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Field-Scale Evaluation of Biostimulation for Remediation of Uranium-Contaminated Groundwater at a Proposed NABIR Field Research Center in Oak Ridge, TN

Description: A hydrologic, geochemical and microbial characterization of the Area 3 field site has been completed. The formation is fairly impermeable, but there is a region of adequate flow approximately 50 feet bgs. The experiment will be undertaken within that depth interval. Groundwater from that depth is highly acidic (pH 3.2), and has high levels of nitrate, aluminum, uranium, and other heavy metals, as well as volatile chlorinated solvents (VOCs). Accordingly, an aboveground treatment train has been designed to remove these contaminants. The train consists of a vacuum stripper to remove VOCs, two chemical precipitation steps to adjust pH and remove metals, and a fluidized bed bioreactor to remove nitrate. The aboveground system will be coupled to a belowground recirculation system. The belowground system will contain an outer recirculation cell and a nested inner recirculation cell: the outer cells will be continuously flushed with nitrate-free treated groundwater. The inner cell will receive periodic inputs of uranium, tracer, and electron donor. Removal of uranium will be determined by comparing loss rates of conservative tracer and uranium within the inner recirculation cell. Over the past year, a detailed workplan was developed and submitted for regulatory approval. The workplan was presented to the Field Research Advisory Panel (FRAP), and after some extensive revision, the FRAP authorized implementation. Detailed design drawings and numerical simulations of proposed experiments have been prepared. System components are being prefabricated as skid-mounted units in Michigan and will be shipped to Oak Ridge for assembly. One manuscript has been submitted to a peer reviewed journal. This paper describes a novel technique for inferring subsurface hydraulic conductivity values. Two posters on this project were presented at the March 2002 NABIR PI meeting. One poster was presented at the Annual conference of the American Society for Microbiology in Salt Lake City, UT in ...
Date: June 1, 2003
Creator: Criddle, Craig S.
Partner: UNT Libraries Government Documents Department

The Use of Radar Methods to Determine Moisture Content in the Vadose Zone

Description: Water content is a critical parameter affecting both liquid-phase and vapor-phase contaminant transport in the vadose zone. This means that accurate estimates of in situ water content must be obtained in order to design for the appropriate handling or remediation of a contaminated region of the vadose zone. Traditional methods of sampling the subsurface by drilling and/or direct sampling are very time consuming, limited in terms of spatial coverage, and have the associated risk of contacting and increasing the size of the contaminated area. One solution is to use geophysical methods which can provide a high-resolution, non-invasive means of sampling or imaging the subsurface. The overall objective of our research, defined at the start of this project, was to advance the usefulness of radar methods (ground-based and borehole) as a means of characterizing water content in the vadose zone. We have met this objective by providing research results that can be used to (1) improve the accuracy of water content estimates from radar measurements; (2) provide estimates of the potential error in water content estimates from radar measurements; (3) improve the clarity of radar images; (4) develop large-scale models of the subsurface ''architecture'' using radar images; (5) develop ways of quantifying the spatial heterogeneity of the subsurface through analysis of radar images. We have also been able to identify the critical areas where more research is needed in order to be able to use radar methods most effectively as an accurate means of subsurface characterization.
Date: December 28, 2003
Creator: Knight, Rosemary
Partner: UNT Libraries Government Documents Department

