Methyl Tert-butyl Ether Removal Research Articles

Biodegradation of methyl tert-butyl ether under various substrate conditions.

Five aerobic enrichments efficient at degrading methyl tert-butyl ether (MTBE) under different substrate conditions were developed in well-mixed reactors containing a polyethlene porous pot for biomass retention. The five substrate conditions were as follows: MTBE alone; MTBE and diethyl ether (DEE); MTBE and diisopropyl ether (DIPE); MTBE and ethanol (EtOH); and MTBE with benzene, toluene, ethylbenzene, and xylene (BTEX). All five cultures demonstrated greater than 99.9% removal of MTBE. Addition of alternative substrate was found to have no effect on the performance of the reactors. The bacterial communities of the reactors were monitored periodically by denaturing gradient gel electrophoresis (DGGE) to determine when homeostasis was achieved. Phylogenetic analysis of the excised DGGE bands was done in order to compare the bacterial community compositions of the reactors. All cultures were found to be mixed cultures, and each enrichment was shown to have a unique composition. A majority of the bands in all reactors represented a group of organisms belonging to the Cytophaga-Flexibacter-Bacterioides (C-F-B) Phylum of bacteria. This was also the only group found in all of the reactors. This study demonstrates that MTBE can be degraded effectively in bioreactors under several substrate conditions and gives insight into the microorganisms potentially involved in the process.

Hydrophobic hollow fiber membranes for treating MTBE-contaminated water.

Soluble contaminants with low Henry's constant, such as methyl tert-butyl ether (MTBE), require innovative solutions for water treatment. Given the increased frequency at which MTBE is detected at contaminated sites, the development of new technologies is of considerable relevance. Hydrophobic hollow fiber membranes (HFM), used in industrial and medical applications, have interesting physicochemical properties that make them particularly suitable to deal with these contaminants. The hydrophobicity of the fiber maintains adequate separation between aqueous and gaseous phases, permitting an efficient separation of volatile and semivolatile compounds from water to gas. The hollow nature of the fiber and its high porosity permit high rates of mass transfer across the membrane. The mass transfer process can be accelerated using pervaporation and by increasing the solution's temperature to increase the Henry's constant and the overall mass transfer coefficient. In these studies, we evaluate the removal efficiency of MTBE from water using a commercial HFM module and develop the corresponding dimensionless mass transfer correlations necessary for the design of industrial-scale systems. We found that the Lévêque correlation for the tube-side mass transfer coefficient is in general applicable for MTBE pervaporation through a hydrophobic HFM. MTBE removal is a strong function of membrane length, water flowrate, and solution temperature but is almost independent of gas-phase parameters.

Aerobic biodegradation of an oxygenates mixture: ETBE, MTBE and TAME in an upflow fixed-bed reactor

Aerobic degradation of ethyl tert-butyl ether (ETBE), Methyl tert-butyl ether (MTBE) and tert-amyl methyl ether (TAME), as tertiary-substrates, was studied in a continuous upflow fixed-bed reactor (UFBR) using an external oxygenator and sintered glass rings as biomass carriers. The UFBR has been shown to be an effective system for the simultaneous and continuous long-term degradation of the three-oxygenates mixture as sole source of carbon and energy. Therefore, the oxygenates feed concentration must be related in conjunction with the hydraulic retention time “HRT” and vice versa. The permissible feed concentration of both MTBE and TAME to achieve more than 99% removal efficiency is about 80 mg L −1 at a constant HRT of 24 h. The same performance can be obtained if the HRT kept at a value equal or above to 15 h for a feed concentration of about 80 mg L −1 of both MTBE and TAME. However, the ETBE removal efficiency was always greater than 99% whatever the ETBE concentration feed (between 10 and 100 mg L −1 at a constant HRT of 24 h) and the HRT (between 24 and 13 h at a constant concentration feed of about 80 mg L −1) tested in this study. The highest ETBE, MTBE and TAME removal rates achieved throughout the UFBR runs, with efficiency better than 99%, were 140±5, 132±2 and 135±2 mg L −1 d −1, respectively. No metabolic intermediates including tert-butyl alcohol (TBA), tert-butyl formate (TBF) and tert-amyl alcohol (TAA) were detected in the effluent during all the reactor runs. Furthermore, based on the chemical oxygen demand balance, all the removed oxygenates were completely metabolized. The results of this study suggest that the higher resistance to biodegradation exhibited by the MTBE and the TAME is probably due to the steric hindrance for the attacking enzyme(s); and the major limiting step to the oxygenate degradation maybe the accessibility and the cleavage of the ether bond, but not the assimilation of their major metabolites such as TBA, TBF and TAA. These results were concomitant with the batch tests using the reactor's immobilized biomass as inoculum.

