No description available.

There is an urgent need to identify novel antibiotics for multidrug-resistant Gram-negative pathogens. These bacteria are intrinsically resistant to many antimicrobials due to a formidable outer membrane barrier. Herein we investigate the potential of perturbing the outer membrane to sensitize Gram-negative bacteria to otherwise inactive antibiotics. In chapter 2, we identify the ability of mcr-1 mediated resistance to confer protection from the lytic but not outer membrane-perturbing activity of colistin. Exploiting this sensitivity, we show that colistin and clarithromycin in combination are efficacious against mcr-1-expressing Klebsiella pneumoniae in murine infection models. This demonstrates the viability of colistin combination therapies against Gram-negative pathogens harbouring mcr-1, and points to a mechanism of mcr-1-mediated resistance extending beyond the predicted reduction in binding affinity of polymyxins to the outer membrane. We continue to investigate the potential of using outer membrane perturbants with otherwise inactive antimicrobials in chapter 3. In this work, we identify the ability of OM disruption to change the rules of Gram-negative entry, render pre-existing resistance ineffective, reduce the development of spontaneous resistance and attenuate biofilm formation. Together, these data suggest that OM disruption overcomes many traditional hurdles encountered during antibiotic treatment and is a high priority approach for further development. / Thesis / Doctor of Philosophy (PhD)

No description available.

Polybenzimidazoles, a class of aromatic heterocyclic polymers, are well known due to their remarkable thermal stability, mechanical properties and chemical resistance which are often required in extreme operation conditions. Because of these properties, polybenzimidazoles are excellent candidates in various application areas including proton exchange membrane fuel cells, gas separation membranes, reverse osmosis and nanofiltration, and high performance coatings. The following studies are focused on the synthesis, characterization and related properties of polybenzimidazoles and polybenzimidazole based materials. A novel sulfonyl-containing tetraamino-substituted monomer (3,3',4,4'-tetraaminodiphenylsulfone) was synthesized and polymerized with three different diacid monomers to make polybenzimidazoles. The new monomer synthesis route with reduced steps relative to the existing literature method increased the overall yield by a factor of three. The sulfonyl-containing polybenzimidazoles have enhanced solubilities in common organic solvents including dimthylsulfoxide, dimethylacetamide and N-methyl-2-pyrrolidone in comparison with the commercial polybenzimidazole, Celazole®, poly(2,2'-(m-phenylene)-5,5'-bibenzimidazole). The improvements in solubility are attributed to the introduction of polar sulfonyl linking moiety in the monomer. Remarkable thermal stabilities (high T_g, > 428 °C) were demonstrated through Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). A well designed film casting process was investigated and established. Polybenzimidazoles were fabricated into transparent thin films (20-30 μm thick) for gas transport measurements. These novel polybenzimidazole films exhibited extraordinary gas separation properties, especially for H₂/CO₂ separation. There is a trade-off relationship between gas permeability and selectivity through dense, non-porous polymer membranes that was discovered by Robeson in 1991. The ultimate goal for developing gas separation membranes is to improve both permeability and selectivity simultaneously. Gas permeability is related to the free volume between polymer chains. In order to improve gas permeability, we hypothesized a concept that increasing free volume could be achieved by thermally degrading sacrificial components and volatilizing their byproducts from a glassy matrix. Volatile components were introduced into the films to preoccupy the spaces between polymer chains. Once they were degraded and removed through the thermal treatment, it was hypothesized that the preoccupied spaces would remain empty due to the glassy nature of the matrix at the heat treatment temperature, thus resulting in more free volume. Two post- modification strategies including grafting and blending were utilized to incorporate the volatile components, poly(propylene oxide) and poly(ethylene oxide). Post-modified polybenzimidazole films impressively showed significant enhancements in both gas permeability and selectivity for H₂/CO₂ separation. The H₂ permeability of the post-modified TADPS-OBA polybenzimidazole increased from 3.1-6.2 Barrers to 5.2-7.5 Barrers (up to 66% increase). The selectivity for H₂/CO₂ increased from 7.5-10.5 to 10.1-13.0 (up to 33% increase). The study on the potential effects of water vapor on the separation performance of PBI membranes was discussed in the appendix. / Ph. D. / Polybenzimidazoles represent a class of polymeric high performance materials due to their remarkable thermal stability, mechanical properties and chemical resistance. They are competitive material candidates for applications involving extreme conditions including high pressure and high temperature. The following studies are focused on the synthesis, characterization and properties of polybenzimidazoles and polybenzimidazole based copolymers and blends. Of particular importance to this dissertation are the gas transport properties. The new materials are excellent candidates for making non-porous membranes that can separate very small molecules such as nitrogen, oxygen, carbon dioxide, and hydrogen. The non-porous membranes achieve separations of such small molecules by having the gases solubilize in the upstream side of a membrane, diffuse through it, then evaporate from the downstream side. This mechanism is known as the solution-diffusion mechanism. The monomer, 3,3’,4,4’-tetraaminodiphenylsulfone, was synthesized via our designed synthesis method that was simpler than previous methods described in the literature and with a 3 times higher yield. A series of polybenzimidazoles with systematically varied chemical structures were prepared and it was demonstrated that they all had enhanced solubilities in common organic solvents over the only known commercial polybenzimidazole, Celazole®. This is particularly important for membrane materials because they must be fabricated into thin films from solution. Remarkable thermal stabilities for polymeric materials with glass transition temperatures above 400 °C were found for these polybenzimidazoles. A well designed film casting process was investigated and established. Polybenzimidazoles were fabricated into transparent thin films (20-30 µm thick) and their gas transport properties were measured. These novel polybenzimidazole films exhibited extraordinary gas separation properties, especially for H₂/CO₂ separation. The gas transport properties involve two important parameters, permeability and selectivity. A trade-off relationship between the two parameters was discovered by Robeson in 1991. The ultimate goal for developing gas separation membranes is to improve permeability and selectivity at the same time. In order to improve gas permeability, we hypothesized a concept that increasing permeability could be achieved by creating more spaces between the polymer chains in non-porous films. Sacrificial components were introduced into the films, then thermally degraded and the byproducts were volatilized to remove them from the film. It was further hypothesized that conducting the heat treatment process at a temperature where the matrix polymer was in the glassy state would allow the matrix polymer to preserve the free volume introduced by the volatization. Two post-modification strategies including grafting and blending were utilized to incorporate the volatile components, poly(propylene oxide) and poly(ethylene oxide). Post-modified polybenzimidazole films impressively showed significant enhancements in both gas permeability and selectivity for H₂/CO₂ separation. This is an important separation that could economically be carried out at elevated temperatures (~250°C) if the polymer membrane would withstand such a temperature. It could be utilized to separate H₂ from CO₂ in pre-combustion syngas. This is the major method for H₂ production worldwide. The study on the potential effects of water vapor on the separation performance of PBI membranes was discussed in the appendix.

