Effect of BTEX on Degradation of MTBE and TBA by Mixed Bacterial Consortium

Methyl tert-butyl ether (MTBE) contamination in groundwater often coexists with benzene, toluene, ethylbenzene, and xylene (BTEX) near the source of the plume. Tertiary butyl alcohol (TBA) is a prevalent intermediate of MTBE degradation. Therefore, there is a significant potential for interference of MTBE and TBA degradation by the presence of BTEX whether treatment is in situ or ex situ. In this study, the effect of BTEX on the degradation of MTBE and TBA was examined using a mixed bacterial culture enriched on MTBE and BTEX. In batch studies, the presence of BTEX did not have a significant effect on MTBE degradation, but did have a slight effect on TBA degradation. Under continuous flow conditions, all compounds degraded simultaneously. Normalizing rates to the MTBE loading to the reactor indicates that BTEX may assist in the development of the biomass for TBA and overall MTBE degradation. Using denaturing gradient gel electrophoresis, several diverse organisms were identified, two of which showed very high similarity with PM1, a known MTBE degrader.     

Biodegradation Kinetics of MTBE in Laboratory Batch and Continuous Flow Reactors

Methyl tert-butyl ether (MTBE) biodegradation was investigated using a continuously stirred tank reactor with biomass retention (porous pot reactor) operated under aerobic conditions. MTBE was fed to the reactor at an influent concentration of 150 mg/L (1.70 mM). An identical reactor was operated as a killed control under the same conditions. Operation of these reactors demonstrated that removal of MTBE was biological and suggests that biomass retention is critical for effective degradation. MTBE removal exceeded 99.99% when the volatile suspended solids concentration in the reactor was above 600 mg/L. Batch experiments conducted using mixed liquor from the porous pot reactor indicated that the individual rates of biodegradation of MTBE and tert-butyl alcohol (TBA) increase with increasing initial concentration. When batch tests were later repeated, the MTBE degradation rates were found to have increased while the TBA degradation rates remained constant. All batch tests confirmed that the degradation rate of TBA governed the overall degradation rate (degradation rate of both MTBE and TBA). The presence of TBA at lower concentrations did not affect the rate of MTBE degradation; however, higher concentrations of TBA did reduce the rate of MTBE biodegradation.     

Performance and Cost Evaluations of Synthetic Resin Technology for the Removal of Methyl Tert-Butyl Ether from Drinking Water

This study investigated the performance of synthetic carbonaceous resin technology for the treatment of methyl tert-butyl ether (MTBE) contaminated waters using rapid small-scale column tests (RSSCTs). The RSSCTs were conducted using Ambersorb 563 carbonaceous resin (Rohm and Haas Corp., Philadelphia, Pa.) under multisolute conditions of typical municipal water source, soluble fuel components or additive/by-product, and MTBE. Specifically, one RSSCT column run was conducted with groundwater from Arcadia Wellfield, Santa Monica, Calif., with tert-butyl alcohol (TBA) and MTBE, while the other RSSCT column run was performed with surface water from Lake Perris, Calif., with benzene, toluene, p-xylene (BTX) and MTBE. The results obtained were compared to RSSCTs performed using PCB coconut shell granulated activated carbon (GAC) (Calgon Corp., Philadelphia, Pa.). The adsorbent comparisons indicate that the performance (as characterized by indicators such as carbon usage rates or integrated column capacity) of the Ambersorb 563 synthetic resin in multisolute conditions of TBA or BTEX with MTBE in typical municipal water source is significantly superior to that of the coconut shell PCB GAC. Cost comparison for the coconut shell GAC and synthetic resin system was also performed. Under multisolute conditions of typical municipal water source, flow rates, and influent MTBE concentrations, the cost of the resin system, for most of the scenarios evaluated, is demonstrated to be significantly lower than the complementary GAC system under the costing procedure used. Further, when soluble fuel components such as BTX or fuel additives/byproducts such as TBA were present along with MTBE, the predicted higher adsorbent usage rates for the coconut shell GAC were translated into significantly higher treatment costs relative to the synthetic carbonaceous resin system.     