Removal of methyl tert-butyl ether from water by pervaporation: bench- and pilot-scale evaluations.

The ability of pervaporation to remove methyl tert-butyl ether (MTBE) from water was evaluated at bench and pilot scales. Process parameters studied included flow rate, temperature, MTBE concentration, membrane module type, and permeate pressure. Pervaporation performance was assessed based on the calculated mass transport coefficient of MTBE, the single-pass removal of MTBE (only at the pilot scale), and the fluxes of water and MTBE. The observations for MTBE are compared to results for toluene and 1,1,1-trichloroethane, compounds for which removal by pervaporation has been demonstrated. MTBE removal and mass transfer coefficients were lower than for toluene and trichloroethane. However, MTBE removal efficiency improved significantly with increasing process temperatures from 40 to 80 degrees C. With one of the pilot-scale systems, MTBE removal efficiency approached that of the other VOCs. The observed response of pervaporation performance to temperature was attributed to the strong effect of temperature on the Henry's law constant of MTBE.

Kinetics of methyl tert-butyl ether degradation and by-product formation during UV/hydrogen peroxide water treatment

Methyl tert-butyl ether (MTBE) was removed from aqueous solution by exposure to a low-pressure mercury lamp in the presence of hydrogen peroxide in a recirculating batch reactor. Dark and UV-only tests were conducted to separate the effects of MTBE loss to system components and photolytic processes. Experiments were conducted at initial peroxide:MTBE molar ratios of 4:1, 7:1 and 15:1. Benzene was added in some experiments to estimate the hydroxyl radical concentration. The concentrations of MTBE, benzene and by-products were measured over a 120-min period using a purge-and-trap GC-MS method. UV/H 2O 2 treatment resulted in >99.9% removal of MTBE with the major purgable by-product identified as tert-butyl formate (TBF). The second order rate constant for the degradation of MTBE from the hydroxyl radical was estimated to be 3.9 (±0.73)×10 9 M −1s −1. The second order rate constant for the reaction of TBF with the hydroxyl radical was estimated to be 1.2 (±0.40)×10 9 M −1s −1. The yield for the formation of TBF from the reaction of MTBE and the hydroxyl radical was 0.28±0.032. After 1 h of treatment the TBF remaining exceeded the remaining MTBE by as much as a factor of 35; this finding is important given the unknown human health impacts of TBF.

Removal of MTBE and Other Organic Contaminants from Water by Sorption to High Silica Zeolites

Select zeolites with high SiO2/Al2O3 ratios were shown to effectively remove methyl tert-butyl ether (MTBE), chloroform, and trichloroethylene (TCE) from water. In laboratory studies using batch sorption equilibria, high Si large-port mordenite and ZSM-5 (silicalite) were found to have sorption properties for MTBE and TCE superior to activated carbon. For example, at an equilibrium solution concentration of 100 μg/L, high Si mordenite retained 8−12× more MTBE than either of two powdered activated carbons used as reference sorbents. Sorption results also highlight the importance of pore size and SiO2/Al2O3 ratio on contaminant removal efficiencies by zeolites.

