DESALINATION OF ACID CASEIN WHEY BY NANOFILTRATION

Acid casein whey was concentrated by using a plate-and-frame nanofiltration unit fitted with a polymeric thin film composite membrane, type HC-50. Initial flux rates were in the range 36-40 L m(-2) h(-1) and declined to 10 L m(-2) h(-1) or less after four times volume concentration reduction (VCR 4). Clarifying whey by microfiltration to remove residual fat greatly enhanced flux rates during nanofiltration with initial flux rates of 60 L m(-2) h(-1) declining to 31 L m(-2) h(-1) after VCR 4. Adjusting the acid casein whey to pH 5.2 in combination with heat treatment (72-80 degrees C for 15 s) optimized the permeation rates, Ash reduction of 35% was obtained after 4x concentration, and this was increased to 41% after diafiltration. Monovalent ions permeated more readily through the membrane than divalent or polyvalent types during the course of whey concentration, Cl- was reduced by 41.1% in acid whey and approximately 72.0% in Cheddar and rennet wheys. The Donnan effect was exploited to enhance chloride permeation from acid whey. The addition of trisodium citrate as a co-ion to either model solutions based on artificial milk serum or acid whey increased the permeation of the Cl-. At the higher levels of addition, the citrate ion had the effect of reducing Cl- in dry matter by 70% after VCR 4 concentration.