Membrane technologies are considered a promising solution for water scarcity in arid regions. However, fouling is a major challenge facing the application of membrane technologies. Fouling limits the economic viability and reduces the overall efficiency of membrane processes. Therefore, fouling mitigation is a crucial factor in spreading the use of membrane technologies for new applications. The first step in fouling mitigation is to predict the propensity of fouling. Unfortunately, there are immense limitations in current industrial practises for fouling propensity prediction. These limitations come from using outdated and inapplicable approaches, in which crucial assumptions are made. For example, in the case of crystallisation fouling or “scaling” one of the major simplifications is the use of pure scaling salt data to predict the propensity of scaling when, in reality, co-precipitation is present. This research work aims to introduce a new approach to systematic assessment of the fouling problem under real and complex conditions and to enhance understanding of the importance of including interactive effects and co-precipitation in the prediction of scaling propensity. In this research work a novel procedure accounting for the local variation of thermodynamic properties along a long membrane channel is proposed. A new approach considering ion interaction and process hydrodynamics for the prediction of the scaling propensity is then introduced. This new approach provides for the first time a completely theoretical assessment for pure salt scaling propensity along a full scale filtration channel without the use of any empirical constants. A new procedure for including the effect of co-precipitation on scaling propensity prediction is developed. The effect of process pressure on solubility products is included theoretically for the first time to enhance the accuracy of scaling propensity prediction during the full scale RO process. This research work helps to produce more reliable and accurate prediction of the onset of scaling which will help strategies to mitigate scaling and increase the overall efficiency of RO/NF processes. The new approach can be applied in practical situations and could be developed to a user-friendly programme able to give an accurate prediction of the fouling propensity in full scale processes allowing the optimisation of membrane processes accordingly. Moreover, comprehensive experimental work has been carried out during this PhD research work to enhance understanding of crystallisation fouling and coprecipitation. The effect of salinity and dissolved organics (DO) in CaSO4 and SrSO4 precipitation and co-precipitation are studied and discussed. Quantitative and qualitative thermodynamic and kinetic analyses combined with structural analyses of deposits are carried out to investigate the effect of salinity, DO presence and coprecipitation on SrSO4 and CaSO4 precipitation. The observations in this experimental study are very important for a deeper understanding of the effect of scaling salts’ coexistence, salinity and DO presence on the behaviour of the scaling salts. This is crucial to reaching a reliable prediction of the scaling propensity within RO/NF processes. Finally, the new developed approaches in this thesis have been validated using set of hydrodynamic tests. This set of tests has been carried out using a newly installed laboratory membrane rig. Moreover, a new technique to simulate full scale membrane processes is proposed using a laboratory membrane rig combined with the programs previously developed in this thesis. This new technique can be used to study the effect of process hydrodynamics on scaling and process performance of full scale membrane processes using a laboratory membrane rig. The outcomes of this research work can be used to investigate the optimal operating conditions and to guide design criteria for different RO/NF practical scenarios.

Current nanofiltration (NF) models are based on the “diluted solution” assumption and cannot successfully predict permeate fluxes at high salt concentrations. The reasons behind the strong differences between the predicted and observed fluxes are still not fully understood. In this work, it is proposed that these deviations are possibly caused by the electrical charges inside the membrane pores. At a nanoscale level, the complex electrostatic interactions between the highly confined charged solutes and the charges inside membrane pores contribute to flow retardation and this phenomena can be characterized using an additional resistance factor, which is defined as the electric resistance factor in this study. To this extent, experiments were carried out with aqueous sodium chloride (NaCl) solutions in a wide range of concentrations (0.05 – 1.96 M) using two commercial membranes (NF270 and Desal-5 DL). Salt retention was fitted and analysed by means of the classical Spiegler-Kedem model (SK). The model has been modified to include the proposed empirical electric resistance factor, Relec, to account for this additional hydrodynamic flow resistance. The modified Spiegler-Kedem model (MSK) was verified by fitting experimental data at relatively low salt concentration to obtain model parameters and then comparing the model prediction with experimental data at higher concentrations. A mathematical equation was developed to describe the dependence of an important model parameter, reflection coefficient (σ), on operational conditions such as pressure and bulk salt concentration. The thesis also discussed the mechanisms of NF separation, highlighting the electrostatic interaction between the co-ions and the membrane charges in the confined nano-environment inside the NF membrane pores.

Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009. / Committee Co-Chair: Huang, Ching-Hua; Committee Co-Chair: Kim, Jae-Hong; Committee Member: Li, Qilin; Committee Member: Mulholland, James; Committee Member: Wine, Paul; Committee Member: Yiacoumi, Sotira. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Zugl.: Stuttgart, Univ., Diss., 2009

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Ching-Hua Huang, Committee Co-Chair ; F. Michael Saunders, Committee Member ; Jae-Hong Kim, Committee Chair.

Thèse (M.Sc.)--Université Laval, 2005. / Titre de l'écran-titre (visionné le 28 novembre 2005). Bibliogr.

Orientadores: Miriam Dupas Hubinger, Jose Carlos Cunha Petrus / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-10T11:58:11Z (GMT). No. of bitstreams: 1 Mello_BeatrizCamargoBarrosDeSilveira_M.pdf: 17558051 bytes, checksum: 463cdbe636b6634ded65ac8cdc69f04b (MD5) Previous issue date: 2008 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The abstract is available with the full electronic document / Mestrado / Mestre em Engenharia de Alimentos

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Aujourd'hui, la nanofiltration (NF) est perçue comme un procédé de séparation efficace et propre permettant d’extraire ou de concentrer des solutés ioniques ou neutres. Son développement à l’échelle industrielle n’est cependant pas encore optimal car les différents mécanismes de séparation sont encore mal compris. Cette thèse a porté d’une part sur l’étude des propriétés charge de surface des membranes de NF/OI et d’autre part sur les mécanismes de transport à travers des membranes de NF. Il a tout d’abord été montré, grâce à des mesures électrocinétiques réalisées sous atmosphère contrôlée, que certaines membranes commerciales subissent un post-traitement afin d’améliorer leurs performances de filtration. La détermination du potentiel zêta, grandeur caractéristique de la charge de surface, s’est révélée être une méthode adaptée pour mettre en évidence la présence d’une couche de post-traitement à la surface d’une membrane. La suite de l’étude a été consacrée à la compréhension des mécanismes de transport lors de la NF de mélanges ternaires contenant deux cations différents (Na+ et Ca2+) et un anion commun (Cl-). L’utilisation du modèle de transport SEDE a permis de montrer que les performances des membranes de NF résultent de la combinaison d’effets stériques, électriques et diélectriques. La dernière partie de ce travail a été consacrée à la NF d’un coproduit de l’industrie agro-alimentaire, le produit fermenté de soja (PFS). Il a été montré que la NF est potentiellement adaptée au dessalement du PFS (réduction de la teneur en cations monovalents) sans perte des sucres d’intérêt. / Today, nanofiltration (NF) is acknowledged as an efficient and environmentally-friendly separation process suited to extract or to concentrate neutral or ionic solutes. However, its development at industrial scale is not yet optimal because separation mechanisms are still poorly understood. This thesis focused on studying surface charge properties of NF/RO membranes and transport mechanisms through NF membranes as well. Firstly it was shown through electrokinetic measurements performed under controlled atmosphere that some commercial membranes undergo a post-treatment to improve their filtration performance. Determining the zeta potential, a physical quantity representative of the membrane surface charge, was shown to be a reliable method to highlight the presence of a post-treatment layer on the membrane surface. The second part of the study dealt with the understanding of transport mechanisms involved in NF of ternary mixtures containing two different cations (Na+ and Ca2+) and a common anion (Cl-). Using the SEDE transport model it was shown that the performance of NF membranes results from the combination of steric, electric and dielectric effects. The last part of this work was concerned with nanofiltration of a food industry co-product, the fermented soy product (PFS). It was shown that NF is potentially suitable for PFS desalination (reduction in the monovalent cation concentration) without loss of the sugars of interest.