Abstract: The worldwide consumption of pharmaceuticals and personal care products for healthcare purposes has resulted in the occurrence of organic micropollutants (OMPs) in freshwater and wastewater resources. These pollutants are not entirely removed by conventional water and wastewater treatment plants, leading to potential human and animal health problems. Membranes are a promising technology capable of solving this problem. This study evaluated the ability of high-pressure driven membranes such as nanofiltration (NF) and reverse osmosis (RO) to remove OMPs. A total of 13 compounds were selected so that a broad range of molecular weights and octanol-water partition coefficients (log Kow) could be studied. Three commercial thin-film-composite polyamide membranes (NF1, NF6, and RO4) were tested. Filtration experiments were conducted using a cross-flow membrane system at pH 6 8 and 10. The membranes were characterized by atomic force microscopy and scanning electron microscopy that allowed a more profound understanding of the membrane surface structures. Experimental results showed that the permeate flux of NF6 is dependent on the pH of the feed solution. An increase in the feed pH from 6 to 10 resulted in an increase on the permeate flux from 14.5 to 24 L m-2 h-1 bar-1, which caused a drop in the rejection of some OMPs by NF6. Nevertheless, for most OMPs, as pH increased to 10, rejection increased for NF1 and RO4 due to electrostatic repulsion between the negatively charged membrane surface and the ionized OMPs. It was observed that ionic hydrophobic compounds could be highly rejected (> 95%) by NF1 and RO4. The study indicated that the rejection of non-ionic hydrophilic and hydrophobic OMPs were rejected effectively by RO4 (> 90%), and the rejection was mostly dominated by size exclusion and hydrophobic interactions between the membrane and the OMPs. Furthermore, the study revealed that the properties of the compounds, the intrinsic properties of the membrane, and the operating conditions have a significant influence on the rejection of OMPs.

A thesis submitted for the degree of Doctor of Philosophy to The Department of Chemical and Metallurgical Engineering, Faculty of Engineering, University of the Witwatersrand, Johannesburg, 2016 / Separation of materials is crucial to the operation of the majority of chemical processes, not only for the purification of final products but also for the processing of feed-stocks prior to chemical reaction. The most commonplace method of materials separation is distillation which, unfortunately, is often an energy-intensive process and contributes significantly to mankind’s energy consumption and carbon dioxide emissions. Alternative approaches to separation are therefore a crucial element of the ongoing pursuit for sustainability in chemical industries. There are two principal ways of going about this. The first is to replace distillation units with alternative unit operations that can achieve the same separation with less energy expenditure. The second approach is overall flowsheet revision, fundamentally changing a separation cycle to minimize its energy requirements. The greatest improvements to energy efficiency will be achieved by applying both approaches in tandem. However, each must be developed separately to make that possible. This thesis lays the groundwork for radical revision of major separation operations by showcasing a new overall flowsheet for bioethanol separation that promises tremendous improvements in separation efficiency, reducing the energy usage involved in ethanol purification by as much as 40% in some scenarios. It also develops a novel method for the design of multi-membrane permeation units, showing how area ratio can be manipulated to fundamentally alter separation performance from such units, resulting in superior separation performance to conventional units, achieving higher recoveries than conventional setups. With membranes being an increasingly popular separation method, the potential for superior performance from multi-membrane units promises improvements in separation efficiency.

