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.

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

No description available.

Approved for public release; distribution is unlimited / This thesis presents a simple, meanline analysis of the impact of blade roughness on the mass flow, work coefficient, and efficiency of a three-stage axial compressor as a function of the location of fouling. First, an extensive review is presented on the state-of-the-art of measuring compressor degradation and on the impact of roughness on loss and deviation in a compressor cascade. The performance of a baseline, three-stage compressor, which has hydrodynamically smooth blades, is predicted. Using this baseline geometry, the influence of roughness in the front, middle and rear stages is calculated using empirical data for the enhanced losses and increased deviation, with a stage stacking technique. Influence coefficients that relate percentage changes in one parameter to percentage changes in other parameters are calculated. This analysis predicts that the most sensitive parameter for predicting fouling in the front stages is the percentage change in mass flow and the most sensitive parameter for predicting fouling in the rear stages is the efficiency. / Lieutenant, United States Coast Guard

Membrane filtrations are widely used in process industries but are almost always limited by fouling, a highly studied and significant problem. This is defined as unwanted material deposited on a membrane surface or within its pores, which can significantly impair performance and/or reduce operating life. The strategies to mitigate fouling include cleaning in place, modified membranes, and optimisation of operating conditions. In order to correctly select or target improvements to any such measures a detailed mechanistic understanding of the fouling process is important, which requires more than just performance data from unit operations. One key mechanism is that of cake fouling, which describes the build-up of particle layers on the surface of the membrane. Its growth and physical properties are difficult to assess. In this project the technique of fluid dynamic gauging (FDG) has been explored as a means to study cake fouling. This simple, yet robust method allows for estimation of thickness and strength of cake fouling at high concentrations and opacity, without any prerequisite knowledge of feed properties. Studies described herein focused on microfiltrations through cellulosic membranes. FDG was used to track cake growth during filtrations of polydisperse yeast suspensions (which contained large agglomerates), demonstrating its capability to work with non-ideal, food-like substances. Later studies used more predictable suspensions of hollow glass spheres, which were used to assess various filtration models. The most effective was found to be an interpretation of the critical flux laws, which were used to successfully identify pore fouling during filtrations of Kraft lignin, an observation supported by FDG measurements. Another novel achievement of this project was the development of an automated apparatus for performing FDG in cross-flow membrane filtration. This allowed for much faster acquisition of results, and demonstrated the potential for its development into an autonomous system capable of making thickness measurements on the fly during filtrations. The most reliable protocol for determining cake growth rates was by repeated filtrations in which destructive thickness testing was performed at selected time points. This was because continuous or even repeated thickness measurements during a single filtration were found to cause too much disturbance to the fouling layer. Computational fluid dynamics was used to simulate shear stress profiles on the fouling layer, while also providing a more accurate means to calibrate the automated apparatus. Erosion caused by FDG readings, when viewed under a microscope, was found to conform to the shear stress profiles predicted by simulations.

Deposition of amorphous silica (SiO2) and calcium oxalate (CaOx) on the calandria tubes of juice evaporators cause serious processing problems in Australian cane sugar mills. The removal of these deposits by mechanical and chemical means is a timeconsuming and costly experience. The cost of downtime and chemical cleaning can be several million dollars per year for the Australian sugar industry. The interactions between CaOx and SiO2 have not been investigated previously because conventional studies only address fouling by individual components. The present work evaluates their interactions using two experimental approaches: batch tests for assessing kinetic and thermodynamic behaviour, and fouling-loop experiments for examining composite fouling behaviour under different operating conditions. The above two approaches were employed both in the absence and in the presence of sugar to elucidate the effect of sugar on composite fouling mechanisms and to determine the controlling species responsible for composite fouling. The composite fouling experiments were performed in a novel closed-loop circulation system simulating the effect of feed composition of successive stages of evaporation cycle in a single run. In addition, the fouling-loop system was operated in a constant composition mode to study the effects of thermal hydraulic conditions on composite fouling. The combined information obtained from both the batch and fouling-loop tests in this study offer a unique insight into the mechanisms of composite fouling of CaOx and SiO2. Some of the highlights of the obtained results are as follows: ??? Identification of a complex interactive process in calcium oxalate monohydrate ??? silica (COM-SiO2) systems by investigation of the kinetics and thermodynamics of COM-SiO2 coprecipitation in water and sugar solutions, and an understanding of the mechanisms of these interactions; ??? Development of a novel fouling-loop system, which is simple, efficient and cost effective for the study of the effect of juice composition on scale formation in various stages of juice evaporation; ??? Elucidation of composite fouling mechanisms, e.g., a feed composition dependent fouling mechanism is proposed; ??? Isolation and verification of the existence of certain species in composite deposits, which is known to be thermodynamically unstable. In other words, it is established that calcium oxalate trihydrate is stable under certain conditions; ??? Evaluation of the role of thermal hydraulic operating parameters in determining the characteristics of subcooled flow boiling heat transfer and in determining the strength of the composite deposit; ??? Development and validation of an empirical model to predict the subcooled flow boiling heat transfer coefficients in water and sugar solutions; ??? Development of an analytical model incorporating the effects of operating parameters for COM and SiO2 composite fouling in sugar solutions. This model predicted the experimental data better than available models. Results of this work are significant, not only because they have made a valuable contribution to advance the fundamental understanding of heat exchanger fouling, but also because they may play a key role in the development of scale control and removal strategies to minimize the composite fouling in Australian sugar mill evaporators. For example it was found that, in order to effectively minimize the rate of composite fouling and reduce the scale tenacity, it would be necessary to control thermal hydraulic operating conditions, especially the fluid velocity, and to adjust the initial CaOx/SiO2 supersaturation ratio to the optimum value. To achieve the optimal CaOx/SiO2 ratio, certain device can be developed to sequentially measure oxalic acid and SiO2 concentrations in juice so that the correct proportions of chemicals can be added. Model simulations of the composite fouling rate may also effectively and economically provide comparative and relevant information essential for process optimisation and evaporator design

