Chemical and Biomedical Engineering - Theses
Now showing items 1-12 of 15
Bio-nano interactions of metal-phenolic networks: the role of metals
Metal-phenolic networks (MPNs) hold great promise for the fabrication of multifunctional hybrid materials owing to their versatile and tunable nature. In particular, the beneficial combination of both organic and inorganic components makes them highly interesting systems for a range of applications. Because of the ease of changing the metal ions and ligands, they are highly interesting materials for drug delivery, cell targeting, medical imaging, and catalysis. Metal ions are known to bind to a variety of biomolecules, for example amyloid beta peptides and antibodies. However, to date, the bio-nano interactions of MPNs are not fully understood, especially for the role of metals. In this PhD research, bio-nano interactions of MPN- coated gold nanoparticles (AuNP@MPNs) with different biomolecules were studied to reveal the role of metals. In the first part of this PhD research, the potential of AuNP@MPNs for amyloid fibril inhibition was investigated. Metal ions and polyphenols have been demonstrated to separately play an important role in the amyloid fibril progression and in the inhibition of fibril formation, respectively, and therefore in combination should have synergistic effects. Numerous diseases, such as Alzheimer’s disease and Type II Diabetes, are potentially associated with the formation of amyloid fibrils. In this systematic study, metal ions were varied in the MPN system, with Co-TA (cobalt-tannic acid)-coated AuNPs showing the highest inhibition ability. Molecular dynamics simulations and quantum mechanics calculations suggested that the geometry of the exposed cobalt coordination site in the cobalt-tannic acid networks facilitated its favorable interactions with histidine and methionine residues in the amyloid beta peptides. Like amyloid fibrils, antibodies can interact with transition metals (e.g., CoII, NiII, CuII, ZnII) via the histidine-rich domain at Fc region in an oriented manner. In the second part of this PhD research, AuNP@MPNs were modified with antibodies by adsorption and their targeting abilities were studied. Similar antibody loading levels were observed for all AuNP@MPNs with different metals. However, the Co-TA coated AuNPs adsorbed with antibodies again showed a different behavior compared to the other metals. It possessed improved targeting towards both antigens and cells by inducing the potential orientation (conformation) change of the adsorbed antibodies, which further confirmed the unique property of cobalt in the bio-nano interactions of MPNs. The third part of this PhD research further investigated the bio-nano interactions of AuNP@MPNs in the complex protein system – human serum. As tannic acid might dominate the bio-nano interactions, the effects of different ligands were examined along with the effects of the different metals. It was found that the protein corona can reduce the cell association of all AuNPs investigated. The amount and composition of corona proteins were evaluated by both SDS-PAGE and LC-MS/MS. MPNs with tannic acid as the phenolic ligand showed no significant difference with varied metals in both corona protein content and cell association. However, MPNs with gallic acid as the ligand showed that FeIII and ZnII exhibited different corona protein content and cell association compared to other metals. These findings suggested that bulky tannic acid may dominate the adsorption of biomolecules while cobalt can contribute to the conformation of biomolecules by coordination. Taken together, this research provides a fundamental understanding of MPNs for future bio-nano related applications.
MOF-mediated destruction of cancer using Fenton reaction
Cancer which is the second greatest cause of death worldwide has reached critical levels. In the past various therapies including photodynamic, photothermal and chemo-therapy are utilized for selective tumor treatment. Unfortunately, these methods suffer from various problems which limit their efficiency and performance. For this reason, novel strategies are being explored which improve the efficiency of these traditional therapeutic methods or treat the tumor cells directly. One such strategy utilizing the Fenton reaction has been investigated by many groups for the possible treatment of cancer cells. This therapy involves the utilisation of existing high levels of H2O2 in cancer cells to react with iron nanoparticles following the Fenton reaction to produce hydroxyl radicals capable of killing the cells. However, studies which attempted to use classical Fenton reaction alone to destroy the tumor cells, requires high concentrations of nanoparticles in order to be toxic to cancer cells. For this reason, there has not seen a successful nanoparticle which can treat cancer cells using the Fenton reaction without the need for external H2O2 sources. The aim of my work was to synthesize and develop novel metal organic frameworks (MOFs) for cancer treatment using the Fenton reaction. These specific nanoparticles can be utilized directly to destroy the cancer cells via the Fenton reaction or indirectly to deliver the Fenton reagent into cancer cells. In the first approach, a novel reduced iron metal-organic framework nanoparticle with cytotoxicity specific to cancer cells was fabricated. Iron present on the MOF can react with high levels of hydrogen peroxide found specifically in cancer cells to increase the hydroxyl radical concentration. The hydroxyl radicals oxidize proteins, lipids and/or DNA within the biological system to decrease cell viability. In vitro experiments demonstrate that this novel nanoparticle is cytotoxic to cancer cells through generation of hydroxyl radical using the cell’s own hydrogen peroxide. However, this emerging method is largely restricted due to the poor selectivity of reported nanoparticles. Subsequent improvements in nanoparticle size were facilitated by PEGylation on the particles through surface-initiated atom transfer radical polymerization, thus improving the stability, reducing the size and increasing the selectivity. In vitro experiments show that the selectivity index increased from 2.45 to 4.48 for HeLa cells, which is significantly higher than those reported in the literature for similar strategies. Finally, in an alternative approach, pH-responsive MOFs have been utilized for hemoglobin (Fenton reagent) and glucose oxidase (starvation reagent) delivery into the cancer cells. In a slightly acidic environment of cancer cells, GOx is released and consumes glucose and molecular oxygen that are essential survival nutrients in cancer cells and produces gluconic acid and hydrogen peroxide, respectively. The produced gluconic acid increases the acidity of the tumor microenvironment so completes MOFs destruction and enhances hemoglobin and GOx release. Fe ion from the heme groups of hemoglobin also releases in the presence of both endogenous and produced H2O2 and generate hydroxyl radical. In vitro experiments demonstrate that this novel nanoparticle is cytotoxic to both cancer (HeLa and MCF-7) cells at very low concentration (>2 µg/mL). Due to the great potential of the reported metal-organic frameworks in this thesis, these interesting particles may function as a new type of agents for controlled delivery and hydroxyl radical generation to treat cancer cells
