Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Modeling The Impact Of Sediment Resuspension And Flocculation On The Fate Of Polychlorinated Biphenyls(2008-07-11) Chang, Chihwei Andrew; Baker, Joel E; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrophobic organic contaminants (HOCs) are important pollutants in urban estuaries. HOCs include polycyclic aromatic hydrocarbon (PAH), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs). Sorption to resuspended particles and sediments plays an important role controlling the water column residence times and spatial distributions of HOC in aquatic environments. Pollutant residence times and the time required to reach sorptive equilibrium are highly dependent on the chemical character, the surrounding environment, and particle types and compositions. If rates of sorption are slow relative to particle residence times, HOC behavior may be described using kinetically-limited partitioning behavior. In this study, a flocculation model that simulates flocculation of activated carbon, organic carbon, and inorganic solids ranging in diameter from 2 to 1000 μm has been developed. A multi-class flocculation-based contaminant fate model is adapted to describe desorption kinetics for contaminants associated with flocculated particles during a resuspension event. The model is effective in predicting transport of hydrophobic organic contaminants among different size flocs, water, and two sediment layers. The model also demonstrates the impact of fractal geometry, bottom shear stress, particle composition, floc size, fraction of organic carbon (fOC), fraction of activated carbon (fAC), organic carbon partition coefficient (KOC), and total suspended solids (TSS) on contaminant desorption rate and residence time. Under different scenarios, this model's results support the importance of multi-floc cluster, sediment-water interaction, and of flocculation for the contaminant desorption rate in the water column. In a floc-rich environment flocculation is an important mechanism redistributing contaminants among flocs. When flocculation is considered in a dynamic particle environment that includes sediment resuspension, settling, and kinetic-limited HOC partitioning, the steady state total PCB concentration in the water column is decreased by 20 % and water column HOC residence time decreased by 36%. When activated carbon is added to contaminated sediments, the total PCB concentration in the water column decreases by 90% (123.4 to 11.4 ng/L). If the activated carbon coagulates with the resuspended sediment, this decrease is partially offset by some activated carbon being entrained in slowly-settling flocs, and the steady-state PCB concentration is 61 ng/L.Item The role of dehalorespiring bacteria in the reductive dechlorination of polychlorinated biphenyls in Baltimore harbor sediment microcosms(2007-03-29) Fagervold, Sonja Kristine; Sowers, Kevin R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Baltimore Harbor sediment microcosms were incubated with the 12 most predominant congeners in Aroclor 1260 and their intermediate products to identify the major dechlorination pathways. Most congeners were dechlorinated in the meta position, although some dechlorination in the para and ortho positions was observed. The major dechlorination products were tetrachlorinated biphenyls with unflanked chlorines. Specific dechlorination rates of parent and intermediate PCB congeners were determined to identify the rate limiting reactions. To identify the microorganisms responsible for the dechlorination pathways, I developed PCR primers specific for the 16S rRNA genes of known PCB dehalogenating bacteria. These PCR primers were used in conjunction with DGGE to selectively identify the microorganisms that catalyzed each dechlorination reaction. Only three phylotypes were identified that catalyze the dechlorination of Aroclor 1260, and the selective activities of these phylotypes were determined. Phylotype DEH10 had high sequence similarity to Dehalococcoides spp., while phylotype SF1 had high sequence similarity to the o-17/DF-1 group of PCB dechlorinating bacteria. The third phylotype had 100% sequence similarity to the ortho-dechlorinating bacterium o-17 described previously from Baltimore Harbor sediments. Most dechlorination reactions for all three phylotypes were growth-linked, indicating that PCB-impacted environments have the potential to sustain populations of PCB dechlorinating organisms. To investigate whether bioaugmentation would be feasible for bioremediation of PCB contaminated sites, Baltimore Harbor sediment microcosms were supplemented with known dechlorinators and their effects on PCBs dechlorination patterns determined. The addition of different dechlorinators resulted in different dechlorination patterns. Finally, novel putative reductive dehalogenases were identified from the PCB dechlorinating bacterium DF-1 using degenerate PCR primers. Comparative sequence analyses indicated that they had high sequence similarity to both confirmed and putative dehalogenases from several Dehalococcoides species. In conclusion, microorganisms that can dechlorinate Aroclor 1260 have been identified for the first time and dechlorination of congener mixtures was shown to occur by the growth-linked complementary activities of bacterial consortia within the Chloroflexi. Demonstration that bioaugmentation with these organisms can influence rates and pathways of dechlorination, combined with the development of molecular assay for monitoring their fate, provide potentially valuable tools for the development of bioremedial strategies for PCB contaminated sediments.