Thesis (Ph.D.)--McMaster University, 2002. / Adviser: James Dickson. Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph.D.)--McMaster University, 2002. / Adviser: James Dickson. Includes bibliographical references. Also available via World Wide Web.

Nanofiltration (NF) membranes have been applied successfully for the removal of inorganic and organic pollutants, including micropollutants, from drinking water for the past two decades. However, a complete and quantitative understanding of NF removal mechanisms has yet to be achieved. Quantifying the factors governing solute transport and retention by NF is necessary in order to achieve higher treatment efficiency at a lower cost. The aim of this research was to contribute to the current state of the knowledge of the mechanisms of solute retention and transport by NF membranes. The focus was on evaluating the contribution of solute-solute interactions and solute-membrane interactions on solute removal and transport mechanisms. To the knowledge of the author, at the start of this research there was a lack of understanding of the simultaneous impacts of both interactions on the performance of NF membranes, which renders this research novel. To highlight challenges faced by modern membrane plants and identify inorganic and organic pollutants of interest, a study of water quality in Scotland was carried out. Experiments were performed in dead-end stirred cells using two commercial NF membranes, TFC-SR2 and TFC-SR3 provided by Koch, which were extensively characterized. Radiolabeled Endosulfan (ES, 10 μg/L), manganese (5-1,500 mg/L) and Humic Acids (HA, 5-250 mgC/L) were spiked in synthetic water with background electrolyte (1 mM NaHCO3 and 20 mM NaCl). Calcium (Ca, 2.5 mM) was employed in fouling experiments. The influence of the complexation of solutes with HA on solute retention by NF was for the first time quantified for the solute concentrations employed in this study. It was found that manganese retention was influenced by membrane pore size and charge (solute-membrane interactions) and solute speciation (solute-solute interactions). Complexation of manganese and HA (solute-solute interactions) occurred at alkaline conditions but did not enhance manganese retention. At high pH manganese precipitated as solid MnCO3 and these precipitates achieved high retention (99%), even without the presence of HA. ES retention by NF membrane was controlled by size exclusion (solute-membrane interactions). For the tighter TFC-SR3, whose pore size are smaller than the size of ES, ES retention increased in the presence of HA, while for the looser TFC-SR2, whose pores are bigger than ES diameter, ES retention decreased in the presence of HA. For TFC-SR3 increase of ES retention in the presence of HA was due to size exclusion (solute-membrane interactions) and formation of ES-HA complexes (solute-solute interactions). For TFC-SR2 HA-membrane interactions were dominant with respect to solute-solute interactions, increasing membrane molecular weight cut-off (MWCO) and in turn passage of ES. The influence of pressure (5-15 bar) on ES retention in the presence of HA was systematically investigated. Results showed that ES transport through TFC-SR2 and TFC-SR3 was dominated by convection. For the tighter TFC-SR3 lower permeate flux was responsible for the increase of retention with pressure, while for the looser TFC-SR2 higher permeate flux increased concentration polarisation, decreasing retention with pressure. The presence of HA lowered the permeate flux, resulting in a less pronounced variation of retention with pressure for TFC-SR2 and in constant retention for TFC-SR3. The impact of manganese scaling on the performance of NF membranes was investigated at neutral pH. The effects of inorganic precipitates on flux and solute retention by NF have been so far scarcely studied and the impact of inorganic scaling on micropollutant retention by NF is unknown. Findings from this research indicated that manganese deposits did not foul the membranes but on the contrary enhanced their flux and prevented fouling by HA and Ca. The retention of ES, manganese and HA by membranes through which manganese was previously filtered was found to decrease with respect to solute retention by virgin membranes. Manganese filtration was shown to increase membrane MWCO and hydrophilicity. It was proposed that manganese-membrane interactions caused swelling of the membrane active layer by increasing the membrane free volume. The findings of this research indicated the importance of investigating simultaneously the impacts of solute-solute interactions and solute-membrane interactions to understand and explain transport and removal mechanisms of organic and inorganic contaminants by NF.