Membrane processes can cover a wide range of separation problems [with a specific membrane (membrane structure) required for every problem]. Thus, there are membranes available that differ in their structure and consequently in the functionality. Therefore membrane characterization is necessary to ascertain, which membrane may be used for a certain separation. Membranes of pore size ranging from 100nm to 1μm with a uniform pore size are very important in membrane technology. An optimum performance is achieved when the membrane is as thin as possible having a uniform pore size. Here in this thesis, membranes were synthesized by particle assisted wetting using mono-layers of silica colloids as templates for pores along with polymerizable organic liquids on water surface. The pore size reflects the original shape of the particles. Thus it is possible to tune the pore size by varying the particle size. This method is effective to control pore sizes of membranes by choosing silica particles of suitable size. This approach gives a porous structure that is very thin, but unfortunately limited in mechanical stability. Thus there is a need for support which is robust and can withstand the various mechanical stresses. A small change in the membrane or defect in the layered structure during the membrane formation can have drastic effect on the assembly. Lateral homogeneity of the layer generated by the particle assisted wetting can be judged by examination of its reflectivity, but once it is transferred on any solid support this option is no more. So a method is needed to detect the cracks or the inhomogenity of the membrane which can be detected even after the transfer. To tackle this problem a very simple and novel technique for characterizing the membrane by fluorescence labeling and optical inspection was developed in this thesis. The idea was to add a fluorescent dye which is poorly water soluble to the spreading solution comprising of the particles and the monomer. If the dye survived the photo-cross linking, then it would be embedded in the cross-linked polymer and would serve as a marker. Defects and inhomogenity would show up as cracks and spots. By the method that we have developed, we can detect our membrane from the support and spot defects.

No description available.

