Fouling, in ultrafiltration

Huisman, I.H., Pradanos, P., and Hernandez, A., The effect of protein-protein and protein-membrane interactions on membrane fouling in ultrafiltration, J. Membr. Sci., 179, 79, 2000. 

One of the factors causing fouling in ultrafiltration membranes is the adsorption of solutes in the membrane pores. Since fouling, in general, has been discussed in the previous chapter, the discussion presented here will be restricted to the adsorption phenomenon. Clark et al. [37] studied the relationship between membrane fouling and protein adsorption on alumina ultrafiltration membranes. Equilibrium adsorption of bovine serum albumin (BSA) was measured by the standard static method at 7°C. Their study covered the concentration range between 1 and 10 g/1, pH values between 2 and 10 and NaCl... 

Hamza A, Pham VA, Matsuura T, Santerre JP. Development of membranes with low surface energy to reduce the fouling in ultrafiltration applications. J. Membr. Sci. 1997 131 217. 

A novel membrane module design. Top Cross-sectional view of a membrane-coated channel. Bottom Channel flow pattern. High surface-area modules could reduce the relative cost of pervaporation. The short, narrow, non-uniform, multi-path channels that create higher shear ate formed. The turbulence promoting pathways could go a long way to mitigate fouling in ultrafiltration and microfiltration membrane systems. 

A second factor determining module selection is resistance to fouling. Membrane fouling is a particularly important problem in Hquid separations such as reverse osmosis and ultrafiltration. In gas separation appHcations, fouling is more easily controlled. Hollow-fine fibers are notoriously prone to fouling and can only be used in reverse osmosis appHcations if extensive, costiy feed-solution pretreatment is used to remove ah. particulates. These fibers caimot be used in ultrafiltration appHcations at ah. 

Two other major factors determining module selection are concentration polarisation control and resistance to fouling. Concentration polarisation control is a particularly important issue in liquid separations such as reverse osmosis and ultrafiltration. Hollow-fine-fibre modules are notoriously prone to fouling and concentration polarisation and can be used in reverse osmosis applications only when extensive, costly feed solution pretreatment removes all particulates. These fibres cannot be used in ultrafiltration applications at all. 

Solute adsorption often involves hydrophobic interactions—hydrophobic membranes have a high tendency to foul in water treatments. However, many hydrophobic membranes remain the most useful media for ultrafiltration due to their superior performance in terms of mechanical, chemical and thermal stability. 

Figure 6.5 Ultrafiltration flux as a function of time of an electrocoat paint latex solution. Because of fouling, the flux declines over a period of days. Periodic cleaning is required to maintain high fluxes [14]. Reprinted from R. Walker, Recent Developments in Ultrafiltration of Electrocoat Paint, Electrocoat 82, 16 (1982) with permission from Gardner Publications, Inc., Cincinnati, OH...

As described above, the initial cause of membrane fouling is concentration polarization, which results in deposition of a layer of material on the membrane surface. The phenomenon of concentration polarization is described in detail in Chapter 4. In ultrafiltration, solvent and macromolecular or colloidal solutes are carried towards the membrane surface by the solution permeating the membrane. Solvent molecules permeate the membrane, but the larger solutes accumulate at the membrane surface. Because of their size, the rate at which the rejected solute molecules can diffuse from the membrane surface back to the bulk solution is relatively low. Thus their concentration at the membrane surface is typically 20-50 times higher than the feed solution concentration. These solutes become so concentrated at the membrane surface that a gel layer is formed and becomes a secondary barrier to flow through the membrane. The formation of this gel layer on the membrane surface is illustrated in Figure 6.6. The gel layer model was developed at the Amicon Corporation in the 1960s [8],... 

Brine Staging Velocity past the membrane is important. If too low, polarization is excessive, local O rises, and rejection declines. Fouling occurs faster. If too high, pressure losses are higher than they need be, and the osmotic pinch is premature. Since the volume of feed declines continuously, the hydraulic design needs periodic rearrangement. This is commonly done as shown in Fig. 22-64, sometimes known as a Christmas tree. This design is commonly used where the fluid is pumped once, as in RO, NF, and gas-separation systems, but not where recirculation is practiced, as in ultrafiltration. 

Vladisavljevic GT, Vukuosavljevic P, and Bukvic B. Permeate flux and fouling resistance in ultrafiltration of depectinized apple juice... 

Rodriguez C, Sarrade S, Schrive L, Dresh-Bazile M, Paolucci D, and Rios GM. Membrane fouling in cross-flow ultrafiltration of mineral oil assisted by pressurized CO2. Desalination 2002 144 173-178. 

Marshall, A.D., Munro, P.A., and Tragardh, G., The effect of protein fouling in microfiltration and ultrafiltration on permeate flux, protein retention and selectivity A literature review, Desalination, 91, 65, 1993. 

Zumbusch P and Kulcke W. Use of alternating electrical fields as anti fouling strategy in ultrafiltration of biological suspensions Introduction of new experimental procedure for crossflow filtration. J Membr Sci 1998 142 75-86. 

M. Tucker and J. Hubble, Membrane fouling in a constant-flux ultrafiltration cell. /. Membr. Sci., 34 (1987) 267. 

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