Theses and Dissertations from UMD
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Item PREVENTION AND TREATMENT OF POLYCHLORINATED BIPHENYLS IN SEDIMENTS - SOURCES AND SOLUTIONS(2019) Jing, Ran; Kjellerup, Birthe Veno; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)PCBs are classified as one of the persistent organic pollutants (POPs) with high toxicity and have undesirable effects on the environment and on humans. Once released into the environment PCBs could bioaccumulate within the food chain, due to their high affinity for organic materials. Recently, studies indicated PCBs can potentially enter a wastewater treatment plant (WWTP) system and be discharged via wastewater effluents thereby further contaminating the downstream environments. This study evaluated the potential for bioremediation of polychlorinated biphenyls (PCBs) in the effluent from a large WWTP. It was found that the continuous effluent was responsible for the majority of the discharged PCB into the receiving river (1821 g for five years), while the intermittent discharge contributed 260 g over the five years. The average number of chlorine per biphenyl for the detected PCB congeners showed a 19% difference between the two types of effluent, which indicated a potential for organohalide respiration of PCBs during the continuous treatment. This was further supported by a high level of tri-, tetra- and penta- chlorinated congeners accounting for 75% of the anaerobically respired PCBs. Potential for aerobic degradation and thus biomineralization of PCBs were identified for both effluents. In addition, the similarity of organohalide respiring (OHR) microbial populations in biosolids and intestinal human biofilms was determined by applying a bioinformatics approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The results of the biosolids analysis showed increased amounts of products from PCB respiration. Simultaneously, experiments with organohalide respiration of PCE in biosolids samples showed significant decreases in PCE concentration after 46 days (28-92%). Subsequently, it was evaluated if the OHR microbial populations in biosolids were similar to those present in intestinal human biofilms by applying a bioinformatic approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The overall groups Proteobacteria, Bacteroides, Actinobacteria, and Firmicutes phyla dominated the microbiomes in all datasets. The OHR groups in biosolids and intestinal biofilms included Dehalogenimonas, Dehalobacter, Desulfitibacter, Desulfovibrio, Sulfurospirillum, Clostridium, and Comamonas. The results of this study showed that several OHR phyla were present in all samples independent of origin. Wastewater and intestinal microbiomes also contained OHR phyla. Finally, biofilms made up by the OHR bacteria Dehalobium chlorocoercia DF-1 were inoculated on the surface of the pinewood biochar particles. The mole percent of the total PCE in the headspace decreased from 100% to 70.4%±17.6% for the rest of nine mesocosms which suggested that the D. chlorocoercia DF-1 biofilm converted PCE to TCE. The gene copy numbers of DF-1 biofilm from nine mesocosms which are ranging from 1.95×108 to 8.30×108 gene copies/g pinewood biochar. The biochar-biofilms were subsequently applied to PCB contaminated sediment from the Grass River in Michigan, USA. The goal was to evaluate the organohalide respiration of the PCB contaminated sediments in the absence/presence of the biofilm and free-floating inoculum.Item USING A HIGH ORGANIC-MATTER PERMEABLE REACTIVE BARRIER TO REMEDIATE TRICHLOROETHYLENE-CONTAMINATED GROUNDWATER AT THE BEAVER DAM ROAD LANDFILL(2018) Nino de Guzman, Gabriela Tejeda; Kjellerup, Birthe V; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trichloroethylene (TCE) is an effective industrial degreaser and known carcinogen. It was frequently improperly disposed of and has become one of the most common groundwater and soil contaminants in the USA. Clean up continues to be difficult due to its physical and chemical properties. TCE and several of its degradation products were detected in the groundwater of the Beaver Dam Road Landfill (Beltsville, MD) at concentrations above their maximum contaminant levels (MCLs). The US Department of Agriculture-Agricultural Research Service together with the University of Maryland, College Park and BMT Designers and Planners designed a permeable reactive barrier, or biowall, to remediate the contaminated groundwater. A series of batch reactor studies were conducted at 12°C to examine biowall fill-material combinations including the effects of zero-valent iron (ZVI) and glycerol amendments. Headspace samples were analyzed over the course of several months to monitor TCE degradation. An unamended, 4:3 mulch-to-compost combination was chosen based on no detectable TCE at the conclusion of the experiment. To increase the biowall degradation capacity, microbial infiltration and colonization of the structure were also studied. PCR, qPCR, and next-generation sequencing were used to survey the site’s indigenous population