1Department of Food Science and Technology, University of Ferdowsi, P.O. Box 91775-1163 Mashhad, I.R. IRAN
2Department of Chemical Engineering, University of Wales Swansea, Singleton Park, Swansea, SA2 8PP, UK
The effect of membrane molecular weight cut off (MWCO) at three levels (10, 20 & 50 kD) on dynamic behavior of permeate flux (JP), hydraulic resistances (total hydraulic resistance, RT; reversible fouling resistance, Rrf; irreversible fouling resistance, Rif and membrane hydraulic resistance, Rm) and milk solutes rejection (protein, RP; fat, RF; lactose, RL; minerals, RM and total solids, RTS) are studied for the ultrafiltration of milk. Experiments are carried out using the pilot plant UF membrane system equipped with a spiral wound module and a polysulfone amide membrane. A three-stage strategy based on a resistance-in-series model (boundary layer-adsorption) was used to determine the different hydraulic resistances. The results showed that the JP decreases greatly with increasing the process time, but the JP values obtained for 20 kD were considerably higher than 10 kD & 50 kD during the whole process. RT increased during operation at all levels of MWCO, but the hydraulic resistance values for 50 kD were significantly greater than 10 & 20 kD. Results for milk solutes rejection showed that the RP and RF are almost constant with process time at the corresponding MWCO, whereas the RL, RM and RTS significantly increased.
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