Geochemical Controls on Nuclear Magnetic Resonance Measurements

Description: OAK-B135 Our research objectives are to determine, through an extensive set of laboratory experiments, the effect of the specific mineralogic form of iron and the effect of the distribution of iron on proton nuclear magnetic resonance (NMR) relaxation mechanisms. In the first nine months of this project, we have refined the experimental procedures to be used in the acquisition of the laboratory NMR data; have ordered, and conducted preliminary measurements on, the sand samples to be used in the experimental work; and have revised and completed the theoretical model to use in this project. Over the next year, our focus will be on completing the first phase of the experimental work where the form and distribution of the iron in the sands in varied.
Date: November 11, 2003
Creator: Knight, Rosemary; Prasad, Manika & Keating, Kristina
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: This report outlines progress in the first quarter of the extension of the DOE project ''High Resolution Prediction of Gas Injection Process Performance for Heterogeneous Reservoirs''. This report presents experimental results that demonstrate combined scaling effects of viscous, capillary, and gravity crossflow mechanisms that apply to the situations in which streamline models are used. We designed and ran a series of experiments to investigate combined effects of capillary, viscous, and gravity forces on displacement efficiency in layered systems. Analog liquids (isooctane, isopropanol, and water) were employed to control scaling parameters by changing interfacial tension (IFT), flow rate, and density difference. The porous medium was a two-dimensional (2-D) 2-layered glass bead model with a permeability ratio of about 1:4. In order to analyze the combined effect of only capillary and viscous forces, gravity effects were eliminated by changing the orientation of the glass bead model. We employed a commercial simulator, Eclipse100 to calculate displacement behavior for comparison with the experimental data. Experimental results with minimized gravity effects show that the IFT and flow rate determine how capillary and viscous forces affect behavior of displacement. The limiting behavior for scaling groups for two-phase displacement was verified by experimental results. Analysis of the 2-D images indicates that displacements having a capillary-viscous equilibrium give the best sweep efficiency. Experimental results with gravity effects, but with low IFT fluid systems show that slow displacements produce larger area affected by crossflow. This, in turn, enhances sweep efficiency. The simulation results represent the experimental data well, except for the situations where capillary forces dominate the displacement.
Date: September 30, 2003
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

SEISMIC AND ROCK PHYSICS DIAGNOSTICS OF MULTISCALE RESERVOIR TEXTURES

Description: As part of our study on ''Relationships between seismic properties and rock microstructure'', we have (1) Studied relationships between velocity and permeability. (2) Used independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. (3) Applied different statistical methods for characterizing heterogeneity and textures from scanning acoustic microscope (SAM) images of shale microstructures. (4) Analyzed the directional dependence of velocity and attenuation in different reservoir rocks (5) Compared Vp measured under hydrostatic and non-hydrostatic stress conditions in sands. (6) Studied stratification as a source of intrinsic anisotropy in sediments using Vp and statistical methods for characterizing textures in sands.
Date: October 1, 2003
Creator: Mavko, Gary
Partner: UNT Libraries Government Documents Department

Characterization of U(VI) Sorption-Desorption Processes and Model Upscaling: Annual Report for Johns Hopkins University (Contract No. DE-FG07-02ER63498)

Description: The objectives of the overall collaborative EMSP effort (with which this project is associated) are to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties. The research is intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to develop approaches by which laboratory-characterized geochemical models can be upscaled for defensible predictions of uranium transport in field.
Date: June 12, 2003
Creator: Ball, William P.
Partner: UNT Libraries Government Documents Department

Coupled Geochemical and Hydrological Processes Governing the Fate and Transport of Radionuclides and Toxic Metals Beneath the Hanford Tank Farms

Description: Project Objective: (1) Provide an improved understanding of how preferential vertical and lateral flow, and the formation of immobile water influence the transport of radionuclides and toxic metals in heterogeneous, laminated sediments. (2) Quantify the rates and mechanisms of radionuclide and toxic metal interaction with the solid phase under various hydrologic conditions. (3) Provide new insights into how physical and mineralogical heterogeneities (e.g. stratification, pore regime connectivity, mineral composition along flowpaths) influence contaminant retardation and the degree of geochemical nonequilibrium during transport.
Date: June 1, 2003
Creator: Fendorf, Scott E.
Partner: UNT Libraries Government Documents Department

Characterization of U(VI) Sorption-Desorption Processes and Model Upscaling

Description: In order to apply predictive reactive transport models to the Hanford site, detailed knowledge of the speciation of contaminants is required. Important speciation parameters include: (1) oxidation state; (2) the local molecular structure surrounding contaminant elements; (3) the type and binding of a contaminant ion sorption complex (if adsorbed); (4) the type(s) of phase within which a contaminant is structurally incorporated [e.g., present in a three-dimensional precipitate(s)]; (5) the phase associations of a contaminant; (6) the microscopic distribution of a contaminant within sediments and soils. In the present study, we have used synchrotron-based X-ray spectroscopic methods to study the speciation of U and Cu in contaminated soil and sediment samples from the Hanford Site. To complement and complete our initial XAFS investigation of U speciation in contaminated vadose zone sediments below tank BX-102, we have also performed mXRD studies of two sediment sample to identify the specific U(VI)-silicate phase present. Samples from the 300 Area were examined by mSXRF to determine the microscopic distribution and element associations of Cu and U. These samples were also analyzed by U LIII- and Cu K-edge XAFS spectroscopy to determine the chemical speciation of these elements. Conclusions to Date (1) Uranium occurs primarily as sodium-boltwoodite [Na2(UO2)2(SiO3OH)2-3H2O] in the BX-102 sediment samples. (2) The dissolution kinetics of sodium-boltwoodite will be a major control on the future transport of U beneath tank BX-102. (3) In the 300 Area soils and sediments, uranium occurs as U(VI) and copper as Cu(II). (4) U and Cu are often found together or adjacent to one another; however, these elements don?t appear to be spatially associated with Fe. (5) U appears to be bound to carbonate groups, and is likely contained in a CaCO3 mineral (calcite or aragonite). (6) It is unclear what phase(s) Cu is bound to or associate with, ...
Date: June 1, 2003
Creator: Brown, Gordon E.
Partner: UNT Libraries Government Documents Department

