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(2023)ThesisHollow fibre (HF) membrane modules implemented in submerged membrane bioreactors (MBR) and pressurised applications have been widely accepted for both wastewater treatment and polishing wastewater treatment plant (WWTP) effluents. Further innovations in membrane technologies and wastewater treatment market competitiveness, however, are restricted by high manufacturing and operational costs, where a trade-off exists between membrane system design and filtration performance. In the current work, the effects of HF lengths, physical characteristics and system fouling mitigation techniques were investigated to further optimize filtration performance. The following experimental approaches were considered, (1) small-scale filtration experiments with various HF membrane lengths and fibre dimensions, (2) the development of theoretical filtration models and the assessment of filtration simulations, and (3) pilot-scale filtration performance of prototype large-scale membrane modules in wastewater. Two mathematical models for constant TMP filtration using dead-end HF membranes were developed using firstly the Darcy friction factor, and secondly, the Hagen–Poiseuille model. The models allowed for the overall theoretical lumen pressure drop values, local flux distributions and overall filtration performance to be extensively studied. Laboratory-scale filtration experiments using HF membranes of different lengths (0.5 – 2.0 m) were undertaken with the objective of demonstrating the influence of lumen pressure drop in overall filtration performance. Though greater permeate volumes were obtained when using modules prepared with longer HF membranes, such systems experienced greater lumen pressure loss. These losses reduced the operating TMPs effectiveness, resulting in greater non-uniformity in local fluxes across the length of the HF membranes. The magnitude of losses and degree of non-uniformity in such longer systems were extensively studied, allowing for the identification of effective loss reduction techniques, such as the incorporation of HF membranes with larger inner diameters (ID) in the membrane modules. Pilot scale investigations were undertaken to evaluate the influence of HF length on overall performance in real wastewater feeds. Prototype full-scale modules were prepared with HF membrane of different lengths (1.6 – 2.0 m) and ID. Longer modules demonstrated greater filtration performance as the influence of increased lumen pressure drop due to longer fibre lengths was effectively offset by the enhanced fibre dimensions. Overall, the results presented in this study reveal that a significant interplay exists between module design (including length, packing density, slack, and fibre size), filtration process design (feedwater quality, biomass concentration, aeration rate, aeration/shear efficiency) and the critical flux (of threshold flux) conditions. In conclusion, the incorporation of longer length HF membranes in pressurised and submerged MBR modules has been proven to be a promising innovation which offers enhanced filtration capabilities.
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(2023)ThesisPhotovoltaic (PV) solar cell is becoming indispensable in the clean energy supply chain. In the past decades, its repaid development and massive installation raise the concern that the massive amount of end-of-life PV panels will be produced and have to be properly treated in the foreseeable future. Therefore, there is an urgent requirement to develop a sustainable and efficient method to recycle end-of-life PV panels to ensure that both valuable and hazardous materials can be properly recovered and/or treated for safe disposal. However, the research and development of PV panel recycling is still at an early stage. In this study, a highly efficient recycling process is designed to investigate the key factors that affect the valuable components’ separation and recycling performance, which covers the thermal delamination, sieving separation, and chemical leaching process that reflect the key steps of the end-of-life PV module recycling process. In this thesis, a highly efficient physical separation method is first studied, which integrates the sieving process customised for PV recycling and a new technology of “sieving aids” (patent pending), achieving the effective separation of PV solar cells and glass fragments that are resulted from the thermal delamination. The results indicate that most of the chip-like PV cell particles (around 99%) can be separated from the debris mixture (glass and PV ribbon) with proper sieving conditions, which greatly contributes to the improvement of metal recovery performance in the chemical leaching process. Second, the chip-like PV cell particles collected by the separation process were further leached by nitric acid for silver extraction. In this part, to understand the mechanism underlying the influences of leaching parameters on the silver extraction performance, a number of experimental investigations were performed combined with a quantitative analysis using SEM-EDS, with a specific focus on the effect of solid/liquid ratio and acid concentration. The findings show that the leaching of the PV particles using nitric acid with higher concentrations generally yields a better silver extraction in a quantitative manner. The experimental results obtained in this thesis serve as a groundwork for future scaling up and optimization studies for the recycling of end-of-life photovoltaic modules.
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(2023)ThesisElectrochromic devices (ECDs) have attracted attention due to their ability to reversibly change colour in response to an applied voltage and show promise in various applications. However, developing large-area, flexible, multicolour electrochromic materials (ECMs) cost-effectively and simply is a significant challenge. Additionally, the traditional five-layer battery-like structure and the mechanism limit ECDs to display multiple colours simultaneously. In this work, we propose a spatiotemporal multistate ECD based on 2D polyaniline, specifically tungstate anion cross-linked polyaniline (TALP), driven by an electric potential gradient, that can deliver a multicolour pattern. High-quality and large-area TALP films were synthesised on various transparent substrates using a simple solution method and assembled into spatiotemporal multistate ECDs. We investigated the device’s mechanism to propose the electric potential gradient driven theory and clarify the errors in previous research. Guided by the proposed theory, we demonstrated to manipulate the multicolour patterns, and for the first time, assembled an ITO-free two-layer ECD. We achieved graphic coding based on complex multicolour patterns as a proof of concept for utilizing its spatiotemporal resolution. Based on the unique structure, mechanism and phenomena, spatiotemporal multistate ECD holds promise for aesthetic decoration, selective sunlight shading, and information transfer.