Impact of cross-flow velocity on skim milk acidification using bipolar membrane electrodialysis with homogeneous ion-exchange membranes

Electrodialysis with bipolar membranes is a separation process of increasing interest in food and dairy applications. In this work, the use of homogeneous cation-exchange membranes and bipolar membranes in combination was examined to increase the acidity of skim milk and reduce its ionic strength. A cross-flow velocity of 7.5 cm·s−1 or greater enabled operation below the limiting current density of the cation-exchange membranes, resulting in high current efficiency. The energy demand required to reduce the pH from 6.6 to 5.7 decreased to around 1.0 Wh·kg−1 of skim milk under these conditions. The use of homogeneous membranes resulted in less fouling than when heterogeneous membranes were used, leading to more stable current densities. The areal resistance, ion-exchange capacity, and permselectivity of the cation-exchange membranes remained unchanged after the experiments, and infrared spectroscopy showed no detectable changes in either the cation-exchange or bipolar membranes, confirming an absence of significant fouling.