In semiconductor manufacturing, silicon wafers are repeatedly cleaned with ultrapure water. As the wafer size increases and the line width shrinks, the ultrapure water consumption continues to increase. More stringent requirements are placed on the rinse water specification. Improvements in water purification must be brought forth to meet the needs. The total concentration of all inorganic ions subject to measurement in ultrapure water is often below 1 ppb. By comparison, the concentration of organic contaminants is often an order of magnitude higher. Organic contaminants in rinse water cause defects and decrease device yield. Removing organic contaminants is therefore very important. The present study focuses on the mechanisms and kinetics of various organic impurity removal processes, particularly, of chemical oxidation processes. A novel photocatalytic filter is developed that incorporates the feature of filtration and chemical oxidation. Organic contaminants are separated through entrapment and adsorption. They are destroyed through photocatalytic oxidation. The oxidation of organic contaminants using UV irradiation, ozone or a combination of UV and ozone is studied. For most model contaminants, UV oxidation is not a first order reaction in terms of the contaminant concentration. UV/ozone oxidation removes organic contaminants synergistically. The removal of dissolved gases and VOCs using a unique membrane degasification technology is also investigated. Another important aspect is the qualitative and quantitative analysis of impurities. In this work, organic impurities are measured using a combination of a total oxidizable organic monitor and a non-volatile residue monitor. A new method is studied using an attenuated total reflection - Fourier transform infrared spectrometer. It has the advantage of detecting the most harmful organic contaminants which adsorb on a silicon wafer. Based on the fundamental information obtained on each process unit, an overall process simulator is developed. Modeling an ultrapure water system will reveal its response characteristics to a possible contamination challenge. This makes it possible to optimize the system configuration and operation. The feasibility of rinse water recycling/reclamation is also studied.

A new real-time in-field interpretation and visualization scheme and software, using neural networks for the detection and localization of buried waste, and the boundaries of waste sites, has been developed. The capabilities and limitations of the high-frequency (1 kHz to 1 MHz and 31 kHz to 32 MHz) electromagnetic ellipticity systems are analyzed by numerically studying the sensitivity of the acquired 3D-ellipticity to model parameters describing the geometry of the systems and the electrical parameters of layered-earth models. Changes in ellipticity due to coil misalignment in standard operating mode are typically just 1% to 2%. Changes due to variations in layered-earth model parameters (resistivity, relative dielectric constant, and thickness) are typically at least one order of magnitude higher. Hence, it will be possible to resolve these parameters. For conductive models (resistivity < 50 Ωm) it will be hard to determine the relative dielectric constant and for models with high relative dielectric constants it will be hard to determine the resistivity, especially if it is greater than 1000 Ωm. The results of the sensitivity analysis contribute considerably to the training of several neural networks to determine the electrical properties of the subsurface. The two classes of artificial neural network paradigms utilized in this study are the radial basis function and the modular neural network algorithms. One-dimensional layered-earth inversions are performed by neural networks using ellipticity data. The three-dimensional localization of metallic objects (e.g. drums) is done by visualizing the results of one particular halfspace neural network technique. Several small conductive objects have been detected by applying this technique to data collected in controlled physical modeling field experiments. Classification neural networks are trained on field data to categorize ellipticity soundings into either a target or a background class. Two environmental geophysics field case studies were analyzed using the developed interpretation system and the visualization software. The first case study involves mapping subsidence areas caused by an underground coal mine fire in Wyoming. The neural network interpretations from the mine survey match comparable inversion results. The second study documents the successful characterization of a simulated hazardous waste pit at the Idaho National Engineering Laboratory.

The migration of tritium during a large-scale natural-gradient tracer experiment in Columbus, Mississippi, was simulated using a three-dimensional finite element model for water flow and transport. The results showed that modeling approaches that assume complete homogeneity of the aquifer or of hydrostratigraphic units within the aquifer failed to reproduce the temporal evolution of the first and second spatial moments of the experimental plume. In contrast, the simulation approach that accounted for aquifer heterogeneity gave first spatial moment estimates that were in good overall agreement with experimental results, but failed to simulate the second spatial moments of the tritium plume. The discrepancy between the experimental and simulated second spatial moments may be caused by the temporal and spatial variability of the actual boundary conditions which were not accounted for in the simulations. The failure of homogeneous approaches to simulate the evolution of the tritium plume raises serious questions about the utility of upscaled effective hydraulic properties for forecasting flow and solute transport in aquifers.