Characterization of U(VI) Sorption-Desorption Processes and Model Upscaling

Description: The objectives of the overall collaborative EMSP effort (with which this project is associated) are to characterize sorption and desorption processes of U(VI) on pristine and contaminated Hanford sediments over a range of sediment facies and materials properties. The research is intended to provide new insights on the mechanisms of U(VI) retardation at Hanford, and to develop approaches by which laboratory-characterized geochemical models can be upscaled for defensible predictions of uranium transport in field.
Date: June 1, 2003
Creator: Zachara, John M.
Partner: UNT Libraries Government Documents Department

HEAVY AND THERMAL OIL RECOVERY PRODUCTION MECHANISMS

Description: This technical progress report describes work performed from January 1 through March 31, 2003 for the project ''Heavy and Thermal Oil Recovery Production Mechanisms,'' DE-FC26-00BC15311. In this project, a broad spectrum of research is undertaken related to thermal and heavy-oil recovery. The research tools and techniques span from pore-level imaging of multiphase fluid flow to definition of reservoir-scale features through streamline-based history matching techniques. During this period, previous analysis of experimental data regarding multidimensional imbibition to obtain shape factors appropriate for dual-porosity simulation was verified by comparison among analytic, dual-porosity simulation, and fine-grid simulation. We continued to study the mechanisms by which oil is produced from fractured porous media at high pressure and high temperature. Temperature has a beneficial effect on recovery and reduces residual oil saturation. A new experiment was conducted on diatomite core. Significantly, we show that elevated temperature induces fines release in sandstone cores and this behavior may be linked to wettability. Our work in the area of primary production of heavy oil continues with field cores and crude oil. On the topic of reservoir definition, work continued on developing techniques that integrate production history into reservoir models using streamline-based properties.
Date: April 1, 2003
Creator: Kovscek, Anthony R.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: This report outlines progress in the second quarter of the third year of the DOE project ''High Resolution Prediction of Gas Injection Process Performance for Heterogeneous Reservoirs''. This report presents results of an investigation of the effects of variation in interfacial tension (IFT) on three-phase relative permeability. We report experimental results that demonstrate the effect of low IFT between two of three phases on the three-phase relative permeabilities. In order to create three-phase systems, in which IFT can be controlled systematically, we employed analog liquids composing of hexadecane, n-butanol, isopropanol, and water. Phase composition, phase density and viscosity, and IFT of three-phase system were measured and are reported here. We present three-phase relative permeabilities determined from recovery and pressure drop data using the Johnson-Bossler-Naumann (JBN) method. The phase saturations were obtained from recovery data by the Welge method. The experimental results indicate that the wetting phase relative permeability was not affected by IFT variation whereas the other two-phase relative permeabilities were clearly affected. As IFT decreases the ''oil'' and ''gas'' phases become more mobile at the same phase saturations.
Date: March 31, 2003
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