Biodegradation of Recalictrant Components of Organic Mixtures

Biodegradation of two recalcitrant compounds, dichloromethane and methyl tert-butyl ether was investigated individually and in combination with toluene and benzene. A vapor phase biofilter operating at an air flux of 1 m3/m2 min and an empty bed residence time of 1 minute was used as the reaction system. Inlet recalcitrant contaminant concentrations were typically 35 ppm on a volume basis while the aromatic compound concentrations were varied from 8 ppm to 150 ppm. Dichloromethane removals were not impacted by the introduction of toluene. However, a rapid decrease in methyl tert-butyl ether removal resulted from the initial introduction of toluene. Complete removal of both methyl tert-butyl ether and toluene was achieved within a week of operation.

Biodegradation of methyl tert-butyl ether by a bacterial pure culture.

A bacterial strain, PM1, which is able to utilize methyl tert-butyl ether (MTBE) as its sole carbon and energy source, was isolated from a mixed microbial consortium in a compost biofilter capable of degrading MTBE. Initial linear rates of MTBE degradation by 2 x 10(6) cells ml(-1) were 0.07, 1.17, and 3.56 microg ml(-1) h(-1) for initial concentrations of 5, 50, and 500 microg MTBE ml(-1), respectively. When incubated with 20 microg of uniformly labeled [(14)C]MTBE ml(-1), strain PM1 converted 46% to (14)CO(2) and 19% to (14)C-labeled cells within 120 h. This yield is consistent with the measurement of protein accumulation at different MTBE concentrations from which was estimated a biomass yield of 0.18 mg of cells mg MTBE(-1). Strain PM1 was inoculated into sediment core material collected from a contaminated groundwater plume at Port Hueneme, California, in which there was no evidence of MTBE degradation. Strain PM1 readily degraded 20 microg of MTBE ml(-1) added to the core material. The rate of MTBE removal increased with additional inputs of 20 microg of MTBE ml(-1). These results suggest that PM1 has potential for use in the remediation of MTBE-contaminated environments.

California MTBE ban hits chemical makers

The decision on March 25 by California's governor to phase out use of the fuel additive methyl tert -butyl ether (MTBE) in gasoline sold in the state has sweeping, and mostly negative, implications for chemical producers. Citing a risk to groundwater from the additive's continued use, Gov. Gray Davis issued an executive order requiring total removal of MTBE from California gasoline by the end of 2002. At the same time, Davis said the state will seek a waiver from the 1990 Clean Air Act Amendments that require California and other states with air pollution problems to add oxygenated compounds to their fuels. Davis and California gasoline suppliers want the waiver because without it, the state will have to replace MTBE with another oxygenate, and currently the only practical alternative is ethanol. Kenneth T. Derr, chairman of Chevron Corp., a leading California refiner, told a press conference last week that Chevron can supply clean-burning gasoline without the ...

Review of MTBE Biodegradation and Bioremediation

Conclusive evidence of methyl tert-butyl ether (MTBE) biotransformation and complete mineralization under aerobic conditions in environmental samples and enrichment cultures is reviewed, in addition to increasing evidence of MTBE biotransformation under anaerobic conditions. The metabolic pathway of MTBE appears to have two key intermediates, tert-butyl alcohol (TBA) and 2-hydroxy isobutyric acid (HIBA). The first enzyme in MTBE biodegradation has been identified as either a cytochrome P450 or a nonhemic monooxygenase in different isolates. Mixed and pure cultures of microorganisms have utilized MTBE as a sole carbon and energy source. Cometabolism of MTBE with n-alkanes at rates of 3.9 to 52 nmol/min/mg protein has been documented. The presence of co-contaminants such as BTEX has either not affected or seemed to limit MTBE biodegradation. Some studies of MTBE natural attenuation have attributed mass loss to biodegradation, while others have attributed mass loss to dilution and dispersion. Recent advances in the assessment of MTBE biodegradation have indicated the potential for natural anaerobic transformation of MTBE. In situ bioremediation of MTBE has been enhanced by adding air or oxygen, or by adding microorganisms and air or oxygen. Bioreactors have attained significant removal of MTBE from MTBE-contaminated influent. Despite historical concerns about the biodegradability of MTBE, several biological methods can now be used for MTBE remediation.