Adsorption Isotherms for Methyl Tert-Butyl Ether and Other Fuel Oxygenates on Two Bituminous-Coal Activated Carbons

Methyl tert-butyl ether (MTBE) is frequently used as a gasoline additive to reduce carbon monoxide emissions from vehicles. Alternative fuel oxygenates are also used separately or in conjunction with MTBE including ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), tert-butyl alcohol (TBA), and ethanol (EtOH). Granular activated carbon (GAC) sorption is a proven technology for the removal of the ether oxygenates while the alcohols are not well adsorbed. In this research, Freundlich and Langmuir isotherms coefficients were developed based on linearized forms of the models for MTBE, ETBE, TAME, and DIPE (R2>0.97) on two common bituminous coal GACs:Calgon F400 and F600. No significant adsorption of either TBA or EtOH was observed on these carbons. The relative capacities on both Calgon F400 and F600 were DIPE>TAME>ETBE>MTBE>TBA, EtOH.     

Co-Occurrence of MTBE and Benzene, Toluene, Ethylbenzene, and Xylene Compounds at Marinas in Large Reservoir

Methyl tert-butyl ether (MTBE) is released into the environment as one of some gasoline components, not as a pure compound. Benzene, toluene, ethylbenzene, and xylene (BTEX) compounds are major volatile constituents found in gasoline and are water soluble and mobile. This study focused on the occurrence of MTBE with BTEX compounds in several marinas in Lake Texoma, which is a large reservoir located on the Oklahoma and Texas border. During a monitoring period from June 1999 to July 2001, MTBE and BTEX were detected in 28 and 5% of samples analyzed, respectively. Methyl tert-butyl ether co-occurred with BTEX compounds in 15% of lake water samples when detectable MTBE was present. The relatively low co-occurrence (15%) of MTBE with BTEX compounds is primarily due to the volume percentage in gasoline mixtures and physicochemical properties such as water solubility and Henry’s law constant. Toluene was the most commonly co-occurring BTEX with MTBE. Values of the ratios of the BTEX concentration to the MTBE concentration generally increase with depth of water.     

Performance Assessment of a New Type of Membrane Bioreactor under Steady State and Transient Operating Conditions

Methyl-t-butyl ether (MTBE) is an additive to gasoline that serves as an oxygenate to increase the octane rating and improve combustion efficiency. Assessment of MTBE biodegradation under aerobic conditions was performed in lab-scale biomass concentrator reactors (BCRs). These reactors were bench-scale microcosms that retain and concentrate biomass thereby enabling biodegradation to sub-μg/L level. The BCRs were run under low hydraulic retention times with a synthetically prepared feed containing 500??μg/L of several oxygenates, MTBE, diisopropyl ether (DIPE), ethyl-t-butyl ether (ETBE), t-amyl methyl ether (TAME), t-amyl alcohol (TAA), and the primary gasoline constituents benzene, toluene, ethyl benzene, and p-xylene (BTEX). The BCRs were effective in the removal of the aforementioned contaminants to concentrations lower than the targeted 5??μg/L, which is below the U.S. Environmental Protection Agency (EPA) taste and odor threshold of 20–40??μg/L. Reactor performance was also evaluated under shock loading and intermittent feeding (starvation tests) of the contaminants of concern to evaluate the reactor’s robustness in recovering from such stresses. The BCRs were found to be highly resilient to fluctuations in substrate and flow conditions.     

Modeling Volatilization of MTBE from Standing Surface Waters

The discovery in California of methyl tertiary-butyl ether (MTBE) in surface waters used for recreational boating has raised concerns over the potential impact on drinking water quality. Concentrations of MTBE above the California secondary maximum contaminant level of 5 ppb have been reported. Here we present a model to predict the fate of MTBE in surface waters as a function of wind speed, water temperature, epilimnion depth, and lake surface area. The model was validated with MTBE concentration data from Lake Perris in southern California and Calero Reservoir in northern California. When applied to typical lake conditions in California [i.e., epilimnion depth <11 m (<35 ft) and water temperature >15°C], the maximum half-life for MTBE is <40 days for quiescent conditions, and as low as 6 days if the average wind speed is >4.5 m∕s (10 mi∕h). The model can be used for management of recreational boating based on a target MTBE concentration in the reservoir.     

