Yes / In this work, an artificial neural network (ANN) model based on the experimental data was developed to study the performance of vacuum membrane distillation (VMD) desalination process under different operating parameters such as the feed inlet temperature, the vacuum pressure, the feed flow rate and the feed salt concentration. The proposed model was found to be capable of predicting accurately the unseen data of the VMD desalination process. The correlation coefficient of the overall agreement between the ANN predictions and experimental data was found to be more than 0.994. The calculation value of the coefficient of variation (CV) was 0.02622, and there was coincident overlap between the target and the output data from the 3D generalization diagrams. The optimal operating conditions of the VMD process can be obtained from the performance analysis of the ANN model with a maximum permeate flux and an acceptable CV value based on the experiment.

Yes / This paper presents a simulation study of vacuum membrane distillation (VMD) for desalination. A simulation model was built on Aspen Plus® platform as user defined unit operation for VMD module. A simplified mathematical model was verified and the analysis of process performance based on simulation was also carried out. Temperature and concentration polarization effects are significant in the conditions of higher feed temperature and/or vacuum pressure. The sign of difference of the vapour pressures between at the membrane interfaces, is a pointer of the vacuum pressure threshold. Increasing the vacuum pressure at lower feed temperature is an effective way to increase the permeate flux and reduce the energy consumption simultaneously.

In this study, membranes were made from three polyvinylidene fluoride (PVDF) polymers individually and the blend systems of high (H) and low (L) molecular weight PVDF by phase inversion process. After investigating membrane casting solutions’ viscous and thermodynamic properties, the membranes so fabricated were characterized by scanning electron microscopy, gas permeation tests, porosity measurement, contact angle (CA) and liquid entry pressure of water (LEPw) measurement, and further subjected to vacuum membrane distillation (VMD) in a scenario that was applicable for cooling processes, where the feed water temperature was maintained at 27℃. It was found that PVDF solutions’ viscosities and thermodynamic instabilities were determined by the types of PVDF employed in single polymer systems and the mixing ratios of two PVDF polymers in blend systems. Thus the membrane properties and performances were influenced by the aforesaid factors as well. In single polymer systems, it was found that the membrane surface roughness and porosity increased with an increase in molecular weight. Among all the membranes casted in this study, the water vapor flux of VMD was found to be the highest at the intermediate range of H:L ratio, i.e., 4:6, at which the thickness of the sponge-like layer showed a minimum, the finger-like macro-voids formed a more orderly single-layer structure, and the LEPw showed a minimum. A conclusion can be made that blend systems of high molecular weight PVDF polymers and low molecular weight PVDF polymers could be used to optimize membrane performance in vacuum membrane distillation.

In this study, membranes were made from three polyvinylidene fluoride (PVDF) polymers individually and the blend systems of high (H) and low (L) molecular weight PVDF by phase inversion process. After investigating membrane casting solutions’ viscous and thermodynamic properties, the membranes so fabricated were characterized by scanning electron microscopy, gas permeation tests, porosity measurement, contact angle (CA) and liquid entry pressure of water (LEPw) measurement, and further subjected to vacuum membrane distillation (VMD) in a scenario that was applicable for cooling processes, where the feed water temperature was maintained at 27℃. It was found that PVDF solutions’ viscosities and thermodynamic instabilities were determined by the types of PVDF employed in single polymer systems and the mixing ratios of two PVDF polymers in blend systems. Thus the membrane properties and performances were influenced by the aforesaid factors as well. In single polymer systems, it was found that the membrane surface roughness and porosity increased with an increase in molecular weight. Among all the membranes casted in this study, the water vapor flux of VMD was found to be the highest at the intermediate range of H:L ratio, i.e., 4:6, at which the thickness of the sponge-like layer showed a minimum, the finger-like macro-voids formed a more orderly single-layer structure, and the LEPw showed a minimum. A conclusion can be made that blend systems of high molecular weight PVDF polymers and low molecular weight PVDF polymers could be used to optimize membrane performance in vacuum membrane distillation.

