Nanofiltration process

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). 

Oh, J.-I., Fee, S.-H. and Yamamoto, K. (2004) Relationship between molar volume and rejection of arsenic species in groundwater by low-pressure nanofiltration process. Journal of Membrane Science, 234(1-2), 167-75. 

Ivnitsky, H., Katz, I., Minz, D., Shimoni, E., Chen, Y Tarchitzky, J., Semiat, R. and Dosoretz, C.G. (2005) Characterization of membrane biofouling in nanofiltration processes of wastewater treatment. Desalination, 185, 255—268. 

See also in this series the chapter by M. Pontie et al. on nanofiltration processes. 

Tu S.-C., Ravindran V., Den W., and Pirbazari M., Predictive membrane transport model for nanofiltration processes in water treatment, AIChE Journal 47(6) 2001 1346-1362. 

The models can be scaled to various sizes to fit the needs of the experiment. For example, a very small-scale nanofiltration system, such as a Planova P-15 hollow-fiber cartridge with O.OOl-m surface area (Asahi Kasei Corporation, Japan), can be used to study virus retention capabilities of a virus reduction step in a biological manufacturing process, whereas a scaled-up version of the same system with a surface area of 0.01 m provides an excellent way to study the nanofiltration process variables. In a nanofiltration validation study, a feed sample is typically spiked with a known quantity of a model virus. The mixture is filtered under the expected process... 

Nanofiltration spans the gap in particle size between reverse osmosis (hyperfiltration) and ultrafiltration. It can separate high molecular weight compounds (100-1(X)0) from solvents, and can also separate monovalent from multivalent ions. The driving force is a pressure difference of about 0.3-3 MPa (even greater than ultrafiltration). The nanofiltration process can reject selected (typically polyvalent) salts and may be used for selective removal of hardness ions in a process known as membrane softening [10]. 

For membrane processes involving liquids the mass transport mechanisms can be more involved. This is because the nature of liquid mixtures currently separated by membranes is also significantly more complex they include emulsions, suspensions of solid particles, proteins, and microorganisms, and multi-component solutions of polymers, salts, acids or bases. The interactions between the species present in such liquid mixtures and the membrane materials could include not only adsorption phenomena but also electric, electrostatic, polarization, and Donnan effects. When an aqueous solution/suspension phase is treated by a MF or UF process it is generally accepted, for example, that convection and particle sieving phenomena are coupled with one or more of the phenomena noted previously. In nanofiltration processes, which typically utilize microporous membranes, the interactions with the membrane surfaces are more prevalent, and the importance of electrostatic and other effects is more significant. The conventional models utilized until now to describe liquid phase filtration are based on irreversible thermodynamics good reviews about such models have been reported in the technical literature [1.1, 1.3, 1.4]. 

Reverse osmosis was applied to concentrate the lactic acid in the permeate of nanofiltration process. The permeate collected from nanofiltration with the HL membrane was used. Two reverse osmosis membranes (DS 11 AG and ADF) were tested at 4.1 and 5.5 MPa. 

Based on the experimental results, a mathematical model that can express efficiency of a nanofiltration process was proposed, and an industrial-scale nanofiltration process that could process 3.61 of chicken carcasses in a day was designed by applying the model. 

Pontalier P.-Y., Ismail A., Dodds J., Ghoul M. (1995), Modelling of convective and diffusive transports in nanofiltration process, Proc. of Euromembrane 95, Vol 1,197-200. 

Likewise, nanofiltration can be integrated into waste water treatment. Combined reverse osmosis/nanofiltration processes can offer higher water recovery than either process alone [122]. Moreover, nanofiltration can be combined with other membrane filtration processes [123], electrodialysis [124], or other waste water treatment processes such as ozonation [125]. 

Nanofiltration. The nanofiltration process is, along with baclq)ulse filtration (Section 7.5.4.3), another example of the new possibilities in processing that are due to recent developments in the field of membrane technology. At conditions intermediate between those used in ultrafiltration and RO, this technology can selectively reject multivalent ions such as 804 while passing monovalent ions [147-149]. The process therefore can remove sulfate and other multivalent anions selectively from alkali chloride brines. Since the equivalent amount of alkali metal ions is held back by electrostatic forces, the net effect is the removal of M2SO4. 

Chemetics is the developer and licensor of the nanofiltration process. By mid-2002, 16 units had been sold or committed [150]. Their removal capacity ranges from 18 to 360kghr of Na2S04. Combined capaeity is for the removal of about 1,400kghr This represents perhaps 350,000 tons per year of NaCl recovered from purge streams. 

Koyuncu I, Topacik D, Yuksel E (2004), Reuse of reactive dyehouse wastewater by nanofiltration process water quality and economical implications , Purifica-... 

Electrospinning is a process utilized by the nanofiltration process, in which fibers are stretched and elongated down to a diameter of about 10 nm. The modified nanofibers that are produced are particularly useful in the filtration process as an ultra-concentrated filter with a very large surface area. Studies have found that electrospun nanofibers can capture metallic ions and are continually effective through re-filtration. 

Boussahel, R., Bouland, S., Moussaoui, K. M., and Montiel, A. (2000). Removal of pesticide residues in water using the nanofiltration process. Desalination 132(1-3), 205-209. 

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