Treatability of Alternative Fuel Oxygenates Using Advanced Oxidation, Air Stripping, and Carbon Adsorption

Methyl tert-butyl ether (MTBE) is a gasoline oxygenate that has become a significant threat to groundwater supplies across the United States. Due to its physiochemical properties it has proven difficult and costly to remove from contaminated sites. This study was conducted to determine whether the alternative oxygenates (AO)—diisopropyl ether (DIPE), ethyltert-butyl ether (ETBE), tert-amyl methyl ether (TAME), tert-butyl alcohol (TBA), and ethanol (EtOH)—present a more efficient and less costly option from a remediation standpoint. Air stripping, carbon adsorption, and ultraviolet/H2O2 and O3/H2O2 advanced oxidation processes were examined at pilot scale to develop design parameters from which technical and economic comparisons were made for each alternative oxygenate versus MTBE. The experimental results showed that the ether AOs—DIPE, TAME, and ETBE—were each more efficiently and more economically treated than MTBE. The alternative alcohol oxygenates—TBA and EtOH—were less efficiently and less economically treated by the processes studied. The paper details the effects of primary process parameters and properties of individual oxygenates on process efficiency.     

Use of Membrane Bioreactor for Biodegradation of MTBE in Contaminated Water

An ultrafiltation membrane bioreactor was evaluated for biodegradation of methyl tert-butyl ether (MTBE) in contaminated water. The system was fed 5 mg/L MTBE in granular activated carbon (GAC) treated Cincinnati tap water containing ample buffer and nutrients. Within 120 days the culture had adapted to membrane operational conditions and was consistently achieving greater than 99.95% biological removal of both MTBE and tert-butyl alcohol. This condition was steadily maintained for the next 200 days of study. Effluent dissolved organic carbon values remained at or below concentrations of the feed GAC treated tap water alone. An increase in biomass concentration as measured by volatile suspended solids was observed to correlate with an increase in MTBE removal efficiency. Some operational observations, including fouling, recovery from an accident, and overall performance, are described.     

Aerobic Biodegradation of Methyl Tert-Butyl Ether in Gasoline-Contaminated Aquifer Sediments

Intrinsic biodegradation of methyl tert-butyl ether (MTBE) in aquifer sediments under oxic conditions was investigated using laboratory microcosms. Aquifer samples were collected from three different areas (source area, upgradient, and downgradient) of a shallow gasoline-contaminated aquifer within the Atlantic Coastal Plain Province located in Virginia. Biodegradation of MTBE was observed in the source-area microcosms in which MTBE declined from a starting concentration of 2.7 to 0.28 mg/L over a 58-day period, following an initial lag period of 20 days. The same set of microcosms was respiked with MTBE to an initial concentration of 4.8 mg/L and MTBE concentrations declined to 0.20 mg/L over a 52-day period with no lag in biodegradation. First-order MTBE biodegradation rates for the first and second periods were 0.037±0.003 and 0.063±0.003 day?1, respectively. When another set of source-area microcosms was spiked with MTBE (5 mg/L), toluene and ethylbenzene (1 mg/L each), the initial lag period increased to 33 days but there was no significant change in the MTBE biodegradation rate (0.065±0.026 day?1) and MTBE was not detected after 134 days. Biodegradation of MTBE was also observed in the microcosms constructed using aquifer sediment with only limited exposure to MTBE but the degradation rate was lower and statistically different (0.022±0.005 day?1) than the source area microcosms. Biodegradation of MTBE ceased when oxygen was depleted. Methyl tert-butyl ether did not biodegrade in the uncontaminated, upgradient microcosms; however, rapid biodegradation of toluene was observed. Methyl tert-butyl ether biodegradation appears to be limited in the absence of dissolved oxygen and in aquifer sediments where petroleum hydrocarbons including MTBE were not previously observed.     

