Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

Chloramines are used for disinfection in many water treatment facilities because of their ability to provide residual protection of water supplies while minimizing the formation of disinfection-by-products. However, chloramines can impart taste and odor to the water, which can lead to customer complaints. Furthermore, the removal of monochloramine from water is essential for certain industries. Previous research at the University of Texas at Austin has demonstrated the potential of several granular activated carbons (GAC) for removal of monochloramine under conditions typical of water treatment plants. The goal of this research project is to further quantify steady-state monochloramine reduction in fixed bed reactors (FBR) with three commercially available GACs, and improve the understanding of the physical and chemical properties that influence removal. The research was divided into 3 phases: 1. A laboratory scale fixed bed reactor experiment was used to quantify steady state monochloramine removal over time. City of Austin tap water viii was used for three GAC types (Jacobi CAT, Norit CAT, Nority CNS) at pH 8 and 9. 2. Physical characterization of each GAC was performed using analysis of nitrogen adsorption isotherms. Specific surface area, pore volume, and pore distribution were determined. Chemical characterization was performed quantitatively using Boehm titrations. Qualitative analysis was performed by analyzing FTIR spectra of untreated activated carbon samples. 3. The Monochloramine Catalysis (MCAT) model was calibrated using results from the Phase 1 and 2 experiments. Simulations of full scale point of use drinking water filters were run for various empty bed contact times and influent monochloramine concentrations. These results were compared against National Sanitation Foundation monochloramine reduction certification criteria. Results show that steady state removal was achieved for all of the activated carbons tested and this removal efficiency can reach nearly 90% using a 0.75-minute empty bed contact time. This steady state performance indicated that catalysis of the monochloramine was occurring, and removal could theoretically occur for very long periods of time. The second stage of the research shows correlation between chemical characteristics (acidity and basicity) and removal efficiency. Furthermore, physical characteristics, mainly micro-porosity, were shown to largely impact performance. Finally, the MCAT model provides a reasonable estimate of steady state removal, and is used to predict full scale point of use performance. / text

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Mobile group II introns are retroelements that site-specifically insert into DNA target sequences. The group II intron mobility pathway is mediated by a ribonucleoprotein particle (RNP) composed of excised intron RNA and an intron-encoded protein (IEP). The intron lariat inserts at a specific DNA target sequence and is then reverse transcribed by the IEP. Both the intron RNA and IEP are required for DNA target site recognition. I have identified the contact sites within the IEP responsible for recognition of two key positions in the DNA target, T+5 and T-23. IEP recognition of T+5 in the 3'-exon is required for endonuclease cleavage of the bottom-strand of the DNA target site, which generates a primer used for initiation of reverse transcription of the intron. The T+5 base is contacted by G498 in the LtrA DNA-binding domain and nearby residues, particularly K499, potentially bolster this interaction. Recognition of T-23 in the distal 5'-exon is required for initial recognition of the DNA target site by the RNP. The T533 side-chain contacts the T-23 base and the L534 side-chain may also contribute to recognition through hydrophobic interactions with the C5 methyl group. A mutant, L534H, that switches target site specificity to T-23G has been characterized. In order for the RNP to make these and other contacts in the 5'- and 3'-exons simultaneously, the DNA must be bent. I have dissected the role of DNA bending in the intron mobility pathway and found that the DNA is bent at two progressively larger angles as the reaction proceeds. The predominant bend angle at earlier time points places the bottom-strand DNA cleavage site at the protein endonuclease active site. The predominant bend angle of later time points places the cleaved DNA site at the RT domain active site for initiation of reverse transcription of intron cDNA. Finally, in a practical application of group II intron mobility, I have used reprogrammed group II introns ("targetrons") to target two genes in Bacillus subtilis to demonstrate the suitability of targetron technology for gene targeting in the Gram-positive Bacillus genus. / text

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REDUCTIVE DEHALOGENATION OF GAS-PHASE TRICHLOROETHYLENE USING HETEROGENEOUS CATALYTIC AND ELECTROCHEMICAL METHODSXiumin Ju, Ph.D.The University of Arizona, 2005Director: Dr. Robert G. ArnoldThe first part of this work investigates catalytic hydrodechlorination (HDC) of gas-phase trichloroethylene (TCE) using 0.5 wt.% Pt/g-Al2O3 and 0.0025 wt.% Pt/SiO2 in packed-bed reactors. TCE was efficiently transformed on the platinum surface using H2 as reducing agent. The main products of the reaction were ethane and chloroethane. In the case of Pt/Al2O3, more than 94% TCE conversion efficiency was maintained for over 700 hours of operation at 100ºC at a residence time of 0.37 seconds. At 22ºC, severe catalyst deactivation was observed. Catalyst deactivation was attributed to coking and chlorine poisoning. A series of treatments including (i) hydrogen gas addition at high temperature (oxygen free) to remove chlorine and (ii) oxygen addition at 500ºC to remove coke were attempted to regenerate the deactivated catalyst. Only hydrogen treatment partially restored catalyst activity. When using Pt/SiO2, catalyst deactivation was severe even at 100ºC, probably due to low surface area of Pt and the silica support. Adding KOH to the packed Pt/SiO2 catalyst during (otherwise) normal operation slowed catalyst deactivation. Adding O2 to the influent improved catalyst activity and slowed deactivation.The second part of this research involves the destruction of gas-phase TCE using an electrochemical reactor similar in design of a polymer electrolyte membrane (PEM) fuel cell. With a proton-conducting membrane in the middle, the anode and cathode comprised of carbon cloth and carbon-black-supported Pt were hotpressed together to form a membrane electrode assembly (MEA). TCE contaminated gas streams were fed to the cathode side of the fuel cell, where TCE was reduced to ethane and hydrochloric acid. The results suggest that TCE reduction occurs via a catalytic reaction with atomic hydrogen that is reformed on the cathode's surface rather than an electrochemical reduction via direct electron transfer. Substantial conversion of TCE was obtained, even in the presence of molecular oxygen in the cathode chamber. The process was modeled successfully by conceptualizing the cathode chamber as a plug flow reactor with a continuous source of H2(g) emanating from the boundary.

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