Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
74 results
Search Results
Item USE OF DRINKING WATER TREATMENT RESIDUALS AS A SOIL AMENDMENT FOR STORMWATER NUTRIENT TREATMENT(2010) O'Neill, Sean William; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stormwater runoff has been implicated as a major source of excess nutrients to surface waters, contributing to the development of eutrophic conditions. Bioretention, a promising technology for urban stormwater pollution treatment, was investigated to determine if an aluminum-based water treatment residual (WTR) amended bioretention soil media (BSM) could adsorb phosphorus to produce discharge concentrations below 25 μg/L. Batch, small column, and vegetated column studies were employed to determine both the optimal BSM mixture and media performance. Media tests demonstrated P adsorption proportional to WTR addition. Final selected experimental media consisted of 75% sand, 10% silt, 5.8% clay, 5.2% WTR, and 3.4% bark mulch (air dry mass basis).This media showed excellent P removal relative to a non-WTR-amended media. Whereas the control media leached P (71.1% increase in mass), the experimental media adsorbed 85.7% of the P mass applied, displaying a cumulative effluent EMC of 16.1 μg/L, below the 25 μg/L goal.Item Evaluation of Leaching Protocols for the Testing of Coal Combustion Byproducts(2010) Becker, Jason Louis; Aydilek, Ahmet; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Beneficial reuse of coal combustion byproducts requires an evaluation of metal leaching potential. Reuse of high carbon fly ash in highway embankment construction was evaluated using different soil-fly ash mixtures and three common leaching tests: the water leach test (WLT), the Toxicity Characteristic Leaching Procedure (TCLP), and the column leach test (CLT). The effect of test methodology and pH on Cu, As, and Cr leaching was examined. TCLP concentrations for Cu and As exceeded those from WLTs in the majority of mixtures due to lower pH conditions, while Cr was higher in the WLT for alkaline fly ash mixtures. Peak CLT concentrations were higher than TCLP and WLT concentrations for the majority of mixtures, but usually decreased rapidly, suggesting that leachate concentrations might exceed regulatory limits, but only for a short time. Based on these results, a combined WLT and CLT leaching protocol for testing fly ash mixtures is presented.Item Kinetics of Tetrachloroethene-Respiring Dehalobacter and Dehalococcoides Strains and Their Effects on Competition for Growth Substrates(2010) Lai, Yenjung; Becker, Jennifer G; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The chlorinated solvents tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. Reductive dechlorination of PCE and TCE at contaminated sites is commonly carried out by dehalorespiring bacteria that utilize these compounds as terminal electron acceptors, but often results in the accumulation of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), rather than non-toxic ethene. This project focused on evaluating how interactions among dehalorespiring populations that may utilize the same electron acceptors, electron donors and/or carbon source may affect the extent of PCE dechlorination in situ. These interactions may be particularly important if both Dehalococcoides ethenogenes (Dhc. ethenogenes) and Dehalobacter restrictus (Dhb. restrictus) are present because these bacteria utilize the same electron donor (H2) and both respire PCE and TCE. However, unlike Dhc. ethenogenes, Dhb. restrictus cannot dechlorinate PCE beyond cDCE. Therefore, the outcome of the population interactions may determine the extent of detoxification achieved. Monod kinetic parameter estimates that describe chlorinated ethene and electron donor utilization by Dhc. ethenogenes and Dhb. restrictus at non-inhibitory substrate concentrations were obtained in batch assays. Substrate inhibition effects on both populations were also evaluated. Highly chlorinated ethenes negatively impacted dechlorination of the lesser chlorinated ethenes in both populations. In Dhc. ethenogenes, cometabolic transformation of VC was also inhibited by the presence of other chlorinated ethenes. PCE and TCE dechlorination by Dhb. restrictus was strongly inhibited by VC. The microbial interactions between Dhc. ethenogenes and Dhb. restrictus was investigated using reactors and mathematical models under engineered bioremediation and natural attenuation conditions. Under engineered bioremediation conditions, Dhc. ethenogenes became the dominant population, and the modeling predictions suggested that the inhibition of Dhb. restrictus by VC was a key factor in determining this outcome. Dechlorination rates by Dhb. restrictus appeared to be affected very little by low acetate concentrations under natural attenuation conditions, giving it an advantage over Dhc. ethenogenes, which requires relatively high acetate concentrations. This study highlighted that substrate interactions among dehalorespiring bacteria can influence their performance and contaminant fate under common bioremediation scenarios. A better understanding of the factors affecting the outcomes of these microbial interactions was achieved, which should aid in the design of successful bioremediation strategies.Item The Hydrologic and Water Quality Performance of the Sligo-Dennis Bioretention