Protein aggregate deposition and fouling reduction strategies with high-flux silicon nitride microsieves

Membrane morphology is a key factor in fouling. Characteristics such as a very thin selective layer, well-structured pore size and shape, and smooth surfaces would be ideal for low-fouling membranes. Microsieves, inorganic membranes with high and controlled porosity, offer all the previous features. The goal of this study was the investigation of the mechanism behind flux decline in crossflow filtration of bovine serum albumin (BSA) solutions with microsieve membranes. Subsequently, several strategies to reduce flux decline were also analyzed. The flux decline rate was pH-dependent, with a more severe reduction at pH close to the isoelectric point. In-line pre-filtering of the BSA solution led to stable fluxes, which indicated that pore blocking was responsible for the decrease in performance. Modelling of the filtration data confirmed a complete pore blocking mechanism. At pH where the decline was lower (6.8), water backflushing helped to recover the flux partially. Water forward flushing was only effective at relatively high permeation rates. As an alternative method, permeate backpulsing was investigated. The permeated volume was successfully increased and the flux decrease retarded when backpulsing was applied. If the permeate was backpulsed at higher frequencies, lower fouling rates were achieved, because aggregates could be removed faster from the microsieve surface.