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This dissertation describes research on the dechlorination of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) by a Dehalococcoides containing mixed culture and in freshwater sediments, including elucidation of pathways, assessment of kinetics and extrapolation of the results to address potential environmental implications. First, the dechlorination pathway of a selected PCDF congener was elaborated. A toxic 2,3,7,8-substituted congener-1,2,3,4,7,8-hexachlorodibenzofuran (1,2,3,4,7,8-HxCDF) was detoxified to non 2,3,7,8-substituted congener upon reductive dechlorination. The amendment of halogenated compounds, including tetrachloroethene (PCE) and 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB), in addition to the selected PCDD/F congeners, resulted in differences in the pattern and extent of PCDD/F dechlorination. The addition of 1,2,3,4-TeCB enhanced the extent of dechlorination of 1,2,3,4,7,8-HxCDF by approximately three fold, while the addition of PCE did not affect 1,2,3,4,7,8-HxCDF dechlorination. Second, the dechlorination kinetics were examined using 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TeCDD) as a model compound. The dechlorination rate increased with an increase in the nominal concentration of the compound and exhibited pseudo-first order kinetics. Kinetic parameters were also estimated based on a Monod-type biokinetic model. Third, the carbon isotope fractionation during reductive dechlorination of 1,2,3,4-TeCDD using compound specific isotope analysis (CSIA) was investigated. A unique pattern was observed in that the dechlorination intermediate, 1,2,4-trichlorodibenzo-p-dioxin (1,2,4-TrCDD) was enriched in 13C relative to the educt, 1,2,3,4-TeCDD. The final product 1,3-dichlorodibenzo-p-dioxin (1,3-DCDD) was depleted in 13C compared to both the educt and the intermediate. The enrichment of 13C in the intermediate could be a result of the further dechlorination of 1,2,4-TrCDD to 1,3-DCDD. Finally, the dissertation addressed approaches to enhance the dechlorination of PCDD/F in sediments. The approaches examined included addition of electron donors, amendment with additional halogenated compounds, bioaugmentation with Dehalococcoides, and combinations of these approaches. The addition of alternate halogenated compounds enhanced the dechlorination of 1,2,3,4-TeCDD in two sediments, those from Gulf Island Pond, ME and Lake Roosevelt, WA. In heavily PCDD/F contaminated River Kymijoki sediment, all active treatments exhibited similar extensive dechlorination of 1,2,3,4-TeCDD, however, the amendment of halogenated compounds and bioaugmentation expedited the dechlorination at the onset of the experiment. This study addressed several theoretical and practical aspects of reductive dechlorination of PCDD/Fs pertinent to the better understanding of this subject. The outcomes could be used to direct the practice of the remedial operations for PCDD/F contaminated sediments.

Ph.D.

Includes bibliographical references (p. 173-186).

http://hdl.rutgers.edu/1782.2/rucore10001600001.ETD.16730

ETD_558

doi:10.7282/T39Z95BH

ETD doctoral

The author owns the copyright to this work.

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