Methyl Tert-butyl Ether Degradation Research Articles

Preparation and characterization of Pd doped ceria–ZnO nanocomposite catalyst for methyl tert-butyl ether (MTBE) photodegradation

A series of binary oxide catalysts (ceria–ZnO) were prepared and doped with different amounts of palladium in the range of 0.5%–1.5%. The prepared catalysts were characterized by SEM, TEM, XRD and XPS, as well as by N2 sorptiometry study. The XPS results confirmed the structure of the Pd CeO2−x-ZnO. The photocatalytic activity of these catalysts was evaluated for degradation of MTBE in water. These photocatalyst efficiently degrade a 100ppm aqueous solution of MTBE upon UV irradiation for 5h in the presence of 100mg of each of these photocatalysts. The removal of 99.6% of the MTBE was achieved with the ceria–ZnO catalyst doped with 1% Pd. In addition to the Pd loading, the N2 sorptiometry study introduced other factors that might affect the catalytic efficiency is the catalyst average pore sizes. The photoreaction was determined to be a first order reaction.

Enhanced Biodegradation of Methyl tert-butyl-ether by a Microbial Consortium

The widespread use of Methyl tert-butyl-ether (MTBE) as a gasoline additive has resulted in a higher detection rate of MTBE in groundwater systems. Therefore, the researchers show more concern about the bioremediation of MTBE-impacted aquifers. In this paper, a MTBE-direct-degrading bacterial consortium was enriched (named RS1) and further studied. In order to identify the microbial community of the consortium, 17 and 12 different single strains were isolated from nutrient medium and MSM media (with MTBE as the sole carbon source), respectively. 16S rDNA-based phylogenetic analysis revealed that these diverse bacteria belonged to 14 genera, in which Pseudomonas was dominant. Several strains which can grow with MTBE as the sole carbon and energy source were also identified, such as M1, related to MTBE-degrading Arthrobacter sp. ATCC27778. Furthermore, the appropriate addition of certain single strain in consortium RS1 (M1:RS1=1:2) facilitates MTBE degradation by increasing the quantity of efficient MTBE-degrading bacteria. This work will provide microbial source and theoretical fundament for further bioremediation of MTBE-contaminated aquifers, which has applied potential and environmental importance.

Synthesis of the building block 2-hydroxyisobutyrate from fructose and butyrate by Cupriavidus necator H16

2-Hydroxyisobutyryl-coenzyme A mutase, originally discovered in the context of methyl tert-butyl ether degradation in Aquincola tertiaricarbonis L108, catalyzes the isomerization of 3-hydroxybutyryl-coenzyme A (3-HB-CoA) to 2-hydroxyisobutyryl-CoA. It thus constitutes the basis for a biotechnological route from practically any renewable carbon to 2-hydroxyisobutyrate (2-HIB) via the common metabolite 3-hydroxybutyrate. At first sight, recombinant Cupriavidus necator H16 expressing the mutase seems to be well suited for such a synthesis process, as a strong overflow metabolism via (R)-3-HB-CoA is easily induced in this bacterium possessing the poly-3-hydroxybutyrate metabolism. However, the recently established stereospecificity of the mutase, dominantly preferring the (S)-enantiomer of 3-HB-CoA, calls for a closer investigation of C. necator as potential 2-HIB production strain and raised the question about the strain's potential to yield 2-HIB from substrates directly providing (S)-3-HB-CoA. We compared two mutase-expressing C. necator H16 strains for their capability to synthesize 2-HIB from fructose and butyrate, delivering either (R)- or (S)-3-HB-CoA. Our results indicate that due to the enantiospecificity of the mutase, fructose is a weaker substrate for 2-HIB synthesis than butyrate. Production rates achieved with the PHB-negative strain H16 PHB(-)4 on butyrate were higher than on fructose. Using the wild-type did not significantly improve the production rates as the latter showed a 34-fold and a 5-fold lower 2-HIB synthesis rate compared to H16 PHB(-)4 on fructose and butyrate, respectively. Moreover, both strains showed concomitant excretion of undesired side products, such as pyruvate and 3-hydroxybutyrate, significantly decreasing the 2-HIB yield.

