Hydrodynamic factors affecting flux and fouling during ultrafiltration of skimmed milk

The effects of independently varying both wall shear stress (tau(w)) and tr ansmembrane pressure (TMP) on permeate flux and fouling during ultrafiltrat ion of reconstituted skimmed milk in total recycle mode have been investiga ted. Irreversible fouling resistance (R-if) increased as TMP increased. Inc reasing tau(w) at constant TMP led to an increase in both the initial flux, and subsequent flux decline, and to a decrease in R-if. At the highest tau (w), increasing TMP resulted in greater initial flux accompanied by increas ing rates of flux decline and more irreversible fouling. Increasing and the n decreasing TMP in a controlled, stepwise manner at constant tau(w) sugges ted that flux is governed by both a reversible, and an irreversible fouling layer which forms at higher TMP; this also controlled the transmission of protein. Critical operating conditions producing the least fouling were eva luated during this procedure.