College of Agriculture & Natural Resources
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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 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 THE ECONOMICS OF WIND POWER AND WHISKY(2015) Page, Ian; Williams, Roberton; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)For many goods, economists tend to ignore the time between the onset of production and the final sale of the good. In some instances, economists do model production with intertemporal considerations such as the extraction of groundwater, population dynamics in fisheries, and manufacturing with costs characterized by learning-by-doing; but even in these cases output at any point in time tends to be unconstrained except when production is limited according to resource availability. In the following three essays, I examine the implications for agent and market behavior when producers cannot perfectly adjust output over time. In the first two essays, I focus on the relationship between electricity markets and both conventional and renewable power producers. Specifically, in the first essay, I quantify the effect a large level of installed wind power capacity (an intermittent renewable energy) has on power market conditions. Because wind power has virtually no marginal costs for generation, and its output cannot be perfectly controlled, a high penetration level of wind power could potentially lower average prices while also impacting price volatility. In the second essay, I construct a computational model of a conventional power producer that cannot perfectly adjust its output over time and faces prices that change according to a stochastic process. Then, I measure the impact price volatility has on producers in two ways. First, I analyze changes in their optimal generation strategies in light of price volatility, and then I simulate and track changes in output, profit, and emissions over time. My third essay pertains to production of whisky. While there are other examples of vintage goods that require a significant amount of maturation, the existing literature typically assumes that there is a unique optimal maturation age for a producer's inventory. However, many Scottish distilleries produce a line of whiskies that vary primarily according to age. I demonstrate that it is possible for a profit-maximizing distillery to mature multiple ages of whisky without market power, but a further exploration of distilleries' product lines indicates the market is far from perfectly competitive.Item ENVIRONMENTAL SUSTAINABILITY AND WASTE TREATMENT CAPABILITIES OF SMALL-SCALE ANAEROBIC DIGESTION SYSTEMS(2012) Moss, Andrew Robert; Lansing, Stephanie A.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anaerobic digestion is a common form of waste treatment and energy production throughout the world, and in the United States the number of agricultural digesters is increasing at a rate of approximately 10% annually. As the number of digesters grows, efforts to assess the environmental cost of their installation and the potential utility of their by-products are required. This research investigates the relative environmental sustainability of small-scale digesters treating dairy manure in the U.S. and human waste in Haiti, and explores the biogas potential and nutrient transformations resulting from the anaerobic digestion of dairy manure. Specifically, the objectives of the research are: 1) to conduct an eMergy analysis on the two digestion systems to assess the effect of waste source, climate, and infrastructure on system sustainability; and 2) to provide an overview of waste treatment and energy production options for agricultural digesters treating dairy manure in the United States.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.