Degradation of methyl tert-butyl ether by catalytic wet air oxidation over Rh/TiO2–CeO2 catalysts

The catalytic wet air oxidation of methyl tert-butyl ether was carried on Rh/TiO2 and Rh/TiO2–CeO2 catalysts. The TiO2–CeO2 (1, 3, 5, 10, and 20wt% CeO2) mixed oxides were prepared by the sol–gel method. The catalysts were characterized by different techniques: surface adsorption–desorption of N2 (BET surface area), X-ray diffraction (XRD), Fourier transform infrared of CO adsorption (FTIR-CO), Fourier transformed infrared of pyridine adsorption (FTIR-pyridine), temperature programmed reduction of H2 (H2-TPR), total organic compound (TOC) and transmission electron microscopy (TEM). A higher specific surface area BET and Lewis acidity sites were obtained on catalysts containing cerium oxide. Small Rh particles <1.8nm were obtained in all catalysts. The Rh catalysts containing cerium oxide showed higher activity than the reference Rh/TiO2 and a maximum in activity at 5wt% loading of CeO2. It is assumed that the acid sites are acting as a tramp for the MTBE molecule increasing the conversion on the Rh particles joined to an additional oxygen supply by cerium oxide redox process. The presence of cerium oxide inhibits the deposit of carbon on the catalyst; the higher cerium oxide concentration, the lower carbon deposited on the Rh surface. The addition of HCl on the initial reaction solution increases the CWAO activity.

Photocatalytic degradation of methyl tert-butyl ether (MTBE) by Fe-TiO2 nanoparticles

Nowadays, since the underground waters are known as the main source for supplying the drinking water, their pollution to the organic contaminants such as methyl tert-butyl ether (MTBE) is a very significant issue. Therefore, in this study, photocatalytic degradation of MTBE was investigated in the aqueous soloution of Fe-TiO2 nanoparticale under UV irradiation (wavelenght 254nm) in a batch reactor. The Fe-TiO2 mixed oxides were prepared by sol–gel impregnation method. The samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and BET specfic surface area. Then, the effect of various operational parameters namely pH, catalyst loading, molar ratio of [H2O2]0/[MTBE]0 and UV light intensity on degradation of aqueous MTBE were evaluated in a batch reactor. The optimal condition to achieve the best degradation for the initial concentration of 75ppm MTBE was found at pH 7, catalyst concentration 2g/L, molar ratio of [H2O2]0/[MTBE]0 4, and UV irradiation 24W. Total degradation of MTBE with initial concentration of 75ppm was reached in optimal condition after 70min. In addition, investigations were also carried out to determine the appropriate kinetics of MTBE degradation using UV/Fe-TiO2/H2O2 process in optimal condition.

Oxidative degradation of alternative gasoline oxygenates in aqueous solution by ultrasonic irradiation: Mechanistic study

Widespread pollution has been associated with gasoline oxygenates of branched ethers methyl tert-butyl ether (MTBE), di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl ether (TAME) which enter groundwater. The contaminated plume develops rapidly and treatment for the removal/destruction of these ethers is difficult when using conventional methods. Degradation of MTBE, with biological methods and advanced oxidation processes, are rather well known; however, fewer studies have been reported for degradation of alternative oxygenates. Degradation of alternative gasoline oxygenates (DIPE, ETBE, and TAME) by ultrasonic irradiation in aqueous oxygen saturation was investigated to elucidate degradation pathways. Detailed degradation mechanisms are proposed for each gasoline oxygenate. The common major degradation pathways are proposed to involve abstraction of α-hydrogen atoms by hydroxyl radicals generated during ultrasound cavitation and low temperature pyrolytic degradation of ETBE and TAME. Even some of the products from β-H abstraction overlap with those from high temperature pyrolysis, the effect of β-H abstraction was not shown clearly from product study because of possible 1,5 H-transfer inside cavitating bubbles. Formation of hydrogen peroxide and organic peroxides was also determined during sonolysis. These data provide a better understanding of the degradation pathways of gasoline oxygenates by sonolysis in aqueous solutions. The approach may also serve as a model for others interested in the details of sonolysis.

