Microfiltration of skim milk using hollow fiber membranes: Impact of membrane length, crossflow velocity and diafiltration cycles

This paper investigates the casein - serum protein fractionation efficiency during both the concentration and diafiltration using hollow fiber membranes and reverse osmosis water at 10°C and the effect of membrane length and crossflow velocity. Membrane module length had no effect on flux and transmission and flux increased with increasing crossflow velocity with no effect on transmission, as the sieving layer made up of casein remained unchanged. Diafiltration at volume reduction factor of 2.5 at 0.5 bar transmembrane pressure gave the highest serum removal. Further diafiltration above three diafiltration cycles is not desired as the purity of the serum protein gets compromised. Usage of reverse osmosis water as the diafiltration medium achieves high serum removal even though it induces structural changes of the concentration polarization layer. Finally, this study verifies that hollow fiber membranes can be used effectively in the dairy industry where reverse osmosis water is the main diafiltration medium. • 750 mm module offers the advantage of shorter filtration times with same level of serum protein transmission as 300 mm module • Skim milk filtration is deposit controlled hence causing same level of serum protein transmission for different lengths • Higher crossflow velocity increases the mass flux of serum protein • Reverse osmosis water as diafiltration medium results in increase in permeate flux due hydration of the deposit layer • Increased number of diafiltration cycles increases the recovery of serum proteins in the permeate at the expense of casein recovery in the retentate