Demineralization of whey and milk ultrafiltration permeate by means of nanofiltration

In this work, the membrane technique of nanofiltration (NF) was used to carry out partial demineralization of whey and milk ultrafiltration permeate (MUP). The experiments were performed in a completely automated NF pilot plant. An aromatic polyamide spiral wound membrane supplied by Osmonics (USA) was selected (DK2540C model). Batch and discontinuous diafiltration (DF) configurations were compared. Permeate fluxes were higher for MUP due to the lower amount of proteins, which can cause severe membrane fouling. The degree of demineralization for the divalent cations was negligible for both feed streams. Protein and lactose permeation were also observed to be very low. Ion permeation was higher for MUP probably due to the lower amount of proteins. When discontinuous DF was performed, ion removal increased in the case of whey, but it did not significantly improve in the case of MUP. The degree of ion removal was higher than 30%. Finally, the Donnan Steric Partitioning pore Model was used to predict lactose and ion rejection. A good agreement between predicted and experimental data was observed.