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Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 74-82). Also available in electronic version.

Thesis (Ph. D.)--University of New South Wales, 2002. / Also available online.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references (p.89-92).

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 93-102). Also available in electronic version. Access restricted to campus users.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xxxvi, 252 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 249-252).

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2006 / A protocol already exists for fabrication of a capillary membrane having an internal ultrafiltration skin supported by a finger-like pore structure in the external capillary wall (Jacobs and Leukes, 1996; Jacobs and Sanderson, 1997). These membranes have been produced at the Institute of Polymer Science, University of Stellenbosch, South Africa. Two major applications emerged from the development of these internally skinned membranes. One application was in the production of potable water by Ultra-filtration (UF) from sources containing coloured water. A second application was in the immobilization of a white rot fungus in a ."gradostat" membrane bioreactor. Here a nutrient gradient through the membrane wall and fungal mat can be established and manipulated in order to stimulate continuous production of secondary metabolites (extra-cellular enzymes). These enzymes are useful in the degradation of polycyclic aromatic compounds, notably PCB species in contaminated water and soils (Jacobs and Sanderson, 1997). Two objectives emerged from experiences with the above applications. The first objective was to improve membrane performance in UF applications. In this case a reduction was sought in trans-membrane pressure differential required to attain a desired flux without sacrificing rejection. The pressure required for a given desired flux across a membrane depends on the resistance of the membrane skin layer and of its supporting sub-layer which together comprises the capillary wall and defmes its overall structure. If any of these resistances could be reduced, the overall resistance to transport of water would be reduced. Then it would be possible to operate the membrane at lower trans-membrane pressure differences. On the other hand, operation with higher pressure would also increase flux but require a thicker capillary wall to resist this pressure. In the attempt to optimise these properties of the capillary membrane, capillary membranes produced in the study reported here were tested to find the relationship of flux performance with the structures that resulted from varying key parameters affecting structure and integrity. The objective in the case of immobilizing fungi in membrane bioreactor applications was to attain thicker walls thus providing better support for the fungal mass. The internally skinned capillary membrane has finger-like microvoids that start next to the UF skin layer and extend across the capillary membrane wall and open at the external membrane periphery, giving an ideal structure for retaining the fungal biomass. The idea of a membrane with this type of morphology to immobilize white rot fungi was to anchor the growing fungus within these microvoids which imitate the natural environment in which these organisms live, that is, in the fibrous structure of decaying wood. The requirement to inoculate the microvoids with fungal spores (reproductive cells), implies that they need to be accessible from the outside, requiring a membrane wall that is externally unskinned. In the formation ofthe capillary membrane the processes of formation of the porous UP skin and the finger-like microvoids are mainly governed by diffusion of solvent out of a polymer dope (gel phase) and of non-solvent into the dope phase. Such exchanges are of primary importance between the bore fluid (containing non-solvent) and dope (containing solvent) or between the external spinning bath (high in solvent content) and dope. Diffusion effects also occur between the nascent pore voids and the precipitating polymer matrix. There are also expected to be some convection effects due to shear between the bore fluid and the moving dope gel phase and due to shrinkage ofthe gel phase. The variables selected for experimentation m the study reported here were: the dope extrusion rate (DER); dope composition (viscosity effects); bore fluid flow rate (BFF); bore fluid composition and wall thickness and diameter effects (determined largely by spinneret dimensions). Each of these has an expected effect on membrane structure and its resulting performance. Most were varied over narrow ranges indicated in the literature and by experience to be effective and critical. In addition, the effects of altering the walI thickness were investigated by using two different spinneret sizes. The external spinning bath composition (solvent content) was reported in the literature to be a particularly important parameter in the formation of externally unskinned membranes. Maintaining a high content of solvent in the external spinning bath could prevent skin formation. Too high a solvent content could, however, prevent phase transition and lead to later precipitation ofa dense skin on contact with the non-solvent in the later (humidification and rinsing) steps in the fmishing of the capillary membrane product. The external bath composition was therefore varied so as to find the bath composition that would match the cloud point for the polymer dope employed. As expected, the thickness of the membranes increased with DER increase. However, it was found that there is a critical wall thickness where an external skin layer is formed as a result of increasing the DER. A certain volumetric ratio ofDER to BFF (1,5:1 for this study) was therefore maintained in order to produce externally unskinned membranes. This shows that although the final membrane structure is detennined by the casting dope formulation, the fabrication protocol plays an equally important role in controlling structural properties and perfonnance. There was no significant change with the membrane thickness as a result of changing BFF but the voids became longer and more in number as the BFF was increased. Too high solvent content (99% NMP in this study) resulted in an external skin layer being formed. According to Smolders et.al. (1992), when the solvent content in the external spinning bath is too high, the polymer at the surface of the newly fonned membrane slowly dissolves in the external spinning bath re-forming a dope-like solution. When the newly formed membrane passes through the humidifier, the dope-like solution solidifies to form an external skin. At the same instance, too low solvent (93% for this study) resulted in external skin being fonned. Externally unskinned membranes were formed at 94 and 96% NMP bath composition. The use of a small spinneret resulted in very thin walled externally unskinned membranes.

No description available.