Nano-scale design of cardiovascular biomaterials
Cardiovascular disease is the leading cause of death worldwide. The development of blood-compatible biomaterials could relieve this burden by improving the performance of cardiovascular devices such assmall-diameter vascular grafts. An attractive strategy for improving blood compatibility of an interface is to generate biomaterials that foster a confluent and functioning endothelial cell layer. Although several strategies have been explored to improve endothelialisation, there are still no commercially available blood-compatible grafts that promotes endothelialization. The lack of a blood-compatible interface is one of the most pressing challenges in the biomaterials field. As such, additional research is required in order to develop new technologies to meet this need. The aim of this work is to design a biomaterial that promotes endothelialization by mimicking cellextracellular matrix interactions. In order to achieve this, we used two biomimetic approaches: (1)nanoclustering of cell adhesive ligands (ligand multivalency) to promote the clustering of cell receptors, especially integrin receptors, and (2) dual functionalization of materials with both integrin- and syndecan-binding ligands to engage both cell receptor types to utilise their synergistic effects. To accomplish this, we synthesized a random copolymer via reversible addition-fragmentation chain transfer (RAFT) polymerization. The polymer was composed of methyl methacrylate and polyethylene glycol methacrylate-containing units. The polymer was functionalized with integrin- and syndecanbinding ligands. A blending technique was used to generate interfaces with ligand multivalency. Specifically, highly peptide-functionalized polymer chains were blended with non-functionalized polymers chains. Upon film casting, these generated surfaces displaying nano-scale islands of high peptide density due to the size and shape of the polymer random coils. Endothelial cells were cultured on these surfaces and their behaviours were investigated under static and flow conditions. Our results show that the biomaterials functionalized with multivalent integrin-binding ligands promote the formation of focal adhesions, improve endothelial cell adhesion, migration, and endothelialization rate compared to surfaces functionalized with random distribution of integrin-binding ligands. Additionally, the biomaterials functionalized with mixed population of multivalent integrin- and syndecan-binding ligands show additional improvement over surfaces with just multivalent integrinbinding or syndecan-binding ligands alone. Specifically, we observed synergistic improvement of endothelial cell adhesion, improved focal adhesion formation and cytoskeletal assembly, an increased rate of endothelialization, and regulation of migration speed. These surfaces also regulate a range of endothelial cell functions when the cells were exposed to laminar flow shear stress including increased spreading, larger and more abundant actin stress fibers, elongation and alignment in the direction of flow, increased capture of endothelial cells from flow, and robust attachment of cells under flow. These results demonstrate that bioengineered materials presenting nanoclusters of both integrin- and syndecan-binding ligands could be used for the development of next-generation biomedical devices, especially small-diameter vascular grafts.
Pulsed solvent extraction column performance: study and comparison of standard disc and doughnut internals and Tenova kinetics internals
Pulsed columns were used as high efficiency solvent extraction contactors for a range of applications including uranium recovery (Olympic Dam Operations, Australia) and for cobalt and nickel extraction (Goro Nickel, New Caledonia). Traditionally, disc and doughnut-shaped internals were used in these systems and their operating performance had been studied extensively and found effective for processes with normal and fast kinetics. For processes with slow kinetics and high feed phase ratios, the new Tenova kinetics internals which included novel contacting elements on the contours of the “disc and doughnut” plates and optimized spacing between the plates may provide enhanced performance. The developers of the new internals expected these internals to result in less back-mixing, higher column holdup and improved mass transfer at the same flux during operations. However independent experimental data and pilot testing was required to verify these improvements. This research aimed to study the effect of operating characteristics (flowrates, pulse frequency and pulse amplitude) on dispersed phase holdup, flood point, drop size distribution, mass transfer and axial dispersion performance for Tenova kinetics internals and quantify the potential improvements over the traditional standard disc and doughnut internals using two different liquid-liquid systems with slow and fast kinetics. It was observed that the solvent extraction column efficiency, especially for the relatively slow kinetics systems, had been optimized to receive higher extraction efficiency and hereby making it more cost-effective. Dispersed phase holdup and drop size, as the parameters to estimate the hydrodynamic performance, were measured in terms of pulsation intensity, dispersed and continuous phase velocities. Holdup decreased with increasing pulsation intensity to a minimum value at (Af)min and then increased with higher pulsation intensity for both types of internals and both liquid-liquid systems. And holdup increased with increasing dispersed phase velocity but neglected change with the continuous phase velocity. Dispersed phase droplets drop size decreased as pulsation intensity increases up to 0.3 m/s for both standard disc and doughnut internals and Tenova kinetics internals, and no noticeable effect of dispersed and continuous phase velocities was observed. At low Af, the Sauter mean diameter for Tenova kinetics internals was higher than the standard disc and doughnut internals. The correlations were refitted with the pilot scale experimental data in this study for both holdup, Sauter mean diameter and the drop size volume distribution, and the overall absolute average relative errors for holdup and Sauter mean diameter were 16% and 11%, respectively. Axial dispersion performance of the pulsed column with two types of internals was estimated in