The present study addresses a systematic evaluation of the effect of crosslinking via terminal maleimide units on the gas transport properties through a dense polymer film of amorphous Poly(Arylene Ether Ketones) or PEK. The methodology for the preparation of crosslinked maleimide terminated PEK (or MIPEK) films from several blend ratios of different molecular weights of MIPEK is discussed in detail. The primary focus of this work has been to investigate the influence of different degrees of crosslinking on gas permeabilities and selectivities, with an objective of producing a highly selective membrane. It has been demonstrated that crosslinking markedly decreases the permeation of methane, without changing the values for molecules such as helium. / Master of Science

Thesis (M. Tech. Chemistry, Dept. of Chemistry, Faculty of Applied and Computer Sciences)--Vaal University of Technology, 2010. / Membrane separation processes offer a promising alternative to energy-intensive separation processes such as distillation and solvent extraction. NF and RO are among the most investigated membrane processes with a potential use in the chemical industry. Carbon-carbon coupling reactions feature in the top ten most used reactions in the chemical industry. These reactions often use homogeneous palladium, nickel and other precious catalysts which are often difficult to separate from reaction products. This leads to potential product contamination and loss of active catalysts. This not only poses a threat to the environment but is also costly to the chemical industry. The purpose of this study was to investigate the efficiency of the recovery of the metal catalysts by selected membrane processes. Four commercial polymeric NF and RO membranes (NF90, NF270, BW30 and XLE) were selected for the study. Palladium catalysts commonly used in Heck and Suzuki coupling reactions were selected. These are Pd(OAc)2, Pd(OAc)2(PPh3)2, PdCl2 and Pd(PPh3)2Cl2. A range of organic solvents were also selected for the study. All the membranes were characterized for pure water permeability, pure solvent permeability, swelling, surface morphology and chemical structure. The chemical and catalytic properties of the catalysts were determined. Catalytic activity was investigated by performing coupling reactions. These catalysts generally performed well in the Heck coupling reaction with sufficient yields realized. The catalysts showed poor activities in the Suzuki and Sonogashira coupling reactions. These coupling reaction systems were affected by rapid palladium black formation. vi Catalyst retention studies showed the influence of membrane-solute interactions such as steric hindrance and size exclusion. The larger catalyst, Pd(OAc)2(PPh3)2 was rejected better by all the membranes irrespective of the solvent used. The smaller catalyst, Pd(OAc)2 was the most poorly rejected catalyst. This catalyst showed signs of instability in the selected solvents. An interesting finding from this study is that of higher rejections in water compared to other solvents for a particular catalyst. In this regard, the influence of solventsolute effects was evident. Generally, higher rejections were observed in solvents with higher polarity. This has been explained by the concept of solvation. It has been shown that solvents with different polarity solvate solutes differently, therefore leading to a different effective solute diameter in each solvent. Catalyst separation using NF90 membrane was attempted for the Heck coupling reaction system. The reaction-separation procedure was repeated for two filtration cycles with rapid activity decline evident. This was regarded as very poor showing of the catalyst separation efficiency of the membrane. Other authors in similar studies using SRNF membranes have reported reaction-separation processes of up to seven cycles. This observation shows the inferiority of polymeric membranes in organic solvent applications such as catalyst separation.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The hydrodynamics of a hollow fibre membrane module for the ultrafiltration of potable water were investigated. The purpose was to use a hydrodynamic model to predict the permeate flux for modules of various dimensions. Various models were considered, but most of them could not account for important effects such as macroscopic radial gradients and wet fibre expansion, found in hollow-fibre membrane modules. The Porous Medium Model was found to be a suitable model and it was used together with a finite element software package, Fastflo, to solve for the pressure distributions inside the membrane modules and predict permeate flux. The permeability of the membranes was obtained using a combination of numerical and experimental procedures and was found to be 2.3 x 10-13m. A cost analysis was performed to find the most economical module dimensions (outer diameter and length) for any required product flow rate. It was assumed that the cost of the fibres and module housing comprised the capital cost, while the operating cost consisted of the pumping energy. A capital recovery factor of 0.3 was used to convert capital costs to a yearly cost. It was found that the optimum module dimensions are an outer diameter of between 90mm and 160mm and a length of 0.6m. Finally the pressure distributions on the lumen and shell sides during both cross-flow filtration and backwash were examined. Shade plots proved useful for identifying possible areas of stagnant flow, as well as indicating where backwash is the most effective. / AFRIKAANSE OPSOMMING: Die hidrodinamika binne-in 'n holvesel membraanmodule vir die ultrafiltrasie van drinkwater is ondersoek. Die doel was om 'n hidrodinamiese model te gebruik om die permeaatvloed vir modules van verskeie dimensies te voorspel. Verskillende modelle is oorweeg, maar die meeste kon nie belangrike faktore soos makroskopiese radiale drukqradiente of nat veselverlenging in ag neem nie. Die Poreuse Medium Model was die mees geskikte model en is gebruik saam met Fastf/o, 'n sagteware pakket wat gegrond is op die eindige element metode, om vergelykings vir die drukverspreiding binne-in die module op te los en permeaatvloed te voorspel. Die permeabiliteit van die membrane is verkry met behulp van numeriese en eksperimentele prosedures en 'n waarde van 2.3 x 10-13 m is bepaal. Hierna is 'n koste-analise uitgevoer om die mees ekonomiese module afmetings (Iengte en buitedeursnit) te bepaal vir 'n gegewe produk vloeitempo. Daar is aanvaar dat kapitaalkoste bestaan uit die koste van vesels en module-omhulsel, terwyl bedryfskoste bereken is deur die hoeveelheid energie benodig om die pomp aan te dryf. 'n Kapitaalherwinningsfaktor van 0.3 is gebruik om kapitaalkoste om te skakel na 'n jaarlikse koste. Die optimum module afmetings is 'n lengte van 0.6m en 'n buite-deursnit van tussen 90mm en 160mm. Laastens is die drukverspreidings tydens beide kruisvloeifiltrasie en die terugspoelproses ondersoek. Areas van stagnante vloei kan deur middel van skadu-grafieke geYdentifiseer word, terwyl dit ook moontlik is om die terugspoelproses te optimeer.