Thesis (PhD)--Stellenbosch University, 2002. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: Membrane fouling is universally accepted as one of the most critical problems limiting the wider application of membranes in liquid separations. The development and utilization of a suitable non-invasive technique for the on-line monitoring of fouling in industrial and laboratory applications may enable the effectiveness of fouling remediation and cleaning strategies to be quantified. The overall objective of this research is to develop ultrasonic time-domain reflectometry (UTDR) and its use as an analytical tool for the real-time study of inorganic-, organic- and protein- fouling of various types of membranes including nylon, polysulfone (PSU) and polyethersulfone (PESU) and modules, including flatsheet and tubular types. Different separation systems including microfiltration (MF) and ultrafiltration (UF), flat-sheet and tubular modules, and suitable ultrasonic probes were used in this study. Results of this study show a good correlation between the UTDR signal response and the development of a fouling layer on a membrane surface. UTDR effectively detected the appearance, growth and movement of a fouling layer echo as fouling proceeded. Cake (fouling)-layer compressibility was observed by UTDR. The structure and compaction of an asymmetric PSU membrane could be detected by UTDR. UTDR was also successfully used for monitoring membrane cleaning and evaluating the cleaning effectiveness o f various cleaning methods. UTDR results corroborated the flux measurements and SEM analyses. The ultrasonic unit is a programmed microprocessor, and can be used to compare reference and test signals to produce a differential signal (a fouling layer echo). A differential signal indicates the state and progress o f a fouling layer on the membrane surface in actual operations. Both amplitude and arrival time of differential signals as a function of operation time provide useful quantitative information, i.e. changes in thickness and density of a fouling layer, on the fouling processes. A predictive modelling program, ultrasonic reflection modelling (URM), was developed to describe the processes of ultrasonic testing related to the deposition of fouling layers on membrane surfaces. The mathematical model could substantiate changes in the densities of the fouling layer as well as the thickness. This is important as deposit resistance to flow is related to both thickness and density (compressibility). The predicted results of cake layer deposition are in good agreement with the actual UTDR measurements obtained in MF and UF. Furthermore, protein fouling was successfully detected in tubular UF by UTDR. Ultrasonic frequency spectra could be used as an additional tool for fouling detection. / AFRIKAANSE OPSOMMING: Membraan-aanvuiling of -verstopping is die grootste struikelblok wat die meer algemene aanwending van membrane vir verskillende watersuiweringsprosesse beinvloed. Die ontwikkeling en gebruik van ‘n geskikte nie-inmengende tegniek vir die in-lyn meting van aanvuiling van membrane in laboratorium-en nywerheidstoepassings mag ‘n geleentheid bied vir die kwantifisering van die verwydering van aanvuiling en skoonmaakstrategiee. Die hoofdoel van hierdie studie was die ontwikkeling van ultrasoniese tydgebiedsweerkaatsing (Eng: ultrasonic time-domain reflectometry, UTDR) en die gebruik daarvan as ‘n analitiese metode vir die studie van anorganiese-, organiese- en bio-besoedeling op verskeie tips membrane, insluitend nylon, polisufoon (PSU) en polietersulfoon (PESU), in beide platvel- en buismodules. Verskeie skeidingsisteme, insluitend mikrofiltrasie (MF) en ultrafiltrasie (UF) is ontwerp en gebruik in hierdie studie. Eksperimentele resultate het goeie ooreenstemming tussen die UTDR seinrespons en die ontwikkeling van ‘n aanvuilingslaag op die membraanoppervlakte bewys. Die ultrasoniese tegniek kon die vorming, groei en beweging van ‘n bevuilingslaagterugkaartsing waarneem namate bevuiling vorder. Aanvuilingslaagsamepersing is deur UTDR waargeneem. Die struktuur en samepersing van ‘n asimmetriese PSU membraan is ook deur UTDR gesien. UTDR is verder suksesvol gebruik om die skoonmaak van membrane te monitor en om die skoonmaakgeskiktheid (cleaning effectiveness) van verskeie skoonmaakmetodes te bepaal. UTDR resultate het permeaatvloeimetings en SEM analyses bevestig. Die ultrasoniese eenheid is ‘n geprogrameerde mikroverwerker, en kan gebruik word om verwysings- en toetsseine te vergelyk, en dan ‘n differensiaalsein te gee (‘n aanvuilingslaagweerklank). ‘n Differensiaalsein dui die toestand en vordering van ‘n aanvuilingslaag op die membraanoppervlakte gedurende gebruik aan. Beide amplitude asook aankomstyd van differensiaalseine as funksies van gebruikstyd verskaf bruikbare kwantatiewe inligting, dws. Veranderings in die dikte en digtheid van ‘n aanvuilingslaag, op die aanvuilingsproses. ‘n Voorspellingsmodelleringprogram - ultrasonieseweerkaatsingsmodellering (Eng: ultrasonic reflection modeling, URM) is ontwikkel om die proses van ultrasoniese toetsing by die deponering van aanvuilingslae op membraanoppervlaktes beter te beskryf. Veranderings in die digtheid en dikte van die aanvuilingslaag teenvloei is verwant aan dikte en digtheid (saampersbaarheid). Die voorspelde resultate van aanvuilingslaagdeponering stem goed ooreen met die werklike UTDR-metings wat in MF en UF gemaak is. Bio-aanvuiling is suksesvol waargeneem deur UTDR in buisvormige UF membrane. Ultrasoniese frekwensiespektra kan dus as ‘n bykomende metode gebruik word vir die waarneming van aanvuiling op skeidingsmembrane.