for dechlorinating clusters. Numerous clusters were identified affirming the use of the native population for bioaugmentation efforts. The ability of the biowall to support said community was investigated by monitoring continuously-fed column reactors containing biowall material spiked with a commercially-available, surrogate population, with and without a 5 mg/L dose of ZVI. The groundwater-fed column sans ZVI had the greatest Dehalococcoides population and while ZVI without biostimulation did decrease the overall population, it did not cause a statistically significant difference. Thus, if ZVI were to be used as a future biowall amendment, biostimulation would not be required to maintain a dechlorinating population. A sacrificial carbon source may be necessary to slow the biological degradation of the biowall’s organic fill-material. These findings will be utilized in future remediation and/or biowall expansion plans to fully employ the site’s natural resources. The biowall was constructed in July 2013 containing the 4:3 mulch-to-compost ratio and has reduced the upstream TCE concentration by ~90%.Item Effect of Terminal Electron Accepting Processes on Acetate Thresholds in Contaminated Sediments(2006-06-09) Davis, Gayle; Seagren, Eric A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Demonstrating the success of in situ bioremediation is challenging, requiring multiple lines of evidence, e.g., "footprints" of microbially-mediated processes that transform contaminants, like metabolic intermediates. This project evaluated the hypothesis that characteristic threshold concentrations of acetate, a key intermediate under anaerobic conditions, occur in contaminant plume regions dominated by different terminal electron accepting processes (TEAPs). The evaluation included characterizing the initially predominant TEAP(s) in sediment-slurry microcosms, and then measuring acetate thresholds in the sediment-slurries when dominated by different TEAPs. Based on the characterization, the sediments were dominated by methanogenesis, consistent with field observations. Interestingly, in the threshold experiments, similar acetate thresholds were observed under methanogenic conditions and in chlorinated-aliphatic degrading microcosms, although thermodynamics predict lower thresholds under the latter conditions. Therefore, this study demonstrated some of the potential, as well as complications, in using and interpreting acetate thresholds as an indicator of the dominant TEAP.Item ISOLATION AND CHARACTERIZATION OF POLYCYCLIC AROMATIC HYDROCARBON-DEGRADING MICROORGANISMS UNDER METHANOGENIC CONDITIONS(2004-08-27) UM, YOUNGSOON; Pulliam-Holoman, Tracey R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polycyclic aromatic hydrocarbons (PAHs) are among the most widely distributed organic contaminants in aquatic sediments due to their presence in coal and petroleum. While it has been demonstrated that PAHs are degraded under anaerobic conditions, little is known about the microorganisms responsible for PAH degradation. This study demonstrates not only the first isolations of naphthalene (NAP)- and phenanthrene (PHE)-degrading microorganisms under methanogenic conditions by utilizing modified plating methods but also the first identification and isolation of a fermentative bacterium responsible for initiating a syntrophic PHE-degradation. Molecular characterization of PAH-degrading methanogenic cultures via comparative 16S rDNA sequence analysis was employed to monitor the microbial community structure and consequently to design isolation strategies for the possible microbial species responsible for PAH-degradation. To isolate PAH-degrading microbes under anaerobic conditions, a modified plating method was first developed for detecting microorganisms degrading solid PAHs on the agar-overlay plate. It was also verified that this method was not only applicable for the isolation of both aerobic and anaerobic PAH-degrading microorganisms but also effective to solve problems existing with other previous isolation methods. By employing the modified plating method, PHE-degrading microorganisms under methanogenic conditions were successfully isolated from the enrichment cultures. The degradation of PHE was partially inhibited by 2-bromoethanesulfonic acid; however, no 14CH4 was detected when [9-14C] PHE was employed, indicating partial mineralization of PHE. One species of bacterium was isolated and identified as an initial microbial catalyst for PHE-degradation. NAP-degrading microorganisms under methanogenic conditions were also isolated by employing an agar-overlay containing evenly dispersed fine particles of NAP. One species of the bacteria was identified to be the same microorganism as a fermentative bacterium initiating a syntrophic PHE-degradation, and the other one showed a syntrophic relationship with methanogen species. The results presented here will likely contribute to the development of the isolation techniques and the identification of microbial consortia for the biodegradation of PAHs under anaerobic conditions.