Hydrodynamic factors affecting flux and fouling during ultrafiltration of skimmed milk

The effects of independently varying both wall shear stress ( τ w ) and transmembrane pres- sure (TMP) on permeate flux and fouling during ultrafiltration of reconstituted skimmed milk in total recycle mode have been investigated. Irreversible fouling resistance ( R if ) increased as TMP increased. Increasing τ 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 τ w , increasing TMP resulted in greater initial flux accom- panied by increasing rates of flux decline and more irreversible fouling. Increasing and then decreas- ing TMP in a controlled, stepwise manner at constant τ w suggested 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 evaluated during this procedure.