terms of pulsation intensity, dispersed and continuous phase velocities for the concentration jump of the continuous phase. The axial dispersion coefficients for both internals decreased with increasing continuous phase velocity, and little impact of dispersed phase velocity on the axial dispersion coefficients was found for both liquid-liquid systems and both types of internals. The axial dispersion coefficients with Tenova kinetics internals were lower compared to the standard disc and doughnut internals using water-Alamine 336 system and high pulsation intensity condition for water-LIX 84 system. Correlations were selected and refitted to the 100 experimental axial dispersion data points and resulted in the overall absolute average relative errors of 54% and 41%. Mass transfer experiments were conducted with two liquid-liquid systems with different kinetics for both types of column internals under the effects of pulsation intensity, dispersed and continuous phase velocities. The height of a mass transfer unit Hoc decreased with increasing pulsation intensity and increased with increasing dispersed and continuous phase velocities for CuSO4-LIX 84, relatively slow kinetics system. For H2SO4-Alamine 336, fast kinetics system, no change of Hoc was observed due to the system reaching the equilibrium state inside the 2 m high solvent extraction column. The height of a mass transfer unit for CuSO4-LIX 84 system was much larger than H2SO4-Alamine 336 system. The correlation of Hoc was regressed to the experimental data with the absolute average relative error of 16%, and the overall mass transfer coefficient of continuous phase could be predicted with correlated values of Hoc, xd and d32. And an approximate estimated value of reaction rate for CuSO4-LIX 84 system was reported.
A fundamental study of concentration polarisation and fouling in skim milk ultrafiltration
Skim milk ultrafiltration (UF) is an important dairy process operation in which milk proteins are preferentially concentrated for downstream manufacturing of cheese and milk protein concentrates (MPC), and also for protein standardisation. However its operational efficiency is impacted by the accumulation of retained particles at the membrane surface (concentration polarisation, CP) and the irreversible deposition of particles onto the membrane surface and in membrane pores (fouling). CP and fouling ultimately result in lower throughput (flux decline), alterations in product quality, significant operational downtime and vast consumption of water and cleaning chemicals. Development of effective optimisation strategies and technologies for the mitigation or prevention of CP and fouling requires the mastery of these flux decline phenomena. However CP and fouling are still not completely understood despite over 30 years of industrial application, owing partly to the complex physicochemical nature of skim milk. This thesis aims to extend our current understanding of CP and fouling in skim milk UF. Specific investigations include the influence of processing temperature and diafiltration (DF) on CP and fouling in skim milk UF, characterisation of the osmotic compressibility of skim milk, and a visual assessment of gel formation during skim milk UF. A comprehensive examination of skim milk UF behaviour as a function of processing temperature (between 10-50 °C) showed, for the first time, that fouling at 10 °C is shown to be primarily proteinaceous, consistent with fouling at 50 °C (mainly alpha-lactalbumin, a-LA, and peptides). This provides a validation of existing fouling observations at 50 °C for UF at 10 °C, for which there are very few fouling investigations despite its widespread use. Despite higher fluxes, higher processing temperatures led to a greater magnitude and rate of fouling. This was found to be caused by increased pore blocking by a-LA and deposition/adsorption of beta-lactoglobulin (b-LG) onto the membrane surface, attributed respectively to thermal pore expansion and reversible conformational changes. Diafiltration involves dilution of the concentrated feed stream with water, followed by filtration to facilitate further removal of salts, lactose and water in order to achieve a higher protein purity. This primarily caused a substantial decrease in ionic strength due to mineral removal, resulting in an increase in electrostatic repulsive interactions between casein micelles and thus a decrease in CP resistance. No effects of DF on irreversible fouling were observed. Restoration of lactose concentrations only resulted in a minor decrease in ionic strength, but had no significant effect on diafiltration behaviour. CP resistance showed a strong correlation with ionic strength (in the range of 32-85 mM), with analyses of existing literature suggesting possible extrapolation (at least qualitatively) to lower ionic strengths (i.e. further extents of DF). Osmotic stressing experiments show that skim milk is more resistant to osmotic compression/concentration than casein micelle dispersions. Comparisons of osmotic pressure profiles between skim milk, heat-treated skim milk and casein micelle dispersions suggest that whey proteins contribute resistance to osmotic concentration via two mechanisms: (a) below the gel point, whey proteins contribute a counteracting osmotic pressure, and (b) above the gel point, denaturation and attachment of whey proteins onto the casein micelle surface by thiol-disulphide reactions, resulting in an increase of mechanical strength of the casein micelles (i.e. more rigid, less susceptible to deformation or compression). The inclusion of whey proteins provides a more accurate representation of the behaviour of casein micelles under concentration in the CP layer during skim milk UF. Visual inspection of gel formation resulting from CP during dead-end and cross-flow skim milk UF reveals that at pressures above the gel point, less concentrated gels (i.e. formed in shorter durations or lower pressures) had a turbid white appearance and were brittle to the touch, while more concentrated gels appeared more translucent and were more mechanically robust. Whereas solid gel sheets were formed in dead-end filtration, gel formation in cross-flow skim milk UF were fragmented in nature, and primarily located in dead-zones or areas of low-flow. This is exacerbated when operating at higher feed concentrations, where gel formation was also observed near the feed inlet (particularly due to the flow geometry of the filtration cell used). Description of gel formation allows distinguishing between the different gels that can potentially form during skim milk UF – information which has not been available despite gel formation being mentioned frequently in literature. Gel formation in low-flow zones is detrimental to cleaning and sanitary operation, and is particularly relevant to spiral wound and plate-and-frame modules which have some degree of flow tortuosity.
