Influence of Spacer Design and Module Geometry on the Filtration Performance during Skim Milk Microfiltration with Flat Sheet and Spiral-Wound Membranes

Spacer design in spiral-wound membranes (SWMs) significantly affects the axial pressuredrop in the flow channel but also the deposit layer removal. However, the effects of the spacerdesign and feed flow distribution in the module on the filtration performance have not yet beeninvestigated during the highly fouling-susceptible fractionation of proteins from skim milk bySWMs. Therefore, a parallel spacer with no turbulence promotion and a less homogeneous feedflow distribution in the SWM was compared to a diamond spacer with regard to its impact ondeposit formation and filtration performance. The experiments were conducted in a flat sheet testcell and in SWMs. The parallel spacer induced a more homogeneous deposit layer formation.However, no difference in filtration performance could be observed in the experiments with the testcell. Even though deposit layer formation dominates the microfiltration, its amount and spatialdistribution could not be directly linked to the filtration performance. Furthermore, both spacerswere assessed in SWM. Despite the higher crossflow velocity applicable in the more open channelsof the parallel spacer, the performance of the parallel spacer was inferior to the diamond spacer.This was independent of the viscosity of the feed. Due to the high curvature of the membrane sheetsclose to the permeate collection tube, the cross-section of the flow channels in the SWM equippedwith the parallel spacer was reduced. This resulted in a distinctly lower deposit layer control andperformance, which could not be compensated by the resulting higher crossflow velocity far fromthe permeate collection tube.