Environmental Research Institute - Doctoral Theses

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    Electrofuels in a circular economy
    (University College Cork, 2023) Rusmanis, Davis; Murphy, Jerry; Wall, David; Science Foundation Ireland
    With the global shift away from traditional dispatchable fossil hydrocarbon fuels, the requirement for energy storage is of increasing importance. Renewable electricity generation is predominately in the form of variable renewable electricity, produced by wind and solar technologies. Intermittent production of electricity leads to an inevitable mismatch in supply and demand between the grid and the consumers. This can lead to periods of surplus power generation – and subsequent dispatch down – during low demand; conversely it can also lead to energy shortages during periods when there is insufficient power generation to match high demand which can lead to grid blackouts. Due to the difficulty in storing significant quantities of electricity via the grid, or batteries, sustainable alternative methods of energy storage must be devised. In recent years, electrofuels have become a centre-stage topic due to the opportunity to store electricity as low-carbon energy vectors which can be utilised where electrification may not be ideal, such as the hard-to-abate sectors of haulage, shipping, agriculture, and industry (iron, steel and chemicals). Further, the generation of these electrofuels could be carried out using electricity which would otherwise be lost, during times of excess production, and low grid demand. Combining technologies such as electrolysers (capable of producing hydrogen and oxygen) and biomethanation (which can combine carbon dioxide with hydrogen to form biomethane), offer a green alternative to fossil natural gas, and can use the existing gas grid as both a distribution system and a sustainable energy storage method. Based on the literature review and previous research, the initial thesis work focused on the design and commission of a prototype three-phase cascading biomethanation system. The fabricated prototype used diffusers as the agitation method and was deemed to be at a technology readiness level (TRL) of 4. The system was designed based on the results of a previously simulated system published by this research group (Voelklein et al., 2019); the results from this study were of similar performance to the previous model. The commissioning process produced carbon conversion rates between 72% and 97% across 3 reactors which can operate in parallel or series. A methane evolution rate of 2.9 L CH4/LVR/d was achieved at medium flow rates. Increasing the flow rates resulted in substantial drops in the conversion efficiency of the system. This limitation was mooted as likely due to the low bubble column height of the system. The design of the system was limited by the dimensions of the system, which were associated with health and safety concerns of the University. Assessing the integration of biomethanation technology into the wider energy, and environment sector, an initial small-scale case study of a circular economy system was carried out, based on local industry. Using a dataset from two local wind turbines to assess available surplus electricity, a small 122 kW electrolyser was proposed to be of a suitable size for the local site. This electrolyser would generate enough by-product oxygen to supply 8.9% of the oxygen demand of the aeration process for the local wastewater treatment plant of approximately 65,000 population equivalent. The product hydrogen could be used directly as a transport fuel, or convert 40% of the CO2 generated by the anaerobic digesters at the wastewater treatment plant into biomethane. This system could reduce the wastewater treatment plant emissions by 3.6% due to the reduced aeration requirement (pumping oxygen instead of air would reduce electricity usage). Should an appropriately sized electrolyser be used, up to a 40% reduction in emissions and energy use could be achieved. However, the small scale of the system was identified as a major barrier to the application of the technology, with the levelised cost of hydrogen evaluated at €8.92/kg H2 (or 27c/kWh). This resulting high cost cannot justify the implementation of a small-scale system to capture intermittent curtailed electricity as initially proposed. Expanding the circular economy system is possible with a carbon-negative emission pathway integrating pyrolysis technology to generate biochar. Anaerobic digesters and pyrolysis systems could potentially reduce greenhouse gas emissions by 42.7 kt CO2 through biomethane production from substrates within a 10km radius and through biochar production from digestate. When considering the sustainability considerations set by the latest version of the EU Renewable Energy Directive, electrofuels may only be certified as a renewable energy supply by affecting a 70% emission saving when compared to the current fossil hydrocarbon fuels. Additionally, the Directive does not allow for emission saving associated with carbon capture and reuse within the biological methanation system despite the added capture and use of otherwise curtailed electricity. Assessing a large-scale circular economy system, once again co-locating electrolysers with anaerobic digesters and biomethanation systems on new or existing large wastewater treatment plants can offer significant benefits. To supply a 10 MW electrolyser operating at an 80% operating capacity, a wind farm of 144MW size (18 x 8 MW turbines) operating at 57 % capacity would be necessary, with an assumed 10% curtailment scenario, reflective of the Irish grid dispatch down of the recent years. The 10 MW electrolyser could supply oxygen for a wastewater treatment plant of 426,000 population equivalent, reducing the plant emissions (and power demand) by 40% when compared to traditional gaseous air aeration. The produced wastewater sludge can be digested to produce biogas. The CO2 component of biogas can be converted to methane using a biomethanation system, requiring 22% of the electrolyser-produced hydrogen. This would result in the capture of 16 ktCO2e per annum while producing enough electrofuels to offset 390 diesel trucks with 94 compressed biomethane trucks and 296 compressed hydrogen trucks.