Evidence for Phytodegradation of MTBE from Coupled Bench-Scale and Intermediate-Scale Tests

This paper presents methodologies and demonstrates the need to couple bench-scale and intermediate tree-scale experiments, to fully understand the transport and fate of organic contaminants, specifically methyl tert butyl ether (MTBE), in mature trees. Bench-scale experiments showed MTBE to be optimally taken up by small poplar saplings with a transpiration stream concentration factor of approximately 1, little or no degradation in soils and, nearly 100±20% recovery in the coupled water-plant-air system, indicating no measurable phytodegradation at the bench-scale. A large 14?ft tree chamber was designed to evaluate MTBE transport and fate through intermediate-scale (12?ft tall) poplar trees. Abiotic MTBE volatilization tests conducted in the tree chamber showed 100±20% MTBE mass recovery, thereby demonstrating the integrity of the large chamber and its air monitoring technique. In contrast, replicate intermediate-scale experiments conducted with large (12?ft) trees irrigated with a known mass of MTBE showed a deficit of MTBE mass recovery (65±20%) in replicate soil-tree-air systems monitored over a 2-week period. More significantly, tert butyl alcohol (TBA), a degradation product of MTBE, was detected in increasing concentrations in leaf biomass while MTBE concentrations in leaf biomass decreased as the experiment progressed. The MTBE mass recovery deficit, coupled with the detection of increasing TBA in leaf biomass, provides preliminary evidence of MTBE degradation in mature trees.     

Process Optimization of an Aerobic Upflow Sludge Blanket Reactor System

Response of an aerobic upflow sludge blanket (AUSB) reactor system to the changes in operating conditions was investigated by varying two principle operating variables: the oxygenation pressure and the flow recirculation rate. The oxygenation pressure was varied between 0 and 25?psig (relative), while flow recirculation rates were between 1,300 and 600% correspondingly. The AUSB reactor system was able to handle a volumetric loading of as high as 3.8?kg total organic carbon (TOC)/m3?day, with a removal efficiency of 92%. The rate of TOC removal by AUSB was highest at a pressure of 20?psig and it decreased when the pressure was increased to 25?psig and the flow recirculation rate was reduced to 600%. The TOC removal rate also decreased when the operating pressure was reduced to 0 and 15?psig, with corresponding increase in flow recirculation rates to 1,300 and 1,000%, respectively. Maintenance of a high dissolved oxygen level and a high flow recirculation rate was found to improve the substrate removal capacity of the AUSB system. The AUSB system was extremely effective in retaining the produced biomass despite a high upflow velocity and the overall sludge yield was only 0.24–0.32?g VSS/g TOC removed. However, the effluent TOC was relatively high due to the system’s operation at a high organic loading.     

Biodegradation of the gasoline oxygenates methyl tert-butyl ether, ethyl tert-butyl ether, and tert-amyl methyl ether by propane-oxidizing bacteria

Several propane-oxidizing bacteria were tested for their ability to degrade gasoline oxygenates, including methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). Both a laboratory strain and natural isolates were able to degrade each compound after growth on propane. When propane-grown strain ENV425 was incubated with 20 mg of uniformly labeled [14C]MTBE per liter, the strain converted > 60% of the added MTBE to 14CO2 in < 30 h. The initial oxidation of MTBE and ETBE resulted in the production of nearly stoichiometric amounts of tert-butyl alcohol (TBA), while the initial oxidation of TAME resulted in the production of tert-amyl alcohol. The methoxy methyl group of MTBE was oxidized to formaldehyde and ultimately to CO2. TBA was further oxidized to 2-methyl-2-hydroxy-1-propanol and then 2-hydroxy isobutyric acid; however, neither of these degradation products was an effective growth substrate for the propane oxidizers. Analysis of cell extracts of ENV425 and experiments with enzyme inhibitors implicated a soluble P-450 enzyme in the oxidation of both MTBE and TBA. MTBE was oxidized to TBA by camphor-grown Pseudomonas putida CAM, which produces the well-characterized P-450cam, but not by Rhodococcus rhodochrous 116, which produces two P-450 enzymes. Rates of MTBE degradation by propane-oxidizing strains ranged from 3.9 to 9.2 nmol/min/mg of cell protein at 28 degrees C, whereas TBA was oxidized at a rate of only 1.8 to 2.4 nmol/min/mg of cell protein at the same temperature.     

