O. R. West

Cardiff University, Cardiff, Wales, United Kingdom

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Publications (42)71.22 Total impact

  • Source
    Journal of Contaminant Hydrology 07/2006; 86:321-321. · 2.89 Impact Factor
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    ABSTRACT: Geochemical and mineralogical changes were evaluated at a field Fe0-PRB at the Oak Ridge Y-12 site concerning operation performance during the treatment of U in high NO3- groundwater. In the 5-yr study period, the Fe0 remained reactive as shown in pore water monitoring data, where increases in pH and the removal of certain ionic species persisted. However, coring revealed varying degrees of cementation. After 3.8-yr treatment, porosity reduction of up to 41.7% was obtained from mineralogical analysis on core samples collected at the upgradient gravel-Fe0 interface. Elsewhere, Fe0 filings were loose with some cementation. Fe0 corrosion and pore volume reduction at this site are more severe due to the presence of NO3- at a high level. Tracer tests indicate that hydraulic performance deteriorated: the flow distribution was heterogeneous and under the influence of interfacial cementation a large portion of water was diverted around the Fe0 and transported outside the PRB. Based on the equilibrium reductions of NO3- and SO4(2-) by Fe0 and mineral precipitation, geochemical modeling predicted a maximum of 49% porosity loss for 5 yr of operation. Additionally, modeling showed a spatial distribution of mineral precipitate volumes, with the maximum advancing from the interface toward downgradient with time. This study suggests that water quality monitoring, coupled with hydraulic monitoring and geochemical modeling, can provide a low-cost method for assessing PRB performance.
    Journal of Contaminant Hydrology 12/2005; 80(1-2):71-91. · 2.89 Impact Factor
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    ABSTRACT: Geochemical and mineralogical changes were evaluated at a field Fe0-PRB at the Oak Ridge Y-12 site concerning operation performance during the treatment of U in high NO3− groundwater. In the 5-year study period, the Fe0 remained reactive as shown in pore-water monitoring data, where increases in pH and the removal of certain ionic species persisted. However, coring revealed varying degrees of cementation. After 3.8-year treatment, porosity reduction of up to 41.7% was obtained from mineralogical analysis on core samples collected at the upgradient gravel–Fe0 interface. Elsewhere, Fe0 filings were loose with some cementation. Fe0 corrosion and pore volume reduction at this site are more severe due to the presence of NO3− at a high level. Tracer tests indicate that hydraulic performance deteriorated: the flow distribution was heterogeneous and under the influence of interfacial cementation a large portion of water was diverted around the Fe0 and transported outside the PRB. Based on the equilibrium reductions of NO3− and SO42− by Fe0 and mineral precipitation, geochemical modeling predicted a maximum of 49% porosity loss for 5 years of operation. Additionally, modeling showed a spatial distribution of mineral precipitate volumes, with the maximum advancing from the interface toward downgradient with time. This study suggests that water quality monitoring, coupled with hydraulic monitoring and geochemical modeling, can provide a low-cost method for assessing PRB performance.
    Journal of Contaminant Hydrology. 11/2005;
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    ABSTRACT: Thermogravimetric analysis (TGA) combined with X-ray diffraction (XRD) was used to identify mineral phases and determine corrosion rates of granular iron samples from a 2-yr field column study. Similar to other studies, goethite, magnetite, aragonite, and calcite were found to be the major precipitated minerals, with Fe2(OH)2CO3 and green rust as minor phases. Based on TGA-mass spectrometry (MS) analysis, Fe0 corrodes at rates of 0.5-6.1 mmol kg(-1) d(-1) in the high NO3- (up to 13.5 mM) groundwater; this rate is significantly higher than previously reported. Porosity reduction was 40.6%-45.1% for the inlet sand/Fe0 interface and 7.4%-25.6% for effluent samples of two test columns. Normalized for treatment volumes, porosity loss values are consistent with studies that use high levels of SO4(2-) but are higher than those using low levels of corrosive species. Aqueous mass balance calculations yield corrosion rates similar to the TGA-MS method, providing an alternative to coring and mineralogical analysis. A severely corroded iron sample from the column simulating a 17-yr treatment throughput showed >75% porosity loss. Extensive porosity loss due to high levels of corrosive species in groundwater will have significant impact on long-term performance of permeable reactive barriers.
