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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Fate of antimicrobials and nutrients in dairy manure management systems(2018) Schueler, Jenna E; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anaerobic digestion (AD) and composting manure management strategies were explored at the field scale to monitor antimicrobial degradation, nutrient transformations, and optimize mitigation of these pollutants in manure fertilizer to decrease their entry to waterways. Removal of antimicrobials and antimicrobial resistance genes (ARGs) were explored at the bench scale, where AD degraded >85% of antimicrobials. At the field-scale, antimicrobials were not consistently removed, persisting in concentrations up to 34,000 ng/g DW in the AD effluent. The tetM genes were reduced during bench-scale AD suggesting that AD could be an effective treatment for removing tetracycline ARGs from manure. The 100% reduction of sulfadimethoxine antimicrobials during AD did not correspond with Sul1 reduction, illustrating differences in antimicrobial versus gene reductions during manure treatment. Antimicrobials did not degrade significantly during field scale composting, likely due to a shortened composting period (33-days). The field-scale results illuminate limitations of tracking antimicrobials in complex treatment systems.Item Prediction Of Air Pollutant From Poultry Houses By A Modified Gaussian Plume Model(2017) Yang, Zijiang; Torrents, Alba; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Concentrated animal feeding operations release a variety of potential pollutants, such as ammonia and particulate matters (PM). Field measurements are time consuming, costly, and only provide a limited amount of spatial and temporal information. Air dispersion models can serve as an alternative solution, especially if coupled with field sampling. The Gaussian plume model (GPM) is a mathematical model that assumes steady state condition. Previous studies have used the GPM to evaluate and analyze source. However, much less is known about utilizing GPM to simulate plumes from horizontal sources, such as the exhaust fans from poultry houses. The purpose of this study is to modify and validate a GPM to predict air pollutant emissions from the poultry houses. Two major assumptions were applied on the model, 1) a virtual releasing point was proposed behind the ventilation fan, and 2) ventilation fan was considered as the dominant wind direction in the model for short distance (< 50 m). The modified model was validated with field experimental data. Performance and sensitivity of the model were also evaluated. Fraction of predictions within a factor of two of observations (FAC2) of NH3 and PM were 0.609 and 0.625. Model-predicted concentrations of NH3 were 1.5 times of the measured values on average. Model-predicted concentrations of PM was 0.98 times of the observed values on average.Item Design and Pilot Study for an Efficient High-Throughput Automated Computer-Vision Guided Intelligent De-Calyxing Machine for Post-Harvest Strawberry Processing(2016) Lin, John; Tao, Yang; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Strawberries harvested for processing as frozen fruits are currently de-calyxed manually in the field. This process requires the removal of the stem cap with green leaves (i.e. the calyx) and incurs many disadvantages when performed by hand. Not only does it necessitate the need to maintain cutting tool sanitation, but it also increases labor time and exposure of the de-capped strawberries before in-plant processing. This leads to labor inefficiency and decreased harvest yield. By moving the calyx removal process from the fields to the processing plants, this new practice would reduce field labor and improve management and logistics, while increasing annual yield. As labor prices continue to increase, the strawberry industry has shown great interest in the development and implementation of an automated calyx removal system. In response, this dissertation describes the design, operation, and performance of a full-scale automatic vision-guided intelligent de-calyxing (AVID) prototype machine. The AVID machine utilizes commercially available equipment to produce a relatively low cost automated de-calyxing system that can be retrofitted into existing food processing facilities. This dissertation is broken up into five sections. The first two sections include a machine overview and a 12-week processing plant pilot study. Results of the pilot study indicate the AVID machine is able to de-calyx grade-1-with-cap conical strawberries at roughly 66 percent output weight yield at a throughput of 10,000 pounds per hour. The remaining three sections describe in detail the three main components of the machine: a strawberry loading and orientation conveyor, a machine vision system for calyx identification, and a synchronized multi-waterjet knife calyx removal system. In short, the loading system utilizes rotational energy to orient conical strawberries. The machine vision system determines cut locations through RGB real-time feature extraction. The high-speed multi-waterjet knife system uses direct drive actuation to locate 30,000 psi cutting streams to precise coordinates for calyx removal. Based on