Ultra-filtration is another pressure separation process. The ultra-filtration membrane retains particles with the dimension of 100–3 nm and the molecular weight of 103–105 Da which corresponds e.g. to viruses, proteins, polysaccharides or colloidal particles. The required pressure difference is 5 to 10 bar.
The most important applications of ultra-filtration are in the food processing industry in milk concentration, production of cheese, obtaining proteins from whey or starch from potatoes.
Other examples of the application of ultra-filtration include preparation of sterile water or purification of proteins in the pharmaceutical industry, purification and stabilization of fruit juices, preparation of drinking water, recycling of water from electrochemical painting or cleaning of cutting or cooling emulsions.
Ultra-filtration membrane modules can be made of hollow fibres (most common use), flat, tubular or spirally wound. Membranes are typically made of polymers, such as cellulose acetate, polyamides and polyesters, but also of inorganic materials like glass, alumina or mix of zirconium dioxide and carbon.
Ultra-filtration was used for instance for pre-treatment of water before reverse osmosis in some of our pilot projects for preparation of inflow water in power engineering.