This is one of the types of membrane filtration, which uses membranes with the smallest pore size, separating molecules and ions with a size of less than 0.0005 µm and allowing only water to pass through. The separation mechanism has a diffusion character. Due to the high osmotic pressure, the operating pressure for reverse osmosis ranges from 1 to 10 MPa.
In practice, the reverse osmosis process is used for two main purposes:
• recovery of a pure solvent (most often water) in a practically pure state without the content of colloidal and other inclusions remaining in the concentrate;
• selective separation of substances between filtrate and concentrate.
Main application of reverse osmosis
• introductory thickening of whey, permeate after ultrafiltration, milk, fruit juice (eg apple juice);
purification of permeate after reverse osmosis (RO-Polisher process) and nanofiltration, condensate after condensing milk, fruit juices on vacuum evaporators.
When using a reverse osmosis plant to thicken milk, the concentration is most often brought to 29% of solids. The resulting permeate is process water. A similar result is obtained using reverse osmosis for skimmed milk concentration with a final thickening rate of 28-29%. This means that the thickening of whole and skimmed milk is extremely efficient when 3x thickened! as it reduces production costs when using vacuum evaporators on the volumes of moisture removed that, in the case of membrane filtration units, can be returned into the production process.
The use of reverse osmosis is especially effective if the company specializes in the production of concentrates or dry milk products. Also, those enterprises that transport whey or milk for drying to neighboring enterprises receive significant savings on transportation costs, since the volume of transportation is reduced significantly.