This microcosm study demonstrated the enhanced anaerobic transformation of vinyl chloride (VC) to ethylene. A previous microcosm study from Point Mugu site showed the accumulation of VC due to the slow transformation step of VC to ethylene. To overcome the rate-limiting step, two laboratory experiments tested the effect of trichloroethylene (TCE) additions on the rate enhancement, repeated low TCE additions and high TCE concentration additions. TCE (2 ��mol) was repeatedly added over a two week interval. In a parallel study, an equal amount of VC was added to another set of microcosms. TCE addition increased VC transformation to ethylene, with nearly 19% VC conversion to ethylene compared to 4% VC conversion in the VC added controls. However, the increased VC transformation rates were not sufficient enough to avoid VC accumulation. Rate of VC transformation decreased once TCE addition was stopped. This indicated the mixed culture required the transformation of TCE to maintain VC transformation rates. With TCE added at high concentrations (100 mg/L and 200 mg/L), nearly complete transformation of TCE to ethylene was observed. After the addition of high TCE concentrations, low concentration TCE (3 ��mol) was added and near 95% transformed to ethylene in 45 days. Two different low hydrogen yielding substrates, butyrate and propionate, were tested. Both were equally effective in promoting TCE dechlorination. Methanogenesis was inhibited at high TCE concentration with both substrates. Kinetic analysis of VC transformation data showed VC transformation followed the first order kinetics with respect to concentrations using a modified Monod equation. First-order kinetic constants increased after the addition of high ICE concentrations. After 200 mg/L of TCE addition, the first-order kinetic constant increased by factor of six compared to the rate obtained from the earlier low TCE concentration addition. However, reintroduction of TCE at low concentration maintained similar enhanced kinetic constants, as achieved at high concentration. This indicated the enhancement of VC transformation to ethylene was likely due to the growth of microorganisms using TCE as a terminal electron acceptor. These microorganisms were likely responsible for the transformation of VC to ethylene. / Graduation date: 2001

No description available.

Perchloroethene and trichloroethene are among the most persistent groundwater pollutants, and Dehalococcoides is the only known species that can degrade these compounds completely to non-toxic ethene. Characterization of the reductive dehalogenase (RDase) enzymes responsible for dechlorination is important to understanding this process. A series of dechlorination assays were performed with whole cell suspensions and cell-free extracts of three Dehalococcoides-containing mixed microbial consortia to compare dechlorination kinetics and to characterize co-contaminant inhibition. Michaelis-Menten kinetic parameters Vmax and Km, as well as non-competitive inhibition coefficients for 1,1,1-trichloroethane and 1,1-dichloroethane inhibitors are reported. Secondly, blue native gel electrophoresis was developed as a method to isolate active protein complexes containing RDases. Thirdly, sources of variability in the isotopic fractionation of vinyl chloride to ethene reaction step were examined using cell-free extracts and whole-cell suspensions. Understanding the function and range of RDases are goals towards the successful application of Dehalococcoides-containing cultures to remediate contaminated sites.

Perchloroethene and trichloroethene are among the most persistent groundwater pollutants, and Dehalococcoides is the only known species that can degrade these compounds completely to non-toxic ethene. Characterization of the reductive dehalogenase (RDase) enzymes responsible for dechlorination is important to understanding this process. A series of dechlorination assays were performed with whole cell suspensions and cell-free extracts of three Dehalococcoides-containing mixed microbial consortia to compare dechlorination kinetics and to characterize co-contaminant inhibition. Michaelis-Menten kinetic parameters Vmax and Km, as well as non-competitive inhibition coefficients for 1,1,1-trichloroethane and 1,1-dichloroethane inhibitors are reported. Secondly, blue native gel electrophoresis was developed as a method to isolate active protein complexes containing RDases. Thirdly, sources of variability in the isotopic fractionation of vinyl chloride to ethene reaction step were examined using cell-free extracts and whole-cell suspensions. Understanding the function and range of RDases are goals towards the successful application of Dehalococcoides-containing cultures to remediate contaminated sites.

Thesis (Ph. D. in Chemistry)--Vanderbilt University, Dec. 2007. / Title from title screen. Includes bibliographical references.

