A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item ENHANCING BIOREMEDIATION OF TCE-CONTAMINATED GROUNDWATER AT THE BEAVERDAM ROAD LANDFILL(2022) Saffari Ghandehari, Shahrzad; Kjellerup, Birthe; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trichloroethene (TCE) is one of the most frequently found groundwater contaminants, thus remediating TCE-contaminated groundwater bodies is crucial in providing safe drinking water to people around the world. However, due to the resistance of its intermediates to degradation and their toxicity, TCE bioremediation is still challenging. Years after the installation of a permeable reactive barrier (PRB), the levels of toxic TCE dechlorination intermediates had increased downgradient from the PRB, indicating the need for actions to prevent the contaminated water from reaching a stream nearby. A review of the reports and monitoring results showed that low groundwater residence time and low pH levels were contributing to the inefficiency of the PRB. A trench was purposed to be installed upgradient from this PRB to increase the groundwater contact time with the microorganisms and organic carbon content of the soil using wastewater biosolids, limestone, and biochar to increase the buffer capacity of the soil and the sorption of TCE to the soil. Bench-scale studies were conducted with biosolids and limestone to observe the effect of the biosolids microbial population on a TCE-dechlorinating mixed microbial community. Both dechlorinating bacteria and methanogens use hydrogen in their metabolism and potentially can compete with each other. While biosolids-limestone reactors produced significantly higher concentrations of methane, the activity of methane-producing microorganisms did not adversely affect TCE dechlorination. Furthermore, the characterization of the microbial community of the reactors indicated the positive effect of biosolids. Based on the results from this study, the trench was installed in January 2020 at the site. The sampling and monitoring results nine months after its installation indicated that the trench filling material had positively affected the soil microbial community and decreased the TCE levels downgradient from the trench. To further characterize the microbial community of the site, passive samplers using biochar were installed upgradient and inside the PRB to compare the activity of the dechlorinating bacteria. It was shown that the PRB microbial population was capable of complete dechlorination of TCE, while dechlorinating bacteria detected in the upgradient samples were not active, resulting in the different TCE concentrations observed in these locations. Overall, the study showed that biosolids can be used as an amendment in the TCE bioremediation purposes. Future work should focus on further monitoring the effect of the treatments, applied in this site.Item FATE OF BACTERIAL AND VIRAL INDICATORS IN AN ADVANCED WASTEWATER TREATMENT PLANT(2013) Liang, Chung-Che; Wigginton, Krista R; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wastewater treatment plants (WWTP) are natural aggregators of pathogenic organisms due to the waste they treat. This study examined the fate of two bacterial indicators, fecal coliforms (FC) and Salmonella, and one viral indicator, Male-specific coliphages (MSCs), throughout an advanced WWTP. Samples were collected from various points in the WWTP from August 2011 to October 2012. Results show both bacteria and viruses preferentially partition into solids and significant reductions in both bacteria and viruses occur prior to final disposal. The total log removals of FC, Salmonella, and MSCs were 4.51, 5.17, and 6.19, respectively for the solids; and the total log removal of FC, Salmonella, and MSCs in liquids was 4.47, 5.16, and 3.62, respectively. This study provides the first holistic survey of bacteria and virus indicator fate in a WWTP. Furthermore, results herein demonstrate that current biosolids liming regulations may underestimate the level of viruses in Class B biosolids.Item ASSESSING THE FATE AND BIOAVAILABILITY OF HYDROPHOBIC ORGANIC POLLUTANTS IN AGRICULTURAL SOILS(2012) Almeida e Andrade, Natasha; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Persistent organic pollutants have been the cause of concern for many decades; however, little information is available about their environmental fate. One goal of this work was to assess whether land application of biosolids represents a source of persistent organic pollutants to agricultural soils. To address this goal, we developed a methodology to quantify low levels of the flame retardants polybrominated diphenyl ethers (PBDEs) in biosolids and soils and conducted field studies to determine the fate and persistence of PBDEs upon the land application of biosolids. We found that biosolids can take up to one year to completely incorporate into the soil matrix after application and biosolids-bound chemicals are released during this time. PBDEs profiles in soils that receive biosolids applications are similar to PBDEs profiles in biosolids and both reflect commercial formulations of these flame retardants, indicating that biosolids are a source of these chemicals to soil. Residence time of these chemicals was reported for the first time and it was estimated at 16 yr. for the sum of BDE-47 and BDE-99. An abiotic methodology to assess bioavailability of aged soil residues was developed and results were compared to earthworms. The study illustrated that the polymer-based abiotic methodology can be used to assess the bioavailability of soil-bound hydrophobic organic chemicals to earthworms. Measured soil-polymer equilibrium concentration ratios of organic pollutants correlated strongly with earthworm bioaccumulation factors using the same soils. A laboratory protocol to introduce the concept of fugacity and bioavailability to undergraduate and graduate environmental science and engineering students was developed based on the methodology developed for research. The experiment provided an excellent opportunity for students to become familiar with the laboratory protocols and techniques for quantitative analysis as well as graphical analysis of data. The totality of this work improves knowledge of the fate of two classes of organic pollutants in soils. This work substantially adds information and understanding of chemical behavior to the general environmental engineering field. Although this unique experiment provided original and essential pieces of information, additional research is crucial to address the difficulties involved in assessing the environmental behavior of organic pollutants.