In this study, effects of nanoparticles, including 7 nm TiO2, 200 nm TiO2, and hydrophilic and hydrophobic SiO2 with mean diameter in the range of 15–20 nm and their concentration on the membrane properties and vacuum membrane distillation (VMD) performance were evaluated. The effect of membrane thickness and support materials were also investigated. The membranes were characterised extensively in terms of morphology (SEM), water contact angle, water liquid entrance pressure (LEPw), surface roughness, and pore size. While the best nanocomposite membranes with 200 nm TiO2 Nanoparticles(NPs) were obtained at 2% particle concentration, the optimal particle concentration was 5% when 7 nm TiO2 was integrated. Using nanocomposite membrane containing 2 wt% TiO2 – 200 nm nanoparticles, VMD flux of 2.1 kg/m2h and LEPw of 34 PSI was obtained with 99% salt rejection. Furthermore, it was observed that decreasing the membrane thickness would increase the portion of finger-like layer in membrane and reduce the spongy-like layer when hydrophilic nanoparticles were used. Using continuous flow VMD, a flux of 3.1 kg/m2h was obtained with neat PVDF membranes, which was 600% higher than the flux obtained by the static flow VMD with the same membrane at the same temperature and vacuum pressure. The fluxes of both static and flow-cell VMD increased with temperature. Furthermore, it was evident that the continuous flow VMD at 2 LPM yielded 300% or higher flux than static VMD at any given temperature, indicating strong effects of turbulence provided in the flow-cell VMD.

Concentrated solar power is a growing but expensive alternative energy resource. One of the most common issues faced when it comes to solar dish design is the complex trade-off between cost and optical quality. A novel solar dish reflector setup that makes use of low-cost, commercial television satellite dishes to support aluminised plastic membranes in a multifaceted vacuum-membrane concentrator was investigated in this work. The design aims to reduce costs while maintaining high optical accuracy with the added benefit of optical adjustability. The flux distribution of the novel solar dish reflector setup had to be determined to make recommendations on the feasibility of the design. This research presents a method to determine the expected solar flux distribution from lunar tests using a Canon EOS 700D camera. Experimental tests and different pollution treatment methods were conducted using lunar flux mapping techniques. A numerical model of the experimental setup, based on photogrammetry results of the membrane surface, was also developed in SolTrace to ascertain the sources of error and allow for further design improvements. Preliminary testing proved that JPEG image formats yielded insufficient accuracy in capturing the incident flux when compared to RAW images. Based on the flux ratio maps, the intercept factor for a large multifaceted dish setup was calculated as 88.6% for an aperture size of 0.25 m × 0.25 m, with a maximum solar flux of 1 395 kW/m2 for a 1 000 W/m2 test case. / Dissertation (MSc (Mechanical Engineering))--University of Pretoria, 2020. / National Research Foundation (NRF) / Mechanical and Aeronautical Engineering / MSc (Mechanical Engineering) / Unrestricted

Poly(vinylidene) fluoride (PVDF) nano-composite membranes were prepared. The dope solution contained varied concentrations of superhydrophobic SiO2 nano-particles. The fabricated flat sheet membranes were characterized extensively by SEM, FTIR, water contact angle, LEPw, surface roughness, pore size diameter and pore size distribution. The effect of the nano-particles on the membrane performance was then analysed. The nano-composite membranes showed increased surface pore diameter, elevated water contact angle measurements with lower LEPw when compared to the neat membrane. The 7 wt. % nano-composite membrane showed the greatest flux in a VMD process with 2.9 kg/m2.h flux achieved accounting to a 4 fold increase when compared to the neat membrane. Desalination test were carried out using a 35 g/L synthetic salt water and rejection >99.98% was obtained. The best performing nano-composite dope solution (7 wt. %) was then further treated for performance enhancement by increasing the water content to increase pore size and pore size distribution followed by coating with nano-fibres. The uncoated and coated flat sheets, were characterized by SEM, surface roughness, LEPw and CAw. Flux analysis showed that the increase in water content had little effects on the VMD flux. It also suggests that; the nano-fibre layer posed very little resistance to mass transfer. A comparison of VMD and DCMD was also done experimentally.

