Browsing by Author "Wills, Michael"
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Item Application of a simplified ADM1 for full-scale anaerobic co-digestion of cattle slurry and grass silage: assessment of input variability(Springer, 2024-01-02) Tisocco, Sofia; Weinrich, Sören; Lyons, Gary; Wills, Michael; Zhan, Xinmin; Crosson, Paul; Grassland and Plant ScienceMathematical modeling of anaerobic digestion is a powerful tool to predict gas yields and optimize the process. The Anaerobic Digestion Model No. 1 (ADM1) is a widely implemented model for this purpose. However, modeling full-scale biogas plants is challenging due to the extensive substrate and parameter characterization required. This study describes the modification of the ADM1 through a simplification of individual process phases, characteristic components and required parameters. Consequently, the ability of the simplified model to simulate the co-digestion of grass silage and cattle slurry was evaluated using data from a full-scale biogas plant. The impacts of substrate composition (crude carbohydrate, protein and lipid concentration) and variability of carbohydrate degradability on simulation results were assessed to identify the most influential parameters. Results indicated that the simplified version was able to depict biogas and biomethane production with average model efficiencies, according to the Nash-Sutcliffe efficiency (NSE) coefficient, of 0.70 and 0.67, respectively, and was comparable to the original ADM1 (average model efficiencies of 0.71 and 0.63, respectively). The variability of crude carbohydrate, protein and lipid concentration did not significantly impact biogas and biomethane output for the data sets explored. In contrast, carbohydrate degradability seemed to explain much more of the variability in the biogas and methane production. Thus, the application of simplified models provides a reliable basis for the process simulation and optimization of full-scale agricultural biogas plants.Item Decision support tool for the construction and seasonal operation of farm-scale anaerobic digestion plants(Elsevier, 2023-04-15) O’Connor, Sean; Ehimen, Ehiaze; Pillai, Suresh C.; Lyons, Gary; Johnston, Chris; Wills, Michael; Bartlett, JohnOptimal plant design and management are critical components for the successful operation of farm-scale anaerobic digestion (AD) plants. However, this often proves challenging due to difficulties in designing and sizing the plant based on specific site conditions. The current investigation aims to address these difficulties by developing a universal decision support tool to assist in the optimal design and management of agriculture-based AD plants, accounting for site-specific practicalities and implications. The tool consists of various mathematical functions, which enable numerous simulations to be created and run. The developed tool was applied to a case study, located in Ireland, to test its usefulness, where the analysis showed the optimal, site-specific, plant design with key assessment indicators. For this case study, the feedstock availability assessment determined that the lignocellulose and non-lignocellulose biomass within a 10 km distance of the site. Based on the local energy demand of the area, the tool modelled an optimal AD plant design, including feedstock storage, digester volume, engine capacity, and digestate storage. The tool applied various technical, economic, and ecological assessment indicators to the plant to gauge its viability. Therefore, demonstrating the tool's usefulness in assisting stakeholders to make informed decisions and reducing costs by optimising plant design and performance.Item Review of two mechanical separation technologies for the sustainable management of agricultural phosphorus in nutrient-vulnerable zones(MDPI, 2021-04) Lyons, Gary A.; Cathcart, Ashley; Frost, J. Peter; Wills, Michael; Johnston, Christopher; Ramsey, Rachel; Smyth, BeatriceThis work reviews two mechanical separation technologies (screw press and decanting centrifuge) which could be used in the dairy, beef, pig and anaerobic digestion sectors in nutrient-vulnerable zones in order to improve the sustainability of manure and anaerobic digestate management by decreasing agricultural phosphorus loss and reducing environmental impact on water quality. Capital and operating costs, separation efficiency and throughput, and management and processing of separated fractions, including transport costs, environmental impacts and the biosecurity of separated solids for export, were considered. Of the two technologies reviewed, screw press separation is a more cost-effective option (5-fold cheaper per tonne of feedstock) when lower amounts of export of phosphorus off farm are acceptable. For farms and those with anaerobic digesters managing larger volumes of manure/digestate, screw press separation is possible. However if higher levels of phosphorus removal are required, the use of decanting centrifugation is a viable option. Centralised processing facilities could also make use of decanting centrifuge technology to act as processing hubs for local farms within a distance that makes it economical for transport of manure/treated manure to/from the processor (the maximum distance for economical transport of raw manure and separated solids is approximately 70 km and 84 km, respectively). Both separation technologies could be integrated into agricultural manure and digestate management systems in order to provide a more sustainable approach to managing agricultural phosphorus loss and its associated impact on water quality. Screw press and decanting centrifuge separation could reduce phosphorous loss to water bodies by 34% and from 30 to 93%, respectively.