Bioenergy with carbon capture and storage; sustainability, challenges, and potential
Bioenergy with carbon capture and storage (BECCS), as a negative emission technology, has been assigned a key role for achieving ambitious mitigation targets in several climate models. BECCS is a multifaceted complex system which consists of a range of variables such as type of biomass resource, conversion technology, carbon dioxide capture process and storage options. Each of the pathways to connect these options has its own environmental, economic and social impacts and needs to be assessed through a holistic sustainability framework. Too often, however, the sole focus of assessment models is on techno-economics of BECCS to produce energy and deliver negative emissions. This study proposes an integrated adaptive management approach to model technical, economic, environmental, social and political aspects of BECCS systems. The adaptive management system employs a multi-criteria decision-making tool to rank BECCS systems against a set of key sustainability criteria. The aim of such adaptive management systems is to facilitate the decision-making process by evaluating the sustainability of the BECCS systems and introducing a systematic methodology to analyse the synergies and trade-offs between different criteria and mitigation scenarios. The technical and economic impact values of the BECCS systems were calculated using a techno-economic assessment model based on published technical data. Environmental impacts were calculated using SimaPro software. With only very limited practical experience on BECCS deployment available, scoring qualitative social and policy criteria was based on prior literature associated with bioenergy systems and carbon capture and storage systems separately, for which social and policy experience is available. It is crucial to adapt the objectives and criteria of an adaptive management system used for implementing a BECCS system according to the regional parameters. To this end, opportunities for application of BECCS in the Australian power sector, using the adaptive management principals, were investigated. Having significant resources of organic waste for bioenergy production and the accumulated practical knowledge through ongoing carbon capture and storage projects, makes Australia a good candidate for deployment of BECCS. A feasibility assessment conducted in this study found that, based on the quantity of biomass resources available, BECCS options in Australia have the potential to remove a total of 25 Mt CO2 per year from the atmosphere as negative emissions and supply up to 13.7 TWh of renewable power. Co-firing in existing power plants equipped with carbon capture and storage could be an effective near-term mitigation option and provides a bridging technology to deliver secure energy for a growing population while cost-effectively lowering CO2 emissions. In this study, the global technical potential and challenges of co-firing biomass with carbon capture and storage to achieve zero or negative emissions was assessed. The results show that direct co-firing of up to 20 per cent biomass in a modern pulverised coal combustion plant equipped with CO2 capture and storage could deliver negative emissions of up to -26 kg CO2 per MWh. One of the main challenges to deploy BECCS at the level required in the stringent emission scenarios is expanding sustainable bioenergy production. Intensification of bioenergy production could result in severe pressure on natural resources, especially land and water, and competition between food, feed, and energy. Thus, it potentially could lead to controversial economic, ethical, and environmental issues. To avoid the social uncertainties and environmental impacts resulting from dedicated energy crop production, this study focuses on BECCS potential restricted to the presumption of no land-use expansion and no increase in water consumption. Hence, it is recommended that any projection of the potential of BECCS to deliver negative emissions in the future should be limited to bioenergy using organic residue and waste. A sensitivity analysis using scenarios with different sustainability paradigms for mitigation was conducted. Selection of a scenario determines the objective of the decision-making analysis. The scenarios examined in this study reflect the effect of socio-economic, technical and environmental drivers on the sustainability ranking of BECCS systems. Water-use, and land-use change, levelised cost of electricity production, and global technical capacity to deliver negative emission were used to demonstrate the trade-off between environmental, economic and technical performance of the BECCS systems using municipal solid waste and residues from agricultural and forestry sectors. The priority was assigned to the technical potential of BECCS to deliver negative emission with minimum environmental ramifications and economic cost. The results endorse BECCS systems using municipal solid wastes under all scenarios and trade-offs. The results of this study show that sustainable agricultural residues have the potential to deliver global negative emissions of 1.7 Gt CO2/year, forestry residues can deliver global negative emissions of 1.1 Gt CO2/year, and organic municipal solid waste can provide global negative emissions of 2 Gt CO2/year. Therefore, globally, the total sustainable BECCS potential is 4.8 Gt CO2/year, with the total energy produced (through sustainable BECCS pathways) is around 50 EJ. It should be noted that 4.8 Gt CO2 is considered to be the maximum amount of negative emission that could be delivered under the holistic sustainability criteria used here. This compares with a value of 20 Gt CO2/year negative emissions used in many global models. Even the annual 4.8 Gt contribution may be constrained further by technical, economic and policy challenge, although advances in biotechnology for example, might conceivably lead to new opportunities for BECCS. However, it would be dangerous to base a global mitigation strategy on as-yet-undiscovered biotechnologies. Lack of integrated governmental and public support has made investment in BECCS a high political and financial risk. Therefore, a more certain way forward to underpin BECCS deployment, is to ensure that there is strong social support and integrated policy schemes that recognise, support and reward negative emission, for without negative emissions delivered through BECCS and perhaps other technologies, there is little prospect of the global targets agreed to at Paris, being met.
