No description available.

Thesis (Ph. D.)--University of New South Wales, 1995. / Also available online.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2006. / Härtill 3 uppsatser.

Thesis (Ph. D.)--University of Oregon, 1999. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 143-152). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9948018.

Thesis (Ph. D.)--University of Virginia, 2005. / Includes bibliographical references (leaves 175-196). Also available online through Digital Dissertations.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 147-156). Also available via the Internet.

Sustainable energy supply and environmental protection are the major global scientific challenges in the 21st century, such as greenhouse gas capture, natural gas production, desalination of seawater for clean water production. Membrane separation technology offers attractive energy-efficient and environmental-friendly solutions to these challenges. This PhD thesis is focused on design and fabrication of membranes from novel molecularly defined polymers and understanding their physical properties, particularly the transport properties of gas molecules in polymer membranes. First, we demonstrate a simple approach of fabricating novel polymer nanocomposite membranes using established colloidal science. Crystalline microporous zeolitic imidazolate frameworks (ZIFs) nanocrystals are incorporated into a polyimide polymer matrix via solution mixing. The resulting nanocomposite membranes show excellent dispersion of nanoparticles, good adhesion at the interface, and enhanced gas permeability while the selectivity remain at high level. We then fabricated membranes from novel microporous polymers, polymers of intrinsic microporosity (PIMs). Using the PIM-1 polymer as a prototype, we discovered that ultraviolet irradiation of PIM-1 membranes in the presence of oxygen induces oxidative chain scission at the surface, resulting in local densification and structural transformation of free volume elements. Consequently, the membrane become asymmetric with a more gas-selective layer formed at the surface, while the overall permeability maintains at high level. Finally, we report a simple thermal oxidative crosslinking method to tailor the architecture of channels and free volume elements in PIM-1 polymer membrane by heat treatment in the presence of trace amounts of oxygen molecules. The resulting covalently crosslinked polymer networks offer superior thermal stability, chemical stability, reasonable mechanical strength, and enhanced rigidity. Most important of all, thermally crosslinked PIM-1 polymer membranes show significantly enhanced molecular sieving functions that yield remarkably high selectivity and high gas permeability, which surpass the upper bound that has been limiting the polymer membranes for decades. We also demonstrate that the thermal crosslinking method is effective for crosslinking of nanocomposite membranes with porous or nonporous fillers. These microporous molecular sieve membranes are promising for a wide range of molecular-level separation applications.