Epiphytic bacterial communities on the surfaces of marine algae are poorly characterised. Most information available on marine bacterial epiphytes is derived from culture-based studies. With the rapid development of molecular community analysis technologies, it is now possible to obtain a more comprehensive picture of marine microbial populations on living surfaces. The intertidal macroalga Ulva australis, belongs to the cosmopolitan group of green marine algae (Ulvales) known to require the presence of bacteria for normal growth and has been suggested to employ specific bacteria for the defence against fouling by micro- and macro-organisms. This thesis has examined the composition and structure of the surface associated bacterial community on Ulva australis using 16S rRNA gene clone library, denaturing gradient gel electrophoresis (DGGE), and catalysed reporter deposition ??? fluorescence in situ hybridisation (CARD-FISH) analysis. The 16S rRNA gene clone library revealed that the five main bacterial groups present in the surface associated community were Bacteriodetes, Planctomycetes, Alpha-, Gamma-, and Delta-Proteobacteria. Twenty-two sequence phylotypes were identified, suggesting that the epiphytic community was of relatively low diversity. A clone similar to an algal morphogenesis inducing Cytophaga strain was identified, indicating that U. australis harbours bacteria important for thallus structural maintenance. DGGE analysis showed that while the bacterial community varied over spatial and temporal (seasons) scales it also included a stable subpopulation consistently associated with the seaweed surface. Sequencing of selected DGGE bands suggested that members of the Alphaproteobacteria and the Bacteriodetes belonged to the stable subpopulation. Using CARD-FISH with different phylogenetic probes demonstrated that Alphaproteobacteria (~ 70%) and Cytophaga-Flavobacteria (~13%) constituted the majority of bacterial cells on the surface of U. australis. A comparison of the results provided by the molecular community analysis methods, employed in this thesis, and those of culturing of epiphytic bacteria from U. australis revealed that each approach provides different patterns of phylogeny and extent of diversity. For example, the culture collection and the clone library detected a relatively high amount of Gammaproteobacteria, however, DGGE and CARD-FISH did not. Also, low species diversity clone sequences and isolates of Alphaproteobacteria contrasted with the high numbers detected by the DGGE analysis. In addition to the phylogentic determination of the epiphytic bacterial community, CARDFISH was also used to assess the organisation and distribution of bacterial cells across different zonal regions on seaweed surface. It was found that approximately 40% of bacterial cells clustered in aggregates, or microcolonies. These aggregations were considered to be heterogeneous in composition and were mainly comprised of multiply species. The occurrence of more non-viable solitary single rather than aggregated cells suggests that aggregates might offer greater protection to bacterial cells from the harsh conditions in the intertidal zone. More broadly, CARD-FISH was found to be a useful tool for studying microcolonies and was also successfully applied to detect slow growing soil microcolonies cultivated using a novel soil substrate membrane system culturing technique without the need to perform an rRNA enrichment incubation. The findings in this thesis, as described from the application of a number of molecular community analysis techniques such as clone library, DGGE and CARD-FISH, have improved our understanding of the diversity and structure of the epiphytic bacterial community associated with U. australis. Morevover, the information provided may to design future studies in the ecology of bacteria-seaweed interactions, including symbiotic interactions, and aid in marine biotechnology applications such as identifying bacteria which produce bioactive secondary metabolites.

