural attenuation (NA) and enhanced natural attenuation (ENA) are possible low-cost alternatives to conventional techniques. Since biodegradation of MTBE is comparably slow under field conditions and often limited by the environmental conditions, optimizing these conditions within the framework of an ENA approach can be a useful means to enhance the natural degradation process.

One potential limitation of the ENA approach is that MTBE is mineralized by only a few specialized bacteria and mainly under aerobic conditions. Co-metabolic biotransformation of MTBE by aerobic, alkane-degrading bacteria has also been reported. Although several studies have demonstrated anaerobic biodegradation, anaerobic MTBE degradation rates are very low compared to aerobic rates.

Introducing a source of pure oxygen into a MTBE-contaminated aquifer has been shown to be a successful means to enhance biodegradation efficiency. At higher organic loadings, H2O2 can be used as an additional oxygen source. There is also some evidence that nitrate can be used as an alternative electron acceptor. Recent investigations have also demonstrated enhanced MTBE degradation under methanogenic conditions generated by the dosing of electron donors such as alcohols.

For the field application of ENA measures, different technological solutions such as direct gas, slurry or liquid injections have been developed during the past few years.

Because of organoleptic issues and potential health risks, groundwater containing methyl -butyl ether (MTBE) and -butyl alcohol (TBA) is of concern. Regulatory limits exist in several countries and remediation of MTBE/TBA is needed. Although an in situ MTBE/TBA-biodegradation capacity is not omnipresent, an increasing number of MTBE/TBA-degrading axenic strains and consortia are being isolated. Bioremediation,in situ or ex-situ in bioreactors, is considered an interesting and cost-effective option. Degradation may occur under in situ conditions (natural attenuation), in other cases additives may be required to increase the activity of naturally present MTBE/TBA degraders (biostimulation). At contaminated sites where an indigenous MTBE/TBA- degradation potential is lacking, bioremediation is feasible upon addition of ex situ cultivated MTBE/TBA-degraders (bioaugmentation).

This chapter explores the role of abiotic reactions such as acid catalysis (hydrolysis) as well as the adsorption of methyl -butyl ether (MTBE) and other fuel oxygenates in environmental issues as the remediation of these substances is notoriously difficult. First of all, these methods are briefly classified with other abiotic technologies. The suitability of hydrolysis and adsorption for the remediation of water contaminated by fuel oxygenates is then discussed in detail, with information being provided about the principle of the reactions, potential catalysts and sorbents, limitations of the reactions, and practical implications. To conclude, the possible application of hydrolysis and adsorption in combination with other remediation techniques is also examined.

The use of methyl -butyl ether (MTBE) has resulted in serious contamination of many groundwater supplies worldwide. Literature investigations were performed with the aim of improving knowledge on the use of bioreactors for removal of MTBE from contaminated groundwater. Among the important findings were: membrane bioreactors and fluidized bed reactors had the highest volumetric removal rates of all reactors studied, in the order of 1000 mg/(l d); competition for oxygen, nutrients and occupancy between MTBE degraders and oxidisers of co-contaminants such as, ammonium and the group of benzene, toluene, ethylbenzene and xylenes, may reduce the removal rates of MTBE, or prevent its removal in reactors. With mathematical modelling, the long startup time required for some MTBE degrading reactors could be predicted. Long startup times of up to 200 days were due to the low maximum growth rate of the MTBE degraders, in the order of 0.1 d or less, at 25 ◦C. However, despite this, high volumetric MTBE removal rates were found to be possible after the startup period when the biomass concentration reached a steady state.