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In this study, the biodegradation potential of MTBE in uncontaminated and previously contaminated aquifer sediments under aerobic conditions was investigated. Laboratory microcosms were constructed using aquifer samples collected from three different areas of a shallow gasoline-contaminated aquifer in eastern Fairfax Co., Va in the Atlantic Coastal Plain province. Uncontaminated aquifer samples were collected upgradient of the plume, and contaminated aquifer samples were collected in the source area and in an area downgradient of the source. Biodegradation of MTBE was observed in microcosms that contained previously contaminated aquifer sediments. More complete degradation was observed in aquifer sediments containing a low level of petroleum contamination than in heavily contaminated aquifer sediments. Biodegradation of MTBE appeared to be limited by a lack of oxygen in heavily contaminated soils. When degradation was discernible it appeared to follow a first order pattern with a rate constant (l) of between 0.037 and 0.066 d-1, following a lag period of 20 to 40 days. In microcosms containing lightly contaminated aquifer material, MTBE was respiked during active metabolism, and degradation occurred with no lag or acclimation period. Results indicated that little or no degradation occurred in the microcosms containing uncontaminated soil. The results of this research suggest that the availability and level of petroleum hydrocarbon compounds influence indigenous microorganisms capable of degrading MTBE. / Master of Science

Methyl tertiary-butyl ether (MTBE) and its degraded form tertiary-butyl alcohol (TBA) are both known carcinogens that have contaminated groundwater aquifers across the United States. MTBE is a synthesized compound, once widely used as an additive in gasoline to increase oxygenation. Because of its popularity, MTBE was released into the environment primarily through fuel combustion and leaking underground storage tanks. These two compounds are known to be recalcitrant to most conventional physico-chemical treatment methods. Previous studies have suggested that bioremediation is effective at degrading MTBE and TBA in contaminated groundwater. Bioremediation involves the injection of oxygen, nutrients, and pre-adapted bacterial cultures into contaminated groundwater to increase the rate of natural biodegradation. In this study, a historically documented spill in Cambria, CA was modeled employing the Groundwater Modeling System software (GMS) to compare the effectiveness of the baseline treatment approach to that of in-situ bioremediation. MODFLOW was used to simulate groundwater flow, while MT3DMS was used to simulate dispersal and biodegradation of MTBE. Well data from public records was used as comparative values for hydraulic head and MTBE concentrations. Additional information from cleanup reports provided data for the physical properties of the aquifer. This included bedrock elevation, soil types, and storativity. Conductance, recharge rate, and hydraulic conductivity were calibrated using Parameter Estimation Software (PEST). The constants applied in MT3DMS simulations, such as dispersivity values, molecular diffusion coefficients, and retardation factors, were calculated manually using available, semi-empirical approaches. The model was first run emulating bioremediation using a high first order biodegradation rate estimated to be 8.6 day-1. This was compared to an instance of natural attenuation, with a first order biodegradation rate of 0.0074 day-1. The case study investigated herein primarily implemented a pump and treat system relying on granular activated carbon and a series of trickling filters and clarifiers. Pump and treat operations began in 2000 and officially ended by the start of 2015. Even though treatment was terminated, the preliminary remedial goal for MTBE was not achieved. In the model created for this project, the bioremediation simulation predicted attainment of this treatment goal by 2010 after starting treatment in 2002. This increase in predicted removal rate over conventional approaches suggests bioremediation may be a viable and effective treatment technique when removing MTBE from groundwater. This predicted rate of removal suggests that bioremediation is more effective than the techniques used during the Cambria cleanup. It is important to note, there were many assumptions and simplifications made during the creation of the model. This includes the calibrated parameter values obtained from PEST iterations along with calculated parameter estimates regarding MTBE fate and transport. During set up, it was assumed that soil type consisted solely of silty clay and the bedrock layer was at a constant 45 ft below ground level. Additionally, the modeled in-situ bioremediation scenario assumes a best-case scenario, with the high first order biodegradation rate. For future modeling improvements, it is recommended to conduct onsite field testing to obtain degradation rates that more closely reflect rates found in the modeled region. A more complete mapping of the aquifer would also provide the model with increased reliability. Future models should also evaluate additional MTBE spill events and how differing terrains impact the effectiveness of in-situ bioremediation of MTBE.

