Micro-filtration (MF) is a pressure membrane process for removing from a liquid of solid particles with the dimension of 0.01 to 10 μm, e.g. bacteria and yeast cells, mould spores and bigger colloid particles (emulsions, suspensions). A commonly used pressure difference for micro-filtration is 10 to 200 kPa.
Micro-filtration is widely used in food processing industry for stabilization of beverage (beer, wine, fruit juices) and treatment of whey and drinking water. In pharmaceutics, it is used for cold sterilization (of raw materials and products) and purification of fermentation liquids and products (e.g proteins). In metallurgy, it serves to process dispersions and colloid solutions of metals. It is often utilized as pre-treatment for ultra-filtration and nano-filtration.
Micro-filtration can have two arrangements, “dead-end” or “cross-flow”. In the dead-end arrangement, the liquid flow is perpendicular to the membrane surface, the liquid and small particles pass through the membrane pores and bigger particles get caught on the membrane and for the filtration cake. In the cross-flow arrangement, the liquid flows parallel to the membrane surface and bigger particles are transported by the liquid that thickens gradually.
Micro-filtration membrane modules typically consist of hollow fibres and they can be flat, tubular or spirally wound. The most typical materials are polymers, such as polyvinylidene fluoride, polypropylene, polysulfone, cellulose derivatives or inorganic materials like glass, alumina, steel or mix of zirconium dioxide and carbon.
To drink producers, especially winemakers, we deliver the micro-filtration unit WFU-2.2 in the cross-flow arrangement. It serves to remove turbidity and microorganisms from wine before bottling or as final filtration. In one step, it replaces standard multilevel desk or diatomaceous earth filtration.