The well documented ineffectiveness of traditional pump-and-treat technology on the cleanup of non aqueous phase liquid (NAPL) contaminated sites has incurred an intensive research activities in improving the efficiency of NAPL removal from subsurface. Surfactant enhanced subsurface remediation has been proposed as one such option. In this dissertation, a series laboratory experiments were conducted to investigate the potential application of a microbially produced surfactant (biosurfactant) on NAPL removal and the effect on bacteria transport. Monorhamnolipid biosurfactant, produced by Pseudomonas aeruginosa ATCC 9027, was used in all the studies. Hexadecane was used as model NAPL to represent petroleum based products which are common NAPLs detected in contaminated sites. Results showed that rhamnolipid biosurfactant is effective in removing residual hexadecane from sandy soil. In the surfactant concentration tested in this study (40 to 1500 mg/L), mobilization of hexadecane is the main mechanism of the removal. In addition to displacement of hexadecane droplets from subsurface porous matrixes, dispersion or emulsification of hexadecane into surfactant solution also played an important role in hexadecane removal. The performance of this anionic rhamnolipid surfactant is greatly affected by the addition of electrolytes and the change of pH. Addition of Na⁺ and Mg²⁺ can significantly increase the solubilization capacity of rhamnolipid and reduce the interfacial tension between hexadecane and surfactant solution, while addition of Ca²⁺ has a competing effects of enhanced solubilization and Ca²⁺ induced rhamnolipid precipitation. Control of ionic strength and pH can be used to optimize surfactant systems to enhance the NAPL removal depending on the nature of NAPL (LNAPL or DNAPL). Addition of rhamnolipid can also enhance the transport of three bacterial cells with varying hydrophobicity, P. aeruginosa ATCC 9027, 27853, and 15442, by decreasing cell adsorption. This is because the adsorption of surfactant to the porous medium surface increases the surface negative charge density, hence the adsorption of bacteria to the surface is reduced. No significant influence of rhamnolipid on the bacteria surface properties is observed. The measured bacteria breakthrough curves were simulated by an advection-dispersion transport model incorporating two domain reversible sorption (instantaneous and rate-limited) and with two first order sink terms for irreversible sorption. Model simulation suggests that rhamnolipid mainly affects the irreversible sorption of cells.

The Monterrey Metropolitan Area is one of the fastest growing areas of Mexico. As a result of this growth, this major urban and industrial center has begun to experience air quality degradation. The Mexican ozone standard (110 ppbv) has been exceeded on 63 days during the period 1993-1995. This study is the first integrated examination of air quality, pollutant emissions, and climate to cover the ozone behavior in Monterrey. Pollutant concentrations and weather conditions were characterized spatially and temporally for all seasons during 1995. Higher ozone concentrations were found in the southwestern region during Spring. Diurnal patterns of ambient concentration ratios and distributions of daily ozone maximum for weekdays and weekends indicate that industrial emissions seem to be a important contributor of ozone formation. Pollutant emissions were estimated from continuous data of air quality network and on-road vehicle emissions. Diurnal patterns of CO and NOx emissions were calculated for January and July 1995 using a flow model based on mass conservation and estimated parameters of lateral advection and chemical loss. To predict how ozone will change in response to prescribed changes in emissions, this emission inventory is consistent and the most reliable. Circulation patterns associated to high-ozone episodes were identified from synoptic meteorological maps. High-pressure systems, migratory anticyclones, elevated mixed layer, cold front passages and mountain-valley winds produced subsidence, flow reversal, and stagnation when elevated ozone affected Monterrey. Hydrocarbon reduction was determined as the most effective strategy for reducing ozone applying a photochemical box model to high-ozone episodes in 1995. Using sensitivity analysis, emissions and meteorological variables were ranked by their relative contributions to ozone formation. The model employs the Carbon Bond Mechanism IV and a hybrid method for solving stiff chemical kinetic equations. The application of this model highlights the major mesoscale and synoptic features of the Monterrey climate. Incursions of air masses of subtropical and midlatitude circulation regimes are highly variable, while high solar radiation occurs all year.