    Environmental Science and Technology 12/2004; 38(21):5757-65. · 5.26 Impact Factor
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    ABSTRACT: This paper reports on the formation and dissolution of CO2/seawater/CO2 hydrate composite particles produced during field experiments in Monterey Bay, CA using a CO2 injector system previously developed in the laboratory. The injector consisted of a coflow reactor wherein water was introduced as a jet into liquid CO2, causing vigorous mixing of the two immiscible fluids to promote the formation of CO2 hydrate that is stable at ambient pressures and temperatures typical of ocean depths greater than approximately 500 m. Using flow rate ratios of water and CO2 of 1:1 and 5:1, particulate composites of CO2 hydrate/liquid CO2/seawater phases were produced in seawater at depths between 1100 and 1300 m. The resultant composite particles were tracked by a remotely operated vehicle system as they freely traveled in an imaging box that had no bottom or top walls. Results from the field experiments were consistent with laboratory experiments, which were conducted in a 70 L high-pressure vessel to simulate the conditions in the ocean at intermediate depths. The particle velocity and volume histories were monitored and used to calculate the conversion of CO2 into hydrate and its subsequent dissolution rate after release into the ocean. The dissolution rate of the composite particles was found to be higher than that reported for pure CO2 droplets. However, when the rate was corrected to correspond to pure CO2, the difference was very small. Results indicate that a higher conversion of liquid CO2 to CO2 hydrate is needed to form negatively buoyant particles in seawater when compared to freshwater, due primarily to the increased density of the liquid phase but also due to processes involving brine rejection during hydrate formation.
    Environmental Science and Technology 05/2004; 38(8):2470-5. · 5.26 Impact Factor
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    AIChE Journal 04/2004; 49(1):283 - 285. · 2.58 Impact Factor
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    ABSTRACT: Quantifying precipitates and determining corrosion rates of zero-valent iron (Fe 0 ) during groundwater treatment were pursued in two field columns by analyzing column core samples using thermo-gravimetric analysis (TGA) combined with x-ray diffraction (XRD) and scanning electron microscopy (SEM). The core precipitates included goethite, magnetite, aragonite, and calcite as major phases with lesser amounts of Fe?(OH)?CO?, and green rust, similar to other studies [1-5]. Corrosion rates derived from TGA-MS analysis of core samples ranged in 0.5 ? 6.1 mmol kg -1 d -1 , higher than a previous report [6] but not unreasonable considering that the influent contained up to 13.5 mM NO? - . At the inlet sand-Fe 0 interface, corrosion rates were similar (4.09 and 4.86 mmol kg -1 d -1 ) for both columns. Corrosion rates derived from pore water chemistry showed a decreasing trend over time. The time-weighted average corrosion rates for both columns of different throughput fell in the range based on TGA-MS results, suggesting that the aqueous mass balance calculation could provide an alternative to estimating corrosion rates in the absence of core analyses. The porosity reduction based on water chemistry was confirmed by TGA-MS results (7?77%), where the high porosity reduction occurred at reactive regions and the low at regions near the effluent. Normalized with the treatment volume, porosity reduction values agree with other studies that used high levels of SO? ?- and HCO? - [2,7,8]. The near 80% porosity reduction in more corroded regions, subjected to high throughput of an equivalent of 17-yr operation, is significant to be considered for long-term performance of permeable reactive barriers.
    Environmental Science & Technology - ENVIRON SCI TECHNOL. 01/2004; 38(21):5757-5765.