Carbon Adsorption and Air-Stripping Removal of MTBE from River Water

Through 1998, methyl tertiary-butyl ether (MTBE) was the most commonly used fuel oxygenate in Reno, Nevada. Winter-use of oxygenated gasolines is required in areas of the country that exceed carbon monoxide air quality standards. MTBE has not been detected in Reno’s raw water sources, but treatment alternatives must be assessed to fully prepare for possible contamination events. In this research, bench-scale studies using activated carbon and air stripping were conducted to evaluate the treatability of a high concentration of MTBE in Truckee River water, which is the primary surface supply for the Reno area. Results indicated that neither method appears practical for treating MTBE-laden water for one day at a 1.14×108?L/day (30 MGD) treatment plant. The capital costs estimated for full-scale application of these processes are approximately $5 million each. Estimated treatment costs for activated carbon and air stripping are approximately $0.043/L ($0.161/gal) and $0.047/L ($0.177/gal), respectively. Temporary closure of treatment facilities may be the best response to an accidental spill.     

Adsorption and Abiotic Transformation of Methyl tert-Butyl Ether through Acidic Catalysts

The fuel additive methyl tert-butyl ether (MTBE) is sometimes considered to be a recalcitrant compound in groundwater. Due to MTBE’s relatively poor adsorption and low volatility, interest is growing in new remediation methods which provide an alternative to using activated carbon or stripping techniques. This study addresses the abiotic degradation (hydrolysis) of MTBE to the intermediate tert-butanol (TBA). Two selected materials with acidic properties were shown to hydrolyze MTBE in batch tests at moderate pH values. The sorption of MTBE and TBA was estimated with Freundlich isotherms. Isotherms and TBA formation were used to calculate MTBE degradation. In another experiment, TBA was degraded aerobically by microorganisms. Since TBA seems to be more easily available as a carbon source to microorganisms than MTBE, the catalytic transformation of MTBE to TBA and methanol could enhance the natural attenuation of MTBE.     

Initiation of MTBE Biotreatment in Fluidized-Bed Bioreactors

Methyl tert-butyl ether (MTBE) is one of the most common ground water pollutants in the United States. Although MTBE has been characterized as a recalcitrant pollutant, it is now established that MTBE is biodegradable. A few bacteria that can grow on MTBE as a carbon and energy source have been identified and a host of bacteria that can cometabolize MTBE are known. There is very little information available concerning the biological treatment of MTBE contaminated ground water, despite the strong interest in applying biological treatment to the decontamination of MTBE laden water. In this paper we examine the treatment of contaminated ground water using a fluidized-bed bioreactor. Field studies demonstrated that the initiation of MTBE biotreatment was unpredictable, with one reactor starting to degrade MTBE immediately and a second reactor never degrading any MTBE. Laboratory studies were conducted to determine if a cosubstrate could be used to reliably enrich MTBE metabolizing microorganisms from a variety of environmental samples. It was determined that a number of compounds could enrich MTBE degrading populations, but that iso-pentane was the most reliable cometabolite of the compounds tested. Iso-pentane was used to initiate MTBE biotreatment in a laboratory fluidized-bed bioreactor. It was found that MTBE biotreatment continues even after iso-pentane addition was halted, suggesting that bacteria can gain maintenance energy from MTBE degradation. The reactor started with iso-pentane was as efficient as MTBE biotreatment as a reactor that started MTBE degradation without cosubstrate addition.     

Granular Bed Baffled Reactor (Grabbr): Solution to a Two-Phase Anaerobic Digestion System

A single unit anaerobic granular bed baffled reactor (GRABBR) is proposed as an alternative to a separately operated two-phase anaerobic digestion system. This overcomes the problems related to wastewater treatment at high loading rates which usually results in accumulation of intermediate acid products, and consequently inhibits methanogenesis. This study was carried out to evaluate the stability of a five compartment GRABBR system when treating synthetic glucose wastewater at various operational conditions. The reactor was started with volumetric organic loading rate (OLR) of 1 kg chemical oxygen demand (COD)/m3?day, equivalent to 120 h hydraulic retention time (HRT), and loading rates were gradually increased at suitable intervals to up to 20 kg COD/m3?day (6 h HRT). At steady state, the overall soluble COD (SCOD) removal was over 95% under all applied loading conditions. At lower loadings, the reactor operated as a completely mixed system, and most of the treatment was achieved in the first compartment. At higher loadings, the entire system transformed into different phases, acidogenesis being dominant near the influent point, whilst methanogenesis was the main activity in the compartments near the effluent point. Granule breaking and flotation was observed in the acidogenic zone, whilst the methanogenic zone retained its original granular form. High assimilation rate of influent nitrogen was observed in the first compartment with the formation of nongranular biomass, identified as Klebsiella pneumoniae. The success of GRABBR as a single unit two-phase anaerobic digestion system could save the cost of an extra unit traditionally employed to achieve similar goals in treatment of high strength wastewaters.     