Fundamental Studies of Fluid Mechanics: Stability in Porous Media

Description: This is the final report for the grant ''Fundamental Studies of Fluid Mechanics: Stability in Porous Media''. This work has been concerned with theoretical, computational and experimental studies of a variety of flow and transport problems that are of generic interest and applicability in energy-related and energy-intensive processes. These include the follow: (1) Problems associated with oil recovery--the global economy continues to be dependent on the stable and predictable supply of oil and fossil fuels. This wil remain the case for the near term, as current estimates are that world production of oil will peak between 2025 and 2100, depending on assumptions regarding growth. Most of these resources reside in porous rocks and other naturally occurring media. Studies of flow-induced instabilities are relevant to the areas of secondary and enhanced oil recovery. (2) Small scale and Stokes flows--flows in microgeometries and involving interfaces and surfactants are of interest in a myriad of energy-related contexts. These include: pore-level modeling of the fundamental processes by which oil held in porous materials is mobilized and produced; heating and cooling energy cycles involving significant expenditure of energy in conditioning of human environments, heat pipes, and compact heat exchangers; and energy efficiency in large scale separation processes such as distillation and absorption--processes that underlie the chemical process industries. (3) Coating flows--these are of interest in information technologies, including the manufacture of integrated circuits and data storage and retrieval devices. It is estimated that 50-70% of the starting raw materials and intermediate devices in information technology processes must be discarded as a result of imperfections and failure to meet specifications. These in turn are often the result of the inability to control fluid-mechanical processes and flow instabilities.
Date: September 14, 2003
Creator: Homsy, G. M.
Partner: UNT Libraries Government Documents Department

The Use of Radar Methods to Determine Moisture Content in the Vadose Zone

Description: Moisture content is a critical parameter affecting both liquid-phase and vapor-phase contaminant transport in the vadose zone. The objective of our three-year research project is to determine the optimal way to use radar methods as a non-invasive means of determining in situ moisture content.
Date: June 1, 2003
Creator: Knight, Rosemary
Partner: UNT Libraries Government Documents Department

Biodegradation of Chlorinated Solvents: Reactions near DNAPL and Enzyme Function

Description: The anaerobic biodegradation of chlorinated solvents is of great interest both for natural attenuation and for engineered remediation of these hazardous contaminants in groundwater. Compounds to be studied are carbon tetrachloride (CT) and the chlorinated ethenes, tetrachloroethene (PCE), trichloroethene (TCE) cis-1,2-dichloroethene (cDCE), and vinyl chloride (VC). The chlorinated solvents often are present as dense non-aqueous-phase liquids (DNAPLs), which are difficult to remove. Biodegradation of DNAPLs was previously thought not possible because of toxicity, but recent evidence indicates that under the right conditions, biodegradation is possible. Anaerobic biodegradation of DNAPLs is the major subject of this research. The specific objectives of this multi-investigator effort are: (1) Evaluate the potential for chlorinated solvent biodegradation near DNAPLs, (2) Provide a molecular understanding of the biological mechanisms involved, (3) Determine cellular components involved in carbon tetrachloride transformation by Pseudomonas stutzeri strain KC without chloroform formation.
Date: June 1, 2003
Creator: McCarty, Perry L.; Spormann, Alfred M. & Criddle, Craig S.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: In this report we present an approach for accurate and consistent implementation of gravity effects in compositional streamline simulation. The approach is based on an operator-splitting technique, successfully applied in streamline simulation of black-oil models. The method is demonstrated to conserve mass. Its application adds only marginally to the overall CPU requirement. We provide a detailed description of the approach to incorporate gravity effects and demonstrate the efficiency of compositional streamline simulation, even for cases where gravity segregation plays an important role in the overall process performance. The new approach is demonstrated to be in excellent agreement with commercial FD simulators for prediction of flows in 2D vertical and multi-well 3D geometries. Finally, we outline the work required to extend the compositional streamline approach to handle three-phase flow modeling, also including gravity.
Date: December 31, 2003
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

Microbially Mediated Immobilization of Contaminants Through In Situ Biostimulation

Description: In most natural environments, a multitude of metabolic substrates are resent simultaneously. Organisms that can utilize uranium as a metabolic substrate for respiration also may have the ability to use a variety of other oxidized substrates as electron acceptors. Thus, these substrates are, in effect, competing for electrons that are being passed through the electron transport chain during respiration. To assess the feasibility of in situ immobilization of uranium in subsurface environments and to understand the cycling of uranium, it is necessary to discern the chemical and/or biological conditions dictating which terminal electron acceptor(s) will be utilized.
Date: July 31, 2003
Creator: Fendorf, Scott
Partner: UNT Libraries Government Documents Department

