Citric Acid-Modified Fenton's Reaction for the Oxidation of Chlorinated Ethylenes in Soil Solution Systems

Fenton's reagent, a solution of hydrogen peroxide and ferrous iron catalyst, is used for an in-situ chemical oxidation of organic contaminants. Sulfuric acid is commonly used to create an acidic condition needed for catalytic oxidation. Fenton's reaction often involves pressure buildup and precipitation of reaction products, which can cause safety hazards and diminish efficiency. We selected citric acid, a food-grade substance, as an acidifying agent to evaluate its efficiencies for organic contaminant removal in Fenton's reaction, and examined the impacts of using citric acid on the unwanted reaction products. A series of batch and column experiments were performed with varying H{sub 2}O{sub 2} concentrations to decompose selected chlorinated ethylenes. Either dissolved iron from soil or iron sulfate salt was added to provide the iron catalyst in the batch tests. Batch experiments revealed that both citric and sulfuric acid systems achieved over 90% contaminant removal rates, and the presence of iron catalyst was essential for effective decontamination. Batch tests with citric acid showed no signs of pressure accumulation and solid precipitations, however the results suggested that an excessive usage of H{sub 2}O{sub 2} relative to iron catalysts (Fe{sup 2+}/H{sub 2}O{sub 2} < 1/330) would result in lowering the efficiency of contaminant removal by iron chelations in the citric acid system. Column tests confirmed that citric acid could provide suitable acidic conditions to achieve higher than 55% contaminant removal rates

Laboratory measurements on core-scale sediment/hydrate samples topredice reservoir behavior

Measurements on hydrate-bearing laboratory and field samplesare necessary in order to provide realistic bounds on parameters used innumerically modeling the production of natural gas from hydrate-bearingreservoirs. The needed parameters include thermal conductivity,permeability, relative permeability-saturation(s) relationships, andcapillary pressure-saturation(s) relationships. We have developed atechnique to make hydrate-bearing samples ranging in scale from coreplug-size to core-size in the laboratory to facilitate making thesemeasurements. In addition to pressure and temperature measurements, weuse x-ray computed tomography scanning to provide high-resolution dataproviding insights on processes occurring in our samples. Several methodsare available to make gas hydrates in the laboratory, and we expect thatthe method used to make the hydrate will impact the behavior of thehydrate sample, and the parameters measured

An inquiry into the phenomenon of enhanced transport of triazines with treated effluents

The use of treated effluents for irrigation has been postulated to facilitate movement of soil-borne pesticides. Factors that may result in enhanced downward movement of pesticides include complexation with dissolved organic material (DOM) present in effluent, coating of soil surfaces with effluent DOM, effluent-induced increases in soil-solution pH, effluent-induced decreases in pore-water velocity, and effluent-induced changes in microbial ecology. The potential of municipal wastewater effluent and swine-derived lagoon effluent to enhance the mobility of prometryn and atrazine was evaluated using batch, column, and modeling techniques. Given the moderate polarity of triazines, facilitated transport of pesticide is most likely not due to complexation with effluent DOM. However, effluent-induced increases in soil-solution pH and decreases in pore-water velocity indicated that there was some potential for enhanced transport under treated-effluent irrigation. Coupled impact of decreased pore-water velocity with wetting and drying event on enhanced pesticide mobility was dependent of soil texture, drying period, and climate conditions

Relative Permeability Parameter Estimation for Laboratory-Formed Hydrate Bearing Sediments 1

Relative permeability is an essential parameter governing flow of water and gas through hydrate bearing sediments during gas production, and has not been extensively examined. We formed methane hydrate in three different kinds of silica sand (Korean sand, F110 sand, and a mixture of F110 sand and fine silt). Hydrate formation and phase saturation were monitored using temperature and pressure measurements as well as x-ray computed tomography (CT). The van Genuchten model relative permeability parameter, m, (van Genuchten, 1980) was estimated using differential pressure (ΔP) across the sand column under steady state flow and average hydrate saturation measured with CT images. We compared the estimated parameters in terms of hydrate saturations (20-35%) and sand types. Further estimations of the relative permeability parameter are underway using numerical inversion of transient CT measured water saturation data and independently measured capillary pressure

