A good example of the successful application of membrane technology is the processing of cheese whey. Table 1 gives some background to the problem. The production of cheese whey is growing at 4% per year and it is estimated that only about 50% of the whey is utilized in any form either for animal feed or in human foods. The proximate composition shown in Table 1 emphasizes some of the problems in treating whey. It has a low solids content, and a very unfavorable protein to lactose ratio of 11:89, which makes it difficult to utilize as animal feed or in human food products. This explains why reverse osmosis (RO) and ultrafiltration (UF) have attracted the attention of cheese producers, since it now affords the possibility of simultaneously purifying, fractionating and concentrating (at low energy cost) the whey and thus enhancing its utilization and reducing its pollution problems.