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    Motivations, incentives, and commitments: financial benefits and citizen participation in onshore wind energy in Ireland
    (University College Cork, 2023) le Maitre, Julia; Ryan, Geraldine; Power, Bernadette; Horizon 2020; Irish Research Council; Sustainable Energy Authority of Ireland
    Social acceptance of onshore wind energy is a fundamental constraint for the delivery of sustainable electricity supply (Wüstenhagen et al., 2007). For a country such as the Republic of Ireland, this is a significant impediment to the decarbonisation of the energy sector (Brennan et al., 2017; Hallan and González, 2020; Van Rensburg et al., 2015), since onshore wind energy is expected to increase from approximately a third of the electricity mix to 80% by 2030 (SEAI, 2023). In 2019, Ireland introduced the Renewable Electricity Support Scheme with the aim of quadrupling its supply of onshore wind energy. The policy introduced a variety of financial benefits directed towards local communities to facilitate social acceptance, including community benefit funding and incentives focused on households closest to the wind farm, in the form of ‘near-neighbour’ compensation (DECC, 2021). The scheme also opened consideration for a new mechanism to encourage citizen investment into wind farms (DCCAE, 2020). The novelty, scope, and value of these mechanisms underscore the need for detailed research to identify how they could be designed and implemented to enhance their fairness, benefit, and acceptance. This thesis asks how specific attributes of financial participation mechanisms aimed at enhancing social acceptance influence citizens' willingness to accept, or to invest in, wind farms in their community. This thesis is based on two specialised surveys to examine how Irish citizens trade-off between different features of wind farm developments and their associated financial benefits. The research provides detailed insights into the preferences of supporters, conditional supporters, and non-supporters for wind farm developments in the community and presents recommendations concerning distributive and procedural issues across each phase of project development. Firstly, the findings show that citizens’ preferences for the distribution of financial benefits from wind farms are affected by procedural factors over planning, construction, and operation. Community participation in the governance of the community benefit fund and in the ownership of the wind farm have particularly high relative importance for strong supporters of wind farms. In addition, the developer and the proximity of the wind farm strongly influence willingness to accept. Secondly, the thesis contributes new evidence towards the design of citizen wind energy investments, and reveals a strong relationship between community acceptance, the proximity of the wind farm, and citizen investment preferences. Overall, financial attributes including the level of risk and expected return on investment have the greatest influence on citizen investment. However, the structure of voting rights, ownership and administration of the investment are generally regarded as having a higher relative importance if the wind farm is within 2km of the community, or a respondent is supportive of wind energy development. Thirdly, familiarity with a wind farm, whether a result of its proximity or phase of development, is a significant determinant of residents’ willingness to accept further development in the community. Critical points for local support of wind farms are at the earliest pre-planning / planning phases of development, as well as for households within the 2km radius of a wind farm. Other latent factors, such as attitudes towards wind electricity, trust in information provided by a developer, or awareness of community energy initiatives significantly affect community acceptance. Lastly, a comparative case study analyses the design of financial benefits, citizen investment and near-neighbour incentives in Ireland with corresponding mechanisms introduced by Denmark, Germany, and the United Kingdom. Based on a critical assessment of the design and adaptation of policy mechanisms over time, the findings suggest that it is becoming more common for these governments to endorse the development of community trusts or municipality community benefit funds. It also suggests that community-led wind farms experience difficulties related to the competitive nature of the auction regime. The chapter recommends that when defining eligibility or boundaries on citizen financial participation, policymakers could use a phased approach, first prioritising residents closest to a wind farm, and then opening opportunities across a wider geography in the second instance. The research is relevant for policy and practice. It enhances the understanding of citizens’ preferences for financial participation mechanisms in onshore wind farms, which is conducive to social acceptance and fairer local energy transitions. It would be valuable for future studies to develop on this evidence in the context of offshore wind energy and demand-side response which are increasingly important for the Irish energy transition. The diffusion of these innovative technologies similarly depends on citizen participation, fairness, and ultimately social acceptance.
