Browsing by Author "Johnston, Chris"
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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 Life cycle assessment of a short-rotation coppice willow riparian buffer strip for farm nutrient mitigation and renewable energy production(Elsevier, 2022-02-02) Livingstone, David; Smyth, Beatrice M.; Lyons, Gary; Foley, Aoife M.; Murray, Simon T.; Johnston, ChrisAs agricultural activity intensifies across Europe there is growing concern over water quality. Agricultural run-off is a leading cause of freshwater degradation. Simultaneously there is a continually increasing drive to promote renewable energy and reduce greenhouse gas emissions. Willow coppice planted as a riparian buffer has been suggested as a solution to help mitigate these problems. However, there is limited research into the use of such a system and several key knowledge gaps remain, such as, the energy ratio of the system is not known, and a fully harvested site has yet to be analysed in the literature. The aim of this research is to fill these knowledge gaps to help inform agri-environmental policy. To do this a life cycle assessment was carried out on an established willow buffer system, considering the global warming potential, eutrophication potential, acidification potential and cumulative energy demand impact categories, alongside the calculation of the energy ratio. To our knowledge it is the first site to be fully harvested and for which a full life cycle assessment has been carried out. The willow was combusted to fuel a district heating system. Key results showed emissions of 4.66 kg CO2eq GJheatout -1 and 0.01 kg SO2eq GJheatout -1, both of which are significant reductions compared to an oil heating system (95% reductions for both impact categories). The system also resulted in the permanent nutrient removal of 55.36 kg PO43-eq ha-1 yr-1 and had an energy ratio of 17.4, which could rise to 64 depending on the harvest method.Item Modelling and experimental investigation of small-scale gasification CHP units for enhancing the use of local biowaste(Elsevier, 2021-10-21) de Priall, Oisín; Gogulancea, Valentina; Brandoni, Caterina; Hewitt, Neil; Johnston, Chris; Onofrei, George; Huang, YeSmall-scale gasification Combined Heat and Power systems, fed by biowaste resources, have the potential to enhance local renewable energy production, reduce carbon emissions and address the challenges of waste disposal. However, there is a lack of understanding on the influence of challenging feedstocks, such as, for example, digestate, poultry litter and municipal solid waste, on the syngas quality and the incidence of the drying stage in the overall process. This paper addresses this gap by analysing and comparing 40 samples of the most common biowaste feedstocks. We developed a stoichiometric-thermodynamic one stage equilibrium model that was experimentally validated and calibrated by laboratory results, with a maximum error of 15% between real and predicted values. Simulation results show that the low heating value of the syngas produced from biowaste resources analysed ranges from 3.1 to 5.4 MJ/Nm3 on a dry basis. Working at the optimal equivalence ratio increases the electricity and thermal output by up to 20%. To achieve a feedstock moisture content of 10%, the drying process may require up to 60% of the heat produced. Furthermore, results show that downdraft gasification based combined heat and power, is a feasible and interesting option to deal with biowaste resources which can potentially avoid the cost, risk and externalities of landfilling while it contributes to the increase of local electricity and heat production from renewable energy sources, both for grid and off-grid applications.Item Phosphorus Removal from Dirty Farmyard Water by Activated Anaerobic-Digestion-Derived Biochar(American Chemical Society, 2022-12-05) Zhang, Chen; Sun, Shuzhuang; Xu, Shaojun; Johnston, Chris; Wu, ChunfeiThe management of anaerobic digestate is important to realize the value of the waste and enhance the whole system sustainability of anaerobic digestion. In this study, the phosphorus treatment of dirty irrigation water by biochar samples derived from digestate of anaerobic digestion were investigated. The biochars were further activated by steam activation with different duration time and KOH activation with different introducing ratios; the textural properties of biochars were optimized after activation from the aspect of biochar characterization. Notably, AD-N2 demonstrates a remarkable adsorption effect of phosphorus, with an adsorption efficiency of 8.99 mg g−1. Besides the effect of biochar dosage on phosphorus removal, adsorption kinetics and thermodynamic isotherms are studied. According to the adsorption kinetics, the adsorption of phosphorus from dirty water fits the Elovich equation (R2 = 0.95). Furthermore, the thermodynamic isotherm results illustrate the process of phosphorus removal by biochar is endothermic (ΔH0 = 17.93 kJ mol−1) and spontaneous (ΔS = 96.24 J mol−1 K−1). Therefore, this work suggests a promising solution to phosphorus-related environmental challenges in industry and agriculture.