Graduation date: 2005

The goal of this research was to mathematically simulate the ability of bioaugmented microorganisms to aerobically cometabolize a mixture of chlorinated aliphatic hydrocarbon (CAH) compounds during in-situ treatment. Parameter values measured from laboratory experiments were applied to the transport model with biotransformation processes included. In laboratory microcosm studies, a butane-grown, enriched culture was inoculated in soil and groundwater microcosms and exposed to butane and several repeated additions of 1,1,1-trichloroethane (TCA), 1,1-dichioroethylene (DCE), and 1,1-dichloroethane (DCA) at aqueous concentrations of 200 ��g/L, 100 ��g/L, and 200 ��g/L, respectively. Microcosms containing the bioaugmented culture showed 1,1-DCE to be rapidly transformed, followed by slower transformation of 1,1-DCA and 1,1,1-TCA. After most of the butane had been consumed, transformation of these latter CAHs increased, indicating strong inhibition by butane. With repeat biostimulations, butane utilization and CAH transformation accelerated, showing the increase in cell mass. These trends occurred in two sets of microcosm triplicates. No stimulation was observed in controls containing only the microorganisms indigenous to Moffett Field, confirming that activity seen in the bioaugmented microcosms was a result of the introduced culture's activity. Batch reactor results were simulated using differential equations accounting for Michaelis-Menten kinetics, transformation product toxicity, substrate inhibition, butane utilization, and CAH transformation. The equations were solved simultaneously by Runge-Kutta numerical integration with parameter values adjusted to match the microcosm data. Having defined the parameter values from laboratory studies, the biotransformation model was combined with 1-D advective-dispersive transport to simulate behavior of the culture and the substrates within an aquifer. The model was used to simulate the results of field studies where the butane-utilizing culture was injected into a 7 m subsurface test site and exposed to alternating pulses of oxygen and butane, along with the contaminant mixture studied in the microcosms. Monitoring wells spaced at 1 m, 2.2 m, and 4 m from the injection well allowed temporal and spatial changes in substrate concentrations to be determined. Model simulations of the field demonstration were performed to determine how well the biotransformation/solute transport model predicted actual field observations. To model the influences of solute transport, simulations were run and compared to breakthrough test data (prior to bioaugmentation) to determine the values for advection, dispersion, and sorption. The simulations showed that flow ranged from 1.0 to 1.5 m��/day (average linear velocity of 2.0 m/day). Dispersion was estimated as 0.31 m��/day. Sediment sorption partitioning coefficients for 1,1-DCE, 1,1-DCA, and 1,1,1-TCA were determined to be approximately 0.69, 0.50, and 0.50 L/kg, respectively. It was more difficult to determine an appropriate value of the mass transfer rate coefficient for non-equilibrium sorption, so simulations were run to compare equilibrium and non-equilibrium cases. Results indicated that non-equilibrium (with mass transfer rate coefficient of approximately 0.2 day�����) better simulated the field data. Using these transport parameters and the biotransformation values determined from the laboratory experiments, simulations of the field data showed that the model was capable of simulating the effects of transformation rates, butane inhibition, and 1,1-DCE product toxicity. Simulations for varying pulsing cycles and durations provided possible improvements for future field demonstrations. Overall, this work proved that there is good potential in extrapolating laboratory based kinetics to simulate biotransformation at a field scale. Although the complexity of such systems makes modeling difficult, such simulations are useful in understanding and interpreting field data. / Graduation date: 2003

