| Glenn Walters presents his final oral dissertation defense on Monday, May 9, 2005 at 10:30 A.M. in the W. Fred Mayes Telecommunications Center (Rosenau 231).Full details are as follows:
STOICHIOMETRIC ANALYSIS OF SURFACTANT-ENHANCED ANAEROBIC 1,1,1-Trichloro-2,2-bis-(p-chlorophenyl)-ethane (DDT) DEGRADATION
The hydrophobic pesticide DDT is a persistent contaminant in soils and sediments, although it has long been known to be biodegradable under anaerobic conditions. The addition of the nonionic surfactant Brij 30 was evaluated as a means of enhancing the solubilization, potential bioavailability and anaerobic biodegradability of DDT and its metabolite DDD.
Experiments were performed with both an aged, DDT-contaminated soil and in soil-free liquid suspension. In addition, detailed analyses of electron donors and potential electron acceptors were performed to provide insights into the dominant mode of microbial metabolism under DDT degrading conditions.
Surfactant-enhanced solubilization of DDX from an aged, contaminated soil was evaluated. It was found that approximately 12 mg Brij 30/g soil was required before surfactant concentrations above the critical micelle concentration (CMC) were observed in the liquid phase in soil microcosms. At higher doses, solubilization of DDX components increased linearly with the Brij 30 dose. Solubilization data were consistent with equilibrium models that account for simultaneous partitioning of hydrophobic compounds between the aqueous, soil and pseudo-micellar phases.
In sealed anaerobic microcosms containing aged contaminated soil and surfactant, DDT was degraded at significantly greater rates than in microcosms without surfactant. It was also observed that DDD increased but did not accumulate stoichiometrically with DDT disappearance. The presence of cellulose did not significantly increase the ultimate extent of DDT degradation. However, high feed rates of cellulose did seem to retard initial DDT degradation rates. Decreases in surfactant concentration over time suggested use of surfactant as either a carbon source or as an electron donor in the dechlorination process. In soil-free microcosms using butyrate or hydrogen as potential electron donors, surfactant was again observed to significantly increase the extent of DDT degradation but with little accumulation of DDD. Significant release of chloride was observed (?3 mol chloride per mol DDT degraded) in butyrate and butyrate+hydrogen-amended microcosms. Microcosms with both hydrogen and butyrate added exhibited the greatest DDT degradation with virtually no accumulation of DDD, while microcosms with hydrogen alone exhibited substantially less degradative activity. Protein yields correlated well with both sulfate reduction and DDT degradation in surfactant-amended microcosms, suggesting that DDT degradation may be mediated by anaerobic sulfate-reducing organisms. Headspace hydrogen threshold concentrations in several of these microcosms were consistent with those typically observed under sulfate-reducing conditions. While Brij 30 may serve as a carbon source in these systems, results from select microcosms are inconsistent with its utilization as an electron donor in DDT dechlorination.
Committee:
Michael D. Aitken, Advisor
Morton A. Barlaz, N.C. State University
Francis A. DiGiano
Hans W. Paerl, UNC Institute of Marine Sciences
Frederic K. Pfaender
Stephen C. Whalen
For further information please contact Rebecca Riggsbee Lloyd by email at Rebecca_Lloyd@unc.edu
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