A combination of surface analytical techniques, colloid probe Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) was used to optimise the grafting density of covalently attached 5, 20 and 40 kDa methoxy-terminated PEO layers (under marginal solvation (cloud point) conditions for the PEO molecules). The combination of these techniques allowed us to relate the PEO layer density and molecular conformations to the range, magnitude and types of forces generated by coatings of various grafting densities. The key optimisation parameter was the grafting time with the concentration of PEO in solution having a weaker effect. Oxidation of the substrate occurred, but did not significantly limit the surface density of the functional groups used to chemically attach the PEO molecules. Interactions between the substrate and silica were electrostatic in origin and did not contribute to the interaction between silica and the PEO surfaces due to salt screening effects Surfaces with dense, highly stretched PEO layers (brushes) generated purely repulsive forces at all separation distances, arising from compression by the silica spherical probe used. The force profiles for lower density surfaces comprised long-ranged attractive and short-ranged repulsive forces. The attractive forces were most likely due to attractive bridging interactions between the PEO chains and the SiO2 surface. For low grafting densities, i.e. inter-chain grafting distances, s &gt ??RF, the PEO layers were not strongly stretched and free to adsorb onto the opposing silica surface. XPS analysis demonstrated that HSA and Fibrinogen adsorbed onto low density 20 kDa PEO coatings (s &gt ??RF), most likely via diffusion through the PEO layer. No protein adsorption was found (detection limit &gt 10 ng/cm2) on high density, ???strongly stretched brush??? coatings (s &lt ?? RF). Analysis of data from the more sensitive Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) techniques indicated that low amounts of adsorbed HSA, lactoferrin, lysozyme, and IgG were present on high density 20 and 40 kDa surfaces; the most likely explanation being attractive interactions between the proteins and the PEO layers during the protein adsorption experiments. ToF-SIMS data obtained for the strongly stretched (s &lt ?? RF) 5 kDa PEO surfaces suggested that no protein was adsorbed, in line with the XPS data for the same surfaces.

The dark-green pigmented marine bacterium Pseudoalteromonas tunicata produces several extracellular compounds against a range of common fouling organisms including bacteria, fungi, protozoa, diatoms, invertebrate larvae and algal spores. The regulator WmpR, which has N-terminal similarity to ToxR from Vibrio cholerae and CadC from Escherichia coli, controls all of the pigment and antifouling phenotypes. These compounds appear at the onset of stationary phase. The role of WmpR as a stationary phase regulator in P. tunicata was investigated in this thesis. Starvation and stress studies demonstrated that WmpR does not appear to control genes necessary for survival during carbon, phosphate or nitrogen starvation and UV/hydrogen peroxide stress. Intriguingly, phosphate starvation caused pigmentation of wmpR mutant (D2W2) logarithmic phase cells, suggesting a second regulation of the pigments (and thus antifouling compounds) that could be mediated by the PhoR/B twocomponent regulatory system. Proteomic analysis using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) found that 11 proteins were differentially regulated by WmpR, and the identities of some of these proteins suggested a role for WmpR as a general stationary phase regulator rather than a specific starvation or stress regulator. Gene expression studies using RNA-arbitrarily primed PCR introduced a new role for WmpR as a regulator of iron acquisition; a TonB-dependant outer membrane receptor gene and a non-ribosomal peptide synthetase (NRPS) gene were up-regulated in the stationary phase Wt strain compared to the D2W2 strain. An assay for iron-binding activity supported the proposal that the NRPS may be making a siderophore. Further studies demonstrated that WmpR is required for survival under long-term low-iron conditions and that the pigments and antifouling genes are down-regulated during low-iron, while biofilm formation is up-regulated. WmpR also appears to constitutively regulate the production of iron-binding compounds, a novel regulation of iron acquisition that has not been seen in other organisms studied so far. A model is proposed that describes WmpR as responding to environmental signals, including iron, and co-ordinating the expression of a complex regulon including a number of genes involved in iron acquisition, general stationary phase physiology and bioactive secondary metabolite production.

Thesis (M.S.)--University of Akron, 2004. / Title from Web page (viewed on Dec. 17, 2007). "December, 2004." Includes bibliographical references (p. 118-124).