Environmental Research Institute - Doctoral Theses
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Item Improved modelling of pumped hydro energy storage(University College Cork, 2012) Deane, John Paul; O'Gallachoir, Brian; McKeogh, Eamon; Eirgrid Plc.Rising greenhouse gas emissions, diminishing fossil fuel reserves and concerns over energy security have led to renewable energy targets that have spurred the growth of variable renewable generation sources such as wind and wave in many countries. The introduction of variable sources of electrical generation makes the operation and modelling of the power system more challenging. Pumped hydro energy storage is a flexible, fast acting generating source with the ability to store large amounts of electricity, and to facilitate the technical integration of variable renewable sources of generation. Recently, there has been resurgence in pumped hydro energy storage as many European countries strive for greater integration of renewables; however, the software tools and techniques used to traditionally model the power system need to be improved in order to capture the operation and role of flexible enabling technologies such as pumped hydro storage. Traditionally deterministic models that simulate the power system at hourly resolution are employed to assess the role and usefulness of pumped hydro storage. In this thesis, techniques are developed and presented to improve the current representation of pumped hydro energy storage, eliminating the weakness of perfect foresight assumption in model simulations. It is also demonstrated that higher temporal resolution simulations of the power system have the ability to capture important aspects of power system operation such as binding ramp rates. New techniques are also put forward for the improved modelling of large pumped storage in the context of wind forecast uncertainty, and it is shown that energy system models can benefit in the modelling of pumped hydro storage by soft-linking with power system models. Overall, this works shows that existing pumped hydro energy storage will play an ever more important role in Ireland as levels of installed wind capacity increase.Item Economic, environmental, and technical assessment of on-farm anaerobic digestion systems in Ireland(University College Cork, 2024) Diaz Huerta, Jorge; O'Shea, Richard; Wall, David; Murphy, Jerry; Sustainable Energy Authority of Ireland; Gas Network IrelandIreland's pursuit of producing 5.7 TWh of biomethane from anaerobic digestion (AD) plants, to reduce reliance on fossil-derived natural gas, necessitates a thorough examination of viable system configurations. The implementation of AD in Ireland is seen as a targeted approach to achieving emissions reduction of 25% in the agricultural sector. On-farm AD unlocks the opportunity to generate biomethane from indigenous feedstock and curtail emissions from livestock farming. Previous assessments of the mitigation potential of AD systems in agriculture have been undertaken through Marginal Abatement Cost Curves in an Irish context. Although this initial assessment deemed AD as a high-cost of abatement solution, recent uncertainty in energy prices, due to recent geopolitical events, might provide new opportunities for the development of biomethane from on-farm AD. Furthermore, using single values for abatement costs may not encompass or describe the impact of the varying system boundary of an AD system, which can have consequences for the financial and environmental performance. Such variables include the scale of the on-farm AD system, the feedstock used, and the biogas energy end-use. AD systems can vary significantly in terms of scale, design, technology, feedstock, and function. This thesis delves into the financial and environmental viability of on-farm AD systems, emphasising the need to consider additional inputs and outputs beyond energy sales that lie within the system boundary. The work evaluates different biogas end-use options and varying farm sizes for on-farm AD systems, revealing a wide range of abatement costs, whilst accounting for the uncertainty of external factors. The findings indicate that, when income from co-products such as biofertilisers are factored into the analysis, as well as the emissions reductions from digestate use, a more optimistic evaluation of AD system viability is attained. Analysis across different scales and process configurations reveals varying mitigation potential, with abatement costs ranging from -7 € tCO2eq-1 to +816 € tCO2eq-1. A key result of the analysis shows that, if a single input variable is changed within the system boundary, the financial and environmental performance of a system can be significantly changed. The efficiency of the AD process emerges as a key determinant, alongside farm conditions such as grass silage yield and synthetic fertiliser use. While heat and electricity production exhibit lower uncertainty, biomethane production faces challenges, necessitating additional incentives for small-scale AD uptake. Novel approaches, such as the integration of microbial electrolysis cell (MEC) technologies, could present an opportunity to enhance small-scale upgrading feasibility, though capital constraints remain Connecting on-farm AD systems through pipelines to centralised upgrading facilities offers a promising alternative to the transportation of materials to a large centralised AD plant, or upgrading biogas at small individual plants, reducing investment requirements. Overall, this research provides insights into enhancing the economic and environmental feasibility of on-farm AD systems, crucial