Civil and Environmental Engineering - Doctoral Theses

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Integrating air quality modelling, low-cost sensing and greenspace quantification for enhanced urban air quality and net-zero cities
(University College Cork, 2024) O'Regan, Anna Claire; Nyhan, Marguerite; Hellebust, Stig; O'Dowd, Colin; SFI Research Centre for Energy, Climate and Marine; University College Cork
Urbanisation is rapidly increasing worldwide. Currently, 55% of the global population live in urban areas and this is projected to increase to 70% by 2050. While urban areas are sites for innovation and economic growth, they are also key hotspots for poor air quality and climate-related impacts. Air pollution poses a significant risk to public health, with 96% of urban populations exposed to unhealthy levels of air pollution. As such, data on urban air quality is essential to identify pollution sources as well as spatial and temporal trends. This can support the formation of policies, ensuring compliance with regulatory limits while striving to meet the stringent World Health Organization (WHO) guidelines to protect public health. Air pollution and greenhouse gas (GHG) emissions often stem from common sources. Consequently, there is significant potential to develop policies that enhance air quality while also maximising reductions in GHG emissions. Rapid urban expansion is significantly impacting greenspace, with a notable decline observed due to increased demand for grey infrastructure. Greenspace offers many environmental benefits, including reducing air pollution and mitigating against the impacts of climate change, while also positively influencing residents’ health. As such, prioritising strategic greenspace developments is crucial. This research is driven by a need to improve our understanding of air pollution, greenspace and their associations, with an overarching aim of decarbonising cities. Firstly, a comprehensive review of global literature was conducted, identifying the current state-of-the-art in air pollution and GHG emissions modelling and monitoring efforts. Furthermore, innovative methods for quantifying urban greenspace were explored. Air pollution, specifically nitrogen dioxide (NO2), was modelled in high spatial and temporal resolution for Cork City, Ireland. The output of the dispersion model enables the identification of pollution sources while also capturing fluctuations in pollution levels over time and space. Moreover, a data fusion technique, regression kriging, was employed which integrated the urban dispersion model output with large-scale citizen science data. The citizen science data was measured using diffusion tubes at 642 locations across the study domain. The data-fusion model provided improved accuracy of air pollution levels and population exposure. Urban greenspace was quantified using 751,644 Google Street View (GSV) images, capturing a street-level view of greenspace at 125,274 locations across three major cities in Ireland. The associations between street-level greenspace, health and socioeconomics were explored. Higher levels of greenspace were associated with improved self-reported health and areas in the upper quartiles of greenspace had higher levels of income and lower levels of unemployment. Furthermore, with the advancements in air pollution sensing technologies such as ‘low-cost’ sensors, this research aimed to explore the relationship between greenspace and air pollution. This analysis demonstrated associations between higher levels of greenspace and lower levels of air pollution in urban areas. This research provides novel contributions across science and policy. It advances scientific knowledge and methodologies in air quality science and urban greenspace. Moreover, the research findings and high-resolution datasets can inform data-driven policies such as the National Clean Air Strategy (CAS) and Climate Action Plan, while also advancing UN Sustainable Development Goals including ‘Goal 11: Sustainable Cities and Communities’, ‘Goal 3: Good Health and Wellbeing’ and ‘Goal 13: Climate Action’. There is great potential to design effective strategies that strive to improve air quality and ensure optimal planning and provision of greenspace, thereby accelerating the transition to net-zero. Adopting an integrated approach in urban planning will ensure the development of cities that have good air quality, ample exposure to greenspace and net-zero emissions.