Contamination of groundwater by petroleum-hydrocarbons is a widespread environmental problem. Because the petroleum-hydrocarbon resulted plumes could be quite diffuse and widespread, some more economic approaches are desirable for groundwater remediation to provide for long-term control of contaminated groundwater. Monitored natural attenuation (MNA) has been considered as a passive remedial approach to degrade and dissipate contaminants in groundwater. In this study, a full-scale and detailed natural bioremediation investigation was conducted at a petroleum-hydrocarbon spill site in Kaohsiung County, Taiwan. In this natural attenuation study, the following tasks were conducted: (1) groundwater analysis; (2) evaluation of the occurrence of natural attenuation, (3) calculation of biodegradation capacity and natural attenuation rate calculation, (4) evaluation of the percent loss of hydrocarbons due to biodegradation processes by BIOSCREEN model, and (5) application of BIOPLUME III model for the development of remedial strategies. Results show that benzene, toluene, ethylbenzene, and xylene isomers (BTEX) concentrations dropped to below detection limit (BDL) before they reached the downgradient monitor well located 280 m from the spill location. A first-order decay model was applied for the natural attenuation rate calculation. Results reveal that natural biodegradation process was the major cause of the BTEX reduction among the natural attenuation mechanisms. Results from the groundwater analyses indicate that mixed anaerobic biodegradation patterns occurred between the source and mid-plume area, and the aerobic biodegradation dominated the mid and downgradient area. Approximately 74% of the BTEX removal was due to intrinsic biodegradation processes. The calculated natural attenuation rates for BTEX, methyl tert-butyl ether (MTBE), and 1,2,4-trimethylbenzene (1,2,4-TMB) were 0.13, 0.06, and 0.19 1/day, respectively. Evidence for the occurrence of natural attenuation was the decreased contaminant mass flux through the plume cross-sections along the transport path. Evidences for the occurrence of natural BTEX biodegradation included the following: (1) depletion of dissolved oxygen (DO) within the plume; (2) production of biodegradation by-products [Fe(II), CO2, and methane] within the plume; and (3) decreased BTEX concentrations and BTEX as carbon to TOC ratio along the transport path. The calculated biodegradation capacity (45 mg/L) at this site is much higher than the detected concentrations of petroleum-hydrocarbons (1.5 mg/L) within the most contaminated area inside the plume. Thus, natural biodegradation should be able to remove the contaminants effectively. Results suggest that natural attenuation mechanisms can effectively contain the plume and cause the significant removal of petroleum hydrocarbons. Moreover, pump-and-treat and air sparging systems are also feasible technologies to remediate contaminated groundwater at this site.

This research reports on an experimental and theoretical study of soil heating/air stripping and steam injection/vacuum extraction for remediation of MTBE and Diesel Contaminated Soils. Two one-dimensional mass transfer models were using to simulate the process of remediaction. Contaminant kinds(MTBE and Diesel)¡A contaminant concentration (152~13,912 mg/kg soil)¡Asoil temperature(38~120¢J)¡Asteam injection pressure(0.5~1.0 atm)¡A and the mass of steam used(0.379~0.730 kg/h)were employed as the experimental factors in this study. In soil heating/air stripping study, rising soil temperature will enhance the MTBE removed efficiency¡A it was shown in the concentration of effluent gas. Further, the flow rate at outlet of column was higher than that at inlet of column, it revealed MTBE transfers from liquid phase to gas phase and was removed by gas flow. The concentration of effluent gas curve in low initial MTBE concentration test was similar with high concentration test, but the mechanisms was quiet different¡Ait need advanced adsorption test to find the reasons. In medium initial MTBE concentration test¡Athe concentration of effluent gas curve showed linear shape. When using steam injection/vacuum extraction treating MTBE contaminated soil, it showed 90¢Mefficiency can be reached in one hour. In steam injection/vacuum extraction study, it showed higher initial diesel contaminant concentration¡Ahigher initial concentration of effluent gas. Further, in high initial diesel concentration test (13.912 g diesel/kg soil test and about 5g/ kg soil tests)¡Athe concentration of effluent gas curves had a dominant drop at early time in remediation, it revealed the