This study evaluated the potential of the aerobic Mycobacterium strain JS6O to grow on a variety of organic acid substrates, and the possible effects an organic acid would have on the degradation rate of vinyl chloride (VC). A series of batch growth tests were designed to determine the time it took to consume the substrate and the overall increase in biomass. Strain JS6O was found capable of growth on acetate, propionate, and butyrate, but could not grow on formate or lactate. Acetate was chosen for further study because strain JS6O consumed acetate the most rapidly of all the organic acids tested, and acetate is a common product of fermentation reactions in the subsurface. Strain JS6O was confirmed to grow on both ethylene and vinyl chloride as the sole carbon and energy source. Comparatively, strain JS6O's rate of growth on VC is much slower than that of ethylene. With acetate as an augmenting growth substrate, ethylene and VC utilization rates increased by 30% and 48%, respectively. Since acetate and VC are often found together in contaminated chlorinated ethene plumes, this makes a strong case for natural attenuation of VC by strain JS6O. A series of kinetic tests were implemented to determine the K[subscript s] and k[subscript max] of strain JS6O for ethylene, VC, and c-DCE. The K[subscript s] and k[subscript max] for ethylene determined through NLSR methods was similar to the values published in Coleman et al. (2002), supporting the maintenance of a pure culture throughout the experimental work. When strain JS6O was exposed to the isomers of DCE (trans-1,2-dichloroethylene (t-DCE), cis-1,2-dichloroethylene (c-DCE), and 1,1-dichloroethylene (1,1-DCE)) the cells were unable to grow on these compounds. However, when growing on acetate, strain JS6O cometabolized c-DCE and t-DCE, but not 1,1-DCE, with c-DCE transformed more rapidly than t-DCE. Transformation of c-DCE was also observed with growth on VC and ethylene. The presence of c-DCE was shown to partially inhibit VC degradation, but had no effect on ethylene degradation. The cometabolism results with acetate further indicate that strain JS6O is a good candidate for natural attenuation of multiple chlorinated ethenes in the subsurface. / Graduation date: 2006

Halogenated organic compounds have had widespread and massive applications in industry, agriculture, and private households, for example, as degreasing solvents, flame retardants and in polymer production. They are released to the environment through both anthropogenic and natural sources. The most common chlorinated solvents present as contaminants include tetrachloroethene (PCE, perchloroethene) and trichloroethene (TCE). These chlorinated solvents are problematic because of their health hazards and persistence in the environment, threatening human and environmental health. Microbial reductive dechlorination is emerging as a promising approach for the remediation of chlorinated solvents in aquifers. In microbial reductive dechlorination, specialized bacteria obtain energy for growth from metabolic dechlorination reactions that convert PCE to TCE, cis-1,2-dichloroethene (cDCE), vinyl chloride (VC), and finally to benign ethene. Field studies show incomplete dechlorination of PCE to ethene due to lack of electron donors or other populations competing for the electron donor. Mathematical models are good tools to integrate the processes affecting the fate and transport of chlorinated solvents in the subsurface. This thesis explores the use of modeling to provide a better understanding of the reductive dehalogenation process of chlorinated solvents and their competition with other microorganisms for available electron donors in continuous flow systems such as a continuous stirred tank reactor (CSTR) and a continuous flow column. The model is a coupled thermodynamic and kinetic model that includes inhibition kinetics for the dechlorination reactions, thermodynamic constraints on organic acids fermentation and has incorporated hydrogen competition among microorganisms such as homoacetogenesis, sulfate reducers and ferric iron reducers. The set of equations are coupled to those required for modeling a CSTR. The system of model equations was solved numerically using COMSOL 3.5 a, which employs finite-element methods. The kinetic model was verified by simulation results compared to previously published models and by electron balances. The simulation process progressed by simulating the anaerobic reductive dechlorination, coupled with thermodynamic limitation of electron donor fermentation in batch systems to the modeling of CSTR, and finally to simulate anaerobic reductive dechlorination in continuous flow column, aquifer column including the processes of advection, dispersion and sorption along with the microbial processes of dehalogenation, fermentation, iron and sulfate reduction. The simulations using the developed model captured the general trends of the chemical species, and a good job predicting the dynamics of microbial population responses either the CSTRs or continuous flow column. Although, the kinetic of anaerobic dechlorination processes of chlorinated solvents in those systems have been researched in the past, little progress has been made towards understanding the combined effects of the dechlorination and thermodynamic constraints in continuous flow systems. This work provides a rigorous mathematical model for describing the coupled effects of these processes. / Graduation date: 2012