Presented at the 2nd Membrane Science and Technology Conference of Visegrad Countries (PERMEA), Polanica Zdroj, Poland, 18–22 September 2005. 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved Desalination 198 (2006) 274–281 Partial demineralization of whey and milk ultrafiltration permeate by nanofiltration at pilot-plant scale Eva Suárez a , Alberto Lobo a , Silvia Álvarez b* , Francisco A. Riera a , Ricardo Álvarez a a Department of Chemical Engineering and Environmental Technology, University of Oviedo, C/Julián Clavería 8, 33006 Oviedo, Spain b Department of Chemical and Nuclear Engineering, Polytechnic University of Valencia, s/n. 46022 Valencia, Spain Tel. +34 (96) 387-7000; Fax: +34 (96) 387-7639; email: sialvare@iqn.upv.es Received 3 November 2005; Accepted 7 December 2005 Abstract The membrane technique of nanofiltration (NF) was used to carry out partial demineralization of whey and milk ultrafiltration permeate (MUP). The experiments were carried out in a completely automated NF pilot plant. An aromatic polyamide spiral-wound membrane supplied by Osmonics (USA) was selected (model DK2540C). Feed, permeate and retentate were analyzed for lactose, protein, ashes, ions (Ca 2+ , Na + , K + , Mg 2+ , P, Cl ! ) and total dry extract content. Different operating conditions were considered. By means of NF total salt content was reduced at least by 30%, depending on the operating conditions and volume concentration ratio. Monovalent ions showed lower retention than divalent ones. Higher salt retention was obtained when whey was used as the feed stream. However, permeate fluxes were higher for MUP due to the lower amount of proteins, which can form a gel layer on the membrane surface. Protein and lactose permeation was observed to be negligible. Keywords: Nanofiltration; Whey; Milk ultrafiltration permeate; Demineralization 1. Introduction Whey and milk ultrafiltration permeate (MUP) are wastewaters obtained during the industrial production of cheese. Whey is the liquid that is separated from cheese after the coagulation of *Corresponding author. milk. It contains proteins (8.4 g/L), lactose (79 g/L), fat (<2.5 g/L) and mineral salts (5.6– 8.4 g/L). MUP is obtained when milk is concen- trated prior to cheese production. Its composition is similar to that of skim milk except for the negligible amount of proteins that it has. It mainly contains minerals, lactose and riboflavin, but it does not have enzymes and microorgan-