A mathematical module was developed to evaluate the effect of the common fuel additive, ethanol, on benzene fate and transport in groundwater, and to discern the most influential benzene plume-elongating mechanisms. The module, developed for the RT3D (Reactive Transport in 3-Dimensions) model, includes previously evaluated fate and transport processes (advection, dispersion, adsorption, biodegradation and depletion of molecular oxygen during ethanol degradation) and substrate interactions (dilution of benzene metabolic flux, catabolite repression and microbial populations shifts) previously not considered. Benzene plume elongation predictions, based on literature model parameters, were on the order of 22%-40% for a constant source of E10 gasoline (10% v/v ethanol), which compares favorably to field observations (56%, Ruiz-Aguilar et al., 2003). Oxygen depletion during ethanol degradation was the principal mechanism hindering benzene natural attenuation, followed by metabolic flux dilution. When oxygen is not limiting, model simulations showed that microbial growth on ethanol could offset negative substrate interactions and enhance benzene degradation, resulting in shorter plumes.

The transport, uptake and degradation of hydrocarbons by microorganisms has been a subject of interest for many years. The inherent low solubility of most hydrocarbons has been thought to be one of the limiting factors in the overall rate of degradation of hydrocarbons. The ability of surfactants to form micelles and increase the solubility of hydrocarbons to many times their normal solubility may overcome this limitation. Designed experiments with well defined surfactant systems of known phase behavior were done to investigate the effects of micellar solubilization by nonionic, ionic, and mixed nonionic and ionic surfactants on the degradation of n-alkanes by pure cultures of three strains of Gram-negative bacteria. It was found that solubilization by nonionic surfactants greatly increased the growth rates and accompanying oxidation of alkanes for two of the three bacterial strains. It also appeared, from initial experiments, that the inhibitory effect of the ionic micelles could be mediated by the addition of nonionic surfactants to form mixed micelles. A mathematical model that treated the solubilized alkanes as soluble substrates via a Monod expression with competitive enzyme interaction successfully described the experimental data. Nonlinear parameter estimation using a maximum likelihood method indicated that $\rm\mu\sb{max}$ was constant for a particular bacterial strain, and independent of surfactant concentration and alkane. The variation in observed growth rates was reflected in the variation of the $\rm K\sb{s}$ parameter which was found to be a function of surfactant type and alkane. The variation appears to represent differences in the rates of transport of the alkanes through the cell membranes.

A previously developed model describing colloidal fouling of membrane filters (Sethi, 1997) predicts that operation under conditions of constant transmembrane pressure should result in less fouling than operation at constant permeate flux. These predictions were tested in a series of laboratory experiments. The influence of particle size and mode of operation on the specific permeate flux performance of a cross-flow flat slit membrane unit, was evaluated using an ultra-filtration membrane mounted in an existing Osmonics SEPA CF membrane module. Experiments of three hours in duration were conducted with polystyrene latex particles (100 nm, 430 nm, and 1000 nm) which resulted in a strong correlation between particle size and specific permeate flux. Consistent with theoretical prediction, less fouling was observed in a constant pressure mode of operation. However difference in between the two modes of operation with different particle sizes were not as great as anticipated. Indications for a strong influence of the flowing layer on the specific permeate flux performance were found for the 1000 nm particles. Future research for a better understanding of the role of the flowing layer and cake resistance in membrane fouling is needed and recommended.

An experiment was designed to test the hypothesis that bioremediation within DNAPL source zones is feasible provided all limiting factors are delivered in adequate amounts. A demonstration-scale aboveground aquifer simulation system was bioaugmented with a mixed anaerobic dechlorinating culture after the addition of neat PCE below the water table. Hydrogen Releasing Compound RTM was introduced to the tank to provide a long-term and steady supply of reducing equivalents for dechlorination. The system effluent was monitored for chlorinated ethene concentrations, and results demonstrated the dechlorination of PCE to trichloroethene (TCE) and cis-dichloroethene (cis-DCE). Measurements at the end of the study indicated the following mole fractions in the effluent: cis-DCE (66%), TCE (24%), and PCE (10%).

A controlled pilot scale aquifer system known as the Experimental Controlled Release System (ECRS) was used to evaluate the bioremediation of PCE DNAPL source zones. The addition of DNAPL in the ECRS made a thorough hydrologic evaluation of the system both more essential and problematic. The focus of this research was to develop a detailed site characterization to help ensure the effective delivery of electron donor (Hydrogen Releasing Compound) and microbes for dechlorination of PCE. Transient water level monitoring, tracer tests, MODFLOW models and spatial analyses of aqueous samples were used to define the hydrogeology of the ECRS. Results of these experiments found that addition of the above constituents resulted in no overall aquifer clogging or impacts on the hydraulics. Additional findings of this investigation contradict some previous laboratory studies with regard to the influence of methanogens on dechlorination and methane production, which is believed to result in aquifer clogging.