Thesis (MScEng (Process Engineering))--Stellenbosch University, 2008. / Nitriles are precursors of important amides and organic acids (e.g. acrylamide, nicotinamide, mandelic acid and acrylic acid) which are used, inter alia, as food additives, in plasticisers, detergents, make-up, medicine and as chemical intermediates in the production of various important polymers. Traditionally, chemical processes are used to convert nitriles to amides and organic acids but these processes are non-specific causing various by-products to form. Chemical processes are also environmentally unfriendly and require harsh conditions. Nitrile conversions through an enzymatic route, on the other hand, have the distinct advantages of excellent chemo-, regio- and stereo selectivities, mild process conditions and reduced downstream processing costs. The enzymatic process is mediated via an initial nitrilase catalysed conversion to amide, followed by an amidase catalysed conversion to acid. This research focused on the latter part of the enzymatic transformation of nitriles, which is the amidase catalysed biotransformation of an amide to an acid, specifically with respect to the development of a membrane immobilised amidase continuous process which has the major advantage of enzyme retention coupled with product separation. The research was conducted in three parts namely the characterisation of the free amidase, the development of the experimental bioreactor system and the quantification of the membrane immobilised amidase process.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The aim of this study was to modify the surface of polyethersulfone (PES) ultrafiltration (UF) membranes to produce a more hydrophilic membrane by cross-linking poly(vinyl alcohol) (PVA) with sodium tetraborate (Na2B4O7.10H2O) (SB) on the surface. Key preparation factors were identified as PVA molecular weight, concentrations of the PVA and SB, cross-linking reaction time, number of coatings and the mode of coating. The effect of these factors on the membrane performance (salt retention and permeate flux) is discussed. These PVA-SB membranes typically had 11.46% retention and 413.30 L/m2.h flux for a feed containing 2000 ppm NaCl (0.45 MPa, 20°C, 45 – 50 L/h). The coating was shown to be uniform and stable by Fourier transform infrared spectroscopy (FT-IR) analyses. Coating significantly increased hydrophilicity and a maximum flux increase of 500 L/m2.h was reached. Measurements showed a reduced water contact angle and this confirmed the obvious enhancement of surface hydrophilicity. As a control, the role of the PVA base layer without cross-linking and the effects of its drying and heating on the water permeability of the PES-UF membrane were also studied, in order to ascertain maximum treatment conditions. Retention and permeate flux were determined (feed solution: 2000 ppm NaCl, applied pressure 0.45 MPa, 25°C, 45 – 50 L/h). It was found that the heating had the largest effect on the reduction of water permeability and therefore 50°C was the limit for treatment of this specific PES-UF membrane. Thin-film composite (TFC) membranes were prepared by an interfacial polymerization (IP) reaction between a polyfunctional amine and tri- or di-functional carboxylic chloride and then evaluated for their reverse osmosis (RO) performance. The salt retention of the PVA-SB membranes was improved when covering the cross-linked PVA gel sub-layer with a polyamide (PA) layer. However, the permeate flux decreased to below 30 L/m2.h (2000 ppm NaCl, 1 – 2 MPa, 20°C, 45 – 50 L/h). Two TFC membranes made from trimesoyl chloride (TMC) with m-phenylenediamine (MPD) or 2,6-diaminopyridine (DAP) exhibited retentions of 96.71% to 89.65% and fluxes of 10.93 to 27.91 L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (2 MPa, 25°C, 45 – 50 L/h). Two TFC membranes made from a n ew 2,5-furanoyl chloride (FC) with MPD or DAP exhibited retentions of 34.22% to 58.54% and fluxes of 49.21 to 25.80 L/m2.h, depending on the type of diamine