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    ABSTRACT: The operating life of an Fe(0)-based permeable reactive barrier (PRB) is limited due to chemical reactions of Fe(0) in groundwater. The relative contributions from mineral precipitation, gas production, and microbial activity to the degradation of PRB performance have been uncertain. In this controlled field study, nitrate-rich, site groundwater was treated by Fe(0) in large-volume, flow-through columns to monitor the changes in chemical and hydraulic parameters over time. Tracer tests showed a close relationship between hydraulic residence time and pH measurements. The ionic profiles suggest that mineral precipitation and accumulation is the primary mechanism for pore clogging around the inlet of the column. Accumulated N(2) gas generated by biotic processes also affected the hydraulics although the effects were secondary to that of mineral precipitation. Quantitative estimates indicate a porosity reduction of up to 45.3% near the column inlet over 72 days of operation under accelerated flow conditions. According to this study, preferential flow through a PRB at a site with similar groundwater chemistry should be detected over approximately 1 year of operation. During the early operation of a PRB, pH is a key indicator for monitoring the change in hydraulic residence time resulting from heterogeneity development. If the surrounding native material is more conductive than the clogged Fe-media, groundwater bypass may render the PRB ineffective for treating contaminated groundwater.
    Journal of Contaminant Hydrology 11/2003; 66(3-4):161-78. · 2.89 Impact Factor
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    ABSTRACT: Rapid CO2 hydrate formation was investigated with the objective of producing a negatively buoyant CO2-seawater mixture under high-pressure and low-temperature conditions, simulating direct CO2 injection at intermediate ocean depths of 1.0-1.3 km. A coflow reactor was developed to maximize CO2 hydrate production by injecting water droplets (e.g., approximately 267 microm average diameter) from a capillary tube into liquid CO2. The droplets were injected in the mixing zone of the reactor where CO2 hydrate formed at the surface of the water droplets. The water-encased hydrate particles aggregated in the liquid CO2, producing a paste-like composite containing CO2 hydrate, liquid CO2, and water phases. This composite was extruded into ambient water from the coflow reactor as a coherent cylindrical mass, approximately 6 mm in diameter, which broke into pieces 5-10 cm long. Both modeling and experiments demonstrated that conversion from liquid CO2 to CO2 hydrate increased with water flow rate, ambient pressure, and residence time and decreased with CO2 flow rate. Increased mixing intensity, as expressed by the Reynolds number, enhanced the mass transfer and increased the conversion of liquid CO2 into CO2 hydrate. Using a plume model, we show that hydrate composite particles (for a CO2 loading of 1000 kg/s and 0.25 hydrate conversion) will dissolve and sink through a total depth of 350 m. This suggests significantly better CO2 dispersal and potentially reduced environmental impacts than would be possible by simply discharging positively buoyant liquid CO2 droplets. Further studies are needed to address hydrate conversion efficiency, scale-up criteria, sequestration longevity, and impact on the ocean biota before in-situ production of sinking CO2 hydrate composite can be applied to oceanic CO2 storage and sequestration.
    Environmental Science and Technology 09/2003; 37(16):3701-8. · 5.26 Impact Factor
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    ABSTRACT: The effects of sediment surfaces on methane hydrate formation and dissociation were investigated using colloidal suspensions and new experimental methods developed for a large volume (72 liters), temperature-controlled pressure vessel. Hydrates were formed by bubbling methane gas through test solutions at temperatures and pressures within the hydrate stability field. Hydrate formation was visually detected by the accumulation of hydrate-encrusted gas bubbles. To measure hydrate dissociation conditions, the pressure vessel was warmed while temperature was monitored within a zone of previously formed hydrate-encrusted gas bubbles. Hydrate dissociation was indicated by a distinct plateau in the hydrate zone temperature, while temperatures of the gas and liquid phases within the vessel continued to rise. The ‘dissociation plateau’ appears to be a phenomenon that is unique to the large volume of the pressure vessel used for the experiments. In experiments where hydrates were formed in pure water, temperature and corresponding pressure conditions measured during the temperature plateau matched model-predicted values for hydrate stability in water, thus confirming the validity of this new method for measuring hydrate dissociation conditions. Formation and dissociation conditions were measured for methane hydrates in colloidal suspensions containing bentonite. Hydrate formation experiments indicated that the presence of bentonite in water at 200 mg/l significantly decreased pressures required for hydrate formation relative to formation in pure water alone. On the other hand, hydrate dissociation conditions measured in bentonite and silica suspensions with solids concentrations of 34 g/l did not differ significantly from that of water. These results are relevant to the origin and stability of natural gas hydrate deposits known to exist in deep permafrost and marine sediments, where the effects of sediment surfaces are largely unknown.
