Desalination of acid casein whey by nanofiltration

Abstract

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 micro filtration 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 °C for 15 s) optimized the permeation rates. Ash reduction of 35% was obtained after 4× 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.