Advancing Irish energy system modelling to inform residential policy
(University College Cork, 2023) McGuire, Jason; Daly, Hannah E.; Rogan, Fionn; O'Gallachoir, Brian; Department of the Environment, Climate and Communications
Anthropogenic greenhouse gas emissions are rising, and a lack of action towards climate policy has sparked a renewed determination to act. Energy Systems Optimisation Models (ESOMs) help guide energy policymaking to meet climate goals. This thesis uses a newly developed ESOM, TIMES Ireland Model (TIM), to explore Ireland’s decarbonisation pathways. TIM incorporates empirical internal temperature variations in buildings. Building Energy Rating (BER) assessments in Ireland, based on Energy Performance Certificates (EPC), measure a building’s expected energy consumption. However, it has been observed that standard BER assessments tend to overestimate residential energy consumption in Ireland by as much as 23%. When empirical internal temperatures are used in place of BER temperature assumptions, 6% fewer thermal retrofits are required to achieve the cost-optimal decarbonisation pathway, but energy savings are 114% less in this case. The new methodology better reflects energy consumption without overestimating the effect of thermal retrofits and provides more accurate climate policy insights. The Danish Energy Agency supported this thesis by exploring the feasibility of district heating (DH) in Ireland. Ireland is a country with low DH deployment, but it has significant surplus heat. Using scenarios that considered different connection rates and maximum annual growth, this thesis consistently showed that DH saturates the heat market before 2050 in all scenarios. If DH is excluded, the average sectoral marginal CO2 emission price over the model’s time horizon is €729/tCO2. However, when DH is permitted, this cost reduces by 13% to 25%, depending on the connection rate and maximum growth constraint. A policy-focused aspect of this thesis explored Ireland’s current fabric-first policy approach to understand if it is cost-effective. Alternative decarbonisation pathways allow for variations in heat pump subsidy thresholds connected to a dwelling’s Heat Loss Indicator (HLI). The thesis also accounted for sub-optimal heat pumps, which do not achieve peak performance due to high HLIs. The findings suggest that the current fabric-first approach is stringent, requiring a BER rating of B2 or equivalent energy consumption, which is not cost-effective. Significant savings can be made, especially post-2030. For example, post-2030, the fabric-first average sectoral marginal CO2 emission price is €675/tCO2. Simply by allowing sub-optimal heat pump installation, this reduces to €312/tCO2. Adjusting the HLI threshold to 2.3 W/K/m² could further reduce this cost to €273/tCO2. This research offers a detailed exploration of the Irish residential sector, emphasizing the complex interactions among different energy sectors and advocating for a more coherent energy planning approach. For policymakers, it is essential to better understand residential energy consumption, embrace district heating through spatial energy system planning, and reevaluate the fabric-first approach. By doing so, Ireland could effectively achieve its climate goals more cost-effectively.
Decarbonisation of whiskey distilleries in a circular economy: investigating biorefinery systems for valorisation of distillery by-products
(University College Cork, 2024) Hackula, Anga Awonke; Wall, David; O'Shea, Richard; Murphy, Jerry; Irish Research Council
Decarbonisation of industrial processes is necessary to mitigate the detrimental impacts of anthropogenic climate change. Innovative technological solutions are sought that will allow for both a reduced carbon footprint and increased security of supply. The whiskey production industry produces by-products that are currently used linearly for animal feed. This thesis examines the use of by-products generated from whiskey production to enact a circular economy philosophy, which may be of further benefit to a distillery. This was achieved by examining various technologies, namely anaerobic digestion (AD), dark fermentation, and pyrolysis, in a cascading biorefinery concept. Central to the evaluation of the whiskey by-product valorisation through anaerobic digestion was the development of a novel two-phase anaerobic digestion system, termed a leach bed reactor – expanded granular sludge bed (LBR-EGSB). Several design modifications, including the implementation of a cost-effective siphon-actuated leachate attenuation system, advanced the configuration beyond comparable designs. The LBR-EGSB could successfully convert the by-products into volatile fatty acids (VFAs) and methane-rich biogas (75 %vol). The LBR-EGSB was compared to traditional anaerobic digesters for energy production capabilities, showing similar biomethane potential, which could satisfy approximately 44 % of the thermal energy demand of a large distillery operating in Ireland. Furthermore, the research investigated the potential of a biorefinery utilising dark fermentation, whereby the whiskey by-products were converted into biogenic carbon dioxide for use in beer carbonation, biohydrogen for use as transport or heating fuel, and VFAs for use as bioplastic beer packaging. A 50 million-litre whiskey distillery could satisfy approximately half of the carbon dioxide requirement of the Irish brewing industry. Biohydrogen was found to be best suited as a transport fuel. The VFAs could be processed into bioplastics which could completely satisfy beer packaging demand in Ireland. Continuous VFA production and demand-driven biogas production to generate electricity during peak demand hours were also evaluated. The systems analysed were a two-phase continuously stirred tank reactor (CSTR) and the designed LBR-EGSB. Both systems exhibited continuous VFA production (up to 10.4 g. L-1Leachate) and rapid biogas production, achieving peak biogas flow rates within 30 minutes. A theoretical evaluation of processing butyric acid into biobutanol, to be blended with diesel, could produce a more sustainable transport fuel than diesel, reducing distillery-associated transport emissions by 16 %. Additionally, the novel use of whiskey barrel-derived biochar was compared to commercial carbonaceous materials, revealing its efficacy in enhancing biohydrogen and biomethane production by 15% and reducing methane production lag time, thereby advancing the understanding of pyrolysis parameters' impact on anaerobic digestion. Overall, this thesis demonstrates that integrating AD systems, biochar application, and innovative biorefinery concepts can significantly enhance the sustainability of whiskey distilleries, proposing a pathway for modern circular economy strategies and decarbonisation of the whiskey distillery industry.