    Marine Geology 01/2003; · 2.73 Impact Factor
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    Environmental Engineering Science - ENVIRON ENG SCI. 01/2003; 20(6):635-653.
  • Environmental Science & Technology - ENVIRON SCI TECHNOL. 01/2003; 37(16):3701-3708.
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    ABSTRACT: This report describes the application of palladized iron (Pd/Fe) to the dechlorination of polychlorinted biphenyls (PCBs) at ambient temperature. Experiments supported by congener-specific analyses demonstrated that dechlorination occurs in a step-wise fashion with the meta-chlorines being more reactive than ortho-chlorines. Over the course of the laboratory experiments, complete conversion to biphenyl was observed. The process was also tested with PCBs dissolved in high (40-60%) concentrations of ethanol and isopropanol as a means of simulating solutions generated by commercial soil and solid waste extraction processes. The reaction rate was sensitive to the percentage of solvent but complete dechlorination was still indicated. Tests with soil extracts from a contaminated site demonstrated that there were no apparent interferences from asphalt and other miscellaneous debris. Short-duration tests with highly contaminated PCB solutions from a hazardous waste site demonstrated efficient dechlorination although there was a reduction in reaction rate with time.
    Waste Management 02/2002; 22(3):343-9. · 3.16 Impact Factor
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    ABSTRACT: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof
    05/2001;
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    ABSTRACT: A seafloor process simulator (SPS) has been developed for experimental investigations of the physical, geochemical, and microbiological processes affecting the formation and stability of methane and carbon dioxide hydrates at temperatures and pressures corresponding to ocean depths of 2 km. The SPS is a corrosion-resistant pressure vessel whose salient characteristics are: (i) an operating range suitable for study of methane and carbon dioxide hydrates; (ii) numerous access and observation ports, and (iii) a large (0.0722 m3) internal volume. Initial experiments have shown that the SPS can be used to produce large amounts of high-purity methane hydrate over a wide range of experimental conditions.
    The Review of scientific instruments 01/2001; 72:1514-1521. · 1.52 Impact Factor
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    ABSTRACT: In July 1996, the US Department of Energy (DOE) Kansas City Plant (KCP), AlliedSignal Federal Manufacturing and Technologies, and Oak Ridge National Laboratory (ORNL), conducted field-scale tests of in situ soil mixing and treatment technologies within the Northeast Area (NEA) of the KCP at the Former Ponds site. This demonstration, testing, and evaluation effort was conducted as part of the implementation of a deep soil mixing (DSM) innovative remedial technology demonstration project designed to test DSM in the low-permeability clay soils at the KCP. The clay soils and groundwater beneath this area are contaminated by volatile organic compounds (VOCs), primarily trichloroethene (TCE) and 1,2-dichloroethene (1,2-DCE). The demonstration project was originally designed to evaluate TCE and 1,2-DCE removal efficiency using soil mixing coupled with vapor stripping. Treatability study results, however, indicated that mixed region vapor stripping (MRVS) coupled with calcium oxide (dry lime powder) injection would improve TCE and 1,2-DCE removal efficiency in saturated soils. The scope of the KCP DSM demonstration evolved to implement DSM with the following in situ treatment methodologies for contaminant source reduction in soil and groundwater: DSM/MRVS coupled with calcium oxide injection; DSM/bioaugmentation; and DSM/chemical oxidation using potassium permanganate. Laboratory treatability studies were started in 1995 following collection of undisturbed soil cores from the KCP. These studies were conducted at ORNL, and the results provided information on optimum reagent concentrations and mixing ratios for the three in situ treatment agents to be implemented in the field demonstration.