Quantification of wastewater dewaterability for understanding sludge dewatering and fouling during membrane bioreactor operation
This thesis investigated the dewatering properties of wastewater treatment sludges, and biofouling layers in membrane bioreactors. An experimental and data analysis methodology was developed that unified existing procedures for lab-scale filtration, centrifugation and gravity settling tests. This unified dewaterability characterisation methodology was used to quantitatively compare fifteen wastewater sludge samples. The comparison highlighted a correlation between lower volatile suspended solids and improved filterability. Further modelling of the extreme compressibility of biofouling layers has provided insights into optimisation of water recycling.
The effect of shredding and freezing on Mozzarella cheese microstructure and functionality
Mozzarella cheese is the third most produced cheese in Australia. A significant proportion of Mozzarella cheese contributes to the 34% of dairy products in Australia that are destined for export, making the extension of shelf life important. Processes that occur after cheese is manufactured (post manufacture) are of great importance to product quality and diversifying product range as well as the optimised storage and handling that will enable the supply of distant export markets. In this thesis the effect of storage format was first investigated, including storage as a block or shredded Mozzarella cheese. The aim was to determine whether the functionality and microstructure were altered between formats or as a function of storage time. Shredding is also a common process prior to the use of Mozzarella as an ingredient, such as on pizza, however the effects of shredding on Mozzarella cheese structure and function are not fully understood. Cheese was shredded at day fifteen or week eight and stored alongside block cheese for a total storage time of eight weeks, based on manufacturer guidance on shredding times. Shredding resulted in alterations to the microstructure examined after eight weeks; the alignment of protein was reduced and the fat globule surface area increased. Interestingly, after eight weeks, shredded samples also had increased proteolysis and a higher level of two bacterial proteases. Between block and both shredded treatments the profile of volatile compounds was slightly altered. The microbial viability was, however, unaffected and the functionality of the cheese was preserved. This work showed that shredding at either time (i.e., two or eight weeks) causes only slight changes in product properties, producing a product with similar microstructure and functionality. This study may provide dairy manufacturers with the flexibility to optimise shredding processes whilst potentially reducing storage and product handling costs. The effect of extended frozen storage was considered next. Temperatures below freezing may be used to extend the shelf life of cheese; however, such storage is known to affect the functionality of Mozzarella cheese. Studies to date have had limited applications as they did not use commercially relevant samples or cooling conditions, as well as the majority of studies testing functionality not assessing biochemical changes in parallel. The effect of frozen storage (-18 °C) as well as tempering at 4 °C for one and three weeks after frozen storage was compared to storage at 4 °C over a six month period using commercially relevant conditions and samples. Frozen storage prevented proteolytic breakdown, however, tempering for longer allowed some proteolysis to occur. In contrast to prior studies, structural damage due to the industrial freezing conditions used was not detected by confocal microscopy. The majority of key measures, including microstructure, proteolytic parameters, meltability and stretchability were altered as a function of time at 4 °C, with tempering leading to a positive improvement in properties. Interestingly, two measures of shreddability were also altered as a function of frozen storage time, suggesting structural or rheological changes with extended frozen storage. These results provide a greater understanding on the link between freezing and tempering and functional properties not previously measured, as well as contributing to the understanding of refrigeration and freezing time on key parameters. This study may provide dairy manufacturers with the guidelines to optimise Mozzarella cheese functionality after frozen storage as well as frozen conditions that make reaching distant export markets possible. The suitability of synchrotron FTIR (S-FTIR) microspectroscopy as a label-free technique to examine cheese microstructure was also assessed in this thesis. S-FTIR microspectroscopy has not been widely applied to dairy products despite the additional molecular information this technique can provide. S-FTIR microspectroscopy in conjunction with multivariate data analysis was successfully able to spatially resolve the characteristic pasta filata Mozzarella cheese microstructure with areas of both high lipid and high protein identified in both transmission and attenuated total reflectance (ATR) modes. The heterogeneity typical of pasta filata Mozzarella cheese was captured with S-FTIR microspectroscopy, highlighting the advantage of the technique over laboratory based spectroscopy for encompassing sample variation. Similar information was obtained with both sampling modes and sample preparations, allowing technique selection to be based on available sample preparation methods, equipment configurations and the time available for experiments. Despite the limited availability of synchrotron based FTIR microspectroscopy, this technique provides a complementary tool that may be used by dairy manufacturers to differentiate cheese with diverse ages and thermal histories. Finally, the S-FTIR microspectroscopy technique in transmission mode was applied to Mozzarella cheese stored for six months at 4 °C and -18 °C, as well as cheese tempered for three weeks after frozen storage and cheese aged at 4 °C for four weeks prior to frozen storage in order to assess the effect of time and treatment on protein secondary structure. This technique has not been applied spatially resolve the secondary structures of cheese samples with commercially storage conditions. When Mozzarella cheese was aged at 4 °C there was a significant increase in α-helical conformation in the first month. A reduction in sample variation, i.e., an increase in sample homogeneity was observed after six months storage, consistent with the greater extent of proteolysis at this time. Freezing initially induced random coil formation; however, frozen storage halted structural and biochemical changes such as proteolysis when assessed over a six month storage period. Ageing prior to frozen storage and tempering after frozen storage caused different effects on secondary structure conformation, confirming that extensive structural changes occur in Mozzarella cheese in the first month post manufacture. Analysis of secondary structures using PCA provided significant information on the effect of frozen storage, tempering and ageing that may be used to improve our understanding of storage and handling conditions. Further study of protein secondary structure will assist the development of guidelines to optimise cheese ageing and freezing based on expected structural conformations. The results presented in this thesis provide the Australian dairy industry and dairy researchers with greater knowledge on the effect of shredding and freezing processes on Mozzarella cheese. They increase our understanding of the effect of these processes on the microstructure, biochemical processes including proteolysis and lipolysis and functionality of Mozzarella cheese. A new S-FTIR microspectroscopy method has been developed for application to dairy products and the ability of this technique to detect structural changes in the protein network as a function of ageing and freezing demonstrated. This technique will be broadly applicable to develop new knowledge on the structure of proteins and lipids in cheese.