for sustainable agricultural practices and emission reduction goals. Through strategic integration and policy support, on-farm AD holds promise as a key contributor to decarbonisation efforts, offering diversified revenue streams for farmers and addressing emissions from the agricultural sector. Further research and policy development are essential to realise the full potential of on-farm AD in contributing to sustainable development and mitigating climate change impacts.Item Sequential temperature phased enhanced anaerobic digestion using bioaugmentation microbes to enhance biomethane production from alkali pretreated late cut grass and late cut grass silage(University College Cork, 2024) Donkor, Kwame O.; Murphy, Jerry; Wall, David; O'Shea, Richard; Bose, Archishman; Gottumukkala, Lalitha D.; Irish Research Council for Science, Engineering and Technology; Celignis LimitedAnaerobic digestion is a biomass and waste conversion technology that uses a consortium of microbes to convert the organic matter to biogas which is primarily made up of methane and carbon dioxide. The technology tackles environmental pollution by reducing the waste going to landfills causing greenhouse gas emissions. Apart from producing biomethane that can substitute for fossil derived natural gas, heat and electricity, the digestate from the anaerobic digestion process can serve as biofertilizer that can also replace fossil-based fertilizer usage. Anaerobic digestion in most commercial scale settings is applied as a standalone system relying on a consistent supply of feedstock including for lignocellulosic feedstock such as late cut grass and late cut grass silage. However, such lignocellulosic feedstock is relatively recalcitrant and suffers from lower biomass biodegradability and lower biomethane production compared to starch and sugar rich waste streams. For the biogas plants to extract maximum biomethane potential from recalcitrant lignocellulosic biomass, further supporting technologies aimed at increasing the feedstock digestibility are required. Hence, an integrated anaerobic digestion concept was proposed which combined alkali pre-treatment, temperature phased anaerobic digestion and microbial bioaugmentation to improve biomethane production from lignocellulosic biomass. The proposed concept was known as Sequential Temperature-phased Enhanced Anaerobic Digestion using Microbes (STEADM). An assessment of the proposed and modelled STEADM concept indicated that biomethane production from lignocellulosic biomass such as late cut grass could increase by 47% as compared to the conventional standalone anaerobic digestion system. Consequently, this propelled the research thesis to develop the Sequential Temperature-phased Enhanced Anaerobic Digestion using Microbes (STEADM) concept. The development of the STEADM concept started with initially investigating an optimum alkali pre-treatment that can enhance biomethane production from late cut grass and late cut grass silage. Alkali pre-treatment targets hemicellulose and lignin solubilization to improve microbial bioconversion of lignocellulosic biomass. The first experimental work examined the effectiveness of alkali pre-treatment of late cut grass and late cut grass silage in improving biomethane production by using a mixture of calcium, magnesium and potassium hydroxides. This involved an optimization batch study that determined the optimum conditions of mixed alkali pre-treatment of biomass to enhance biomethane production. The optimum conditions of the mixed alkali pre-treatment for anaerobic digestion of late cut grass silage were found at an alkali loading of 16 wt.% (16g/100 g dry matter) at 50 °C. This generated a 78% increase in biomethane yield compared to anaerobic digestion of untreated late cut grass silage. Also, the optimal conditions for late cut grass were 14.8 wt.% alkali loading at 36 °C, which delivered a 98% increase in biomethane yield as compared to anaerobic digestion of untreated late cut grass. After optimization study, an energy and techno-economic assessment was conducted to assess the cost-effectiveness of the optimized mixed alkali pre-treatment anaerobic digestion system as compared to the conventional anaerobic digestion system. The essence of integrating the techno-economic analysis with the optimization batch study was to determine at an early stage whether the mixed alkali pre-treatment to improve grass biomethane was a potentially worthwhile route to take in developing the STEADM concept. The techno-economic analysis indicated that mixed alkali pre-treatment improved the process economics, as the levelized cost of biomethane energy production (LCOE) was 21% and 45% lower for late cut grass silage and late cut grass respectively as compared to the conventional anaerobic digestion system. The LCOE for late cut silage was determined to be 19.0 and 23.9 c€/kWh for the alkali pre-treatment AD system and conventional AD system, respectively. The LCOE for late cut grass was 23.2 and 42.0 c€/kWh for the alkali pre-treatment AD system and conventional AD system, respectively. The mixed alkali pre-treatment proved to be cost-effective and thus the study progressed to develop the STEADM concept by performing continuous digestion experiments at increasing organic loading for various anaerobic digestion (AD) scenarios. The investigated AD scenarios were single stage and temperature phased anaerobic digestion of untreated late cut grass silage [S0 & T0-M0], single stage and temperature phased anaerobic digestion of pre-treated late cut grass silage [S1 & T1-M1] and single stage and temperature phased