Effect of multivalent cations on membrane‐foulant and foulant‐foulant interactions controlling fouling of nanofiltration membranes
Oranso T. Mahlangu, Bhekie B. Mamba, Arne Verliefde
Abstract
Insight was gained into the various factors influencing membrane fouling in the presence of different cations. Membrane‐foulant interaction energies were computed from contact angle measurements following the Lifshitz‐van der Waals/acid‐base approach. A unique approach was used to investigate cake‐enhanced concentration polarization (CECP) effects. Calcium worsened organic fouling through organic‐calcium complexation and increasing foulant affinity for the membrane surface, whereas magnesium and lanthanum had less influence on membrane fouling as they moderately decreased the foulants' affinity for the membrane surface. Fouling was facilitated by permeation drag and reduction in membrane‐foulant electrostatic repulsive interactions due to slight neutralization of foulant and membrane zeta potential. Although cake layers formed in the presence of magnesium and lanthanum had low resistance to water flow, the cake layers resulted in severe CECP effects. Initial membrane fouling rates related well to energies of adhesion, whereas later fouling rates did not show clear correlation to energies of cohesion.