used, when tested with a 2000 ppm NaCl solution (1 MPa, 25°C, 45 – 50 L/h). Novel PVA-SB-DAP-FC membranes made from the DAP with FC had the highest hydrophilicity value and exhibited >58.54% NaCl retention and 25.80 L/m2.h flux, and 75.08% MgSO4 retention and 34.75 L/m2.h flux, when tested with (2000 ppm feed, 1 MPa, 25°C, 45 – 50 L/h). The effect of the chemical structures of the different amines and carboxylic chlorides used on the RO performances of the TFC membranes prepared by two amines reacting with TMC or FC, on the surfaces of the modified asymmetric PES-UF membranes, was investigated. FT-IR and water contact angle determination were used to characterize the chemical structure, morphology and hydrophilicity of the PA layers of the composite membranes. The response surface methodology (RSM) was used to optimize the preparation conditions that had the largest effects on the RO performance of the PVA-SB-DAP-FC membranes. Good membrane performance could be realized particularly by manipulating three variables: DAP concentration, FC concentration and polymerization time (PT). The regression equation between the preparation variables and the performance of the composite membranes was established. Main effects, quadratic effects and interactions of these variables on the composite membrane performance were investigated. The membranes were characterized in terms of pure water permeation (PWP) rate, molecular weight cut off (MWCO), solute separation and flux. Mean pore size (μp) and standard deviation (σp) of the membranes were determined using solute transport data. The results revealed that PVA-SB membranes have almost the same pure water permeation that PES-UF membranes have. The MWCO of the PES-UF membranes decreased from 19,000 to 13,000 Daltons when the membrane was coated with PVA. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie is die modifikasie van die oppervlakte van poliëtersulfoon ultrafiltrasie (PES-UF) membrane om meer hidrofiliese membrane te berei deur die kruisbinding van polivinielalkohol (PVA) met natriumtetraboraat ((Na2B4O7.10H2O) (NaB) op die membraanoppervlakte. Sleutelfaktore in die bereidingsproses is geïdentifiseer, naamlik: PVA molekulêre massa, PVA en NaB konsentrasies, kruisbindingsreaksietyd, die aantal bestrykingslae, en die manier waarop die bestrykingslae aangewend is. Die invloed van hierdie faktore op die membraanontsouting en vloed is ondersoek, en word hier bespreek. Hierdie PVA-NaB membrane het die volgende tipiese resultate getoon: 11.46% ontsouting en 413.30 L/m2.h vloed (Kondisies: 2000 dpm NaCl oplossing, 0.45 MPa toegepaste druk, 20 °C, vloeitempo 45–50 L/h). Die deklaag was uniform en stabiel, soos bepaal d.m.v. FTIR. Die aanwesigheid van die deklaag het die hidrofilisiteit verhoog en 'n maksimum vloed van 500 L/m2.h is behaal. Die waterkontakhoek is ook gemeet; 'n laer waarde het 'n verbetering in die hidrofilisiteit van die oppervlakte bevestig. Die rol van die PVA basislaag, sonder kruisbinding (kontrole), en die effek van uitdroging en verhitting hiervan, is ook bestudeer, om sodoende optimale behandelingskondisies te bepaal. Membraanontsouting en vloed is bepaal (Kondisies: 2000 dpm NaCl oplossing, 0.45 MPa toegepaste druk, 25 °C, vloeitempo 45–50 L/h). Verhitting het die grootste effek gehad op die afname in vloed. Daar is bevind dat 'n maksimum temperatuur van 50°C geskik is vir die behandeling van hierdie spesifieke PES-UF membraan. Dunfilmsaamgestelde (DFS) membrane is berei d.m.v. 