injection steam flow was quiet large, so diesel didn¡¦t has enough time to transfer to gas phase, that the gas couldn¡¦t been saturation at outlet of column. But in low initial diesel concentration test (about 1 g diesel/kg soil tests), the concentration of effluent gas curves showed the typical NAPL remediation curve. The different with in high and low initial concentrations might from the complex composition of diesel. Because at the early time in remediaction of high initial diesel concentration, the low carbon numbers diesel could abundantly evaporate, it caused the high concentration of effluent gas. With the remediation time go by, the low carbon numbers diesel exhaust. So the main composition of effluent gas transfer to high carbon numbers diesel, that the concentration of effluent gas curve showed the slowly decline. For high initial diesel concentration test (13.912 g diesel/kg soil)¡A the efficiency was the highest (73.7¢M). For low initial diesel concentration test (about 1 g diesel/kg soil), the efficiency was the lost (about 20¢M). Further, the remediation of diesel contaminated soil exited a rapid removed period. Under the conditions of this study, the rapid removed period could remove more than 95¢Mcontaminant of diesel removed at hold remediation time. The experiment results also showed that larger the mass of steam injection, shorter the rapid removed period, and larger the steam injection pressure, longer the rapid removed period. When using soil heating/air stripping treating diesel contaminated soil, the removed efficiency was worse 10-20¢Mthan the same initial diesel contaminated concentration. In simulating remediation process, the prediction with the MTBE measured concentration yielded good agreement in NAPL model. But to get the better fit of diesel in NAPL model, it might set the ¡§could removed mass¡¨ to initial condition of model. In non-NAPL model, MTBE also showed good agreement with model, and the model enabled the prediction of the initial contaminant level in the soil.

Contamination of groundwater supplies by gasoline and other petroleum-derived hydrocarbons released from underground or aboveground storage tanks is a serious and widespread environmental problem. Corrosion, ground movement, and poor sealing can cause leaks in tanks and associated piping. Petroleum hydrocarbons contain methyl tertiary-butyl ether (MTBE) (a fuel oxygenate), benzene, toluene, ethylbenzene, and xylene isomers (BTEX), the major components of gasoline, which are hazardous substances regulated by many nations. MTBE possesses all the characteristics of a persistent compound in the subsurface: high solubility, low volatility, low sediment sorption, and resistance to biodegradation. The objectives of this study were to (1) evaluate the biodegradibility of MTBE under aerobic conditions, and (2) assess the potential of using the aerobic bioremediation technique to clean up aquifers contaminated by MTBE. In this study, microcosms were constructed to determine the feasibility of biodegrading MTBE by intrinsic microbial consortia (aquifer sediments) under aerobic and aerobic cometabolic conditions. In the cometabolic microcosms, propane, ethanol, and BTEX were applied as the primary substracts to enhance the biodegradation of MTBE. The inocula used in this microcosm study were aquifer sediments collected from the contaminated-zones of a petroleum-hydrocarbon (including MTBE) contaminated site. Microcosms were constructed with nutrient medium (or site groundwater), sediments, and MTBE solution in 70-mL serum bottles sealed with Teflon-lined rubber septa. MTBE was analyzed using purge-and-trap instrument following gas chromatography (GC)/flame ionization detector (FID). Results show that the indigenous microorganisms were able to biodegrade MTBE under aerobic conditions using MTBE as the sole primary substrate. Microcosms with site groundwater as the medium solution show higher MTBE biodegradation rate. This indicates that site groundwater might contain some trace minerals or organics, which could enhance the MTBE biodegradation rate. Results show that the addition of BTEX would also enhance the MTBE removal. However, no significant MTBE biodegradation was observed in microcosms with propane and ethanol as the primary substrates. This reveals that the supplement of the second carbon source might inhibit the degradation of MTBE due to the preferential removal of some organics over MTBE. Results from the microcosm study suggest that aerobic biodegradation plays an important role on the MTBE removal. Intrinsic bioremediation is a feasible technology to remediate the studied MTBE-contaminated site.