HEAVY AND THERMAL OIL RECOVERY PRODUCTION MECHANISMS

Description: This technical progress report describes work performed from October 1 through December 31, 2002 , for the project ''Heavy and Thermal Oil Recovery Production Mechanisms.'' In this project, a broad spectrum of research is undertaken related to thermal and heavy-oil recovery. The research tools and techniques used are varied and span from pore-level imaging of multiphase fluid flow to definition of reservoir-scale features through streamline-based history-matching techniques. During this period, experimental data regarding multidimensional imbibition was analyzed to obtain shape factors appropriate for dual-porosity simulation. It is shown that the usual assumption of constant, time-independent shape factors is incorrect. In other work, we continued to study the mechanisms by which oil is produced from fractured media at high pressure and high temperature. High temperature significantly increased the apparent wettability and affected water relative permeability of cores used in previous experiments. A phenomenological and mechanistic cause for this behavior is sought. Our work in the area of primary production of heavy oil continues with field cores and crude oil. On the topic of reservoir definition, work continued on developing techniques that integrate production history into reservoir models using streamline-based properties.
Date: January 1, 2003
Creator: Kovscek, Anthony R.
Partner: UNT Libraries Government Documents Department

Third-Year Progress Report on DOE-EMSP Grant DOE-DE-FG07-99ER15022: ''Immobilization of Radionuclides in the Hanford Vadose Zone by Incorporation in Solid Phases''

Description: Research Group at Stanford University, we have investigated adsorption processes that could lead to the sequestration of Cr, Co, Sr, and U on minerals representative of the Hanford Vadose Zone sediments and precipitation processes resulting in alkali aluminate solids that form from the highly alkaline and aluminum-rich leachates reacting with these sediments. These elements are among the most important pollutants of concern to the Department of Energy at the Hanford Site in Washington State. The aqueous solutions used in these experiments were simplified surrogates of Tank leachates (i.e., they contained high Na and Al and had pH values of 10-12 in many cases). We have examined the following processes that could lead to sequestration of these pollutant elements: (1) the sorption/coprecipitation of these elements in solids formed from reaction of alkaline aluminate solutions with simple systems of minerals representative of those found in the soils and sediments underlying the Hanford Tank Farm (e.g., quartz, feldspars, clay minerals, iron oxides); (2) the sorption/coprecipitation of these elements in solids formed from reaction of alkaline aluminate solutions with soil and sediment samples obtained from the Hanford site; and (3) the effect of aging on the stability of sorption complexes on Al-oxide and Al-oxyhydroxide surfaces formed from neutralization and homogeneous nucleation of alkaline aluminate solutions. Our investigations have utilized X-ray Absorption Fine Structure (XAFS) spectroscopy, electron and X-ray microprobe analyses, X-ray diffraction and small angle X-ray scattering, and inductively coupled plasma emission spectrometry analysis, as described below.
Date: June 1, 2003
Creator: Brown Jr., Gordon E.; Catalano, Jeffrey G.; Warner, Jeffrey A.; Shaw, Samuel & Grolimund, Daniel
Partner: UNT Libraries Government Documents Department

HEAVY AND THERMAL OIL RECOVERY PRODUCTION MECHANISMS

Description: The Stanford University Petroleum Research Institute (SUPRI-A) studies oil recovery mechanisms relevant to thermal and heavy-oil production. The scope of work is relevant across near-, mid-, and long-term time frames. In August of 2000 we received funding from the U. S. DOE under Award No. DE-FC26-00BC15311 that completed December 1, 2003. The project was cost shared with industry. Heavy oil (10 to 20{sup o} API) is an underutilized energy resource of tremendous potential. Heavy oils are much more viscous than conventional oils. As a result, they are difficult to produce with conventional recovery methods. Heating reduces oil viscosity dramatically. Hence, thermal recovery is especially important because adding heat, usually via steam injection generally improves displacement efficiency. The objectives of this work were to improve our understanding of the production mechanisms of heavy oil under both primary and enhanced modes of operation. The research described spanned a spectrum of topics related to heavy and thermal oil recovery and is categorized into: (1) multiphase flow and rock properties, (2) hot fluid injection, (3) improved primary heavy-oil recovery, (4) in-situ combustion, and (5) reservoir definition. Technology transfer efforts and industrial outreach were also important to project effort. The research tools and techniques used were quite varied. In the area of experiments, we developed a novel apparatus that improved imaging with X-ray computed tomography (CT) and high-pressure micromodels etched with realistic sandstone roughness and pore networks that improved visualization of oil-recovery mechanisms. The CT-compatible apparatus was invaluable for investigating primary heavy-oil production, multiphase flow in fractured and unfractured media, as well as imbibition. Imbibition and the flow of condensed steam are important parts of the thermal recovery process. The high-pressure micromodels were used to develop a conceptual and mechanistic picture of primary heavy-oil production by solution gas drive. They allowed for direct visualization of ...
Date: December 31, 2003
Creator: Kovscek, Anthony R. & Castanier, Louis M.
Partner: UNT Libraries Government Documents Department