Submitted in fulfillment of the academic requirements for the Master’s Degree in Technology: Chemical Engineering, Durban University of Technology. Durban. South Africa, 2015. / Increased public concern over health and the environment, the need to expand existing wastewater treatment plants due to population increase, and increasingly stringent discharge requirements, have created a need for new innovative technologies that can generate high quality effluent at affordable cost for primary and secondary re-use. The membrane biological reactor (MBR) process is one of the innovative technologies that warrant consideration as a treatment alternative where high quality effluent and/or footprint limitations are a prime consideration. MBR processes have been applied for the treatment of industrial effluent for over ten years (Harrhoff, 1990). In this process, ultrafiltration or microfiltration membranes separate the treated water from the mixed liquor, replacing the secondary settling tanks of the conventional activated sludge process. Historically, energy costs associated with pumping the treated water through the membranes have limited widespread application for the treatment of high volumes of municipal wastewater. However, recent advancements and developments in membrane technology have led to reduced process energy costs and induced wider application for municipal wastewater treatment (Stephenson et al., 2000). This report describes a small and pilot scale demonstration study conducted to test a woven fabric microfiltration immersed membrane bioreactor (WFM-IMBR) process for use in domestic wastewater treatment. The study was conducted at Durban Metro Southern Wastewater Treatment Works, Veolia Plant, South Africa. The main objective of this project was to develop and evaluate the performance of an aerobic woven fabric microfiltration immersed membrane bioreactor (WFM-IMBR) for small scale domestic wastewater treatment. The experiments were oriented towards three sub objectives: to develop the membrane pack for immersed membrane bioreactor based on WF microfilters; to evaluate the hydrodynamics of WF membrane pack for bioreactor applications; and to evaluate the long-term performance and stability of WFM-IMBR in domestic waste water treatment. The literature was reviewed on membrane pack design for established commercial IMBR. The data collected from literature was then screened and used to design the WF membrane pack. Critical flux was used as the instrument to measure the WF membrane pack hydrodynamics. Long-term operation of the WFM-IMBR was in two folds: evaluating the performance and long term stability of WFM-IMBR. The membrane pack of 20 flat sheet rectangular modules (0.56 m by 0.355 m) was developed with the gap of 5 mm between the modules. The effects of parameters such as mixed liquor suspended solids or aeration on critical flux were examined. It was observed that the critical flux decreased with the increase of sludge concentration and it could be enhanced by improving the aeration intensity as expected and in agreement with the literature. Hence the operating point for long term subcritical operation was selected to be at a critical flux of 30 LMH and 7.5 L/min/module of aeration. Prior to the long term subcritical flux of WFM-IMBR, the operating point was chosen based on the hydrodynamic study of the WF membrane pack. The pilot scale WFM-IMBR demonstrated over a period of 30 days that it can operate for a prolonged period without a need for cleaning. Under subcritical operation, it was observed that there was no rise in TMP over the entire period of experimentation. Theoretically this was expected but it was never investigated before. Good permeate quality was achieved with 95% COD removal and 100% MLSS removal. The permeate turbidity was found to be less than 1 NTU and it decreased with an increase in time and eventually stabilized over a prolonged time. Woven fibre membranes have demonstrated great potential in wastewater treatment resulting in excellent COD and MLSS removal; low permeate turbidity and long term stability operation. From the literature surveyed, this is the first study which investigated the use of WF membranes in IMBRs. The study found that the small scale WFM-IMBR unit can be employed in fifty equivalence person and generate effluent that is free of suspended solids, having high levels of solid rejection and has acceptable discharge COD for recycle. Future work should be conducted on energy reduction strategies that can be implemented in WFM-IMBR for wastewater treatment since high energy requirements have been reported by commercial IMBRs.

