Environmental Science & Technology
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Item INCREASING EFFICIENCY AND SUSTAINABILITY OF WASTE-TO-ENERGY SYSTEMS USING BIOCHAR FOR HYDROGEN SULFIDE CONTROL AND LIFE CYCLE ASSESSMENT(2019) Choudhury, Abhinav; Lansing, Stephanie; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The research aim was to increase energy production efficiency and reduce the environmental impacts of waste-to-energy technologies, specifically anaerobic digestion (AD) of dairy manure (DM) and combustion of poultry litter (PL). The first objective was co-digestion of DM with gummy vitamin waste (GVW) to increase methane (CH4) yield. The GVW co-digestion treatments significantly increased CH4 yield by 126% - 151% compared to DM-only treatment and significantly decreased the H2S concentration in the biogas by 66% - 83% compared to DM-only. The second objective was understanding the effect of hydrogen sulfide (H2S) scrubber management, operation, and maintenance parameters on H2S removal efficiency. Even though the capital and operating costs for the two H2S scrubbing systems in this study were low (< $1500/year), they showed ineffective performance due to insufficient air injection, substitution of proprietary iron oxide-based H2S adsorbents for cheaper alternatives, and the lack of dedicated operators. The third objective was adsorption of H2S using Fe-impregnated biochar as a substitute for activated carbon (AC). Fe-impregnation of biochar led to a 4.3-fold increase in the H2S adsorption capacity compared to AC. When compared to unimpregnated biochars, Fe-impregnation led to an average 3.2-fold increase in the H2S adsorption capacity. The fourth objective was in-situ use of biochar in AD to remove H2S. In-situ biochar addition at the highest dose (1.82 g biochar/g manure total solids (TS)) resulted in an average H2S removal efficiency of 91.2%. Biochar particle size had no significant effect on H2S reduction. In-situ addition of Fe-impregnated biochar resulted in an average H2S removal efficiency of 98.5%. The fifth objective was a life cycle assessment (LCA) of a PL fluidized bed combustion (FBC) system. The LCA assessment showed that heating poultry houses using heat obtained from the combustion of PL in the FBC system had 32% lower climate change potential (CCP) compared to use of propane for heating poultry houses. However, analyzing the FBC system under a net positive electrical output scenario resulted in 66% less impact on CCP and a 48 – 98% reduction in environmental impacts compared to the previous scenario with net electricity input.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 Energy Balance, Water Balance, and Plant Dynamics of a Sloped, Thin Extensive Green Roof Installed in the Mid-Atlantic Region of the United States(2014) Tjaden, Scott William; Tilley, David; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Vegetated extensive green roofs can reduce peak runoff amounts during rain events. As the desire to install green roofs expands beyond roofs with little slope to those with steeper slopes, often found on residential homes, there is a need to understand how slope affects runoff. WaterShed, the University of Maryland's winning entry in the 2011 U.S. Department of Energy Solar Decathlon competition, is used as an applied research site where studies like the runoff analysis can be completed, while helping to promote and demonstrate environmental sustainability and energy consumption efficiency. Instrumentation installed on the roof will allow high-resolution data analysis, producing hydrographs. The research has related the sloped green roof to different moisture holding capacities throughout the different elevations, resulting in a unique energy balance for the installed green roof. The thin substrate did not significantly contribute to overall runoff reduction, rather it helped to reduce the overall peak runoff and elongate the runoff lag after a rain event. This living technology's performance over time in a new application to sloped roofs is crucial both to ensure regulatory standards are met and to provide feedback for future improvements to the design and technology itself.Item FATE AND TRANSPORT OF NITROGEN AT A DEEP ROW BIOSOLIDS APPLICATION HYBRID POPLAR TREE FARM(2012) Maimone, Diana; Felton, Gary K; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study evaluates deep row applied biosolids as a nutrient source for hybrid poplar trees grown on a gravel mine reclamation site in Brandywine, Maryland from November 2003 to April 2009. The study included biosolids application rates of 386, 773, and 1,159 dry Mg/ha (172, 345, and 517 dry ton/ac.) and hybrid poplar tree densities of 0, 716, and 1,074 trees/ha (0, 290, and 435 trees/ac.). Soil water samples taken from suction lysimeters located 15 - 120 cm (6 - 48 in.) vertically below the biosolids were analyzed for total ammoniacal-nitrogen (TAN) and nitrate-nitrogen (NO3-N). The majority (96.3%) of NO3-N values were less than EPA drinking water MCL of 10 mg/L. No NO3-N values within the tree plots exceeded 2 mg/L. The TAN concentrations increased with application rates, but decreased with distance from the biosolids, except there was no difference between 60 cm (24 in.) and 120 cm (48 in.).