The impact of impurities on the performance of cellulose triacetate membranes for CO2 separation
Natural gas and coal are the essential energy resources that will continue to occupy over 50% the global electricity market in the coming decades. The natural gas streams normally contain several components that require removal so that the fuel meets pipeline specifications. Membrane separation technology is an outstanding approach for gas processing with advantages in land footprint and energy efficiency. In particular, cellulose triacetate (CTA) membrane have been widely applied in natural gas processing for decades and remain the dominant material on the market share due to their competitive gas separation performance and acceptance by industry. However, the raw natural gas streams also contain several impurities that can negatively affect the performance of the CTA membrane unit. Although several studies on gas separation performance of CTA membrane have been conducted, the impact of impurities on the membrane performance is not fully understood. Cellulose triacetate membranes also have competitive CO2/N2 selectivity and are thus a prospective candidate for post-combustion carbon capture. However, studies on the impact of impurities in the flue gas, including liquid water of variable pH, sulphur oxides and nitrogen oxides, on the gas separation performance of CTA membrane are very limited. In this thesis, the impact of solutions of variable pH on CTA membranes was studied by exposing the dense membranes to solutions of pH 3, 7 and 13 solutions for up to 60 days. It was found that the membranes were relatively stable when exposed to water at pH 3 and pH 7 with a 30% increase in CO2 and N2 permeability and no loss in CO2/N2 selectivity. However, the membrane failed at pH 13 due to hydrolysis of the CTA polymer chains. Similarly, the membrane performance declined significantly when exposed to 0.74 kPa NOx at 22oC over a 120 day aging period. This was due to the reaction of trace NO2 in the gas mixture with the alcohol functional groups within the membrane structure. Interestingly, the CTA membrane was more selective for SO2 than CO2 and N2 and stable in 0.75 kPa SO2 at 22oC over a 100 day aging period. The results suggest that CTA is a viable membrane material for post-combustion capture if it can form into an ultrathin film to increase permeance. In natural gas processing, the performance of CTA membranes can also be affected by ethylene glycol, which can be entrained into the membrane separation unit from the upstream dehydration unit. In this thesis, the impact of two common ethylene glycols, monoethylene glycol and triethylene glycol, on the gas separation performance of CTA membranes was investigated. It was found that the glycols initially absorbed into the membrane reducing the permeation of He, CO2 and CH4 by a “pore-blocking” mechanism, but after a period of time, plasticised the membranes and enhanced the transport of CO2 and CH4. This plasticisation effect had less effect on He, which may be due to the lower solubility of He in these glycols which limited the transport of this gas through the swollen membrane structure. Interestingly, the membrane performance recovered when the glycols were removed from the polymer using a methanol wash. The findings highlighted the potential to recover the membrane performance when glycol flooding occurs in industrial plants. Hydrogen sulfide in the raw natural gas might also affect CTA membrane performance. This impurity is also of concern in pre-combustion carbon capture. To fulfil the gap of knowledge in the literature, this thesis studied the permeability of H2S across a range of partial pressures (up to 0.75 kPa) and temperature (22oC - 80oC). At 0.75 kPa H2S at 22oC, the CTA membrane showed stable CO2 permeability for up to 300 days which confirmed the long-term resistance of this material to the experimental H2S conditions. Other impurities that might challenge the performance of CTA membranes in natural gas processing and pre-combustion capture are condensable aromatic hydrocarbons. In this thesis, the performance of CTA membranes at 35oC in the presence of toluene and xylene with variable vapour activity was studied. At low CO2 partial pressure (0.75 bar), the permeation of CO2 and CH4 through the CTA membrane declined when adding toluene and xylene up to 0.5 vapour activity. However, the CTA membrane was plasticised when toluene vapour activity increased above 0.5 activity. A similar impact was not clearly observed in the case of high xylene vapour activity. At high CO2 pressure (7.5 bar), the membranes were plasticised by both hydrocarbons at 0.3 vapour activity. This finding demonstrated the co-operative effect of CO2 and condensable hydrocarbons on the CTA membrane. In addition, the sorption and permeability of toluene and xylene through the CTA membrane at vapour activity up to 0.8 at 35oC was also recorded. Overall, the thesis demonstrates that cellulose triacetate membrane is an outstanding material for CO2 separation in natural gas processing, pre- and post-combustion capture with high gas selectivity and resistance to most impurities in these industrial gas streams.