A 3-Dimensional discrete fracture network generator to examine fracture-matrix interaction using TOUGH2

Water fluxes in unsaturated, fractured rock involve the physical processes occurring at fracture-matrix interfaces within fracture networks. Modeling these water fluxes using a discrete fracture network model is a complicated effort. Existing preprocessors for TOUGH2 are not suitable to generate grids for fracture networks with various orientations and inclinations. There are several 3-D discrete-fracture-network simulators for flow and transport, but most of them do not capture fracture-matrix interaction. We have developed a new 3-D discrete-fracture-network mesh generator, FRACMESH, to provide TOUGH2 with information about the fracture network configuration and fracture-matrix interactions. FRACMESH transforms a discrete fracture network into a 3 dimensional uniform mesh, in which fractures are considered as elements with unique rock material properties and connected to surrounding matrix elements. Using FRACMESH, individual fractures may have uniform or random aperture distributions to consider heterogeneity. Fracture element volumes and interfacial areas are calculated from fracture geometry within individual elements. By using FRACMESH and TOUGH2, fractures with various inclinations and orientations, and fracture-matrix interaction, can be incorporated. In this paper, results of flow and transport simulations in a fractured rock block utilizing FRACMESH are presented

Preliminary Evaluation of Drift Seepage Model Using Seepage Information from the ESF South Ramp at Yucca Mountain, Nevada

The overall objective of this study is to examine whether the modeling approach employed to estimate seepage into waste emplacement drifts yields results that are consistent with the observed seepage in the ESF South Ramp. It is important to realize that the modeling study reported here is not an attempt to predict, reproduce, or analyze the South Ramp seepage data. Such an effort would require the development of a specific model and a specific characterization and analysis approach best suited for capturing the hydrogeologic conditions in the South Ramp as they prevailed before and during the period of the seepage observations. Instead, the conceptual framework and analysis approach developed for the estimation of long-term seepage into waste emplacement drifts in the Topopah Spring unit is used with minimal adjustments to examine whether the results of the probabilistic approach employed in the TSPA-LA (which considers uncertainty and spatial variability in fracture permeability, capillary strength, and local percolation flux) would provide reasonable seepage estimates, even if applied to the conditions in the South Ramp. If so, confidence can be gained that the TSPA-LA approach captures the processes relevant for the prediction of natural seepage into large underground openings

A 3-Dimensional discrete fracture network generator to examine fracture-matrix interaction using TOUGH2

Water fluxes in unsaturated, fractured rock involve the physical processes occurring at fracture-matrix interfaces within fracture networks. Modeling these water fluxes using a discrete fracture network model is a complicated effort. Existing preprocessors for TOUGH2 are not suitable to generate grids for fracture networks with various orientations and inclinations. There are several 3-D discrete-fracture-network simulators for flow and transport, but most of them do not capture fracture-matrix interaction. We have developed a new 3-D discrete-fracture-network mesh generator, FRACMESH, to provide TOUGH2 with information about the fracture network configuration and fracture-matrix interactions. FRACMESH transforms a discrete fracture network into a 3 dimensional uniform mesh, in which fractures are considered as elements with unique rock material properties and connected to surrounding matrix elements. Using FRACMESH, individual fractures may have uniform or random aperture distributions to consider heterogeneity. Fracture element volumes and interfacial areas are calculated from fracture geometry within individual elements. By using FRACMESH and TOUGH2, fractures with various inclinations and orientations, and fracture-matrix interaction, can be incorporated. In this paper, results of flow and transport simulations in a fractured rock block utilizing FRACMESH are presented