the observations and studies performed within this dissertation, the AVID machine is seen to be a viable option for automated high-throughput strawberry calyx removal. A summary of future tasks and further improvements is discussed at the end.Item INCREASING THE SUSTAINABILITY OF PSYCHROPHILIC SMALL-SCALE ANAEROBIC DIGESTERS(2015) Witarsa, Freddy; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The research was aimed at increasing the energy production efficiency of small-scale anaerobic digesters in temperate climates while quantifying their environmental impacts. Biochemical methane potential tests were used to quantify methane (CH4) production from separated and unseparated manure during psychrophilic digestion, and compare CH4 production when pre-incubated alternative inocula (wetland sediment (WS), landfill leachate (LL), mesophilic digestate (MD)) were used. Methanogenic and Archaeal communities were analyzed using T-RFLP and qPCR. At 24 ºC, unseparated manure produced significantly higher (40%) quantity of CH4 than separated manure due to higher volatile solids (VS) content, but differences were insignificant at digestion times of ≤16 days. At lower digestion times, farmers could digest liquid, separated manure without sacrificing CH4 production, but at longer digestion times, the VS in unseparated manure has the time necessary for CH4 conversion. The alternative inocula studies showed that LL inoculum after incubation for 91 days at 25 ºC produced significantly higher quantity (≥20%) of CH4 than MD and WS during digestion at the same temperature, and was not significantly different in CH4 quantity than MD that was incubated and digested at 35 ºC (202 ± 4 L/kg VS). Methanosarcinaceae was dominant in the LL reactor, while the other reactors were abundant in Methanosaetaceae, indicating that inoculum rich in Methanosarcinaceae may be beneficial for starting digestion at lower mesophilic temperature ranges. Longer incubation time generally reduced the inoculum amount needed for batch digestion and prevention of volatile fatty acids accumulation. In batch systems with long digestion time (90 days), MD inoculum from well-established digesters, 35% inoculum to substrate ratio, and 35 ºC operation temperature are recommended for highest CH4 production per unit of digester volume. Additionally, life cycle assessments (LCA) were conducted to compare the sustainability of an unheated Chinese fixed-dome digester with a heated and insulated small-scale plug-flow digester in the US. The LCA showed that the US plug-flow digester was more sustainable than the Chinese fixed-dome system only in climate change category, but contributed negatively towards 17 impact categories. Digester heating and heating infrastructure were the main contributors towards the negative impacts observed in the US plug-flow digester.Item DESIGN AND ECONOMICS OF PLUG-FLOW, SMALL-SCALE ANAEROBIC DIGESTERS FOR TEMPERATE CLIMATES(2011) Klavon, Katherine Heléne; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anaerobic digestion is a manure treatment option that is gaining popularity throughout the world as a result of its multiple environmental and economic benefits. There exists a need for further research to make anaerobic digestion and methane recovery more readily available, cost effective, and manageable to small dairy facilities in the United States. This research analyzes the design and economics of plug flow digesters, modeled after low-cost digesters utilized in the developing world and modified to operate on small to medium-scale farms located in the temperate United States. The objectives of this research are to: 1) Describe the modified design and construction of the research plug flow digesters and analyze the barriers and design challenges to implementing this technology in the United States and 2) Conduct an economic analysis to determine the feasibility of installation and operation of these types of systems in the temperate United States.Item Portable Hyperspectral Imaging Device for Surface Sanitation Verification in the Produce Industry(2011) Wiederoder, Michael; Lo, Y. Martin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Produce processors must clean and sanitize surfaces before production to reduce the risk of foodborne illness. Current surface hygiene verification methods require direct surface sub-sampling at selected locations and a wait time. To augment these methods, a portable hyperspectral imaging device was developed to find potential contaminants in real-time and increase sub-sampling effectiveness. Analysis of hyperspectral fluorescence images showed that fresh-cut produce processing exudates in the regions of 460-540 and 670-680 nm are detectable from background materials, while select cleaning agents are not. The portable single operator imaging system includes a charge coupled device (CCD) camera, tunable optical filter, laptop, light emitting diodes (LED's) for fluorescence excitation, and a touchscreen display. Within a commercial plant, fluorescence imaging identified produce processing residuals following routine cleaning procedures that were not readily visible to the naked eye. These tests demonstrate the system's potential to enhance post-cleaning inspection, and helped improve routine cleaning procedures.