Quantifying interactions between nanoengineered particles and cells
Nanoengineering has recently emerged as a promising technology for the understanding, treatment, and diagnosis of disease. One of its most compelling potential uses is in the design of particles with controlled interactions with particular cell types. Significant research effort has been devoted to developing particles that exhibit a variety of interesting behaviors, including stealth, targeting, cargo carrying capabilities, or responsiveness to biological environments. In vitro experiments with cultured cells are fundamental to understanding and studying the interface between nanoengineered particles and biological systems. However, partially due to the wide range of physicochemical properties nanomaterials exhibit, quantification and generalization of data from in vitro bio-nano experiments has unique challenges when compared to traditional small-molecule drugs or materials in bulk. As the fields of bio-nano research and nanomedicine have matured, in vitro quantification has become a significant barrier to understanding, characterizing, and comparing newly developed particle systems. This thesis addresses three interrelated areas that are necessary to accurately quantify in vitro interactions between nanoengineered particles and cells. First, particle-dependent variation between the amount of material administered and that which reaches the surface of cells (in vitro dosimetry) is studied. Second, instrument independent quantification of cell-particle association is used to study differences in association induced by labeling and cytometry technique. Third, a theoretical framework to isolate the biological kinetics of association is developed, and is used to compare cell-particle association results from experiments varying in particle type and cell line. Though the primary focus of this thesis is computational, a mixture of experimental, mathematical, and computational strategies are utilized. This thesis addresses three interrelated areas that are necessary to accurately quantify in vitro interactions between nanoengineered particles and cells. First, particle-dependent variation between the amount of material administered and that which reaches the surface of cells (in vitro dosimetry) is studied. Second, instrument independent quantification of cell-particle association is used to study differences in association induced by labeling and cytometry technique. Third, a theoretical framework to isolate the biological kinetics of association is developed, and is used to compare cell-particle association results from experiments varying in particle type and cell line. Though the primary focus of this thesis is computational, a mixture of experimental, mathematical, and computational strategies are utilized.
Carbon dioxide separation from natural gas: evaluation of adsorbents and influence of process variables
The use of natural gas in place of coal offers a method to effectively reduce greenhouse gas emissions. Adsorption processes, specifically, pressure swing adsorption (PSA), offers an energy efficient method to perform bulk removal of CO2 from high pressure sour natural gas. A selection of zeolitic imidazolate frameworks (ZIFs) were chosen and evaluated using PSA process simulation. ZIFs -8, -14 and -71 were synthesised and gas adsorption isotherms measured. Using these isotherms, process simulation over a range of feed conditions from 15 %mol to 35 %mol CO2 at 100 bar(a) and 303 K, process performance metrics including CO2 and CH4 purity and recovery were observed. Considering CH4 is the saleable product, it was decided that its purity target of 98 %mol could not be compromised, and was thus set as a requirement. Using a 9 step, 3 bed PSA cycle, ZIF-14 was not able to meet this CH4 purity requirement; however, ZIF-8 and ZIF-71 were able to meet it while achieving CO2 purities of 24 – 45 %mol with good recovery (89 – 96 %mol), and CH4 recoveries of 48 – 34 %mol. A thorough investigation of the adsorption properties and thermodynamics of the ZIF adsorbents was also carried out. It was known that ZIF-8 demonstrated a structural transition upon adsorption; based on this work, it is quite likely that such transitions are also taking place in ZIF-14 and ZIF-71, however, definitive experimental evidence of this is required such as in-situ X-ray diffraction. Some artefacts seen in the adsorption isotherms of ZIF-71 were found to correlate with the adsorbate liquid phase surface tension. It was also found that these ZIF adsorbents deteriorated over time, contrary to existing claims in the literature. During the thermodynamic analysis, it was found that temperature invariant properties such as the differential enthalpy of adsorption were affected by temperature, and this was attributed to the structural transition. It was also found that the adsorbed phase was not ‘liquid like’ at low loadings, but was at higher loadings. A published method (osmotic potential) was used in evaluating the thermodynamics of the structural transition, and it was found that this method was inconsistent and inconvenient when multiple isotherms are used. An alternative method based on van ‘t Hoff plots was proposed and better results were observed, however, further application of this method is required to confirm its general applicability. In order to form a more general view on the topic, the literature was reviewed for high pressure adsorption isotherms of CO2 and CH4. These adsorbents, in addition to the ZIF adsorbents synthesised in this work, and a family of zeolite-Y adsorbents for which adsorption isotherms were measured for, were evaluated for process performance using a simple PSA model. It was found that ZIF-71 was most often the best performing adsorbent over the range of conditions investigated. The adsorbents were evaluated over a range of process conditions such that the output could be used as an adsorbent screening method. Feed temperature, pressure, and desorption pressure were all varied for feed compositions of 10 %mol and 30 %mol CO2. This finding implied that ZIF-71 should be investigated further for high pressure CO2/CH4 separations, with the belief that a more advanced PSA cycle could be developed or used to give better performance than was found earlier in this work. It was originally thought that the bed void fraction would be a significant limitation for high pressure separations. It was found, however, that the void fraction of the adsorbent bed did not have as great an influence as was imagined, although minor gains in CO2 purity and CH4 recovery could be found. Finally, a range of model adsorbents/isotherms were made in order to uncover the key adsorbent properties that result in good process performance. It was found that adsorbents with either a moderate loading, low heat of adsorption and low selectivity or low loading, moderate heat of adsorption and high selectivity yielded the best results. The unexpected outcome of this finding was that these characteristics align very well with ZIF-71. A range of future work was also recommended. ZIF-71 should be investigated further in different PSA cycles, and high pressure binary adsorption data should also be measured to investigate the true effects of multicomponent adsorption as they are currently unknown. A series of experiments were also suggested to confirm findings regarding the adsorption properties of the ZIF adsorbents, including in-situ X-ray diffraction for the suspected structural transitions of ZIF-14 and ZIF-71, and isotherm measurements using a wider variety of adsorbates regarding the suggested surface tension related phenomenon in ZIF-71. A selection of adsorbent development tasks were also recommended including, post-synthesis modification of the ZIF adsorbents in an effort to tune adsorption properties, further investigation into an adsorbent called ZSM-25 for which adsorption properties are not well known at the time of writing, and a hierarchical LTA-FAU adsorbent was also suggested. Regarding the separation process, it was speculated that a hybrid PSA-membrane based separation process may offer enhanced process performance, with the PSA system helping to overcome issues such as membrane plasticisation and the membrane system increasing the attainable CO2 purity and CH4 recovery.