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    Development of ultrasensitive electrochemical sensors based on nanocomposites for environmental applications
    (University College Cork, 2023) Albalawi, Ibtihaj; Moore, Eric; Ministry of Education – Kingdom of Saudi Arabia
    Water quality assessment is an essential component of environmental monitoring, which affects not only aquatic life but the surrounding ecosystem as well. The presence of organic and inorganic micropollutants such as carbamate pesticides and heavy metals in water is a crucial water problem generated from industrial effluents, mining wastes, or domestic sewage, and the widespread use of pesticides in pest control in the environment. In the last years, heavy metals have risen significantly, especially in the developed country where most pollutants are used. According to the World Health Organisation (WHO), with only 8 % of the world’s population, Germany, the United States, and Russia consume about 75 % of the most widely used metals in the world. The United States only consumes approximately 20 % of the metal pollutants and 25 % of the production of fossil fuels each year. Heavy metals such as lead, and cadmium are among the most critical pollutants and the focus of international legislative bodies because of their nonbiodegradability and toxicity and their long-term negative health effect. Carbamate pesticide use is extensively reported, and the trend in their use is anticipated to rise significantly in the next few decades. Among them, carbaryl is extensively applied in grain and has an adverse impact on the cellular metabolic mechanism and mitochondrial function. Moreover, the pH of the water solution is another vital factor affecting biological and chemical processes in water, which in turn affects the environment and human health. Typically, the used conventional analytical techniques are expensive and time-consuming due to sample transportation, trained personnel, and failure to deliver water quality parameters in real-time. Therefore, electrochemical sensing technology has the potential to change the way we see quality control analysis in the environment. It can provide a cheap, sensitive, portable, and easy-to-use method of application in quality control analysis. Thus, this research aims to develop multi-sensors based on screen-printed electrodes, which have characteristics of low cost, high sensitivity, selectivity, and rapid analysis. The novel methods in this research proved their efficiency to detect analytes of interest in environmental media with high sensitivity, excellent stability, short response time, and have the potential to be integrated into a multi-parameter system sensing for on-field monitoring.
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    Applications of big data and machine learning in global energy system modelling
    (University College Cork, 2022) Joshi, Siddharth; O'Gallachoir, Brian; Holloway, Paul; Glynn, James; Science Foundation Ireland
    Global efforts to limit atmospheric warming well below 2 degree celcius above pre-industrial levels form the backbone of our response to mitigate the detrimental effects of climate change. The energy sector contributes circa 75% of global GHG emissions, amongst which the Electricity and Heat sectors each contribute ~40%, and the Transport sector contributes ~20% to the total global energy-related GHG emissions. The recent IPCC AR6 report finds that in nearly all possible emission scenarios considered, the world is heading towards a 1.5 degree celcius global temperature rise by the early 2030s. Pursuant to this, Energy Systems Models (ESMs) and Integrated Assessment Models (IAMs) are essential tools that provide energy system pathways to limit global warming below the temperature threshold. Thus, improving the accuracies of ESMs and IAMs will lead to measurable improvement in energy policy formulation and evaluation,thereby increasing the likelihood of meeting the commitments under the Paris Climate Agreement. This thesis develops and applies novel frameworks and methods that use a big data and machine learning driven strategy to improve the technology potential assessment of global decentralised solar PV technology and projection of transport energy service demand. The frameworks and methods developed in this thesis are presented in a format of methodological design principles followed by a case study using them. Specifically, on the supply side, the thesis investigates the global high-resolution spatiotemporal technical potential of rooftop solar PV for 2015 and further growth in the technical potentials from 2020-2050. For this assessment case study, the developed framework utilises a suite of GIS derived geospatial metrics in conjunction with a custom machine learning framework to calculate the global rooftop area at a high spatial resolution. Further using an IAM, the role of decentralised solar PV in global future energy transitions is explored. On the demand side, the thesis introduces a new machine learning model called ‘TrebuNet’ that is capable of high accuracy in estimating future energy service demand in the transport sector. The thesis thus provides the first development of machine learning and GIS based methods to improve the accuracy of global ESMs and IAMs. Particular attention is also paid towards the reproduction and transparency of the methods and the frameworks developed in this thesis for cross- disciplinary research. The thesis contributes to the important task of climate change mitigation by providing a bridge between mature IAM and ESM modelling and emerging machine learning-big data-driven tools. In doing so, this thesis demonstrates how the emerging methods in conjunction with large geospatial open source data, can aid in improving the technology representation of variable renewable energy technology in energy systems. The thesis also lays the foundation for providing solutions to energy system related tasks that are currently limited by high computational costs and data. The datasets and analysis generated by this thesis are presently assisting in unlocking the global role of decentralised renewable energy technologies in future energy systems and are also encouraging shifts in national decarbonisation pathways.