'n tussenvlakpolimerisasiereaksie tussen 'n polifunksionele amien en 'n di- of tri-funksionele karbonielchloried, en daarna is die tru-osmose (TO) gedrag bepaal. Die ontsouting van die PVA-NaB membrane was hoër nadat die kruisgebinde PVA jel sub-laag met 'n poliamied (PA) laag bedek is. Die vloed het egter afgeneem, tot onder 30 L/m2.h (Kondisies: 2000 dpm NaCl oplossing, 1–2 MPa toegepaste druk, 20 °C, vloeitempo 45–50 L/h). Twee DFS membrane is berei met trimesoïelchloried (TMC), naamlik met m-fenieldiamien (MFD) of 2,6-diaminopiridien (DAP). Afhangend van die diamien wat gebruik is, is die volgende ontsoutingsresultate en vloede verkry: 96.71% tot 89.65% en 10.93 to 27.91 L/m2.h (Kondisies: 2 000 dpm NaCl oplossing, 2 MPa toegepaste druk, 25 °C, v loeitempo 45–50 L/h). Twee DFS membrane is ook berei met 'n nuwe verbinding, 2,5-furanoïelchloride (FC), en MFD of DAP. Afhangend van die diamien wat gebruik is is die volgende ontsoutingsresultate en vloede behaal: 34.22% tot 58.54% en 49.21 tot 25.80 L/m2.h (Kondisies: 2000 dpm NaCl oplossing, 1 MPa toegepaste druk, 25 °C, vloeitempo 45–50 L/h). Die PVA-NaB-DAP-FC membrane het die hoogste hidrofilisiteit getoon: 58.54% NaCl ontsouting en 25.80 L/m2.h vloed, en 75.08% MgSO4 ontsouting en 34.75 L/m2.h vloed (2000 ppm NaCl oplossing, 1 MPa toegepaste druk, 25 °C, vloeitempo 5–50 L/h). Die invloed van die chemiese struktuur van die verskillende diamiene en karboksielsuurchloriedes wat gebruik is in die bereiding van die DFC membrane op die oppervlakte van die gewysigde PES-UF membrane is in terme van TO ondersoek. FTIR en kontakhoekbepalings is gebruik om die chemiese struktuur, morfologie en hidrofilisiteit van die PA lae van die saamgestelde membrane te bepaal. Die eksperimentele oppervlakte ontwerp metode is gebruik om die bereidingskondisies vir die TO aanwending van die PVA-NaB-DAP-FC membrane te optimiseer. Goeie resultate is verkry deur die volgende veranderlikes te manipuleer: DAP en FC konsentrasies en die tydsduur van die polimerisasie. 'n Regressie-vergelyking tussen die bereidingsverandelikes en die funksionering van die saamgestelde membrane is bepaal. Die volgende is ook ondersoek vir hul effek op die funksionering van die saamgestelde membrane: hoof-effekte, vierkantseffekte, en interaksie tussen veranderlikes. Die eienskappe van die membrane wat bepaal is, is: deurlatingstempo van suiwer water (DSW), molekulêre massa-afsnypunt (MMAP), skeiding van opgeloste sout en vloed. Deurlating van opgeloste sout data is gebruik om gemiddelde poriegrootte (μp) en standaard afwyking (σp) van die membrane te bepaal. Resultate het getoon dat die PVA-NaB membrane amper dieselfde DSW gehad het as die PES-UF membrane. Die MMAP van die PES-UF membrane het afgeneem van 19,000 tot 13,000 Daltons na behandeling met PVA.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 1997. / This study focuses on the preparation and characterization of palladium-silver-nickel composite membranes. Electroless plating was used to deposit thin metal films on aluminazirconia membrane supports. Palladium conversion, in the electroless palladium plating process, was optimized with the aim of minimizing expensive palladium losses. The effect of deposition order on alloy composition and heat treatment on structural characteristics of the composite membrane was investigated. The inorganic support membranes were thoroughly cleaned and pretreated prior to plating to catalyze the surface. Factorial designs were used to obtain the maximum palladium conversion. Tetra amine palladium nitrate gave better solution stability and resulted in higher conversions than tetra amine palladium chloride. Buffer pH values of 9 to 11 caused little variation in palladium conversion. Moving outside this range resulted in a sharp decline in palladium conversion. At a pH of 9 to 11 the stabilizer is in the correct ionic form (EDTA3 and EDTA4,) to best stabilize the palladium ions, and hydrazine acts as a proper reducing agent. Significant interactions existed between the EDTA concentration (stabilizer) and hydrazine concentration (reducing agent) and between EDTA and temperature. The EDTA concentration was the most sensitive variable. A 27.5 g 10% tetra amine palladium nitrate solution per liter plating solution was used. Conversions exceeding 80% were obtained after three hours plating with 20 ml plating solution at the following conditions: temperatures from 71 to 77 DC, 40-60% molar excess hydrazine, EDTA:Pd-salt molar ratios between 30:1 and 40: 1 and buffer pH = 11. Silver plating