Bacterial Acyl-CoA Mutase Specifically Catalyzes Coenzyme B12-dependent Isomerization of 2-Hydroxyisobutyryl-CoA and (S)-3-Hydroxybutyryl-CoA

Coenzyme B(12)-dependent acyl-CoA mutases are radical enzymes catalyzing reversible carbon skeleton rearrangements in carboxylic acids. Here, we describe 2-hydroxyisobutyryl-CoA mutase (HCM) found in the bacterium Aquincola tertiaricarbonis as a novel member of the mutase family. HCM specifically catalyzes the interconversion of 2-hydroxyisobutyryl- and (S)-3-hydroxybutyryl-CoA. Like isobutyryl-CoA mutase, HCM consists of a large substrate- and a small B(12)-binding subunit, HcmA and HcmB, respectively. However, it is thus far the only acyl-CoA mutase showing substrate specificity for hydroxylated carboxylic acids. Complete loss of 2-hydroxyisobutyric acid degradation capacity in hcmA and hcmB knock-out mutants established the central role of HCM in A. tertiaricarbonis for degrading substrates bearing a tert-butyl moiety, such as the fuel oxygenate methyl tert-butyl ether (MTBE) and its metabolites. Sequence analysis revealed several HCM-like enzymes in other bacterial strains not related to MTBE degradation, indicating that HCM may also be involved in other pathways. In all strains, hcmA and hcmB are associated with genes encoding for a putative acyl-CoA synthetase and a MeaB-like chaperone. Activity and substrate specificity of wild-type enzyme and active site mutants HcmA I90V, I90F, and I90Y clearly demonstrated that HCM belongs to a new subfamily of B(12)-dependent acyl-CoA mutases.

Biological‐activated carbon process for removing mtbe from groundwater

Methyl tert‐butyl ether (MTBE) is a common gasoline additive; it has become a worldwide groundwater pollutant. Granular activated carbon (GAC) adsorption treatment is not cost effective for removing MTBE because it is not well adsorbed. Bioaugmentation of enriched MTBE degraders originated from the soil sample of a gasoline station enhanced the performance of the column filled with the MTBE degrader containing spent GAC of the La Mirada remediation site, and made it an effective biological activated carbon (BAC) system producing a high quality effluent that will meet the US EPA's recommended &lt;20 μg/L for source of drinking water. The carbon samples of this system were successfully employed to start up several highly efficient BAC columns in 30 days producing stable effluents under variable treatment conditions with long term effluent MTBE concentration mostly &lt;10 μg/L, more than 99% reduction of 1–1.3 mg /L in the influent. On the basis of the similarity of 16 s rDNA sequence of the PCR‐DGGE procedures, five major bacterial species of stable biochemical properties were found in the BAC effluent samples; one of the five was Bacterium RS58G, whereas the other four were uncultured bacteria. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 512–523, 2013

Anaerobic Methyl tert -Butyl Ether-Degrading Microorganisms Identified in Wastewater Treatment Plant Samples by Stable Isotope Probing

Anaerobic methyl tert-butyl ether (MTBE) degradation potential was investigated in samples from a range of sources. From these 22 experimental variations, only one source (from wastewater treatment plant samples) exhibited MTBE degradation. These microcosms were methanogenic and were subjected to DNA-based stable isotope probing (SIP) targeted to both bacteria and archaea to identify the putative MTBE degraders. For this purpose, DNA was extracted at two time points, subjected to ultracentrifugation, fractioning, and terminal restriction fragment length polymorphism (TRFLP). In addition, bacterial and archaeal 16S rRNA gene clone libraries were constructed. The SIP experiments indicated bacteria in the phyla Firmicutes (family Ruminococcaceae) and Alphaproteobacteria (genus Sphingopyxis) were the dominant MTBE degraders. Previous studies have suggested a role for Firmicutes in anaerobic MTBE degradation; however, the putative MTBE-degrading microorganism in the current study is a novel MTBE-degrading phylotype within this phylum. Two archaeal phylotypes (genera Methanosarcina and Methanocorpusculum) were also enriched in the heavy fractions, and these organisms may be responsible for minor amounts of MTBE degradation or for the uptake of metabolites released from the primary MTBE degraders. Currently, limited information exists on the microorganisms able to degrade MTBE under anaerobic conditions. This work represents the first application of DNA-based SIP to identify anaerobic MTBE-degrading microorganisms in laboratory microcosms and therefore provides a valuable set of data to definitively link identity with anaerobic MTBE degradation.