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

Nanofiltration (NF) can be used in water and wastewater treatment as well as water recycling applications, removing micropollutants such as hormones. Due to their potential health risk it is vital to understand their removal mechanisms by NF membranes aiming at improving and developing more effective and efficient treatment processes. Although NF should be effective and efficient in removing small molecular sized compounds such as hormones, the occurrence of adsorption onto polymeric membranes results in performances difficult to predict and with reduced effectiveness and efficiency. This study aims firstly at defining, understanding and quantifying the relevant filtration operation parameters and, secondly, in identifying the physical mechanisms of momentum and mass transfer controlling the adsorption and transport of hormones onto polymeric NF membranes in cross-flow mode. The hormones estrone (E1) and 17-b-estradiol (E2) were chosen as they have very high endocrine disrupting potency. The NF membranes used and tested were the NF 270, NF 90, BW30, TFC-SR2 and TFC-SR3 since they have a wide span of pore sizes. The first step is to experimentally acquire the knowledge of how fluid flow hydrodynamics and mass transfer close to the membrane affect hormone adsorption. The focus will be particularly on the effect of operating pressure, circulating Reynolds numbers (based on channel height, Reh) and hormone feed concentration. These hydrodynamic parameters play an important role in concentration polarisation development at the membrane surface. A Reh increase from 400 to 1400 for the NF 270 membrane caused the total mass adsorbed of E1 and E2 to decrease from 1.5 to 1.3 ng.cm-2 and 0.7 to 0.5 ng.cm-2, respectively. In contrast, a pressure increase from 5 to 15 bar yielded an increase in the adsorbed mass of E1 and E2 from 1.0 to 1.8 ng.cm-2 and 0.5 to 0.7 ng.cm-2, respectively. Moreover, increasing hormone feed concentration caused an increase in the mass adsorbed for both hormones. These observations led to the conclusion that adsorption is governed by the initial concentration at the membrane surface which, in turn, depends on the hormone feed concentration, operating Reh and pressure. Membrane retention, however, depends on the initial polarisation modulus, defined as the ratio between the initial concentration at the membrane surface and the initial feed concentration. The same trends were obtained for the TFC-SR2 membrane. However, this membrane has a much lower permeability compared to the NF 270 one (7.2 vs 17 L.h-1.m-2.bar-1, respectively) and concentration polarisation is less severe. The experimental variations in mass adsorbed and retention as a function of the operating filtration parameters (Reh and pressure) were therefore lower. Based on these experimental results, a sorption model was developed. This model predicts well both feed and permeate transient concentrations for both hormones and membranes (NF 270 and TFC-SR2) in the common range of operating pressures and Reh of spiral-wound membrane modules. The model was further applied for E2 in the presence of background electrolyte, yielding good predictions. These findings are an important advancement in determining which membrane would be more suitable to effectively remove hormones with a substantial reduction of experimental work. The above-mentioned developed model does not give insight into the phenomena occurring inside the membrane since it focuses on the feed conditions. However, membrane characteristics, such as material and pore radius were found to have an impact in adsorption and retention of hormones. It was found experimentally that polyamide, from which the active layer of the NF membranes is made, adsorbs three times more mass of hormone than any other polymers constituting the membranes. Since this active layer is the membrane selective barrier of the membrane that is in contact with the largest hormone concentration (due to concentration polarization in the feed solution) it is concluded that the active layer adsorbs most of the hormones. Further experimental work carried out in this thesis showed that increasing the pore radius from 0.32 nm to 0.52 nm increased the E2 mass adsorbed from 0.17 ng.cm-2 to 1.1 ng.cm-2 and decreased the retention from 88% to 34%. These results show that the wider the pore, the larger the quantity of hormone that penetrates (i.e. partitions) inside the membrane and, therefore, the more the membrane adsorbs the hormone. For membranes of similar pore radius, the membrane with larger internal surface area was found to adsorb more. All the previous results led to the establishment of a new model for the hormone transport inside the membrane pore taking convection, diffusion and adsorption into account. Since the differential equation describing the transport with adsorption inside the pore has no analytical solution, a numerical model based on the finite-difference approach was applied. With such a model, its validation against experiments and parametric studies it was possible to understand the transport mechanisms of adsorbing hormones through NF membranes. The results show that for low pressures the hormone transport is diffusion dominated. In contrast, for higher pressures (above 11 bar) the transport is convection dominated, showing that a purely diffusion transport model does not describe well the actual transport phenomena of hormones in NF membranes. Furthermore, it was found that two similar molecules can behave very differently in terms of adsorption on the membrane. E1, which adsorbs 20% more than E2 in static mode, being slightly smaller than E2, partitions more inside the membrane pore and adsorbs double under filtration conditions. This study contributes to illuminating the adsorption mechanisms of hormones onto NF membranes by understanding what parameters control adsorption such as hydrodynamics, materials, structure, etc. This not only identifies a potential problem in large scale applications, but it also provides an understanding of the mechanisms involved in the removal of these hormones and a tool that can be used to design future membranes for the improvement of micropollutant removal.

