On the reversibility of deposit formation in low temperature milk microfiltration with ceramic membranes depending on mode of adjustment of transmembrane pressure and wall shear stress

Abstract

During the microfiltration of skim milk, flux and protein permeation decrease due to the formation of a deposit layer. For a better understanding of the deposit formation during the microfiltration of skim milk at 10 °C, flux and protein permeation were studied with a ceramic multichannel membrane (nominal pore size (nps) = 0.1 µm) at wall shear stress (τw) values from 45 to 341 Pa. When the limiting transmembrane pressure was applied, the flux showed a nearly linear increase with increasing wall shear stress and peaked at a critical τw. A further increase of τw resulted in a reduction of the flux until it levelled off. Thus, we could define a limiting τw additionally to the critical τw, at which no further changes in flux were observable. The limiting flux indicates that no structural changes in the deposit layer occur beyond the limiting τw. This conclusion is reassured by the development of the protein permeation. Beyond the limiting τw, no changes in the protein permeation could be observed. The critical and limiting τw are useful values for the design of fractionation processes by means of ceramic microfiltration.