anaerobic digestion of untreated late cut grass silage enhanced with bioaugmentation [S2 & T2-M2]. Assessment of the various AD scenarios indicated that mixed alkali pre-treatment improved biodegradability and allowed for biomass feeding at high organic loading up to 4.0 g VS L-1 d-1. Furthermore, bioaugmentation increased biomass solubilization about 1.4 to 2.8 times in bioaugmented digesters. Phase separation in temperature phased anaerobic digestion additionally improved anaerobic digester stability by limiting FOS-TAC below 0.400, even at high organic loading of 4.0 g VS L-1 d-1. The developed STEADM system was able to operate at a high organic loading rate of 4.0 g VS L-1 d-1 but was limited to a short term 30-day digestion because of mechanical mixing difficulties in the digester. This was not a biological operational issue and thus in a commercial scale setting, appropriately designed mixers for fibrous materials will be able to operate the STEADM process at organic loading rates of 4.0 g VS L-1 d-1. As a result of the mechanical mixing limitation in this study, long term 90-day operation of the developed STEADM concept was conducted at operationally feasible organic loading of 3.0 g VS L-1 d-1 and produce a stable biomethane yield of 339 ± 27 L CH4 kg VS-1. This was 97% methane increase as compared to the conventional single stage anaerobic digestion of untreated late cut grass silage which produced a daily average methane yield of 172 ± 46 L CH4 kg VS-1 at organic loading of 1.0 g VS L-1 d-1. In conclusion, this thesis demonstrated that considerable improvement in biomethane production from recalcitrant lignocellulosic biomass such as late cut grass silage can be achieved by integrating alkali pre-treatment, temperature phased anaerobic digestion and microbial bioaugmentation. The results from this thesis can provide future pathways to developing improved versions of the STEADM concept to further enhance the anaerobic digestion of various biomass feedstock.Item The taphonomy of anurans from the Eocene Geiseltal Konservat-Lagerstätte(University College Cork, 2024) Falk, Daniel; McNamara, Maria; Wings, Oliver; Irish Research Council for Science, Engineering and TechnologyThe Eocene Geiseltal fossil site is represented by ca. 50,000 fossil specimens that were recovered from open-cast lignite mines in central Germany in the early to mid-20th century. The fossils were excavated primarily from organic-rich sediments of lacustrine and fluvial deposits and are curated in the Geiseltal Collection of the Natural Sciences Collections of the Martin Luther University Halle-Wittenberg in Halle (Saale). The fossil collection includes vertebrates, invertebrates, plants and trace fossils. Despite its rich fauna and flora, the taphonomy of the biota is poorly understood. This is because the primary fossil collections, studied extensively in the early 20th century, were not accessible for study using modern techniques. The Geiseltal biota is famous for reports of three dimensionally preserved soft tissues; the subcellular anatomical details described for various soft tissues in different vertebrate groups and in the anurans in particular, represent a fidelity of preservation that is among the highest known for any Konservat-Lagerstätte. Intriguingly, the proposed mode of preservation, direct replication in silica, is not known in other fossils, but has not been verified using modern approaches. This thesis addresses these issues using quantitative taphonomic approaches, microbeam techniques (scanning electron microscopy, micro-Fourier transform infrared spectroscopy, micro-Raman spectroscopy, X-ray diffraction and synchrotron rapid scanning-X-ray fluorescence) and statistical analysis to elucidate the taphonomy of the Geiseltal anurans (i.e., frogs and toads). Critical assessment of trends in the articulation and completeness of the fossil anurans reveals a hierarchy of taphonomic controls, whereby preservation is controlled at the specimen level by the size and location of bones, by the three-dimensional configuration of joints, by the impact of predators and scavengers, by the duration of pre-depositional transport and the impact of bottom currents on the lake floor. The studied Geiseltal anurans lack most of the soft tissues reported originally; there is no evidence for preservation in silica. Instead, the only soft tissue features present are melanosome films and the anuran-specific mid-dermal Eberth-Katschenko (E-K) layer, preserved as sulfurised organic remains and as a phosphatised replacement, respectively. Multivariate analysis of geometry data of melanosomes preserved in anurans from Geiseltal, other fossil biotas and extant anurans reveals that the evolution of melanosomes in the skin is decoupled from that of melanosomes in the eyes and internal tissues. This most likely reflects disparate physiological constraints on melanosome function since the Middle Eocene. In summary, comparison of the taphonomy of the Geiseltal anurans with fossils from other lacustrine Konservat-Lagerstätten reveals that the skeletal and soft tissue features of the Geiseltal anurans are not unique. The mode of preservation of the Geiseltal anurans also applies to anurans from other lacustrine Konservat-Lagerstätten, revealing high-level controls on the preservation of anurans in the fossil record. The major controls on skeletal taphonomy are the broad palaeoclimatic setting, which controls lake water temperature, lake physiography, which controls the lake depth and lake size and anatomy, which control the size and location, respectively, of bones. These results potentially apply