rates for two hours plating of up to 2 mg/cm2 were obtained using a dilute silver nitrate solution with hydrazine as reducing agent. Electroless nickel plating was performed in a low temperature bath (40 DC) with nickel sulphate as source of metal ions and sodium hypophosphite as reducing agent. Metal films were fully characterized before and after heat treatment for 5 hours in a hydrogen atmosphere at 650 dc. Scanning electron microscopy (SEM) was used to analyze the surface structure. X-ray diffraction (XRD) patterns were taken to examine alloying and detect changes in the crystal structure .after heating. Energy dispersive X-ray maps (EDS) were used to visualize the diffusion process and particle induced X-ray emission (PIXE) was used to construct concentration profiles across the thickness of the metal films. Palladium deposits were dense, but columnlike, with a purity of 99.75%. Silver deposits were non-homogeneous, in other words it did not cover the entire substrate. The purity of the silver films was 99.5%. The nickel films were about 97% pure, very dense and defect free. When silver was deposited on palladium, the alloy penetrated more than 3 microns into the support and the palladium and silver concentrations varied across the thickness of the film after heating. By depositing palladium on silver, there was very little penetration into the support membrane pores (about 1 micron) and the palladium to silver ratio remained constant across the thickness of the film after heating. Silver-palladium-nickel alloy films call be prepared by first depositing silver, then palladium and finally nickel. During heat treatment, a counter diffusion process took place and the smaller nickel atoms penetrated into pores and defects that might be present in the palladium-silver solid solution. By adding more than 3% nickel, dense defect free films can be prepared, which is much thinner than conventional palladium-silver films. This method makes it possible to reduce the film thickness of dense, non-porous films to less than 5 microns, reducing fabrication cost and increasing the hydrogen flux through the film. Dense, non-porous palladium-silver films are usually in the range of 10-15 microns.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Membrane fouling is universally considered to be one of the most critical problems in the wider application of membranes in filtration separation. Fouling is caused by the deposition of particles not only on the surface of the membrane, but also inside the membrane pores, which reduces permeate flux and leads to a reduction of the efficiency and the longevity of the membrane. The backpulsing cleaning method can be used to remove deposited foulants from the surface of the membrane, without having to shut down the plant. Ultrasonic time-domain reflectometry (UTDR) is a nondestructive technique, used to detect and measure the growth of fouling layer on the membrane surface during microfiltration and ultrafiltration processes. In this study flat-sheet microfiltration (MF) and ultrafiltration (UF) membranes were fouled during a cross-flow filtration processes using dextrin, yeast or alumina (feed pressure 100 kPa and feed flow rate 0.45 liter/minute), in a flat cell. Infrasound frequency backpulsing, in the permeate space, was used to clean the membranes. Backpulsing was carried out using the permeate water or soap solutions. The peak pressure amplitude of the pulses used to clean the membranes was 140 kPa, the pulsing was applied at a frequency of 6.7 Hz. The main objectives of this research were: (1) to obtain a fundamental understandimg of how foulants deposit on membrane surfaces and how the foulant deposits can be removed using the backpulsing cleaning technique during MF and UF, (2) to use the ultrasonic measurement technique for monitoring the growth and removal of the fouling layer on the membrane surface and (3) Use scanning electron microscopy (SEM) as a direct measurement technique to analyze the structure the foulant