Fouling nanofiltration

Bartels, Craig, Kirk Lai, and Mark Wilf, "New Generation of Low Fouling Nanofiltration Membranes," paper presented at the 2007 EDS Conference, Halkidiki, Greece, April, 2007. 

A bottleneck in all membrane processes, applied in practice, is fouling and scaling of the membranes. These processes cause a decrease in water flux through the membrane and a decrease in retention. Much attention is paid, especially in case of nanofiltration and hyperfiltration, to prevent fouling of the membrane by an intensive pretreatment and the regular removal of fouling and scaling layers by means of mechanical, physical or chemical treatment. 

In temperate climate zones it may be more appropriate to install a nanofiltration process rather than reverse osmosis. Nanofiltration allows the production of drinking water from polluted rivers. As for reverse osmosis, pretreatment is important to control fouling of the membranes. One of the largest such plants produces 140,000 m3/day of water for the North Paris region(26). 

Nanofiltration Compared to microfiltration and ultrafiltration, nanofiltration and reverse osmosis are more expensive and susceptible to fouling (Shih, 2005, 95). Most of the expenses result from the high densities of the membranes, which require high pressures (0.34-6.9 MPa) and a considerable... 

Manttari, M., Puro, L., Nuortila-Jokinen, J., and Nystrom, M. (2000). Fouling effects of polysaccharides and humic acid in nanofiltration. J. Membr. Sci. 165,1-17. 

Concentration polarization can dominate the transmembrane flux in UF, and this can be described by boundary-layer models. Because the fluxes through nonporous barriers are lower than in UF, polarization effects are less important in reverse osmosis (RO), nanofiltration (NF), pervaporation (PV), electrodialysis (ED) or carrier-mediated separation. Interactions between substances in the feed and the membrane surface (adsorption, fouling) may also significantly influence the separation performance fouling is especially strong with aqueous feeds. 

D. Violleau, H. Essis-Tome, H. Habarou, J.P. Croue, M. Pontie, fouling studies of a polyamide nanofiltration membrane by selected natural organic matter an analytical approach, Desalination 173 (2005) 223-238. 

Schafer, A. I., A. G. Fane, and T. D. Waite, "Nanofiltration of Natural Organic Matter Removal, Fouling, and the Influence of Multivalent Ions," Desalination, 118 (1998). 

Seidel, Arza, and Menachem Elimelech, Coupling Between Chemical and Physical Interactions in Natural Organic Matter (NOM) Fouling of Nanofiltration Membranes Implications for Fouling Control," Journal of Membrane Science, 203 (2002). 

Membrane pretreatment includes microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF). Microfiltration and UF membrane processes can remove microbes and algae. However, the pores of MF and UF membranes are too large to remove the smaller, low-molecular weight organics that provide nutrients for microbes. As a result, MF and UF can remove microbes in the source water, but any microbes that are introduced downstream of these membranes will have nutrients to metabolize. Therefore, chlorination along with MF and UF is often recommended to minimize the potential for microbial fouling of RO membranes. The MF or UF membranes used should be chlorine resistant to tolerate chlorine treatment. It is suggested that chlorine be fed prior to the MF or UF membrane and then after the membrane (into the clearwell), with dechlorination just prior to the RO membranes. See Chapter 16.1 for additional discussion about MF and UF membranes for RO pretreatment. 

Nanofiltration membranes are "tighter" then either MF or UF membranes but "looser" than RO membranes. They can be used to remove dissolved species, such as hardness and color. Recent developments in NF membranes have made them applicable to de-color feed water without chlorination and with minimal membrane fouling (see Chapter 16.2). 

Li, Qilin, and Menachem Elimelech, "Organic Fouling and Chemical Cleaning of Nanofiltration Membranes Measurements and Mechanisms," volume 38, number 17,2004. 

Tang, C.Y., Criddle, Q.S., Eu, C.S., and Leckie, J.O. 2007. Effect of flux (transmembrane pressure) and membranes properties on fouling and rejection of reverse osmosis and nanofiltration membranes treating perfluorooctane sulfonate containing waste water. Environmental Science and Technology, 41 2008-14. 

Many industrial activities, such as gas production [81-83], catalysis [84], and fuel cells [83], require gas separation. Fouling in gas separation processes, however, is less severe than in microfiltration, nanofiltration, and reverse osmosis where it is the main cause of permanent flux decline and loss of product quality [81],... 

Shaalan H.F., Development of fouling control strategies pertinent to nanofiltration membranes. Euromed May 2002. 

During the last two decades, pressure-driven membrane processes namely reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF) have found increased applications in water utilities and chemical industries. Unlike RO, NF, and UF, the Donnan membrane process (DMP) or Donnan dialysis is driven by an electrochemical potential gradient across an ion-exchange membrane. Theoretically, the DMP is not susceptible to fouling because particulate matter or large organic molecules do not concentrate on the membrane surface, as commonly observed with pressure-driven membrane processes. DMP has been used in the past in hydrometallurgical operations [19,20], for concentration of ionic contaminants [21,22] and for separation of... 

Vrijenhoek EM, Hong S, and Elimelech M. Influence of membrane surface properties on initial rate of colloidal fouling of reverse osmosis and nanofiltration membranes. J. Membr. Sci. 2001 188 155-128. 

Manttari M, Martin H, Nuortila-Jokinen J, and Nystrbm M. Using a spiral wound nanofiltration element for the filtration of paper miU effluents pretreatment and fouling. Adv. Env. Res. 1999 3(2) 202-214. 

Hong, S. and Elimelech, M., Chemical and physical aspects of natural organic matter (NOM) fouling of nanofiltration membranes, J. Membr. ScL, 132, 159, 1997. 

Membrane filters are made in a wide variety of pore sizes (Fig. 1). The effective pore size for membranes vary, and membranes can be used in reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). RO membranes are widely used in water treatment to remove ionic contaminations from the water. These membranes have an extreme small pore size and, therefore, require excellent pretreatment steps to reduce any fouling or scaling of the membrane, which would reduce the service lifetime. RO membranes are used by extensive pressures on the upstream side of the filter membrane to force the liquids through the pores. 

R. Liikanen, J. Yli-Kuivila, and R. Laukkanen, Efficiency of various chemical cleanings for nanofiltration membrane fouled by conventionally-treated surface water. Journal of Membrane Science 195, 265-276 (2002). 

Various treatments of Eqs. (12.5) to (12.8) are proposed in the literature for those cases where charge effects cue negligible (microfiltration, ultrafiltration or nanofiltration of neutral solutes), and low concentrated solutions are considered, i.e. with negligible non-idealities and activities assimilated to concentrations. Most of the time, membrane morphology is just considered through simple parameters such as effective pore size, tortuosity accounting for the effect of fouling on measurable transport properties. A well-known model thus obtained is due to Kedem and Katchalsky [5] ... 

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