Filtration flux changes

Figure 5.10. (A) Experimental set-up of membrane and US wave. (B) Permeate flux change with the filtration time for (a-to-c) filtration. The working frequency for (a) (m), (b) (n) and (c) ( ) was 45 kHz. (o) corresponds to an experiment in configuration (a) without US. The feed flow-rate of 1 wt% dextran solution was 325 ml/min. (Reproduced with permission of Elsevier, Ref [92].)...

If the studied mass transport model has sufficiently limited length, which affects the distribution of components dissolved in it, it is called bounded. If the filtration flux is drained into a large basin of actively mixed surface water (sea, lake, river, etc.), where the concentrations of studied components practically do not change, the boxmdary conditions of first or third type are used, same as at the beginning of flux. If the composition of... 

Liithi and Luisi [44] have used a hoUow fiber membrane reactor for peptide synthesis catalyzed by a-chymotrypsin in microemulsion. Chang et al. [110] described the immobilization of lipase on liposomes, which, in turn, were solubilized in AOT/isooctane reversed micelles and used for the continuous glycerolysis of olive oil in an ultrafiltration cell. The half-Ufe of the Chromo. viscosum lipase was 7 weeks. The development of an ultrafiltration ceramic membrane bioreactor for the simultaneous lipolysis of olive oil and product separation in AOT/isooctane reversed micellar media has been also reported [106,107], Cutinase performance was also evaluated in a ceramic membrane reactor [9]. An attempt to minimize the surfactant contamination problem was based on the use of an electro-ultrafiltration method which can decrease the gel formation in the membrane surface, improving the filtration flux, achieving the separation of the AOT reverse micelles [187],... 

To determine the filtration flux we need to know <5 -how it changes with time as the cake layer builds up (Davis and Grant, 2001). To develop an equation for 5c with time, we need to make a mass balance for the solids in the slurry/suspension being filtered. Define the following quantitites ... 

Effects of Membrane Filtration Method on Membrane Filtration Flux Figure 5.12 shows the changes in ozone dosage, dissolved ozone concentration of MF permeate, and membrane filtration fluxes when ozone was injected with an ejector and water was filtrated with cross-flow (Run 11) and dead-end (Run 12) methods. Membrane filtration flux for the dead-end method was higher than that of the cross-flow method, and high membrane filtration flux operation (about 6 m /m /day) was achieved with 3 mg/L ozone dosage. 

Figure 5.15 Changes in membrane filtration flux before and after air scrubbing.

Volume changes, by vitreous silica, 22 438 Volume flux, of droplets, 23 187 Volume fraction, in filtration, 11 328 Volume fraction calculation, in equivalent box model, 20 345—346 Volume mean diameter, 23 186 Volume of activation, 13 407-408... 

The change of flux velocity with transmembrane pressure can be explained by the concentration polarisation phenomenon. The physical processes at the membrane surface during the filtration procedure may be described by theo-... 

Filtration experiments were carried out using this prepared membrane in a cross-flow apparatus, which was the same as the PWF measurement apparatus. PMMA particles (1000 mg-r, 0.8 pm in diameter) were used as model particle pollutants. When the PMMA solution was introduced by the feed magnet gear pump, the flux of the same object declined to a certain level. In this time, membranes needed regeneration, we used the technique of back washing. To cany out the back washing, we changed the flow direction by niddle valve and used pure water at a pressure of 2 kg cm for 1 minute. 

FIGURE 8.39 Effect of gas velocity on final flux in filtration with submerged membranes. (From Figure 7 in Chang, S. and Fane, A.G., J. Membr. Sci., 184, 221, 2001. With permission.)... 

Chang S and Fane AG, The effect of fiber diameter on filtration and flux distribution-relevance to submerged hollow fiber modules, J. Membr. Sci. 2001 184 221-231. 

During TFF, species retained by the membrane form a concentrated boundary layer, called concentration polarization layer, on the surface of the membrane that creates a resistance to the filtrate flow and reduces flux [11], The effect of polarization is a flux—usually called limiting flux—that does not change with TMP above a critical pressure as shown in Figure 14.2. 

For the UF of proteins, the concentration polarization model has been found to predict the filtration performance reasonably well [56]. However, this model is inherently weak in describing the two-dimensional mass transport mechanism during crossflow filtration and does not take into account the solute-solute interactions on mass transport that occur extensively in colloids, especially during MF [21,44,158,159]. The diffusion coefficient, which is inversely proportional to the particle radius, is low and underestimates the movement of particles away from the membrane [56]. This results to the well-known flux paradox problem where the predicted permeate flux is as much as two orders of magnitude lower than the observed flux during MF of colloidal suspensions [56,58,158]. This problem has then been underlined by the experimental finding of a critical flux for colloids, which demonstrates the specificity of colloidal suspension filtration wherein just a small variation in physicochemical or hydrodynamic conditions induces important changes in the way the process has to be operated [21]. 

It has been suggested in the literature [34] that filtration devices producing Taylor or Dean vortices can help depolarization of the solute build up on membranes. This seems to be an attractive way because of excellent bulk fluid mixing, high wall shear rates and weakly decoupled cross-flow with transmembrane flux. Unfortunately there are some severe limitations on a technical and economical point of view with such devices. Build up and scale up of these modules are expensive with difficulties in repairing and changing membranes. A good compromise between economic and technical constraints has been described by Charpin et al. [39]. It consists in the preparation of mineral (metal... 

Chang et al. [89] filtrate a alcohol-distillery waste with 50 run and 0.4 pm membranes from TIA (Frcmce). Although the 0.4 pm membrane has a higher initial flux, the flux of the 50 nm membrane is always higher in the long nm. At a concentration factor of 2, the flux for the 50 nm pore size amoimts to 2151/m h, for the 0.4 pm pore size it is 1851/m h. The dependence of flux on concentration factor also depends on the type of raw material for the distillation process. 

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