Biogas is becoming a more important source of green, renewable energy however, its production results in a liquid wastewater, known as centrate, which must be treated due to its high levels of total dissolved solids (TDS), and chemical oxygen demand (COD). Currently, biogas generation facilities treat centrate using a combination of biological and physical treatments (via a membrane bioreactor (MBR)), which produces a stream known as MBR permeate. While MBR permeate achieves improved quality, MBR usage has several challenges including difficulty of scaling biological processes, and handling capacity limitations. In this study, membrane only treatment of centrate, collected from an operating biogas generation facility, was investigated to determine if similar quality permeates could be obtained without any biological treatments. Single- stage treatment of centrate using either polymeric or ceramic nanofiltration membranes with molecular weight cut offs between 400 and 800 Da, produced a permeate similar to MBR permeate. These membrane types caused average COD rejections of 92% and 90% respectively. However, the permeates from the nanofiltration membranes had very high levels of ammonia, which was not present in the MBR permeate. The ceramic nanofiltration membranes can achieve higher permeate fluxes than the polymeric nanofiltration membranes. Both membrane types experienced significant fouling which was removed using cleaning procedures. Two-stage treatment of centrate using ceramic nanofiltration membranes followed by polymeric reverse osmosis membranes further improved the quality of permeate and achieved COD rejections of 99% overall. While the reverse osmosis membranes did remove some ammonia, the levels were still higher than what was seen in the MBR permeate. The two-stage treatment of centrate can provide the permeate which is closest to the MBR permeate however, further studies are required to address the higher ammonia concentration values. The research shows that only using membranes is a potential treatment pathway for real centrate samples. / Thesis / Master of Applied Science (MASc) / The production of biogas, which is a green, renewable energy source results in a liquid wastewater known as centrate. This wastewater is very dirty and complex and requires treatment as it cannot be dumped and disposed of in its current state. Current treatment methods for centrate use combinations of biological treatment and filtration processes, which has its own challenges due to the complexity of biological treatments. An alternative treatment method for the centrate is nanofiltration membranes which offer the ability to treat large volumes of centrate wastewater without the complexity of relying on biological treatment options. Four different nanofiltration membranes, including two polymeric and two ceramic membranes, were used to treat real industrial wastewater samples of centrate collected from a biogas generation facility. Both types of nanofiltration membranes provided similar quality permeate to the current treatment method of centrate, which uses a combination of biological and physical treatment methods.

Le manque croissant en eau potable dans le monde est un problème d’envergure pour la population. La filtration par des membranes des eaux usées, insalubres ou la désalination apparaît comme une alternative viable pour le futur. La modification de membranes d’ultrafiltration par l’assemblage couche-par-couche permet d’obtenir des propriétés de nanofiltration en contrôlant avec une précision nanométrique l’épaisseur de la couche active de séparation déposée. Lors de cette thèse, nous avons étudié la construction de la couche de séparation ainsi que sa régénérabilité. Pour ce faire, nous avons développé des surfaces « membrane-like » pour étudier la construction sur des surfaces possédant des fonctions chimiques similaires à l’applicative. Par ailleurs, le temps de déposition a aussi été investigué afin de déterminer si les propriétés de séparation des membranes modifiées dépendaient du nombre de couches déposé ou du temps de dépôt. Les membranes ainsi développées présentent une couche de séparation régénérable et des propriétés de nanofiltration. / The increasing lack of drinking water in the world is of major concern for the population. Membrane filtration of brackish water, seawater appears to be a viable alternative for the future. Nanofiltration membranes can be obtained by modifying ultrafiltration membranes by the Layer-by-Layer (LbL) technique. This method also the deposition of an ultra-thin separation layer with a nanoscale precision and with tunable properties. During this PhD thesis, the build-up and the regenerability of the separation layer was investigated. For this purpose, mimicry surfaces were developed in order to study the LbL-assembly on surfaces presenting similar chemical functions as the applicative one. In addition, the deposition time was also investigated in order to determine if the separation properties of the membrane depend on the number of deposited layers or on the coating time. The developed membranes possessed a regenerable separation layer presenting nanofiltration properties.

