Comparison of commercial membranes in nanofiltration of sweet whey

Abstract

The performance of commercial nanofiltration membranes was studied during concentration and demineralization of sweet whey. The tested membranes were Desal-5 DK, NF45 and Koch SR1. Two different generations of the NF45 membranes were studied. Concentration of whey was made both with a flat-sheet module and in a pilot plant equipped with one spiral wound element. The new generation of the NF45 membrane has comparable retention characteristics with the Desal-5 DK. The Koch SR1 membrane has lower salt and lactose retention than the Desal-5 DK and similar retention characteristics to the older generation of the NF45, which is no longer commercially available. When using the new generation of the NF45 membrane one can expect lower permeate flux and higher retention of salts and lactose than before with the older generation of the NF45 membrane. The highest permeate fluxes of the tested membranes were reached with the Koch SR1 membrane. Concentration of sweet whey with a flat-sheet module and a spiral wound element resulted in similar concentrate composition. Therefore, the flat-sheet module may be used when information on product composition is being investigated. The permeate flux was higher with the flat-sheet module than with the spiral wound element. Thus, either the spiral wound module is more prone to concentration polarization than the flat-sheet module or one can assume that the whole membrane area of the spiral wound module is not used effectively.