Cell(2010) Olszewski, Jennifer Marie; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention cells have been found to improve the hydrologic and water quality performance of impervious areas such as parking lots. The current study recorded hydrologic data from a bioretention cell in Silver Spring, MD, over a period of 2 years, collecting water quality data from 14 storm events. Data showed the cell completely captured storm events that produced less than or equal to 1.27 cm of rainfall, after which a linear relationship between cell outflow and cell inflow was observed. The cell was found to reduce the site CN from 96 down to 79 and to have a CN of 96 when assessed as a separate land use. The hydrologic performance was also compared to that of a forested stream near Baltimore, MD. While the cell performed similarly volumetrically for storms producing less than or equal to 2 cm of rainfall, the Sligo-Dennis flow-durations were typically half the length and double the flowrate of those of the forested stream.Item Design and testing of a microbial fuel cell for the conversion of lignocellulosic biomass into electricity(2010) Gregoire, Kyla Patricia; Becker, Jennifer; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Previous research has demonstrated that microbial fuel cells (MFCs) have the ability to degrade soluble substrates such as wastewater; however, very few studies have attempted the conversion particulate biomass to electricity in an MFC. A single-chamber, air cathode MFC was developed using a solid, lignocellulosic substrate (corncob pellets) as the electron donor. The first trial, using a prototype reactor with a graphite rod anode, ran for 415 hours, and generated a maximum open circuit voltage and current of 0.67 V and 0.25 mA, respectively. The second trial employed graphite brush anodes and multiple microbial inocula. A pasteurized soil inoculum resulted in negligible power (P = 0.144 mW/m3). The addition of rumen fluid, which naturally contains cellulose-degrading microorganisms, and Geobacter metallireducens, resulted in Pmax values of 77 mW/m3 and 159 mW/m3, respectively. Analysis of hydrogen, methane, organic acids, and the mass of substrate consumed provided insight into the relationship between cellulose oxidation, methanogenesis, and power production.Item SPILL AND BURNING BEHAVIOR OF FLAMMABLE LIQUIDS(2010) Benfer, Matthew; Quintiere, James G; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Unconfined liquid spill depths were measured for two liquid fuels and three non-flammable liquids atop a smooth concrete pad. Unconfined liquid spill thicknesses were found to be less than 0.1 cm in all fuels and liquids similar to fuels. Spill fires were conducted with volumes ranging from 0.2 ml to 450 ml for gasoline and denatured alcohol. Average burning rates for both unconfined liquid fuel spill fires increased linearly with increasing volume spilled. A liquid spill thickness model was developed and compared to experimental data. Comparisons showed good predictions for half of the liquids used. In addition, a liquid spill fire burning rate model was also developed and checked with experimental data. This model provided good qualitative results, however further development is still needed.Item Redoximorphic Features Induced by Organic Amendments and Simulated Wetland Hydrology(2010) Gray, Adam Lincoln; Rabenhorst, Martin C; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)During wetland construction, it is common to add organic amendments to the soil, although little research has evaluated the effects of organic additions on the development of redoximorphic features. The objective of this study was to evaluate the effects of adding different types of organic materials, using different methods of incorporation, on the formation of redoximorphic features under hydric soil conditions. Five types of organic materials were incorporated into soil cores lacking redoximorphic features, using three incorporation methods. Cores were established as mesocosms in a controlled greenhouse environment or transplanted into a natural wetland. Mesocosms were periodically dissected and examined for newly formed redoximorphic features. The method of incorporating organic materials had a significant influence on the development of redoximorphic features, but the type of organic material had no significant effect. Organic materials should be concentrated into deeper zones during wetland construction to maximize development of redoximorphic features.Item USE OF INORGANIC BY-PRODUCT AMENDED COMPOST/MANURE TO SEQUESTER METALS AND PHOSPHORUS FROM DIFFUSE SOURCE POLLUTION(2010) Kim, Hunho; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Heavy metals and nutrients released from diffuse sources by urban and agricultural runoff are important pollutants causing aquatic toxicity and/or eutrophication in water bodies. Diffuse source pollution is difficult to address because of the dispersed and often dynamic nature of the flows, which often lead to economic impracticality of traditional approaches. Beneficial use of industrial and agricultural byproducts as amendments or media/barriers to treat diffuse source pollution can provide cost-effective solutions over various ranges of pollutants and flows. Two applications of this concept were examined in this research study: 1) Immobilization of phosphorus