The precipitation of ferrous and calcium phosphonates was performed in batch experiments under acidic conditions for a range of temperatures and ionic strengths. The stoichiometries of the precipitates were found to be Fe1.25H3.5NTMP and Ca1.25H3.5NTMP, where NTMP is a phosphonate. Using a speciation model, concentrations of free iron and phosphonate were calculated, from which the solubility product constants were derived as a function of temperature and ionic strength. The temperature and ionic strength dependence of solubility product constants (pKsp) were thus determined: pKSP&parl0; Fe1.25H3.5NTMP&parr0;= 53.23&parl0;+/-0.74&parr0;-8.35&parl0;+/-1.03&parr0; *IS0.5+2.67&parl0;+/-0.33&parr0;*IS-4 787&parl0;+/-83&parr0;T pKSP &parl0;Ca1.25H3.5 NTMP&parr0;= 40.96&parl0;+/-1.16&parr0;-5.07&parl0;+/-0.79&parr0; *IS0.5+1.79&parl0;+/-0.31&parr0;*IS-1 985&parl0;+/-375&parr0;T Simulations using field data suggested the possible formation of these acidic phases during squeeze treatment. In addition, column experiments were performed to test the presence of these phases and the effects of iron ions on the retention of NTMP.

Organic matter is one of the major components of the fine particles in Houston. In the present study, fine particulate samples collected at three sites (plus one temporary site) in Houston have been investigated to determine the molecular composition and seasonal variation patterns of individual organic compounds, including n-alkanes, PAH compounds, petroleum biomarkers, alkanoic and alkenoic acids, dicarboxylic acids and levoglucosan. Next, chemical mass balance (CMB) model has been applied to calculate quantitative contributions from major primary emission sources to ambient PM2.5 levels. These emission sources include diesel engine trucks, gasoline powered vehicles, wood combustion, paved road dust, food preparation process, vegetative detritus and natural gas combustion. Source profiles suitable for the present CMB model have been developed based on source test results published in literature and our road dust resuspension experiment. Source apportionment shows diesel and gasoline vehicle exhaust to be the major primary contributors to ambient PM2.5 collected in Houston. Moreover, 52% of annual average PM2.5 mass measured in the present study can be attributed to secondary formation in the atmosphere.

Adsorption and desorption of naphthalene from C60 fullerene solids in different aggregation forms was studied in this work, where C 60 was used as purchased; or dispersed in water by magnetic mixing; or deposited as a thin film. Finally C60 colloidal dispersion was produced in water with the help of high-energy sonication probe. Sorptive properties of C60 colloidal particles were also studied with naphthalene. Sorption partition coefficients could vary by orders of magnitude and have been observed to be related to the different C60 aggregation forms. Sorption/desorption hysteresis, a common phenomenon observed in natural soils and sediments, was also observed in this work with naphthalene sorbed to well dispersed C60 aggregates. Data were fitted with dual-equilibrium desorption model and results were comparable to literature reported results for natural organic carbons.

A new generation of distributed hydrologic models has been developed to be compatible with recent advancements in remotely sensed and GIS data. In contrast to lumped conceptual rainfall-runoff models, physics-based distributed parameter models attempt to preserve the spatial variability of the model inputs and outputs and use parameters that are directly measurable. This study applied one such distributed model called Vflo(TM) to Brays Bayou, a flat, highly urbanized watershed located in southwest Houston, Texas. The effectiveness and accuracy of Vflo(TM) and distributed modeling for Brays Bayou was demonstrated by using multiple historical storms events from 1998 to 2002. The performance of the calibrated model was also evaluated in a real-time flood alert system application. Initial tests indicate that the model is capable of accurately quantifying lead-time in advance of observed measurements. This research builds a solid foundation for future flood alert verification of this model.

Over the years, our groundwater sources have become contaminated with chlorinated organics, in particular trichloroethene (TCE) due to its exposure as a solvent to degrease metals and electronic parts in the automotive, metals, and electronic industries. Due to its prevalence and toxicity, TCE has been listed as one of the most hazardous organic compounds. Physical displacement methods (air stripping and carbon adsorption) are not as desirable as the catalytic breakdown of TCE into ethane using palladium-based materials. This thesis reports on the design, synthesis, characterization, and testing of Pd supported on gold nanoparticles (Au NPs) as a remediation catalyst for the hydrodechlorination (HDC) of TCE in water at ambient temperature and atmospheric pressure. The unique surface, structural, and electronic properties of 20 nm Pd/Au particles were found to contribute to the significantly enhanced HDC activity. Pd/Au NPs synthesized with smaller diameters (4 nm) reduced metals cost and increased effectiveness. Mass transfer effects during batch reactions were analyzed for the NP catalysts. Pd/Au NPs were immobilized on a support through electrostatic attractions, and demonstrated higher HDC activity compared to conventionally impregnated Pd and Pd-Au supported catalysts. Pd/A1 2O3, Pd NPs, and Pd/Au NP catalysts were found to be active for HDC of other chlorinated ethenes, with reaction mechanism studies supporting a sequential dechlorination pathway for TCE HDC. The reaction was found to be first-order in TCE and half-order in H2 for our Pd/Au catalysts, but was different from the half-order TCE and first-order H2 dependence of pure Pd catalysts. The Pd/Au nanostructure was more resistant to catalyst deactivation from chlorides and sulfides, relative to pure Pd catalysts. As a different example of using NPs as a catalyst support, a sol-gelation method was developed for the synthesis of molybdenum oxide (MoO3) supported on zirconia (ZrO2) NPs. It was hypothesized that ZrO 2 NPs can support amorphous MoO3 as a thermally stable, highly active oxidation catalyst. MoOX/ZrO2 containing up to 23 wt% amorphous MoOX was successfully synthesized and the nanostructure was analyzed in the context of colloid chemistry. They were more active for methanol oxidation on a gram-catalyst basis than conventionally prepared MoO X/ZrO2 catalysts, due to their higher MoOX content.