deposits on membrane surfaces before and after cleaning. Results showed that a flux value of between 55% and 98% of the clean water flux value can be achieved by backpulsing cleaning. UTDR was successfully applied to monitor membrane cleaning and provide information about the growth and removal of fouling layers on the membrane surface. / AFRIKAANSE OPSOMMING: Membraanaanvuiling is wêreldwyd bekend as een van die mees kritieke probleme wat die wyer aanwending van membrane vir skeidingsprosesse benadeel. Aanvuiling word veroorsaak deur die deponering van partikels, nie net op die oppervlak van die membraan nie, maar ook binne-in die membraanporieë, wat die volgende tot gevolg het: 'n afname in vloed deur die membraan, 'n afname in die effektiwiteit van die membraan, en 'n korter membraanleeftyd. Die teenpulsskoonmaakmetode kan gebruik word om die aanvuilingslaag vanaf die membranoppervlakte te verwyder sonder dat dit nodig is om die membraantoetsapparaat af te skakel. Ultrasoniese-tydsgebied-weerkaatsing (UTW) is 'n nie-vernietigende tegniek wat gebruik kan word om die groei van 'n aanvuilingslaag op 'n membraanoppervlakte tydens mikrofiltrasie (MF) of ultrafiltrasie (UF) te identifiseer en te meet. In hierdie studie is plat-vel MF en UF membrane bevuil gedurende 'n kruisvloeifiltrasieproses deur gebruik to maak van dekstraan, gis of alumina, in 'n plat sel. Infraklank-frekwensieteenpols, in die permeaatgebied, is gebruik om die membrane skoon te maak. Hiervoor is die proseswater of 'n seepoplossing gebruik. Die maksimum drukamplitude van die pulse wat gebruik is was 140 kPa, en die puls was aangewend teen 'n frekwensie van 6.7 Hz. Die hoofdoelwite van hierdie studie was die volgende: (1) om inligting in te win oor hoe aanvuilingsmateriale op membraanoppervlaktes gedeponeer word tydens MF en UF en hoe hulle verwyder kan word deur gebruik te maak van die teenpulsskoonmaaktegniek; (2) om van die teenpulsskoonmaaktegniek gebruik te maak om die groei van die bevuilingslaag asook die verwydering daarvan op die membraanoppervlakte te monitor; en (3) om van skandeerelektronmikroskopie (SEM) as 'n direkte analitiesetegniekgebruik te maak om die struktuur van die aanvuilingsmateriaal voor en na die die skoonmaakproses te analiseer. Deur gebruik te maak van teenpulsskoonmaak kon die membraanvloed tot tussen 55–98% van die oorspronklike suiwerwatervloed verbeter word. Sodoende is ultrasoniese-tydsgebiedweerkaatsing suksesvol gebruik om die skoonmaak van membrane te monitor asook om inligting in te win i.v.m. die groei en verwydering van die aanvuilingslae op die membraanoppervlaktes.

Thesis (MEng.)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The aim of the thesis was to investigate the use of flow destabilization methods, combined with permeate backflushing (BIF) or on their own, on flux recovery and maintenance in capillary UF membrane systems under cross-flow (XF) and dead-end (DE) operating conditions. Various hydraulic and mechanical methods have been used to remove the accumulated cake layer and improve steady state process flux. Permeate backflushing (B/F) is the most widely used but the drawbacks are loss of product and extensive down-time. In a pilot plant study for ultrafiltration of surface waters containing high NOM, turbidity and cation loads, the use of flow destabilization, or feed flow reversal (FFR) combined with cross-flow B/F was able to improve the normalised flux by 10.7 ± 3.4 %, compared with 3.2 ± 1.6 % improvement for BIF without FFR. When a second B/F included FFR, the flux improvement was 7.0 ± 2.0 % compared with 4.3 ± 2.5 % for a B/F without FFR. The hypothesis was proposed that the flow destabilization caused slight lifting of the oriented cake layer, while the cross-flow B/F was able to sweep the lifted cake out of the lumen. If the flow destabilization may be effected by a simple but effective and low-cost method, and if this flow destabilization may be combined with reverse flow for short durations, the "lift-and-sweep" approach will be