Contamination of soil and groundwater environments by toxic metals and organic compounds is of major concern because of the potential health hazard posed for humans. Remediation of such sites may require the addition of chemical agents that help in the mobilization of contaminants which are likely to be bound to solid surfaces. Surfactants are one of the agents proposed for addition to enhance the removal of soil-bound contaminants. In this dissertation, a series of laboratory experiments were conducted to investigate constraints to the potential application of a microbially produced surfactant (biosurfactant) for removal of metal contaminants from soil. The first part of the dissertation describes the measurement of stability constants and 13 metals including ten of the metals most frequently found in contaminated sites as well as three of the most common metal cations found in soil, Ca²⁺, Mg ²⁺, and K⁺. The second part of the dissertation describes a series of experiments designed to determine the interaction of the biosurfactant with soil matrix components including clays, metal oxides, and organic matter. The biosurfactant used in this research was monorhamnolipid produced by Pseudomonas aeruginosa ATCC 9027. A mixture of mono- and dirhamnolipid produced by P. aeruginosa UG2 was also used in some cases. Results showed that selectivity of the monorhamnolipid followed the order: Al³⁺ > Cu²⁺ > Pb²⁺ > Cd²⁺ > Zn²⁺ > Fe³⁺ > Hg ²⁺ > Ca²⁺ > Co²⁺ > Ni²⁺ > Mn²⁺ > Mg²⁺ > K⁺. These results suggest that monorhamnolipid binds common metal contaminants in preference over common soil cations such as Ca²⁺, Mg²⁺, and K⁺. Rhamnolipid was shown to bind to some soil constituents very strongly including hematite, illite, kaolinite, and montmorillonite. These results indicate that the effectiveness of rhamnolipid in soils with high amounts of iron oxide or clay may be limited due to extensive sorption. Finally, it was found that monorhamnolipid sorbed more strongly than a rhamnolipid mixture containing both monorhamnolipid and dirhamnolipid. This suggests that the use of a biosurfactant mixture may improve the effectiveness of rhamnolipid in the removal of organic and metal contaminants from soil.

In-situ bioremediation is a promising biotechnology for removing aqueous phase contaminants from groundwater. Utilizing indigenous bacteria to degrade organic contaminants into non-toxic components, bioremediation is relatively inexpensive, fast, and complete. Making predictions about its applicability and success is difficult because of the complexity and variability intrinsic to the subsurface environment. Analytical studies of models, independent of this detailed subsurface data, are essential to finding accurate quantitative results, yet few have been obtained. This dissertation is a collection of three mathematical reports on a one-dimensional model for bioremediation. Using degree theory, the elliptic maximum principle, and comparison theorems, existence of traveling wave solutions to the biodegradation model is proved, a formula for the speed of the traveling concentration front is derived, and bounds on the biomass concentration are obtained. In the second section, the model is shown to reduce to a single equation in the relaxation limit by using properties of systems of hyperbolic conservation laws. In the third section, a formula is found for the parameters at which an unstable traveling wave solution bifurcates to a stable limit cycle (oscillatory solution). These results provide practical information about the structure of concentration fronts for the contaminant, nutrient, and biomass. The fronts travel at speeds that are either constant or time-periodic, depending on the kinetic parameters of the bacteria and the sorption properties of the contaminant. When there is little growth in biomass, many critical properties of the concentrations are derived. For aquifers with low permeability, the model is reduced to a much simpler system, also allowing the derivation of many analytical properties. Though comparisons with experimental data have not yet been done, numerical simulations support these results.

An integrated wastewater treatment facility at a dairy in Glendale, Arizona, consisting of an upper subsystem (solids separators, anaerobic lagoons, and aerobic ponds) and lower subsystem (wetland subsystems) has been proven to be successful in reducing indicator organisms and potential pathogens (bacteria, enteric viruses, and parasites). The collection sump of the new integrated system collects all dairy wastewater and pumps it to solid separators, which then flows by gravity to anaerobic lagoons and aerobic ponds. The upper subsystem achieved significant microbial reductions of >98 percent for total coliform, >91 percent for coliphage, >95 percent for enterococci, >91 percent for Listeria monocytogenes, and >99.9 percent for Cryptosporidium . Additional reductions although limited were observed in the outflow from the wetland cells.