Thesis (M. Tech.(Chemistry)--Vaal University of Technology)), 2010 / Mining industry produces metals which are economical and serve as high valuable commodities in South Africa. This country is regarded as the world leading producer of precious metals such as platinum group metals (PGMs). Silver (Ag), which is also a precious metal, contribute to the country’s economy wealth due to its significance during industrial applications. Base metals such as copper (Cu) and nickel (Ni), though they are low valued, play a significant role in the republics economic wealth. Mining wastewater contains some of these metals, which end up polluting the environment. A possibility to recover this was investigated using NF membranes. Mine effluent was simulated by using relevant reagents. Characterization of NF90, NF- and NF270 membranes, was done by using scanning electron microscopy (SEM), clean water permeability, single charged salts of NaCl and MgCl2 and binary mixture of NaCl/MgCl2 studies. All the rejection experiments were conducted at pH 2.0 with varying pressure and concentrations. Flux measurements indicated that water permeability through the membranes trend, NF270 > NF90 > NF-. The experiments were performed at pressures of 5 bar, 10 bar, 15 bar and 20 bar. For NF90 membrane, a rejection of Na+ monovalent ion in 20 ppm solution was less than of Mg2+ (divalent) ion. Percentage rejections of 90% (Na+) and 98% (Mg2+) were achieved. NF- had rejection of 83% and 90% for Na+ and Mg2+, respectively. In the case of NF270, the membrane had rejection of 92% (Na+) and 94% (Mg2+), respectively. At 100 ppm, all three membranes showed a decreasing trend in rejection while increasing pressure. For binary-solution mixture, Mg2+ ion still had the highest rejection compared to Na+ ion with about 94% and 85% on NF90 than on NF270 and NF-. The high rejection of divalent ion as compared to monovalent ion for charged solutes was due to solute size and electrostatic interaction between the membrane surface layer and the solute. In the case of transition metal rejection studies, Pd2+ ion had an average of 90%, with Ni2+ ion ≈ 95% and Cu2+ ion ≈ 98% as single salts on NF90 compared to NF270 and NF-. However, as for binary and trinary solution mixture, the competition amongst ions was high, where Pd2+ ion rejection was ≈ 99,0%, while Ni2+ and Cu2+ ions was > 90% on NF90 and NF-. Therefore it was excluded from the tests. For the monovalent metal ions (Ag+ and Cu+), the rejection was > 90% in almost all concentrations mixtures. During membrane fouling evaluation, AgCl salt fouled the most, compared to other metal ions, forming a concentration polarization accumulation on the membrane surface for both 20 and 100 ppm solutions. This situation leads to cake layer formation which causes a flux decline, reduces membrane life time and lowers the rejection performance of NF membranes. The aim of this study was to evaluate the performance of three commercial polymeric membranes (NF90, NF270 and NF-) during rejection of the metal

Ce travail de thèse a été consacré à l'élaboration d'un nouveau type de membranes de nanofiltration efficaces avec des propriétés améliorées (flux élevé et rétention élevée, et de bonnes propriétés mécaniques) en déposant un revêtement assemblé couche-par-couche (LbL) sur des supports poreux. Après avoir systématiquement étudié le mécanisme de croissance des films assemblés couche par couche des polyélectrolytes choisis et la relation entre les structures de ces films et les performances des membranes résultant, nous avons identifié avec succès les meilleures structures multicouches pour la construction de membranes de nanofiltration de référence avec des performances optimales. En outre, en prenant avantage de la technique LbL, nous avons introduit une couche de diffusion latérale assemblée soit de nanofibrilles de cellulose ou de nanotubes de carbone, qui permet d’augmenter le flux de 30% tout en conservant la même rétention par rapport à la membrane de référence. En plus, les films assemblés à base de chitosan et nanofibrils de cellulose ont montré une forte résistance à la traction allant jusqu’à 450 MPa et un module d’Young jusqu’à 50 GPa. / This thesis work was devoted to the development of a novel and efficient nanofiltration membrane with improved properties (high flux and high retention, good mechanical strength) by coating Layer-by-Layer (LbL) assembled films onto porous membrane support. After having systematically studied the growth mechanism of LbL-assembled films of chosen polyelectrolytes and the relationship between the structures of these films and the membrane performance of the resulting NF membranes, we successfully identified the best multilayer structures for constructing nanofiltration membranes (NF) of reference with optimal membrane performance. Furthermore, taking advantages of the LbL-assembly, we successfully introduced LbL-assembled lateral diffusion layer that is made of either cellulose nanofibrils or carbon nanotubes, which in turn led to membranes with 30% higher flux. In addition, the LbL-assembled films of chitosan and cellulose nanofibrils showed surprisingly strong tensile strength of up to 450 MPa and a high Young modulus of up to 50 GPa.