CROSS-FLOW MICROFILTRATION OF BETA-LACTOGLOBULIN SOLUTIONS AND THE INFLUENCE OF SILICATES ON THE FLOW RESISTANCE

With the aim of studying the mechanism of fouling during cross-flow mi crofiltration (CF-MF) of beta-lactoglobulin (beta-lg) solutions, it wa s found that the presence of particles severely influenced the membran e filtration process. Capturing these particles by a dead-end prefiltr ation of the feed removed the particles adequately but not completely. The formation of beta-lg particles due to aggregation during processi ng was excluded as the cause of the initial flux decline. By infrared absorption and energy dispersive spectroscopy analysis it was found th at silicates were present in the experimental system. A complex interp lay of silicates, an unidentified aliphatic component, beta-lg and the membrane surface properties is responsible for the formation of parti cles in the system and the development of a deposit on the membrane su rface, which results in flux decline. The practical implication of the se findings is that small quantities of particles present in protein s olutions completely determine flux behaviour during CF-MF. The presenc e of particles (non-protein material, protein aggregates, bacteria) in industrial feed is inevitable, which means that during industrial CF- MF they also determine the decline in flux. It was also shown that wat ers meeting cleaning-in-place (CIP) standards for membrane processing can still cause flux decline. By analysing the deposition mechanism oc curring during CF-MF of beta-lg using a method combining two procedure s recently discussed by Bowen et al. [1] and Field and Arnot [2], it w as found that four successive stages occurred: (i) pore blocking in th e presence of a back flux of particles, (ii) pore blocking which is ir reversible, (iii) irreversible cake formation and (iv) the build-up of a reversible cake including the development of a concentration polari zation layer. In addition, the method allowed the identification of th e build-up of a reversible and an irreversible flow resistance.