Reverse Osmosis of Dairy Liquids

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Abstract
Permeate flux during reverse osmosis of skim milk, Gouda cheese whey at various pH, desalted whey, ultrafiltration permeate, and lactose solutions were studied. The flux-limiting factors of the feed appeared to be osmotic pressure and fouling agents. Protein in Gouda whey at pH 6.6 did not give rise to fouling; however, after desalting or decrease of pH to 4.6, fouling by whey protein occurred. If Gouda whey was concentrated at 30 C over a concentration ratio of 1.6:1, calcium-phosphate precipitation caused strong fouling of the membrane. This fouling can be prevented by removing calcium from the whey or by acidifying to a pH of about 6.0. During reverse osmosis of skim milk, casein is the principal fouling material. To understand better the influence of the process conditions on the permeate flux, the effect of concentration polarization and fouling was calculated for various conditions. It appeared possible to achieve a reasonably low concentration polarization and fouling by applying, in a tubular system, flow velocities of 2 m/s for whey and of 2.5 m/s for skim milk. Furthermore, for skim milk an optimum process pressure was about 3.5 MPa.

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