the ideal method of maintaining process flux and increasing membrane life. Such a flow destabilization method, now named "reversepressure pulsing" (RIP), was developed. The method involves circulation of feed water in a recycle loop for 2 s to gain momentum, followed by closure of a fast-action valve upstream of the modules. The momentum of the water in the concentrate loop carries it into an air-filled feed accumulator, while concentrate and reverse-flow permeate (which also lifts the fouling layer) are discharged to the atmosphere using the recycle pump for 15 s. When the valve opens again, the air in the accumulator forces the water under pressure through the membrane lumens, causing a pressure pulse and flow perturbations that lift, shift and break up the fouling layer. During 3 such "lift-and-sweep" events, the cake is lifted and the debris is swept out of the lumen. Experimental results for uninterrupted dead-end filtration at a UF pilot plant using RIP only on a severely fouled membrane, indicated that the RIP increased the flux by 18.4 % and decreased the dP by 8.2 % over a 7.2 h period. The method is effective in removing the cake layer intermittently and no long-term flux decline occurred for a period of 555 h since the previous chemical cleaning. / AFRIKAANSE OPSOMMING: Die doel van die tesis was om die gebruik van vloei-destabiliserings metodes, alleen of gekombineer met permeaat-terugwas, op vloed-herwinning en instandhouding in kapillêre UF membraan-stelsels tydens kruisvloei en doodloop bedryf, te ondersoek. Verskeie meganiese en hidrouliese metodes word gebruik in membraan stelsels om die koeklaag op die membraan se oppervlak te verwyder en die gestadigde-toestand vloed te verbeter. Vanhierdie metodes word permeaat-terugwas die meeste gebruik, maar het sy nadele insluitend verlies van produk en produksietyd. In 'n loodsstudie vir die ultrafiltrasie van oppervlakwaters wat hoë beladings NOM, turbiditeit en katione bevat, is die waarneming gemaak dat kruisvloei terugwas met vloeidestabilisering (voerrigting-verandering) die genormaliseerde vloed met 10.7 ± 3.4 % kon verbeter, vergeleke met 'n 3.2 ± l.6 % verbetering sonder voerrigting-verandering. Vir 'n tweede terugwas was die verbetering 7.0 ± 2.0 % vergeleke met 4.3 ± 2.5 % sonder voerrigtingverandering. Die hipotese was voorgestel dat die vloei-destabilisering die geoiënteerde koeklaag van die oppervlak gelig het, en die kruisvloei terugwas die geligde koeklaag uit die lumen kon vee. Indien hierdie vloei-destabilisering bewerk kan word deur 'n eenvoudige maar effektiewe manier, en indien dit gekombineer kan word met terugvloei van produk vir kort tydperke, sal hierdie "lig-en-vee" benadering die ideale metode wees om die membrane se vloed te verbeter en leeftyd te verleng. So 'n vloei-destabiliseringsmetode, nou genoem "terugdruk-pulsering", is ontwikkel. Die metode behels die sirkuiering van voer-water vir 2 s in 'n hersirkulasielus om momentum op te bou, gevolg deur die toemaak van 'n snel-aksie klep stroom-op van die modules. Die water in die konsentraat-lus se momentum dra dit vorentoe tot in In lug-gevulde voer-akkumulator, terwyl konsentraat en terug-vloei permeaat (wat ook tot 'n mate die koeklaag lig) ook na die atmosfeer gewend word vir 15 s deur die hersirkulasiepomp. As die klep weer oopgaan, ontspan die lug in die akkumulator, en forseer die water daarin onder druk deur die membraan-lumens. Die druk-puls en vloei-perturbasies lig, skuif en breek die koeklaag op. Tydens 3 agtereenvolgende "lig-en-vee" aksies word die koeklaag effektief opgebreek en uit die lumen gevee. Eksperimentele uitslae vir ononderbroke doodloop bedryf op uitermate aangevuilde membrane van 'n ultrafiltrasie loodsaanleg toegerus met terugdruk-pulsering, het getoon dat die vloed met 18.4 % verbeter kon word en die dP met 8.2 % verminder kon word in slegs 7.2 h. Die metode breek die koeklaag effektief op, en geen langtermyn vloed-afname is waargeneem vir meer as 555 h sedert die vorige chemiese was-prosedure nie.