Microfiltration is one of the most important processes in membrane sciences that can be used for separating drops/particles above 1 ??m. Depth microfiltration membranes retain drops/particles inside the surface of the membrane, the process is expensive and membranes quickly become fouled. On the other hand, surface microfiltration membranes stop drops/particles on the surface of the membrane and the process is less fouling. Higher permeate flux and lower trans-membrane pressure is obtained with a shear enhanced microfiltration technique. Production of specific size of drops and stability of the drops are very important in testing the microfiltration of crude oil drops/water emulsions. Oil drops from 1-15 ??m were produced with a food blender, operated at its highest speed for the duration of 12 mins. In addition, vegetable oil drops were stabilised with 1% polyvinyl alcohol (PVA), Tween 20 and gum Arabic, stability was assessed on the basis of consistency in the size distribution and number of drops in each sample analysed at 30 mins interval. A slotted pore Nickel membrane with the slot width and slot length of 4 and 400 ??m respectively has been used in the filtration experiments. The slot width to the slot length ratio (aspect ratio) of the used membrane is 100. Vibrating the membrane at various frequencies created shear rates of different intensities on the surface of the membrane. Membrane with a tubular configuration is preferred over the flat sheet because it is easy to control in-case of membrane oscillations both at lab and industrial scale. Besides this, a tubular membrane configuration provides a smaller footprint as compared to the flat sheet. The influence of applied shear rate on slots/pore blocking has been studied. Applying shear rate to the membrane reduced the blocking of the slots of the membrane; and reduction of slots blocking is a function of the applied shear rate. At higher shear rate, lower blocking of the slots of the membrane was verified by obtaining lower trans-membrane pressure for constant rate filtration. The experiments are in reasonable agreement with the theoretical blocking model. Divergence of the experimental data from the theory may be due to involvement of deforming drops in the process. During microfiltration of oil drops, the drops deform when passing through the slots or pores of the membrane. Different surfactants provided different interfacial tensions between the oil and water interface. The influence of interfacial tension on deformation of drops through the slots was studied. The higher the interfacial tension then the lower would be the deformation of drops through the slots. A mathematical model was developed based on static and drag forces acting on the drops while passing the membrane. The model predicts 100% cut-off of drops through the membrane. Satisfactory agreement of the model with the experiments shows that the concept of static and drag force can be successfully applied to the filtration of deformable drops through the slotted pore membranes. Due to the applied shear rate, inertial lift migration velocities of the drops away from the surface of the membrane were created. Inertial lift velocities are linear functions of the applied shear rate. A mathematical model was modified based on inertial lift migration velocities. The critical radius of the drops is the one above which drops cannot pass through the surface of the membrane into the permeate due to the applied shear rate and back transport. The model is used as a starting point and is an acceptable agreement with the experiment. The model can be used to predict the 100% cut-off value for oil drops filtration and a linear fit between this value and the origin on a graph of grade (or rejection) efficiency and drop size to slot width ratio was used to predict the total concentration of dispersed oil left after filtration. Hence, it is shown how it is possible to predict oil discharge concentrations when using slotted filters.

A major challenge facing widespread implementation of membrane-based water purification is fouling, which results in increased operating costs and reduced membrane lifetime. This thesis focuses on various methods, including novel membrane surface modifications and polymers that resist degradation when exposed to oxidizing agents used as disinfectants, to alleviate membrane fouling. Fouling-resistant ultrafiltration membrane coatings were prepared from poly(ethylene glycol) diglycidyl ether-crosslinked chitosan (chi-PEG hybrid). Composite membranes were prepared for oil-water emulsion filtration by coating the most promising chi-PEG hybrid onto a polysulfone ultrafiltration membrane. Optimization of the coating layer thickness led to composite membranes that exhibited water flux values more than 5 times higher than that of uncoated membranes after one day of oily-water crossflow filtration. The organic rejection of the coated membranes was also higher than that of the uncoated polysulfone membranes. Polydopamine (PDOPA) deposition was discovered to reduce fouling in water purification membranes. PDOPA was found to deposit from solution onto virtually any surface. When deposited on water purification membranes, PDOPA rendered the membrane more hydrophilic and less susceptible to fouling. Moreover, covalent binding of other molecules, such as amine-terminated poly (ethylene glycol) (PEG), to PDOPA is simple and performed using benign chemicals and conditions. Commercially-available polymeric membranes were modified with polydopamine, and all showed improved fouling resistance while filtering oil-water emulsions. To demonstrate the versatility and ease of PDOPA modification scalability, PDOPA was deposited on entire membrane modules, and the resulting modified module exhibited improved fouling resistance. Finally, high ion rejection, chlorine-tolerant sulfonated polysulfone thin-film composite membranes were prepared and characterized. Interestingly, freestanding thick sulfonated poly(arylene ether sulfone) (BPS) films exhibit nearly neutral electrostatic charge, even though sulfonation introduces fixed negative charge into the polymer structure. As a result, charge exclusion ion partitioning is not a dominant rejection mechanism in these films. However, composite membranes prepared from a BPS coating layer and a porous Udel polysulfone support exhibit a negatively charged surface and, presumably, charge exclusion would be a more important partitioning mechanism for these membranes. Therefore, thick BPS films do not exhibit certain drawbacks, such as reduced salt rejection of mixed-valence feeds, that are observed in BPS thin-film composite membranes. / text

<p>Over the past 40 years, research pertaining to membrane technology has lead to the development of a wide range of applications including beverage production, water purification and the separation of dairy products. For the separation of gases, membrane technology is not as widely applied since the production of suitable gas separation membranes is far more challenging than the production of membranes for eg. water purification. Hydrogen is currently produced by recovery technologies incorporated in various chemical processes. Hydrogen is mainly sourced from fossil fuels via steam reformation and coal gasification. Special attention will be given to Underground Coal Gasification since it may be of great importance for the future of South Africa. The main aim of this study was to develop low temperature CsHSO4/SiO2 composite membranes that show significant Idea selectivity towards H2:CO2 and H2:CH4.</p>