GIS techno-economic tool development and application for wave and tidal energy
(University College Cork, 2023) O'Connell, Ross; Murphy, Jimmy; Devoy McAuliffe, Fiona; European Regional Development Fund
The ocean energy sector is progressing towards commercialisation, with wave and tidal energy demonstration projects now being deployed across the globe. Well informed site selection and project feasibility analysis for commercial farms will be reliant on high-quality geospatial data and techno-economic tools/models respectively. The research undertaken for this doctoral thesis involved the modelling of new geospatial data which will be critical to future site suitability analyses for ocean energy farms in Ireland and the UK. This included new high-resolution geodata on the ocean energy resources, met-ocean characteristics, farm accessibility, device availability and energy production based on real wave and tidal energy devices. Other relevant criteria mapped as part of the research included proximity to port and grid access, bathymetry, seabed character, marine traffic and fishing activity. A fully open-access Web-GIS tool has been developed to host this data and includes functionality enabling the user to perform interactive site suitability and project feasibility analysis through the integration of a built-in site selection aid and techno-economic calculator, the latter of which couples geodata with techno-economic data to facilitate the calculation of project feasibility estimates. Site selection case studies performed using this geodata in conjunction with ocean energy technology developer input have revealed vast areas, primarily in the west of the study area, suitable for wave energy deployment and less extensive areas, primarily in the east of the study area, suitable for tidal energy deployment, varying somewhat depending on technology type. Advanced geospatial modelling of the levelized cost of energy for wave energy in the region has also been performed, revealing the areas likely to achieve the best return on investment for future commercial scale deployment in the region. A detailed site-specific project feasibility case study using the techno-economic calculator demonstrated its application for tidal energy.
Monitoring and modelling the long-term performance of Dublin Port Tunnel
(University College Cork, 2023) Wang, Chao; Li, Zili; Friedman, Miles; Science Foundation Ireland; Transport Infrastructure Ireland
Dublin Port Tunnel, the biggest urban road tunnel in Ireland, functions as a critical part of an arterial road network between Dublin Port and the rest of Dublin city. Since its opening in 2006, the tunnel has been observed with progressively developing deteriorations; onsite observations and maintenance records have identified three main types, i.e., tunnel leakage, lining crack and concrete spalling, as the greatest engineering concerns to asset owners. The increasing structure deformation may disrupt tunnel operation, threaten tunnel serviceability, and/or even endanger tunnel integrity and safety in the long term. To better the understanding of the structural health condition of this critical underground infrastructure, this thesis specifically investigates the long-term ageing performance of a cross passage twin tunnel section of Dublin Port Tunnel subject to various deteriorations through an integrated assessment based on innovative field monitoring (i.e., wireless sensor network) and advanced numerical modelling (i.e., finite element modelling), where previous investigations mainly concentrated on the responses of a single tunnel section to short-term external disturbances (e.g., adjacent construction and surcharge). Characterisation of the selected deteriorated tunnel section on the basis of historical data, maintenance records, geotechnical and hydraulic reports is conducted first. Ground and tunnel parameters are obtained through applying theories and principles of soil and rock mechanics, followed by the determination of the current hydraulic permeability (conductivity) of the deteriorated section on the basis of monitored water flow. A modified analytical model for ground-lining relative permeability is proposed by assuming radial groundwater flow through all three ground layers and the hydraulic health status of the tunnel section is evaluated to be partially permeable. To quantitatively investigate the tunnel structural behaviour, an innovative wireless sensor network field monitoring system is adopted to monitor the long-term structural performance of the select cross-passage twin tunnel section, with the system’s reliability and robustness being tested inside an underground cave in the first place. The trial deployment of the wireless sensor network monitoring system inside the cave proves it functionally effective and environmentally adaptable in harsh underground conditions. In the case study of Dublin Port Tunnel, wireless field measurements of the cross-passage tunnel section show that its deformation is still increasing with time even after more than a decade’s operation. The mode and magnitude of the observed ongoing tunnel deformation are believed to be caused by three effects: twin tunnel interaction effect, cross passage effect and seasonal effect, and the mechanisms behind these observations are deemed to be related to both the surrounding ground and tunnel: ground hydro-geological degradation and tunnel hydro-mechanical deterioration. The seasonal temperature change contributes to the cyclic variation of the elastic and reversible deformation whilst tunnel deteriorations lead to the plastic and irreversible deformation. The field measurements are then compared against the numerical results from a series of soil-fluid coupled three-dimensional finite element analyses where the time-dependent ground and tunnel deteriorations are considered. The three-dimensional finite element (FE) analyses evaluate the individual effect of tunnel hydraulic and mechanical deterioration, ground permeability anisotropy, and ground creep. The numerical rate of tunnel deformation is compared against the field measurements to examine the numerical model. The FE results suggest that limestone rheology is the dominant factor contributing to the ongoing tunnel deformation, despite a slight difference between the deformation modes possibly due to the neglection of localised ground creep in the ground in between the twin tunnels. Parametrically, coupled deterioration leads to greater deformation than that individual deterioration does, and localised deterioration induces more accurate tunnel performance than that uniform deterioration does.

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