Effects of selective layer properties of ceramic multi-channel microfiltration membranes on the milk protein fractionation

The objective of this study was to determine the influence of the selective layer properties of ceramic multi-channel microfiltration (MF) membranes on the filtration performance during milk protein fractionation. Membranes with selective layer material of Al₂O₃, TiO₂, or ZrO₂ (nominal pore size 0.1 µm) were compared with respect to flux and β–Lactoglobulin (β-Lg) permeation at different transmembrane pressures (Δp_TM) at 10 °C and 55 °C. Differences in the membrane performance could be linked to the specific characteristics of the selective layer material, zeta-potential, pore size distribution as well as the membrane and fouling resistance. Furthermore, it could be shown that the flux decreases for Al₂O₃ and TiO₂ after reaching the limiting flux, when a stepwise increase in Δp_TM was performed. This effect was caused by the over-proportional increase in the fouling resistance due to a pressure-driven increase of the pore fouling. Caustic and acidic conditioning of the membrane were shown to affect flux as well as β-Lg permeation in the dependence of the selective layer material. After an acidic conditioning, the decrease in flux became more pronounced for materials with a wider pore size distribution, whereas the β-Lg permeation was reduced, which could be explained by the related zeta-potentials.