    10/1998;
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    ABSTRACT: In situ chemical oxidation is a developing class of remediation technologies in which organic contaminants are degraded in place by powerful oxidants. Successful implementation of this technology requires an effective means for dispersing the oxidant to contaminated regions in the subsurface. An oxidant delivery technique has been developed wherein the treatment solution is made by adding an oxidant to extracted groundwater. The oxidant-laden groundwater is then injected and recirculated into a contaminated aquifer through multiple horizontal and/or vertical wells. This technique, referred to as in situ chemical oxidation through recirculation (ISCOR), can be applied to saturated and hydraulically conductive formations and used with relatively stable oxidants such as potassium permanganate (KMnO{sub 4}). A field-scale test of ISCOR was conducted at a site (Portsmouth Gaseous Diffusion Plant) where groundwater in a 5-ft thick silty gravel aquifer is contaminated with trichloroethylene (TCE) at levels that indicate the presence of residual dense non-aqueous phase liquids (DNAPLs). The field test was implemented using a pair of parallel horizontal wells with 200-ft screened sections. For approximately one month, groundwater was extracted from one horizontal well, dosed with crystalline KMnO{sub 4}, and re-injected into the other horizontal well 90 ft away. Post-treatment characterization showed that ISCOR was effective at removing TCE in the saturated region. Lateral and vertical heterogeneities within the treatment zone impacted the uniform delivery of the oxidant solution. However, TCE was not detected in groundwater samples collected from monitoring wells and soil samples from borings in locations where the oxidant had permeated.
    08/1998
  • L. Liang, O.R. West, N.E. Korte
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    ABSTRACT: The dehalogenation of chlorinated solvents by zero-valence iron has recently become the subject of intensive research and development as a potentially cost-effective, passive treatment for contaminated groundwater through reactive barriers. Because of its successful application in the laboratory and other field sites, the X-625 Groundwater Treatment Facility (GTF) was constructed to evaluate reactive barrier technology for remediating trichloroethylene (TCE)-contaminated groundwater at the Portsmouth Gaseous Diffusion Plant (PORTS). The X-625 GTF was built to fulfill the following technical objectives: (1) to test reactive barrier materials (e.g., iron filings) under realistic groundwater conditions for long term applications, (2) to obtain rates at which TCE degrades and to determine by-products for the reactive barrier materials tested, and (3) to clean up the TCE-contaminated water in the X-120 plume. The X-625 is providing important field-scale and long-term for the evaluation and design of reactive barriers at PORTS. The X-625 GTS is a unique facility not only because it is where site remediation is being performed, but it is also where research scientists and process engineers can test other promising reactive barrier materials. In addition, the data collected from X-625 GTF can be used to evaluate the technical and economic feasibility of replacing the activated carbon units in the pump-and-treat facilities at PORTS.
    08/1997;
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    ABSTRACT: Researchers at the Oak Ridge National Laboratory (ORNL) have been investigating the use of in situ chemical oxidation to remediate organic contaminants (VOCs, SVOCs, and PCBs) in soils and groundwater at the laboratory and field scales. Field scale design parameters (e.g., oxidant loading rates and oxidant delivery techniques) are often dictated by site conditions (e.g., soil properties and initial contaminant concentrations). Chemical destruction of organic compounds can be accomplished using a variety of oxidants. Recent research has involved field scale in situ chemical oxidation demonstrations using H{sub 2}O{sub 2} and KMnO{sub 4} in conjunction with soil mixing as the oxidant delivery mechanism. A description of some of these fields activities and future field-scale work is presented here.
    03/1997
  • O.R. West, L. Liang, W.L. Holden
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    ABSTRACT: Contamination from polychlorinated biphenyls (PCBs) is a persistent problem within the Department of Energy complex, as well as in numerous industrial sites around the US. To date, commercially available technologies for destroying these highly stable compounds involve degradation at elevated temperatures either through incineration or base-catalyzed dehalogenation at 300{degrees}C. Since the heating required with these processes substantially increases the costs for treatment of PCB-contaminated wastes, there is a need for finding an alternative approach where PCB can be degraded at ambient temperatures. This report describes the degradation of PCB`s utilizing the bimetallic substrate of iron/palladium.
    05/1996;

Publication Stats

295 Citations
71.22 Total Impact Points

Institutions

  • 2006
    • Cardiff University
      • School of Engineering
      Cardiff, Wales, United Kingdom
  • 1997–2006
    • Oak Ridge National Laboratory
      • Environmental Sciences Division
      Oak Ridge, Florida, United States