Mechanistic considerations for the degradation of methyl tert-butyl ether (MTBE) by sonolysis: Effect of argon vs. oxygen saturated solutions

The ultrasonic degradation mechanism of methyl tert-butyl ether (MTBE) in aqueous solution is complex because of the competition between hydroxyl radical attack, pyrolysis, and hydrolysis reactions. A detailed investigation of degradation pathways using sonolysis has been performed using reaction byproducts identification. The observed bi-product distributions are rationalized in terms of hydroxyl radical (OH) mediated processes and pyrolysis. The role of oxygen mediated and pyrolytic pathways were assessed using O2 and Ar saturated solutions. Chemical destruction by sonolysis is often rationalized using hydroxyl radical chemistry. Pyrolysis is unique to this advanced oxidation process, and is important in the case of MTBE because it transfers into the cavitating bubbles. While α-hydrogen abstraction by OH and low temperature pyrolysis was important, it was also shown that β-hydrogen abstraction leads, in some cases, to the same reaction byproducts, which emphasized the importance of α-hydrogen abstraction. High temperature pyrolysis resulted in minor degradation reactions based on the formation of reaction by-products.

Role of back diffusion and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial media

A methyl tert-butyl ether (MTBE) / tert-butyl alcohol (TBA) plume originating from a gasoline spill in late 1994 at Vandenberg Air Force Base (VAFB) persisted for over 15 years within 200 feet of the original spill source. The plume persisted until 2010 despite excavation of the tanks and piping within months after the spill and excavations of additional contaminated sediments from the source area in 2007 and 2008. The probable history of MTBE concentrations along the plume centerline at its source was estimated using a wide variety of available information, including published details about the original spill, excavations and monitoring by VAFB consultants, and our own research data. Two-dimensional reactive transport simulations of MTBE along the plume centerline were conducted for a 20-year period following the spill. These analyses suggest that MTBE diffused from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. The model reproduces the observation that after 2004 TBA was the dominant solute, diffusing back out of the silts into the aquifer and sustaining plume concentrations much longer than would have been the case in the absence of such diffusive exchange. Simulations also suggest that aerobic degradation of MTBE or TBA at the water table in the overlying silt layer significantly affected concentrations of MTBE and TBA by limiting the chemical mass available for back diffusion to the aquifer.

Degradation of methyl tert-butyl ether (MTBE) in water by glow discharge plasma

This study evaluated the ability of the glow discharge plasma (GDP) technique to degrade methyl tert-butyl ether (MTBE) in an aqueous solution. The results showed that a large amount of hydrogen peroxide and highly active *OH free radicals were produced during the treatment. Various experimental parameters including discharge current, initial MTBE concentration and initial pH played significant roles on MTBE degradation. In addition, Fe2+ had a catalytic effect on the degradation of MTBE, which is potentially attributable to the reaction between Fe3+ and the hydrated electron. It was also confirmed that GDP was comparable to electrocatalytic oxidation and high-density plasma and more efficient than photocatalytic degradation techniques. These results suggest that GDP may become a competitive MTBE wastewater treatment technology.

Removal of MTBE by novel Exiguobacterium in seawater

For over three decades, methyl-tert-butyl ether (MTBE) has been used as an additive to either increase the octane number in high and medium grade gasoline in substitution of tetraethyl lead or to raise its oxygen content. However, the fate of MTBE in the environment is a great concern. In this work, biomass of novel toluene degradator Exiguobacterium, isolated from toluene enriched seawater, could utilize MTBE by 72% and produced CO2 and formate during degrada tion. Production of ketone and tert-butyl alchol (TBA) has not been seen by gas chromatogra phy (GC). Degradation of MTBE has been seen in aerobic and anaerobic conditions from 4 to 30 °C. It is interesting that the highest degradation occurred during growth in aerobic and cold condition (4 °C). This suggested that in cold areas Exiguobacterium is a very good candidate to degrade MTBE. Since this novel isolate could tolerate high salt, it is useful for removal of MTBE from seawater.