Effects of Ethanol versus MTBE on Benzene, Toluene, Ethylbenzene, and Xylene Natural Attenuation in Aquifer Columns

The increased use of ethanol as a replacement for the gasoline oxygenate, methyl tert-butyl ether (MTBE), may lead to indirect impacts related to natural attenuation of benzene, toluene, ethylbenzene, and the three isomers of xylene (BTEX compounds). Ethanol could enhance dissolved BTEX mobility by exerting a cosolvent effect that decreases sorption-related retardation. This effect, however, is concentration dependent and was not observed when ethanol was added continuously (at 1%) with BTEX to sterile aquifer columns. Nevertheless, a significant decrease in BTEX retardation was observed with 50% ethanol, suggesting that neat ethanol spills in bulk terminals could facilitate the migration of pre-existing contamination. MTBE (25 mg/L influent) was not degraded in biologically active columns, and it did not affect BTEX degradation. Ethanol (2 g/L influent), on the other hand, was degraded rapidly and exerted a high demand for nutrients and electron acceptors that could otherwise have been used for BTEX degradation. Ethanol also increased the microbial concentration near the column inlet by one order of magnitude relative to columns fed BTEX alone or with MTBE. However, 16S-ribosomal ribonucleic acid sequence analyses of dominant denaturing gradient gel electrophoresis bands identified fewer species that are known to degrade BTEX when ethanol was present. Overall, the preferential degradation of ethanol and the accompanying depletion of oxygen and other electron acceptors hindered BTEX biodegradation, which suggests that ethanol could increase the length of BTEX plumes.     

Primary care: detection of women with alcohol use disorders

DNA damage of human leukemia (HL-60) cells caused by methyl tert-butyl ether (MTBE), a new gasoline additive, and its metabolites tert-butyl alcohol (TBA), a-hydroxyisobutyric acid (HIBA) and formaldehyde was determined by single cell gel electrophoresis (SCGE), with release of lactate dehydrogenase as an indicator for evaluating its cytotoxicity. Results showed that MTBE, TBA and HUBA at levels of 1 to 30 mmol/L could cause DNA damage in a dose-dependent pattern. Formaldehyde at level of 5 mumol/L could cause DNA damage, but at a higher level could decrease DNA migration. It suggested that MTBE and its metabolites could have genotoxicity, however, with doses causing genotoxic effects, no cytotoxic effect by MTBE, TBA and HIBA was observed, but formaldehyde presented obvious cytotoxic effect.     

Modeling TOC Breakthrough in Granular Activated Carbon Adsorbers

Linear regression techniques were used to develop practical models to predict total organic carbon (TOC) breakthrough in bituminous granular activated carbon (GAC) adsorbers. Models were developed for two field-scale GAC sizes (8×30 and 12×40?mesh) and two empty bed contact times (EBCTs) (10 and 20 min). Model input parameters include two water quality variables, influent TOC concentration (TOC0) and pH, that impact performance. The dependent variables for the models were normalized breakthrough time, throughput in bed volumes, to six fractional (TOC/TOC0 = 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7) and three mass (TOC = 1.0, 1.5, and 2.0 mg/L) effluent concentrations. Model development was performed using small-scale breakthrough data from 35 different source waters; external model validation was performed with small-scale breakthrough data from 14 source waters; a sensitivity analysis was performed to ensure that the models effectively capture expected breakthrough trend; and a scalability test was performed to verify the models’ ability to predict breakthrough for field-scale GAC adsorbers.