to other vertebrate groups. The major controls on the preservation of anuran soft tissues are the availability of phosphate ions and reduced sulfur species, the development of microenvironments during decay and the tissue chemistry. This thesis highlights the power of combining quantitative, analytical and comparative approaches to assess the skeletal and soft tissue taphonomy of fossil vertebrates in order to develop models for the preservation of fossil vertebrates in lacustrine environments. This thesis also demonstrates that comparative analysis of melanosome data from fossil and extant specimens in a single vertebrate group can inform on the evolution of melanin in that group. Finally, scientific investigation of fossil collections using modern analytical techniques is essential to critically re-evaluate both historical fossil interpretations and established scientific paradigms.Item The spatial ecology and conservation of an important game bird in Ireland: the Eurasian woodcock(University College Cork, 2024) O'Neill, James B.; Quinn, John; Holloway, Paul; Hoodless, Andrew; Irish Research Council; National Association of Regional Game Councils; Game and Wildlife Conservation Trust; National Parks and Wildlife ServiceA wide range of species are targeted by human hunters, including those with uncertain or poor conservation status. However, the direct and indirect effects of this exploitation can be complex and are often poorly understood. The Eurasian woodcock (hereon woodcock) is a largely migratory ground-nesting bird in the family Scolopacidae associated with forested habitat, and is commonly hunted by humans across its European range. The direct and indirect effects of hunting on this species are generally poorly known, and it can be difficult to study owing to its elusive and crepuscular habits. On the island of Ireland, the woodcock population comprises both resident breeding birds and migratory overwintering birds which originate from areas such as Fennoscandia, the Baltic States and Russia. The breeding population is thought to have declined in recent decades, with available evidence suggesting a range contraction of over 70% between 1968 and 2011, whilst trends for migratory birds are unknown. However, the species is popular among hunters in Ireland, and no information exists as to how hunting activity affects its population or ecology. To address these knowledge gaps, this research had four main objectives: i. Establish an understanding of the current distribution and abundance of breeding woodcock in Ireland, and the environmental drivers that influence these, through a nationwide ‘roding’ survey from 2017 to 2021 and a two-step species distribution modelling (SDM) method. ii. Explore whether hunting and bird age affected the survival of non-breeding woodcock using radiotelemetry to monitor the fates and activity of 168 tagged birds across three hunted and three not hunted sites. iii. Explore whether hunting and bird age affected the use of space and movement ecology of non-breeding woodcock using global positioning system (GPS) tracking of 42 birds across three hunted and three not hunted sites. iv. Assess woodcock habitat preferences in the context of heterogenous Irish landscapes, and explore whether hunting affects habitat preferences using GPS tracking of 42 birds across three hunted and three not hunted sites. These objectives produced the following key results: i. National roding survey results and SDM outputs estimated that breeding woodcock are more widespread in Ireland than recently reported, with a population estimate of 27,434 males (95% CL: 16,947 - 36,288). Bioclimatic variables, including precipitation and temperature seasonality and mean winter temperature, were important determinants of woodcock distribution, whilst forest habitat availability and composition at different landscape scales significantly influenced their abundance. ii. Survival of overwinter woodcock across the six sites was high relative to the findings of comparative studies, with an estimated monthly survival rate during the hunting open season of 98.0%. The predominant cause of recorded mortality was hunting, followed by natural predation. Too few mortalities were recorded to meaningfully investigate the effect of hunting and bird age on mortality rates. iii. Both hunting and bird age affected the use of space and movement ecology of non-breeding woodcock. Hunted and juvenile birds recorded larger diurnal and nocturnal home ranges than not hunted and adult birds, respectively, and hunting disproportionately affected adult woodcock commuting movements. Juveniles showed a slightly higher level of localised exploratory movement than adults. iv. Diurnal and nocturnal habitat preferences of non-breeding woodcock were ranked. Hunting affected habitat preference, with hunted birds showing greater preference for broadleaved forest and less preference for hedgerows and scrub; these three habitats were of equal importance to not hunted birds. Nocturnally, hunted birds showed greater preference for grassland habitats at night and lower preference for closed habitats. The results are discussed in the context of wider knowledge of woodcock and other species, and the scope for further research and species monitoring effort is explored. This research provides novel information and methodology with international appeal on the spatial ecology and impacts of human activity on this species. It is hoped that this work will contribute to the implementation of sustainable landscape and species management practices with a view to reducing human impacts on the natural world.