The membrane bioreactor (MBR) is becoming increasingly popular for wastewater treatment, mainly due to its capability of producing high quality effluent with a relatively small footprint. However, high plant maintenance and operating costs due to membrane fouling limit the wide spread application of MBRs. Membrane fouling generally depends on the interactions between the membrane and, the activated sludge mixed liquor, which in turn, are affected by the chosen operating conditions. The present research study aimed to explore the process performance and membrane fouling in the membrane enhanced biological phosphorus removal (MEBPR) process under different operating conditions by, (1) comparing two MEBPRs operated in parallel, one with constant inflow and another with a variable inflow, and by, (2) operating the MEBPRs with different solids retention times (SRT). On-line filtration experiments were conducted simultaneously in both MEBPR systems by using test membrane modules. From the transmembrane pressure (TMP) data of the test membrane modules, it was revealed that fouling propensities of the MEBPR mixed liquors were similar in both parallel reactors under the operating conditions applied, although the fouling propensity of the aerobic mixed liquors of both reactors increased when the SRT of the reactors was reduced. Routinely monitored reactor performance data suggest that an MEBPR process with a varying inflow (dynamic operating condition) performs similarly to an MEBPR process with steady operating conditions at SRTs of 10 days and 20 days. Mixed liquor characterization tests were conducted, including critical flux, capillary suction time (CST), time to filter (TTF) and, bound and soluble extracellular polymeric substances (EPS) were quantified, to evaluate their role on membrane fouling. The tests results suggest that the inflow variation in an MEBPR process did not make a significant difference in any of the measured parameters. With decreased SRT, an increase in the concentrations of EPS was observed, especially the bound protein, and the bound and soluble humic-like substances. This suggests that these components of activated sludge mixed liquors may be related to membrane fouling. No clear relationship was observed between membrane fouling and other measured parameters, including critical flux, normalized CST and normalized TTF. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The plasma membrane (PM) of live cells has a striking phospholipid asymmetry between bilayer leaflets, yet the purpose of this fundamental structure remains elusive. It is also unknown whether and how this phospholipid asymmetry impacts on the lateral organization of the PM, such as microdomains or lipid rafts that are thought to facilitate specific protein-protein interactions. Here, we generated asymmetric giant unilamellar vesicles (GUVs) and found that microdomain formation is inhibited by outer leaflet very long acyl chain (24:0) sphingomyelin (SM), the primary sphingolipid species in mammalian cells. Interestingly, although cholesterol is believed to associate favourably with SM, molecular dynamic (MD) simulations of asymmetric membranes indicate a strong preference for cholesterol in the inner leaflet when 24:0 SM is in the outer leaflet, as well as, interdigitation of 24:0 SM acyl chain across the centre of the bilayer. We thus hypothesized that the outer leaflet-localized 24:0 SM interdigitates across the leaflets of the bilayer and facilitates cholesterol enrichment in the inner leaflet. Indeed, we obtained evidence that, in asymmetric unilamellar vesicles with 24:0 SM exclusively in the outer leaflet, 75-80% of cholesterol was partitioned into the inner leaflet, which was correlated with the disappearance of microdomains in GUVs. Importantly, in live cell PM, where 24:0 sphingolipids are the predominant species and exclusively in the outer leaflet, cholesterol was similarly enriched in the cytoplasmic leaflet. SM with shorter acyl chains such as 16:0, a minor species in mammalian cells, failed to generate cholesterol asymmetry and promoted microdomains in both symmetric and asymmetric GUVs. Furthermore, we generated live mammalian cells with either 16:0 or 24:0 SM and analyzed submicron domains in these cells, using density-dependent FRET of GPI-anchored proteins. Indeed, 16:0 SM cells are capable of forming submicron domains. The 24:0 SM cells, by contrast, are nearly devoid of submicron domains, as are unmodified control cells. Moreover, we silenced ceramide synthase 2 (CerS2), the enzyme that generates very long acyl chain sphingolipids. We found that silencing CerS2 alters diffusional properties of membrane proteins, consistent with enhanced microdomain formation. Together, our results establish a surprising and central role of very long acyl chain sphingolipids in regulating membrane lateral organization, including in the native plasma membrane, by creating cholesterol asymmetry. We propose that sphingolipid asymmetry functions to dynamically regulate microdomains in live cells.

To minimize membrane fouling many water treatment plants pre-treat water prior to microfiltration (MF) or ultrafiltration (UF). Coagulation/flocculation/sedimentation is a common form of pre-treatment, but little research has been conducted on floatation as a part of the pre-treatment. The objective of this thesis is to compare pre-treatment with floatation and with sedimentation for Ottawa River water, a typical Northern Canadian water with a high natural organic matter (NOM) content and a large hydrophobic (HPO) NOM fraction. Fouling tests consisted of multiple filtration/backwashing cycles performed by an automated bench-scale UF hollow fiber membrane system. Test were conducted with Ottawa River water (ORW) and ORW subjected to three different types of pre-treatment conducted at closely-located full-scale water treatment plants, including one using floatation. Both Alum pre-treatments resulted in decreases in NOM (63% and 68% TOC) and HPO NOM (56% and 68%TOC) which helped to reduce fouling. However, the remaining NOM and HPO NOM still caused significant hydraulically and chemical irreversible fouling. The water pre-treated with floatation produced the least severe hydraulically irreversible fouling for all experiments while Raw ORW produced the highest. During the early stages of membrane filtration (~10 hours), the TMP sharply increases which may imply that adsorption is dominant. Statistical analysis during the initial stages of filtration showed that the HPO fraction of NOM was linked to hydraulically irreversible fouling, which may be attributed to adsorption. Raw ORW also had the highest hydraulically reversible fouling while all pre-treatments were able to reduce this type of fouling. Statistical analysis suggested that the transphilic (TPI) fraction of NOM and particulate organic carbon (POC) were responsible for hydraulically reversible fouling during subcritical flux experiments, which may be attributed to cake formation on the membrane surface. It was found that for all waters and experiments, hydraulically irreversible fouling was greater than hydraulically reversible fouling. This may be because of the high HPO concentrations in the ORW. Hydraulically reversible fouling and backwash efficiencies were found to fluctuate with time. It is hypothesised that the cake formation adheres to the membrane surface and is not fully removed until enough backwash pressure has developed. Further investigation into alternative cleaning procedures is required as the NaOH cleaning was not very effective for some of the pre-treated waters.