Cleaning is a very important part of milk processing because milk spoils easily, producing toxins and bacteria. Because of the nature of the milk stream, processing plants get fouled and must be cleaned every day. There may be complex built-up products from the organic milk streams, making cleaning difficult. Often dairies pre-treat feed to minimize fouling.
Typical CIP systems require three factors for proper cleaning: turbulent flow, chemical concentration, and high temperatures. Most polymeric spiral membrane elements are temperature limited to 50°C (122°F). There are also pH limitations because the membrane material is most often cast onto a polyester backing. This backing is very easily hydrolyzed at high and low pH, so concentrated chemical cleaning is undesirable. Membranes are also somewhat limited by their structural integrity and ability to withstand the high velocity and turbulence of cleaning processes. So all three of the factors required for proper cleaning are limited.
Over the past ten years great advances have been made to make cleaning easier, and more gentle, while retaining its effectiveness. This has allowed the more widespread use of membrane separation and eliminated some of the cleaning problems. These new systems use a mild caustic with enzymes to help break down fouling molecules and chelators, and to hold broken-down products in solution.
In general membrane separation systems have a lower initial investment, but cleaning requirements make the operating costs higher. Cleaning procedures must be followed strictly with little deviation, so service is crucial to make sure dairy operators are running the plant properly and cleaning it adequately and according to guidelines.
Certain types of membranes can be cleaned with chlorine, but many, including polymeric membranes, will not tolerate chlorine treatment. Today’s dairy operations have segregated systems so chlorine cannot come into contact with polymeric membranes and cause damage.