Electrochemical removal of MTBE from water using the iridium dioxide coated electrode

Methyl tert-butyl ether (MTBE) is always the most likely found compound at the front of a gasoline plume due to its chemical characteristics. In this study, an iridium dioxide (IrO 2) coated electrode was utilized to perform electrochemical removal of MTBE in a lab-scale bath electrolyzer. Depending on the constant-potential controls, electrochemical removal of MTBE can be conducted either through direct oxidation, water electrolysis competition, or indirect oxidation. Direct oxidation mechanism performed MTBE removal up to 39% as electrolyzing below 1.2 V, and the occurrence of water electrolysis competition dropped MTBE removal as increasing the operative potential up to 2.0 V. The continual increase of operative potential above 2.0 V brought about indirect oxidation of MTBE through the chain reactions of the redox mediator S 2O 8 2−/SO 4 2−. The matrix effect of iron enhances electrochemical oxidation of MTBE to provide about 2 times improvement on MTBE removal. The products of MTBE degradation were identified as tert-butyl alcohol (TBA), acetone, and CO 2 by GC/MS, and the distributions of carbon atoms in TBA, acetone, CO 2, and MTBE were found 18, 12, 62, and 8% through the optimum control of electrochemical oxidation.

Synthesis of Poly-3-Hydroxybutyrate Reduces Maintenance Demand In Bacteria Growing Slowly on Methyl Tert-Butyl Ether

Availability of usable energy for biosynthesis and maintenance is a primary condition of life. In the case of microbial degradation of so-called recalcitrant compounds, growth is often prevented due to low energy production rates not exceeding maintenance requirements. However, any process that reduces biomass maintenance under these threshold conditions will increase the chance that productive degradation can occur. We have developed a growth model to explain the surprising observation that the growth of Aquincola tertiaricarbonis L108 and other bacterial strains on the groundwater pollutant methyl tert-butyl ether (MTBE) and its degradation product tert-butyl alcohol is accompanied by the accumulation of poly-3-hydroxybutyrate (PHB). The growth-coupled production of this storage polymer is remarkable since slow growth of all MTBE degraders indicates the difficulty to utilize this substrate. The modified model distinguished an active biomass fraction for which maintenance energy is required and a passive PHB fraction without maintenance requirements. Consequently, the presence of a PHB fraction saved specific maintenance costs and due to PHB accumulation, calculated overall growth yields were increased. More important, the structured model predicted an increased specific growth rate and a decreased minimum substrate concentration for growth Smin. Using experimentally determined parameters, it could be demonstrated that at low maximal growth rates PHB synthesis allowed for growth, whereas in its absence Smin became infinite. Additional reduction of maintenance in dependence on the rate of PHB formation was considered as the stoichiometry of PHB synthesis from MTBE resulted in a gain of energy equivalents. Our model thus showed that coupling of growth on slowly metabolized substrates with PHB synthesis is energetically advantageous. Hence, we propose a not yet considered role of PHB in delivering energy to compensate high maintenance costs while growing on recalcitrant xenobiotics.

Hydraulic performance of a proposed in situ photocatalytic reactor for degradation of MTBE in water

Methyl tert-butyl ether (MTBE) groundwater remediation projects often require a combination of technologies resulting in increasing the project costs. A cost-effective in situ photocatalytic reactor design, Honeycomb II, is proposed and tested for its efficiency in MTBE degradation at various flows. This study is an intermediate phase of the research in developing an in situ photocatalytic reactor for groundwater remediation. It examines the effect of the operating variables: air and water flow and double passages through Honeycomb II, on the MTBE removal. MTBE vaporisation is affected by not only temperature, Henry’s law constant and air flow to volume ratio but also reactor geometry. The column reactor achieved more than 84% MTBE removal after 8 h at flows equivalent to horizontal groundwater velocities slower than 21.2 cm d −1. Despite the contrasting properties between a photocatalytic indicator methylene blue and MTBE, the reactor efficiency in degrading both compounds showed similar responses towards flow (equivalent groundwater velocity and hydraulic residence time (HRT)). The critical HRT for both compounds was approximately 1 d, which corresponded to a velocity of 21.2 cm d −1. A double pass through both new and used catalysts achieved more than 95% MTBE removal after two passes in 48 h. It also verified that the removal efficiency can be estimated via the sequential order of the removal efficiency of one pass obtained in the laboratory. This study reinforces the potential of this reactor design for in situ groundwater remediation.

