Influence of pulsed and alternating flow on the filtration performance during skim milk microfiltration with flat-sheet membranes

Abstract

Control of deposit formation during skim milk microfiltration (MF) remains challenging, particularly in membranes with spacer nets between membrane layers like flat-sheet and spiral-wound membranes, due to the extensive occurrence of flow shadows behind spacer filaments. One approach to improve process control and efficiency is applying pulsed or alternating flow, which creates regular fluctuations in shear stress, pressure and, for alternating flow, in flow direction. This study assessed the effects of these alternative flow types and compared them to conventional steady crossflow on deposit formation and filtration performance. Flux and protein permeation were monitored during filtration. After filtration, the membranes were removed and deposited proteins stained by Coomassie-blue. The visual analysis of the stained membranes confirmed that the alternative flow types improved access to flow shadows behind spacer filaments by causing a significantly reduced deposition or enhanced removal. Consequently, the reduced deposit formation with pulsed and alternating flow led to enhancements in the steady-state whey protein mass flow by > 8% and > 37% over any steady flow conditions. Considering the flow-specific pump energy demands, pulsed and alternating flow not only improved filtration performance, but also reduced specific energy consumption relative to whey protein mass transfer by > 60%.