Groundwater contamination by petroleum hydrocarbons has become one of the serious environmental problems in many countries. The sources of petroleum-hydrocarbon contaminants may be released from above ground and underground storage tanks, and pipelines. Petroleum hydrocarbons are mainly composed of benzene, toluene, ethyl- benzene, and xylems (BTEX), and other constituents such as methyl-tert-butyl ether (MTBE), naphthalene, 1,3,5-trimethylbenzene (1,3,5-TMB), and 1,2,4-trimethylbenzene (1,2,4-TMB). It is generally recognized that petroleum hydrocarbons have high risks to environmental receptors when hydrocarbon releases occur. Various biological, physical, and chemical remediation technologies (e.g. pump and treat, air sparging, enhanced bioremediation, and chemical oxidation) can be used to remediate petroleum-hydrocarbon contaminated groundwater. However, many of these techniques are typically costly or have limited applications. Permeable reactive barriers (PRBs) are a promising technology for the passive and in situ treatment of contaminated groundwater. A PRB can be defined as ¡§an emplacement of reactive materials in the subsurface designed to intercept a contaminant plume, provide a preferential flow path through the reactive media, and transform the contaminant(s) into environmentally acceptable forms to attain remediation concentration goals at points of compliance.¡¨ The oxygen release materials can be emplaced in the PRBs to passive increase dissolved oxygen (DO) in the subsurface to enhance the intrinsic biodegradation of dissolved hydrocarbons. In the first part of this study, guidelines for PRBs installation have been developed for the remediation of petroleum hydrocarbons, heavy metals, and organic solvents contaminated groundwater. PRB is a cost-effective approach for the remediation of contaminated aquifers. As contaminated groundwater moves through a permeable reactive barrier, the contaminants are scavenged or degraded, and uncontaminated groundwater emerges from the downgradient side of the reactive zone. The permeable reactive barrier concept has several advantages over other remediation technologies currently in use (e.g., pump and treat, air sparging), including absence of mechanical facilities and the electric power, no groundwater extraction and reinjection, treatment in situ, and cost-effective. The first part of this study presents the designs, applications, and case studies of PRB systems on groundwater remediation. In the second part of this study, oxygen release materials have been constructed and evaluated for the appropriate components in batch experiments. Microbial degradation of petroleum hydrocarbons in groundwater can occur naturally. Since the petroleum-hydrocarbons are generally degraded faster under aerobic conditions, aerobic bioremediation can be applied to enhance the biodegradation of petroleum-hydrocarbons within of the plume if oxygen can be provided to the subsurface economically. Batch experiments were conducted to design and identify the components of the oxygen-releasing materials. Cement and gypsum were used as a binder in this mixtures experments. (1) using cement as the binding material The mixtures of the oxygen release material were prepared by blending cement, peat, sand, ethylene-vinyl acetate copolymer(EVA), calcium peroxide (CaO2), and water together at a ratio of 1.0¡G0.18¡G0.20¡G0.10¡G1.12¡G1.74 by weight. Cement was used as a binder and regular medium filter sand was used to increase the permeability of the mixture. Calcium peroxide releases oxygen upon contact water. The designed material with a density of 1.9 g/cm3 was made of 3.5 cm cube for the batch experiment. Results show that the oxygen release rate of the material is 0.046 mg O2/day/g rock. The oxygen release material was able to remain active in oxygen release for more than three months. (2) using gypsum as the binding material The mixtures of the oxygen release material were prepared by blending gypsum, CaO2, sand, and water together at a ratio of 1¡G0.5¡G0.14¡G0.75 by weight. Gypsum was used as a binder and regular medium filter sand was used to increase the permeability of the mixture. Calcium peroxide releases oxygen upon contact water. The designed material with a density of 1.1 g/cm3 was made of 3.5 cm cube for the batch experiment. Results show that the oxygen release rate of the material is 0.031 mg/day/g. The oxygen release material was able to remain active in oxygen release for more than three months. In the third part of this study, immobilization technology was applied to produce the low permeability wrapping film for the construction of oxygen-releasing granular materials. The mixtures of the oxygen release material were prepared by blending alginate, CaO2, and sand together at a ratio of 8.3¡G1.0¡G1 by weight. The low permeability wrapping film of the oxygen release material was able to remain active in oxygen release for two months. In the fourth part of this study, a laboratory-scale column experiment was conducted to evaluate the feasibility of this proposed system on the bioremediation of petroleum-hydrocarbon contaminated groundwater. This system was performed using a series of continuous-flow glass columns including four consecutive soil columns. Simulated petroleum-hydrocarbons contaminated groundwater with a flow rate of 0.263 m/day was pumped into this system. In the column experiment, the samples of column influent and specified sampling ports were collected and analyzed for pH, DO, BTEX, MTBE, and microbial populations. Results show that up to 99% of BTEX removal was observed in this passive system. Results from this study would be useful in designing an efficient and cost-effective passive oxygen-releasing and bioremediation system to remediate petroleum- hydrocarbon contaminated aquifer.