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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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(2024)ThesisThe design of advanced hollow fibre ultrafiltration (UF) membrane technologies for use in wastewater treatment facilities has culminated from a combination of improvements in plant operation and optimising feed water interactions. With global demands in water quality increasing, this has placed increased pressure on MBR factories to develop high strength, anti-fouling fibre modules with improved permeabilities. The fabrication of such membranes, however, is restricted by the trade-off that exists between mechanical strength and filtration properties, as well as scalability concerns that arise when transitioning from laboratory trials to field testing of prototypes. This places increased importance on the need to establish a reliable formulation plan that addresses these trade-off limitations, in addition to furthering our understanding of membrane-foulant interactions. Modifications of polymer concentration will offer deeper insight into the role that polymer phase materials have on membrane formation and high strength performance. Further variations in pore-former content will provide a route towards optimising membrane surface porosity, translating into potential improvements in fibre permeability and anti-fouling propensity. Three different experimental approaches were implemented to assess the impact of fibre composition on membrane performance. These include (1) modifying the total concentration of poly(vinylidene fluoride) (PVDF) material, (2) tailoring the composition of PVDF material with distinct molecular weights, and (3) adjusting the proportion of poly(vinyl pyrrolidone) (PVP) and poly(ethylene glycol) (PEG) pore-forming additives. Microscopy techniques were used to document any structural changes across each formulation series, whilst porometer and tensile testing instruments were utilised to provide insight into membrane permeability and strength, respectively. Membranes formulated with elevated PVDF concentrations were found to exhibit improvements in mechanical integrity at the expense of reduced clean water fluxes. This was overcome by optimizing the incorporated PVDF molecular weight, which allowed for incremental boosts in toughness without adversely affecting permeability. Testing also revealed that fibres formed with higher concentrations of pore-forming agents, most notably PEG material, were found to be more permeable. Feedwater filtration cycling was implemented to provide insight into the relative fouling behaviour of membranes formed via these three approaches. Changes in resistance were found to be primarily dictated by membrane pore size, with intermediary pore size distributions being desirable targets for balancing out the effects of short- and long-term filtration. By tracing these trends in fouling propensity back to underlying fibre compositions, this study reinforces the importance of adjusting polymer formulations for achieving high strength, anti-fouling membranes. This study also acknowledges the limitations that exist in comparing laboratory-scale filtration data of fibre samples to prototype field testing of full-scale modules. Addressing these drawbacks through an analysis of feedwater conditions used in research and industry allows us to reach an informed decision on selecting appropriate formulations in the design of innovative membrane technologies.