In this work, an electrochemical method was developed to destroy liquid chlorinated solvents, and a thermochemical technique was invented to reduce gas-phase chlorinated solvents to hydrocarbons. The developed electrochemical method belongs to the most potential technique for wastewater treatment--only electrochemical method is possible to simultaneously destroy all water contaminants; the invented thermochemical method is the fastest way to destroy chlorinated solvents. In the first part of this work, the anodic oxidation of trichloroethylene (TCE) on an Ebonex ceramic electrode was investigated. TCE could be oxidized to CO₂, CO, Cl⁻, and ClO₃⁻. The disappearance of TCE was first-order, independent of pH, and initial TCE concentrations. TCE oxidation occurred only on the anodic surface and was limited by mass transport at Ea > 4.3 V vs SSCE ( i > 5 mA cm⁻²). Hydroxyl radicals generated on anode surface were detected using a spin trap. A kinetic model was successfully correlated with experimental results. In the second part of this work, TCE and CF were rapidly dechlorinated to hydrocarbons on the Ebonex ceramic cathode using Pt or Pd as catalyst. Pt was found to possess great resistance to sulfur and chlorine poisoning. Pd was quickly deactivated in sulfate solution. TCE and CF cathodic transformation were strongly dependent of pH. The reaction rate was limited by mass transport at Ec<-1.6 V (i > 5 mA cm⁻²). The mass transfer to cathode surface was found to be three times faster than to anode surface. The main products of TCE reduction were ethane, ethylene, and chloride, and for CF were methane and chloride. The proposed reaction mechanism and kinetic model were consistent with experimental results. In the third part of this work, a new hydrodechlorination method was invented for gas-phase chlorinated solvent destruction. Gas-phase chlorinated solvents, such as PCE, TCE, 1,1-DCE, VC, and CF were rapidly reduced to ethane, ethylene, and methane in a continuous-flow column reactor at ambient temperature and pressure. This is the fastest way to destroy chlorinated solvents. The catalyst could be easily regenerated and had a long-life time (over one and half year). The reaction mechanism and kinetics were studied. In the forth part of this work, the first three parts of work were combined together to invent a new destruction method for chlorinated solvents in real wastewater. Ebonex ceramic materials served as electrodes and Pt was plated on cathode used as catalyst in the electrolytic cell. The headspace of the electrolytic cell was connected to the Pd/Ni catalyst column. Liquid chlorinated solvents were destroyed on electrode surface, and gas-phase chlorinated solvents were reduced to hydrocarbons in the Pd/Ni catalyst surface in the presence of hydrogen. Water scale or other deposited materials on Pt coated Ebonex cathode could be removed, and the catalyst could be regenerated by reversing electrode polarity.

Soil venting, which includes gas injection as well as gas extraction in subsurface media, has become the primary method used in the United States to remove volatile organic compounds (VOCs) from unsaturated subsurface media. The popularity and widespread use of venting is due to its simplicity of operation and proven ability to remove contaminant mass inexpensively compared to competing technologies. Despite the common use of venting in the Superfund program, there is little consistency in approach to assessment of performance and closure. Assessment of the technology's performance and eventual decisions on closure are based primarily on negotiations between responsible parties and regulators. In this process there is widespread use and reliance on empirical methods as opposed to an emphasis on understanding fundamental physical, chemical, and biological processes controlling mass removal during the venting operation. This results in the technology not being used to its fullest potential, nor its limitations being well understood. The overall purpose of the work described in this dissertation was to improve the "state of the art" and "state of the science" of soil venting application. This purpose was accomplished by attainment of three specific objectives. The first objective was to develop an overall regulatory approach to assess venting performance and closure including measures to ensure consistency in ground-water and vadose zone remediation. The second objective was to provide comprehensive and detailed literature reviews on gas flow and vapor transport. These reviews formed the basis of recommendations and methods to improve venting design and monitoring. The third objective was to perform research to improve various aspects of venting application. This research consisted of: (1) analysis of linearization of the gas flow equation, (2) one-dimensional steady-state analysis of gas slippage, (3) two-dimensional steady-state analysis of gas flow and permeability estimation in a domain open to the atmosphere, (4) two-dimensional steady-state analysis of gas flow and permeability estimation in a semi-confined domain, (5) two-dimensional transient gas flow analysis and permeability estimation, (6) analysis and comparison of radius of influence versus critical pore-gas velocity based venting design, (7) modification of a gas extraction well to minimize water-table upwelling, (8) simulation of rate-limited vapor transport with diffusion modeling, (9) assessment of respiration testing, (10) development of a one-dimensional, analytical, vadose zone transport code to simulate mass flux to and from the capillary fringe, and (11) analysis of water-table mounding during sparging.