HIGH RESOLUTION PREDICTION OF GAS INJECTION PROCESS PERFORMANCE FOR HETEROGENEOUS RESERVOIRS

Description: This report presents a detailed analysis of the development of miscibility during gas cycling in condensates and the formation of condensate banks at the leading edge of the displacement front. Dispersion-free, semi-analytical one-dimensional (1D) calculations are presented for enhanced condensate recovery by gas injection. The semi-analytical approach allows investigation of the possible formation of condensate banks (often at saturations that exceed the residual liquid saturation) and also allows fast screening of optimal injection gas compositions. We describe construction of the semi-analytical solutions, a process which differs in some ways from related displacements for oil systems. We use an analysis of key equilibrium tie lines that are part of the displacement composition path to demonstrate that the mechanism controlling the development of miscibility in gas condensates may vary from first-contact miscible drives to pure vaporizing and combined vaporizing/condensing drives. Depending on the compositions of the condensate and the injected gas, multicontact miscibility can develop at the dew point pressure, or below the dew point pressure of the reservoir fluid mixture. Finally, we discuss the possible impact on performance prediction of the formation of a mobile condensate bank at the displacement front in near-miscible gas cycling/injection schemes.
Date: June 30, 2003
Creator: Franklin M. Orr, Jr.
Partner: UNT Libraries Government Documents Department

SEISMIC AND ROCK PHYSICS DIAGNOSTICS OF MULTISCALE RESERVOIR TEXTURES

Description: As part of our study on ''Relationships between seismic properties and rock microstructure'', we have studied (1) Effects of pore texture on porosity, permeability, and sonic velocity. We show how a relation can be found between porosity, permeability, and velocity by separating the formations of rocks with similar pore textures.
Date: June 30, 2003
Creator: Mavko, Gary
Partner: UNT Libraries Government Documents Department

SEISMIC AND ROCK PHYSICS DIAGNOSTICS OF MULTISCALE RESERVOIR TEXTURES

Description: As part of our study on ''Relationships between seismic properties and rock microstructure'', we have studied (1) Methods for detection of stress-induced velocity anisotropy in sands. (2) We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments.
Date: June 30, 2003
Creator: Mavko, Gary
Partner: UNT Libraries Government Documents Department

Biodegradation of Chlorinated Solvents: Reactions near DNAPL and Enzyme Function

Description: Chlorinated solvents are among the most widespread groundwater contaminants in the country, contamination which is also among the most difficult and expensive for remediation. These solvents are biodegradable in the absence of oxygen, but this biodegradation requires both a food source for the organisms (electron donor) and the presence of chlorinated solvent biodegrading organisms. These two requirements are present naturally at some contamination sites, leading to natural attenuation of the solvents. If one or both requirements are absent, then engineered bioremediation either through addition of an external electron donor or through bioaugmentation with appropriate microorganisms, or both, may be used for site remediation. The most difficult case for cleanup is when a large residual of undissolved chlorinated solvents are present, residing as dense -non-aqueous-phase- liquid ( DNAPL). A major focus of this study was on the potential for biodegradation of the solvents when pre sent as DNAPL where concentrations are very high and potential for toxicity to microorganisms exist. Another focus was on a better understanding of the biological mechanisms involved in chlorinated solvent biodegradation . These studies were directed towards the chlorinated solvents, trichloroethene (TCE), tetrachloroethene or perchloroethene (PCE), and carbon tetrachloride (CT). The potential for biodegradation of TCE and PCE DNAPL was clearly demonstrated in this research. From column soil studies and batch studies we found there to be a clear advantage in focusing efforts at bioremediation near the DNAPL. Here, chlorinated solvent concentrations are the highest, both because of more favorable reaction kinetics and because such high solvent concentrations are toxic to microorganisms, such as methanogens, which compete with dehalogenators for the electron donor. Additionally, biodegradation near a PCE DNAPL results in an enhanced dissolution rate for the chlorinated solvent, by factors of three to five times, leading to a more rapid clean-up of the DNAPL zone. ...
Date: December 11, 2003
Creator: McCarty, P. L.; Spormann, Alfred M. & Criddle, Craig, S.
Partner: UNT Libraries Government Documents Department