Membrane capacitive deionisation as a novel approach to wastewater treatment
In this thesis, Membrane Capacitive Deionisation (MCDI), an energy-efficient desalination technology, was studied through laboratory experiments and mathematical modelling. An MCDI cell consists of a pair of porous carbon electrodes in front of which ion-exchange membranes are placed. A comprehensive literature review on operational modes of CDI and MCDI, performance evaluation metrics, recent developments on novel carbon electrodes and ion-exchange membranes, and the dynamic ion transport models available for (M)CDI is initially presented. Following that the scope of the thesis is introduced by specifying gaps in demand of more investigation. An MCDI cell built in house is used as the basis for all experiments in this thesis. In the first instance, the properties of the carbon materials, the ion-exchange membranes (IEMs) and the flow channel compartment of the MCDI cell were determined. To understand the underlying physico-chemical properties of the carbon electrodes, the electrode material was characterized using N2 isotherms, Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The N2 isotherms showed that the dominant pore diameter is < 2nm, confirming that the overlapping Electrical Double Layers could be assumed as the basis to describe the temporary ion adsorption in the carbon micropores. FTIR and XPS enabled the author to identify the surface functional groups on the carbon source. SEM images taken from the fabricated electrodes provided details on adhesion of the carbon slurry to the current collector and the apparent thickness of the carbon layer as 150 µm. The commercial ion-exchange membranes used in this work were also characterized thoroughly by measuring their water content and ion sorption capacity at different concentrations and in different electrolyte solutions; as well as counter and co-ion permeabilities. The significant outcomes of this section enabled the author to obtain membrane properties to be used in the later ion transport model. As the first research question, the feasibility of regenerating the MCDI cell with a brine stream (a stream at higher concentration compared with the feed concentration) was investigated. The idea of brine management and its effect on water recovery and water productivity was identified as an unsolved research question in the area of MCDI. In this section, the effect of brine concentration on the desorption time and water recovery was first evaluated through experimental work. Following that, an improved MCDI set-up was suggested in which the stream is recirculated via a recycle tank during the desorption period. 40% water recovery enhancement could be achieved employing the aforementioned proposed set-up. In the final part of this section, the dependency of the salt adsorption and water recovery on the residence time within an MCDI cell was investigated using an improved MCDI ion-transport model. To understand the effect of competing ion effects, the feed stream to CDI and MCDI was extended to more realistic solutions involving mixed salt feed streams. In a comprehensive study the performance of the CDI cell was compared with that of MCDI in terms of the adsorption and desorption rate of the various ions, total salt removal and normalized charge efficiency. A slower adsorption rate of divalents was observed in the CDI cell relative to the monovalent ions. Additionally, it was observed that in an MCDI cell, the ion transport through the IEMs is the rate-controlling step out of all transport resistances. In the case of the MCDI, a sharp desorption peak of divalent ions was noticeable both for Ca2+ and SO42-. This behavior could be justified by the sorption results collected in the IEM characterisation section. In the first step toward enhancing the currently available models, the ion-transport model developed in this thesis eliminates the symmetry assumption of the MCDI cell by identifying the controlling IEM, and includes the effect of the ion activity coefficient in the membrane. The mathematical model was then further extended to make it more accurate and capable of predicting the CDI and MCDI behaviors with a wide range of feed solutions. While it is shown that this extended model is capable of predicting the CDI and MCDI cell performance to a great extent, a faster rate of adsorption and desorption was observed in the model. This behavior can be explained by the quasi-steady state assumption which is employed in the mathematical approach. This assumption assumes an instantaneous equilibrium between the macro and micro pores of the carbon as well as the surface of the IEMs with the electrode macropores. Including a time-dependency for these two transport steps will reduce the model rate of change. In the final section, the effect of organic fouling was studied using two model foulants, the sodium salt of alginic acid and humic acid. While the effect of fouling on the salt removal and charge efficiency of the CDI cell was significant, the effect on MCDI was more limited. Fouling on the IEMs could be further reduced by increasing the flow rate during the desorption step, showing that the fouling on the IEMs is predominantly reversible. The effect of foulant concentration and feed pH were also studied. In the case of CDI, where the fouling had a detrimental effect on its desalination performance, the effect of alkaline cleaning on the performance recovery was investigated. It was observed that activated carbon eroded from the electrode material during such alkaline cleaning (4% carbon mass loss). In summary, some of the unresolved aspects of MCDI were tackled in thesis which will provide more insight into this energy efficient technology and pave its way to commercialization. Comprehensive characterisation, an improved ion transport model, a brine management study, a comparison of CDI and MCDI performance in salt mixtures, and finally the effect of organic fouling in MCDI were the main focuses of this work.