M.Sc. / Carbon nanotubes (CNTs) have been of utmost scientific interest since their discovery in 1991 by a Japanese physicist - Sumio Iijima. This is due to their extraordinary properties which make them one of the most promising options for the design of novel ultrahigh strength polymer nanocomposites. It is believed that the high aspect ratio, mechanical strength, and high electrical and thermal conductivity of these CNTs will enhance the performance of many polymer / CNT nanocomposites and open up new applications. However, poor dispersibility and lack of interfacial adhesion of the CNTs in the polymer matrix have remained a challenge towards fabrication of these nanocomposites. This has been due to the atomically smooth surface of the nanotubes and their intrinsic van der Waals forces which make them chemically inert. This study was aimed at exploring this concept by using novel phosphorylated multiwalled carbon nanotubes (p-MWCNTs) and polyvinyl chloride (PVC) polymer. Phosphorylation of MWCNTs has been successfully achieved in our laboratories, with the p-MWCNTs showing improvement in thermal stability. PVC on the other hand, is the world’s second largest thermoplastic material and has physical properties that are key technical advantages for its use in various and diverse fields such as building and construction, electronics, food packaging and in medical applications. A novel solvent-free method was used to synthesize p-MWCNTs / PVC nanocomposites. MWCNTs were synthesized by nebulized spray pyrolysis, a modification of catalytic vapour deposition and purified by soxhlet extraction using toluene. This method proved to be convenient and economical, producing a high yield of carbon nanotubes. The MWCNTs were phosphorylated with alkylazido phosphonate compounds through a 1,3-dipolar cycloaddition reaction between the phosphonate azides and the C=C bonds of the MWCNTs, with nitrogen loss occurring upon thermolysis. These p-MWCNTs were then melt compounded with PVC to form the p-MWCNTs / PVC nanocomposites. vii The phosphorylation of the MWCNTs and their dispersion in the PVC matrix were characterized by FTIR, SEM, TEM and Raman spectroscopy. Thermal analysis of the nanocomposites by TGA and DSC showed an enhanced thermal stability when comparing the nanocomposites with neat PVC. The modulus of the MWCNTs / PVC nanocomposites increased whilst there was a reduction in their tensile strength, indicating a decrease in polymer toughness.

No description available.

The extensive use of tetrachloroethene (PCE) and trichloroethene (TCE) as cleaning solvents has resulted in widespread contamination of groundwater systems with vinyl chloride (VC). VC, a known human carcinogen, is primarily formed in groundwater via incomplete anaerobic reductive dechlorination of PCE and TCE. Aerobic, methane-degrading bacteria (methanotrophs), which are capable of VC cometabolism while growing on methane, could be important in natural attenuation of VC plumes that escape anaerobic treatment. Real-time PCR (qPCR) represents an innovative approach for detecting and quantifying the presence and activity of these VC-degrading microbes. Immediate applications of this technique include use in a laboratory setting to help elucidate the potential bacterial-substrate interactions occurring in the subsurface environments at these contaminated sites; interactions that could ultimately affect the role of methanotrophs in VC degradation. This technique could also provide lines of evidence for natural attenuation of VC, thus support existing anaerobic bioremediation technologies that generate VC as a metabolic intermediate. In this work, we evaluated several PCR primer sets from the literature for use in methanotroph qPCR assays of groundwater samples. PCR primers targeting two functional genes involved in VC cometabolism, pmoA (sub-unit of particulate methane monooxygenase (pMMO)) and mmoX (sub-unit of soluble MMO (sMMO)), as well as 16S rRNA gene primers that targeted Bacteria, and Type I and Type II methanotrophs were tested. These assays were made quantitative by constructing standard curves with DNA from Methylococcus capsulatus (Type I) and Methylocystis sp. strain Rockwell (Type II). Primer sets were evaluated by comparing gene abundance estimated against known amounts of Type I and Type II methanotroph DNA. After primer validation, an effort to substantiate this methanotroph qPCR method was made by attempting to investigate methanotroph populations in groundwater samples from VC-contaminated sites. Some samples studied were also subjected to 16S rRNA gene pyrosequencing, allowing for relative abundance comparisons with qPCR analyses. Following our primer assessment experiments, effective primer sets were used to estimate the presence of methanotrophs at environmental sites in Soldotna, Alaska; Naval Air Station Oceana, Virginia Beach, Virginia; and Carver, Massachusetts. Results showed that methanotrophs were present in nearly all wells sampled from all environmental sites. Estimations of methanotroph relative abundance in environmental samples were determined by comparing the Type I and Type II primer estimates to those of the 16S universal primers. Methanotrophs in these groundwater samples ranged from 0.2% to 6.6% of the total bacterial population. Pyrosequencing analysis of the same samples showed methanotroph relative abundances that ranged from 1.7% to 54%. In groundwater samples where both DNA and RNA was extracted, the quantities of functional gene transcripts per gene copy was compared, revealing that the transcripts/gene ratio for both pmoA and mmoX was less than one, implying relatively low methanotroph activity. Analysis of mmoX environmental sample dissociation curves revealed a double peak, indicating possible non-specific PCR products. Our data suggests that most of the qPCR primer sets used in the environmental samples adequately detect methanotrophs, though the mmoX primers need to be further validated. These primer sets will be useful for supporting VC bioremediation strategies by providing a rapid, convincing, and cost effective alternative the enrichment culture technique currently employed. Comparison of qPCR and pyrosequencing analysis revealed biases in either one, or both techniques. Finally, our preliminary transcripts/gene data suggests that the methanotrophs at the Carver site are not actively expressing pMMO and sMMO genes above basal levels.

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

No description available.