Characterization and expression of the genes encoding the 2-hydroxyisobutyryl-coa mutase, a key enzyme in methyl Tert-Butylether degradation by Aquincola tertiaricarbonis L108

Characterization and expression of the genes encoding the 2-hydroxyisobutyryl-coa mutase, a key enzyme in methyl Tert-Butylether degradation by Aquincola tertiaricarbonis L108

Aerobic degradation of methyl tert-butyl ether in a closed symbiotic system containing a mixed culture of Chlorella ellipsoidea and Methylibium petroleiphilum PM1

The contamination of groundwater by methyl tert-butyl ether (MTBE) is one of the most serious environmental problems around the world. MTBE degradation in a closed algal–bacterial symbiotic system, containing a mixed culture of Methylibium petroleiphilum PM1 and Chlorella ellipsoidea, was investigated. The algal–bacterial symbiotic system showed increased MTBE degradation. The MTBE-degradation rate in the mixed culture (8.808 ± 0.007 mg l −1 d −1) was higher than that in the pure bacterial culture (5.664 ± 0.017 mg l −1 d −1). The level of dissolved oxygen was also higher in the mixed culture than that in the pure bacterial culture. However, the improved efficiency of MTBE degradation was not in proportional to the biomass of the alga. The optimal ratio of initial cell population of bacteria to algae was 100:1. An immobilized culture of mixed bacteria and algae also showed higher MTBE degradation rate than the immobilized pure bacterial culture. A mixed culture with algae and PM1 immobilized separately in different gel beads showed higher degradation rate (8.496 ± 0.636 mg l −1 d −1) than that obtained with algae and PM1 immobilized in the same gel beads (5.424 ± 0.010 mg l −1 d −1).

Biodegradation of methyl tert-butyl ether by newly identified soil microorganisms in a simple mineral solution

Methyl tert-butyl ether (MTBE) is a widely used fuel ether, which has become a soil and water contaminant. In this study, 12 microbial strains were isolated from gasoline-contaminated soils and selected because of their capacity to grow in MTBE. The strains were identified by 16S/ITS rDNA gene sequencing and screened for their ability to consume MTBE aerobically in a simple mineral solution. Solid phase microoextraction and gas chromatography were used to detect MTBE degradation. High levels of MTBE biodegradation were obtained using resting cells of the bacteria Achromobacter xylosoxidans MCM1/1 (78%), Enterobacter cloacae MCM2/1 (50%), and Ochrobactrum anthropi MCM5/1 (52%) and the fungus Exophiala dermatitidis MCM3/4 (14%). Our phylogenetic analysis clearly shows that bacterial MTBE biodegraders belong to the clade of Proteobacteria. For further insight, MTBE-degrader strains were profiled by denaturing gel gradient electrophoresis (DGGE) of PCR-amplified 16S rRNA gene sequences. This approach could be used to analyse microbial community dynamics in bioremediation processes.

Oxidative Degradation of MTBE by Pyrite-Activated Persulfate: Proposed Reaction Pathways

This bench-scale study investigated the feasibility of activated persulfate (S2O82−) oxidation of methyl tert-butyl ether (MTBE), using pyrite (FeS2) as the source of ferrous ion activators. Under the FeS2-activated S2O82− condition, the sulfate free radical (SO4−•) is the predominant reactive species generated. The oxidation reactions were able to completely degrade MTBE when given sufficient doses of FeS2 and S2O82− and sufficient reaction time (e.g., 3 g FeS2/L and 5 g Na2S2O8/L within 4 h) and exhibited generation and subsequent degradation of the primary MTBE degradation intermediate products including tert-butyl formate, tert-butyl alcohol, methyl acetate, and acetone. The detailed reaction mechanism proposed for a SO4−•-driven oxidation process in this paper indicates that the destruction of MTBE most likely happens through α-hydrogen abstraction via attack of the SO4−• at the intermediate methoxy group.