using Fe/Mn inorganic materials and an anaerobic incubation process; (2) Heavy metal removal from roof/wall runoff using a Biomat barrier supplemented with compost and inorganic byproducts. Through the first study, three different low cost Fe/Mn-rich materials (iron ore, steel slag and Mn tailings) were evaluated as amendments to decrease phosphorus mobility from manure. Anaerobic incubation of fresh dairy manure with the Fe/Mn rich materials was also evaluated. Steel slag addition significantly decreased water soluble phosphorus by 93% and Mehlich III extracted phosphorus by 80%, compared to manure-only control. An anaerobic incubation of manure with Fe ore decreased 62% water extractable P compared to fresh manure and 76% compared to incubated manure, due to oxalate extractable Fe (considered as amorphous Fe) increase. This work suggests possible anaerobic incubation use for non-active crystalline byproducts to decrease P loss from manure. Through the second study, the feasibility of Biomat use, a mixture of sand, compost and inorganic byproducts, was evaluated through column and bench-scale experiments to remove dissolved heavy metals. A 25% grass/food waste compost + steel slag + sand column was the best media, not only demonstrating excellent metal removals from diffuse sources but also exhibiting the immobility of sorbed metals on the media. Throughout bench scale experiments, hydraulic characteristics and heavy metal removal performance of the mat media were evaluated in perpendicular flow. After all bench scale experiments, metal extractions showed performed very limited metal mobility in the media. Design parameters, implementations, and recommendations for future full scale Biomat application in a field were established.Item GIS-Based Odor Impact Assessment from Biosolids Land Application Sites(2010) Intarakosit, Eakalak; Baecher, Gregory B.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biosolids applied to agricultural land may upset neighboring communities due to the inherent malodorous smell of biosolids. The problem of the odor becomes a major concern in the wastewater treatment industry when community responses could vary from complaints to legal action to ban or reduce biosolids recycling through land. Unlike odor at a wastewater treatment facility, which is produced from the characteristics of wastewater itself and from individual unit processes, land-applied biosolids odor depends not only on the quality of biosolids, but also on the biosolids emissions levels, unfavorable weather conditions and topographic characteristics, and variation of human perception. Those factors increase the complexity of nuisance odor at land application sites. This dissertation aims to assess biosolids emission impacts on surrounding communities by estimating the level of biosolids odor emissions, simulating odor dispersion, and quantifying human perception to biosolids odor. Odor emission rates at land-applied biosolids fields were estimated using three different approaches: assumed flow rate, statistical inference, and simulated-flux chamber. The estimated emission rates were used as an input to dispersion models. The U.S. Environmental Protection Agency Regulatory Models, both screening and refined models, were used to simulate dispersion of biosolids odor at land application sites. A Geographic Information System (GIS) was employed to support modeling steps and to create maps. Appraisal of odor perception by receptors was assessed by use of Steven's psychophysics power law. The District of Columbia Water and Sewer Authority (DCWASA) land application fields in Virginia were used as case studies. More specifically, 45 fields in Albemarle and Orange Counties were focused on. Concentration prediction maps along with probability maps were created to support visualization and provide information on potential odor impacts to communities. Possible human perceptions were expressed in Intensity maps. The methods and results described in this dissertation can support decision makers in selecting appropriate land application sites prior distributing biosolids to reduce adverse effects from land-applied biosolids.Item Evaluation of solder-joint reliability for a 10mm Quad Flat Leadless package with top-side paddle using classical models for a leadless device and accelerated life testing(2009) Levin, Mark Alan; Barker, Dr. Donald; Reliability Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The standard QFN package consists of a leadless perimeter array and a bottom solderable thermal paddle. The thermal performance of the package can be improved by moving the paddle to the topside. The soldered surface area of the package reduces by about 80% with a top-side paddle. The soldered-joint life will also reduce due to the significant thermal coefficient of expansion mismatch between the QFN package and the circuit board. The solder-joint reliability of a large QFN package with top-side paddle is not well understood. This thesis evaluates the solder-joint reliability of a 10mm square leadless QFN package with top-side paddle. The analysis includes several classical models for a leadless package and compares modeling results to accelerated reliability testing. The accelerated tests include the influence mold compound and lead finish play on solder-joint life and ways to improve solder-joint reliability.