MTBE oxidation byproducts from the treatment of surface waters by ozonation and UV-ozonation

In recent years, there has been considerable concern over the release of methyl tert-butyl ether (MTBE), a gasoline additive, into the aquifers used as potable water sources. MTBE readily dissolves in water and has entered the environment via gasoline spills and leaking storage tanks. In this paper, we investigate ozonation and UV-ozonation for treatment of MTBE in contaminated drinking water sources. We report the test protocol and results of using solid-phase microextraction (SPME) to determine the level of MTBE and its oxidation byproducts in samples drawn from laboratory-scale ozone and UV-ozone reactors being evaluated at a US EPA research facility. Analysis of a prepared MTBE standard indicated a detection limit on the order of 0.1 microgl(-1) with a repeatability of +/-0.4%. Results show that the overall rate of removal of MTBE via UV-ozonation in a relatively turbid surface water (15 ntu) is twice that of ozonation alone. In addition, GC-MS analysis of decomposition products showed that tert-butyl formate (TBF), methyl acetate, butene, acetone, and acetaldehyde were produced by both processes. TBF and butene reach similar maximum yields from the two processes, but are more efficiently degraded by UV-ozonation treatment. This indicates that these treatment processes also degrade these byproducts. In contrast, the remaining byproducts (methyl acetate, acetone, and acetaldehyde) are formed at similar levels during treatment, but are not degraded once formed. These byproducts may be resistant to hydrogen abstraction by hydroxyl radical.     

Semi-volatile and particulate emissions from the combustion of alternative diesel fuels

Motor vehicle emissions are a major anthropogenic source of air pollution and contribute to the deterioration of urban air quality. In this paper, we report results of a laboratory investigation of particle formation from four different alternative diesel fuels, namely, compressed natural gas (CNG), dimethyl ether (DME), biodiesel, and diesel, under fuel-rich conditions in the temperature range of 800-1200 degrees C at pressures of approximately 24 atm. A single pulse shock tube was used to simulate compression ignition (CI) combustion conditions. Gaseous fuels (CNG and DME) were exposed premixed in air while liquid fuels (diesel and biodiesel) were injected using a high-pressure liquid injector. The results of surface analysis using a scanning electron microscope showed that the particles formed from combustion of all four of the above-mentioned fuels had a mean diameter less than 0.1 microm. From results of gravimetric analysis and fuel injection size it was found that under the test conditions described above the relative particulate yields from CNG, DME, biodiesel, and diesel were 0.30%. 0.026%, 0.52%, and 0.51%, respectively. Chemical analysis of particles showed that DME combustion particles had the highest soluble organic fraction (SOF) at 71%, followed by biodiesel (66%), CNG (38%) and diesel (20%). This illustrates that in case of both gaseous and liquid fuels, oxygenated fuels have a higher SOF than non-oxygenated fuels.     

Trace-level measurement of complex combustion effluents and residues using multidimensional gas chromatography-mass spectrometry (MDGC-MS)

The identification and quantitation of non-method-specific target analytes have greater importance with respect to EPA's current combustion strategy. The risk associated with combustion process emissions must now be characterized. EPA has recently released draft guidance on procedures for the collection of emissions data to support and augment site-specific risk assessments (SSRAs) as part of the hazardous waste incineration permitting process. This guidance includes methodology for quantifying total organic (TO) emissions as a function of compound volatility. The ultimate intent is to compare the amount of organic material identified and quantified by target analyte-specific methodologies to organic emissions quantified by the TO methodology. The greater the amount accounted for by the target analyte-specific methodologies, the less uncertainty may be associated with the SSRAs. A limitation of this approach is that the target analyte-specific methodologies do not routinely quantify compounds of low toxicological interest; nor do they target products of incomplete combustion (PICs). Thus, the analysis can miss both toxic and non-toxic compounds. As a result, it is unknown whether the uncharacterized fraction of the TO emission possesses toxic properties. The hypothesis that we propose to test is that organic emissions and organics extracted from particulate matter (PM) are more complex than standard GC-MS-based instrumentation can currently measure. This complexity can affect quantitation for toxic compounds, thereby potentially affecting risk assessments. There is a pressing need to better characterize these organic emissions from hazardous waste incinerators and PM extracts from various other combustion sources. We will demonstrate that multidimensional gas chromatography-mass spectrometry (MDGC-MS) procedures significantly improve chromatographic separation for complex environmental samples. Sequential repetitive heart-cutting MDGC, with coupled mass spectrometry will be shown to be a complete analysis technique. The ability of this technique to disengage components from complex mixtures taken from hazardous and municipal waste incinerators will be shown.