Tangential microfiltration

The role of carbohydrate colloids in wine clarification and stability has been studied much more extensively. Pectic substances in wine foul filter layers (Castino and Delfini, 1984) during filtration. This phenomenon is particularly marked in tangential microfiltration (Section 11.5.2) (Feuillat and Bernard 1987 Serrano et al., 1988) as the carbohydrate colloid retention rate may be over 50%. A much higher proportion of AGPs than yeast mannoproteins is retained in this process (Brillouet et al., 1989 Belleville et al., 1990). 

Synthetic membranes with calibrated pores are used for various operations in the wine industry ultrafiltration, front-end microfiltration, tangential microfiltration and reverse osmosis. Electrodialysis and pervaporation, special separation techniques described elsewhere in this book (Section 12.5.1), also make use of membranes. 

Tangential microfiltration has been used in many wine treatment applications over the past 10 years. Suitable membranes are now available for clarifying must or untreated wines, as well as the final clarification of prefiltered wines. This technique may also provide an alternative to filtration through diatomaceous earth precoats, especially in cases where waste discharges could lead to excessive pollution. Tangential microfiltration is still. 

Clarifying wines it is now possible to integrate tangential microfiltration into the winemaking process, especially for white wines, which achieve better flow rates than reds. 

All types of tangential microfiltration produce higher quality clarification than those achieved by filtration through a kieselguhr precoat. However, the filtrates are not always sterile, particularly when unclogging by reversed flow has destroyed the polarization layer. 

Analysis shows that concentrations of polysaccharides and volatile fermentation products in white wines are reduced by tangential microfiltration, as compared to filtration through a kieselguhr precoat. Anthocyanins and tannins are affected in red wines. However, in view of the natural modifications that occur in wines during aging, these differences tend to become less marked over time. The standard tests used in organoleptic analysis did not identify any significant differences (threshold of 5%) after samples had been kept for 1, 6, and 12 months. 

Three different milk samples were analysed by P solid-state NMR spectroscopy a milk powder sample ( PL60 obtained from a tangential microfiltration of skim milk, Triballat, France) rehydrated at 68% (32% PL60 w/w in D2O, pH=6.37), a lipoproteic matrix as a model cheese sample and a semi-hard cheese. 

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.). 

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. 

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. 

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. 

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. 

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... 

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