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    Integration of anaerobic digestion with bio-electrochemical technologies in cascading circular bioeconomy systems producing biofuel and chemicals
    (University College Cork, 2023) Ning, Xue; Murphy, Jerry; Lin, Richen; O'Shea, Richard; Sustainable Energy Authority of Ireland; Gas Networks Ireland
    Anaerobic digestion is a waste treatment technology, which can alleviate greenhouse gas emissions, reduce environmental pollution whilst simultaneously generating biomethane (a clean energy source which can be used as a direct replacement for natural gas), biofertilizer (which can reduce fossil fertiliser use), and biogenic CO2 (which can be further valorised). However, many anaerobic digestion systems are implemented as standalone systems without optimizing circularity in system design. Conventional anaerobic digestion systems can face challenges such as: low biomethane production rate (in particular from feedstocks with high portions of lignin and cellulose), and inefficient biogas upgrading to biomethane. In an endeavour to simultaneously increase biogas production and upgrading, the potential for integrating anaerobic digestion with three emerging bio-electrochemical technologies in a circular cascading bioeconomy was assessed, including for power to gas, microbial electrolysis cell, and microbial electrosynthesis. An energy balance assessment indicated that these three circular cascading bio-electrochemical systems could display positive energy outputs if the electricity used would have been otherwise curtailed or constrained. This drove the thesis to develop bio-electrochemical cascading anaerobic digestion systems for value-added biofuel and chemical production. Anaerobic digestion is a complex microbial process that involves multiple syntrophic interactions with interspecies electron transfer as a crucial factor influencing digestion efficiency. Biochar has been shown to support direct interspecies electron transfer between fermentative bacteria and methanogenic archaea, thereby increasing biomethane production and reducing reaction times. The first experimental work investigated the biomethane potential in batch two-stage co-digestion of grass silage and cattle slurry, with varying dosages of biochar supplementation. Biochar addition at the optimal dosage of 10 g/L in two-stage digesters led to the highest methane yield of 253 L per kilogram (kg) volatile solid (VS), which was 24% higher than that from two-stage digesters without biochar supplementation. Continuous single-stage and two-stage co-digestion of grass silage and cattle slurry with 10 g/L biochar supplementation were compared in the second experimental work. In continuous trials, operated at an organic loading rate of 4.0 g VS/L/d, the second-stage digester in two-stage digestion produced a methane yield of 237 L/kg VS with 10 g/L biochar addition; this was 7% higher than the second-stage digester without biochar addition. The incorporation of two-stage anaerobic digestion and the addition of biochar was shown to be a promising approach to enhance system stability and improve biomethane production. To expand on the application of conductive materials in improving biogas production in anaerobic digestion, biochar was added to an integrated microbial electrolysis cell and anaerobic digestion system (the MEC-AD system) in the third experimental work. The results demonstrated that the biomethane yield and methane content in biogas in the MEC-AD system (with plain graphite cathode) increased by 68% and 17%, respectively, compared to conventional anaerobic digestion when co-digesting grass silage and cattle slurry. Biochar supplement (10g/L) in the MEC-AD system was shown to further increase biomethane yield by 9% as compared to the MEC-AD system without biochar addition. The combination of an enhanced electric field and biochar addition in the MEC-AD system provides a pathway for effective in-situ bioconversion of carbon dioxide to biomethane and improved substrate utilisation. The overall carbon utilisation of biomass conversion in AD and MEC-AD can be limited by the presence of carbon dioxide (CO2; approximately 30–45%) in the off-gas. This residual CO2 can be upgraded into valuable chemical products (such as acetic acid and ethanol) in microbial electrosynthesis, a process by which microorganisms utilize electrical energy to convert CO2 into value-added compounds. A 3D cobalt and nickel coated carbon felt (CoNi-CF) cathode was developed in this last experimental work and applied in microbial electrosynthesis reactors. The highest acetate concentration obtained from the microbial electrosynthesis reactor was 18.4 mmol/L, with a carbon conversion efficiency (C in acetate) of 75.4%, while the maximum ethanol production achieved was 4.5 mmol/L, with a carbon conversion efficiency (C in ethanol) of 18.6%. This thesis explored the synergistic integration of anaerobic digestion and bio-electrochemical technologies in cascading circular bioeconomy systems, and demonstrated that simultaneously enhanced biogas production and CO2 upgrading can be achieved through efficient direct interspecies electron transfer by adding biochar and/or by imposing an external electricity supply. The results from this thesis can provide guidance on designing future cascading circular bio-systems to produce advanced biofuel and value-added chemicals.