Tangential-flow microfiltration

F. Pouet, F. Persin, M. Rumeau, Intensive treatment by electrocoagulation - flotation - tangential flow microfiltration in areas of high seasonal population, Water Res. 25 (1992) 247-253. 

One disadvantage of this type of filtration is that it involves discharging large volumes of diatomaceous earth that represent a source of environmental pollution. Furthermore, staff handling these filters work in an atmosphere contaminated with dust. Tangential flow microfiltration (Section 11.9.1) may be a suitable replacement technique. 

Vaks B, Mory Y, Pederson JU et al. (1984) A semi-continuous process for the production of human interferon- ac from E. coli using tangential-flow microfiltration and immuno-affinity chromatography. Biotechnol Lett 6(10) 621-626... 

Wickramasinghe, S. R., Kalbfuss, B., Zimmermann, A., Thom, V., and Reichl, U. (2005). Tangential flow microfiltration and ultrafiltration for human influenza A vims concentration and purification. Biotechnol. Bioeng. 92(2), 199. 

Filtration Cross-flow filtration (microfiltration includes cross-flow filtration as one mode of operation in Membrane Separation Processes which appears earlier in this section) relies on the retention of particles by a membrane. The driving force for separation is pressure across a semipermeable membrane, while a tangential flow of the feed stream parallel to the membrane surface inhibits solids settling on and within the membrane matrix (Datar and Rosen, loc. cit.). 

Cross-flow filtration is also referred to as tangential flow filtration or microfiltration, but all three terms refer to a process by which membranes are used to separate components in a liquid solution (or suspension) on the basis of their size. The development of robust membranes in polymeric and ceramic materials has provided a powerful new technology for bioseparations, which is already widespread in the process industries as well as for water treatment processes. 

Microfiltration. Microfiltration, the use of tangential flow anisotropic membranes to permeate the product of choice while retaining solids, can be an attractive cell separation technique because it does not require the use of flocculants or filter aids. It is, in principle, a more technically sophisticated version of classic dead-end filtration processes. Microfiltration yields can be low due to progressive fouling of membranes. Advanced engineering has overcome many of the early... 

It has been previously shown that dynamically formed or formed-in-place ultrafiltration membranes naturally set down when biological molecules such as proteins tangentially flow along a ceramic microfiltration membrane. This new membranes directly result from infiltration/deposition of macromolecules, i.e. fouling mechanisms, that develop on the original filtering element. 

As shown in Figure 7.2.6(a), consider a microfiltration membrane with the tangential flow of the suspension over it in the direction of the membrane length coordinate z. The suspension pressure is likely to be 1 to 2 atmospheres above the pressure on the other side of the membrane. The coordinate normal to the membrane into the suspension is y. A suspension having a solids volume firaction contacts the membrane at z = 0 and flows along z. As filtrate goes through the membrane, rejected solid particles build up... 

Consider a typical antibiotic production process, as illustrated in Figure 11.1.1. The antibiotic is present in a fermentation broth as a very dilute solution in the presence of considerable soluble impurities, as well as a significant concentration of whole cells and cellular debris. The particulate materials, such as whole cells, cell debris, etc., are removed first by filtration or centrifugation. The filtration method is described under rotary vacuum filtration (Section 7.2.1.5) or microfiltration (Section 7.2.1.4) of the tangential-flow type (TFF). Centrifugation is illustrated in Sections 7.3.2.1 and 7.S.2.2 via different types of centrifuges. This step has heen characterized as removal of insolubles (Belter et al, 1988) - it is essentially separation of cellular particles from a liquid solution of the product. 

Tangential-flow filtration is typically operated in one of two modes concentration or diafiltration (see Fig. 20.2). For microfiltration, in the concentration mode, the product of interest usually passes through the pores of the membrane and is collected in the permeate. However, since MF membranes are nonselective, flie concentration of the product of interest will be the same in the retentate and permeate streams. 

While vims filtration is generally conducted using normal flow filtration, tangential-flow filtration may be useful especially when the difference in size between the vims particles and product species is less than an order of magnitude. If microfiltration is used for bio-reactor harvesting, flocculating the feed prior to microfiltration can lead to significant vims clearance in the permeate. 

Tangential crossflow filtration Process where the feed stream sweeps the membrane surface and the particulate debris is expelled, thus extending filter life. The filtrate flows through the membrane. Most commonly used in the separation of high-and-low-molecular weight matter such as in ultrapure reverse osmosis, ultrafiltration, and submicron microfiltration processes. 

In cross-flow flltration, the wastewater flows under pressure at a fairly high velocity tangentially or across the filter medium. A thin layer of solids form on the surface of the medium, but the high liquid velocity keeps the layer from building up. At the same time, the liquid permeates the membrane producing a clear filtrate. Filter media may be ceramic, metal (e.g., sintered stainless steel or porous alumina), or a polymer membrane (cellulose acetate, polyamide, and polyacrylonitrile) with pores small enough to exclude most suspended particles. Examples of cross filtration are microfiltration with pore sizes ranging from 0.1 to 5 pm and ultrafiltration with pore sizes from 1 pm down to about 0,001 pm. 

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