Cette thèse de doctorat concerne l’étude de la distillation membranaire sous vide pour l’élimination de l’arsenic contenu dans les eaux souterraines. En effet, la contamination des nappes phréatiques par l’arsenic est une problématique majeure dans de nombreux pays, et en particulier au Vietnam. Dans ce pays, choisi comme cas d’étude pour ce travail, environ 13% de la population est empoisonnée par des eaux souterraines contaminées par l’arsenic. De plus, ces eaux souterraines présentent des salinités élevées (5-10 g.L-1) dues à des infiltrations d’eau de mer dans les nappes. Ce travail de thèse a permis de démontrer la faisabilité de la distillation membranaire sous vide (DMV) pour éliminer l’arsenic contenu dans ces eaux et réduire leur salinité afin de les rendre propres à la consommation humaine. Les concentrations en As(III) dans le perméat de DMV sont toujours inférieures aux limites de la norme en eau potable (10 μg.L-1), même pour de très fortes concentrations en As(III) dans l’alimentation (jusqu’à 2000 μg.L-1). La DMV ne nécessite pas de pré-oxydation de l’As(III) en As(V), étape nécessaire dans de nombreux procédés conventionnels de traitement. De plus, un couplage entre l’osmose inverse (OI) et la DMV a été étudié : l’étape d’OI permet une pré-concentration en NaCl et As(III), puis ce rétentat est alors sur-concentré grâce à laDMV. La DMV a montré de très bonnes performances pour traiter un concentrat contenant de très fortes concentrations en As(III) (7000 μg/L). La DMV permet toujours de limiter les teneurs en arsenic dans le perméat à des valeurs en-dessous de la norme. Enfin, unesimulation d’un procédé global, incluant OI et DMV, et fonctionnant à un taux de conversion global de 96%, a été effectuée. Ce couplage ouvre la voie vers un traitement global de l’arsenic permettant de générer de très faibles quantités d’effluents finaux / This PhD work deals with vacuum membrane distillation (VMD) for arsenic removal from groundwaters. Contamination of water resources with arsenic was identified in 105 countries. Approximately 150 million people are being exposed to arsenic contamination, and 147 million of these people live in Asia. In Vietnam, chosen as the case study of this work, 13% of the population is being in risk of arsenic poisoning. Drinking water resources present not only high arsenic concentration (1 – 3050 ppb) but also high salinity (5 – 15 g/L). This work allowed demonstrating the feasibility of VMD to remove arsenic and also salts contained in groundwaters. As(III) concentration in the permeate of VMD was always lower than the standard level for drinking water (10 μg.L-1), even for high As(III) concentrations in the feed (up to 2000 μg.L-1). With VMD, a pre-oxidation step was not necessary to convert As(III) into As(V), as it is the case for other conventional treatment processes. Moreover, a coupling between reverse osmosis (RO) and VMD was studied. RO was considered as a first step to concentrate NaCl and As(III) before this retentate stream was further concentrated by the VMD. VMD could work efficiently with 99.9% of As(III) andNaCl rejections at a very high RO retentate concentrations ([NaCl] = 300 g/L and [As(III)] = 7000 ppb). Arsenic in the permeate was still lower than the required standard for drinking water. Finally, a simulation of the coupling was performed. By coupling of RO and VMD, ahigh global recovery of 96% could be achieved

La presente tesis estudia el desarrollo de tecnologías de separación y recuperación de aromas. Se busca obtener dos clases distintas de productos, concentrados aromáticos y bebidas parcialmente desalcoholizadas. En ambos productos se requiere una alta calidad aromática.Distintos casos de estudio se han seleccionado:i) La separación concentración del 2,4-decadienoato de etilo, aroma impacto de la pera, y ii) la separación-concentración del trans-2-hexen-1-ol, aroma impacto de los arándanos. En ambos casos, se tratan corrientes acuosas de la etapa de concentración de zumos en la indsutria. Para el estudio de la separación /concentración del aroma de pera se aplica adsorción en Carbón Activo Granular y Destilación con Membranas a Vacío, y para el aroma del arándano se selecciona la Pervaporación. Para todos estos casos se analiza el rendimiento del proceso y se desarrolla el modelo matemático obteniéndose sus principales parámetros de transporte.iii) La reducción del contenido de etanol en vino mediante Destilación Osmótica. Se ha desarrollado el modelo matemático que describe el transporte del etanol y los compuestos aromáticos. La validación del modelo y el análisis sensorial se llevaron a cabo mediante vino real. / The thesis document deals with the development of technologies for the separation and recovery of aromatic compounds. Two different kind of products are sought, aroma concentrates from fruit juices and partially de-alcoholised beverages. On both products high aromatic quality is required.Several cases of study have been selected: i) The separation of separation-concentration of ethyl E-2, Z-4-decadienoato, pear impact aroma compound, and ii) separation-concentration of E-2-hexen-1-ol, bilberries impact aroma compound. In both cases, aqueous streams to be treated in the industry would come from the juice concentration stage. The study of the separation and concentration of the pear aroma compound was made by using Adsorption onto Granular Activated Carbon and Vacuum Membrane Distillation, and for the bilberry aroma compound, Pervaporation was selected. For all of these cases of study, the performance analysis and mathematical modeling have been performed and the main transport parameters.iii) The reduction of the alcohol content of wine by Osmotic Distillation. A mathematical model describing both the ethanol and aroma compounds transport was developed. Model validation and sensorial analysis on real wine were made.