Protein fouling of nanofiltration, reverse osmosis, and ultrafiltration membranes—The role of hydrodynamic conditions, solution chemistry, and membrane properties

The effect of hydrodynamic conditions, membrane properties, and feed solution chemistry on membrane fouling by bovine serum albumin (BSA) was systematically investigated under crossflow conditions over a 4-day fouling period. The initial flux behavior was highly dependent on membrane properties, where membranes with smoother and more hydrophilic surface and those with favorable electrostatic repulsion experienced less initial fouling. Interestingly, the flux at the end of the 4-day tests (J96 h) showed little dependence on membrane properties, with reverse osmosis, nanofiltration, and ultrafiltration membrane fluxes all converged into a nearly identical value. This suggests that the long-term flux was primarily controlled by the foulant–fouled-membrane surface interaction. Membranes tested at different initial fluxes had a strong tendency to approach to a surface-interaction-limited value, although slightly lower J96 h was observed at increased applied pressure, likely due to foulant layer compaction. BSA fouling was more severe at pHs close to its isoelectric point (IEP), at high ionic strength and in the presence of Ca2+ and Mg2+ as a result of reduced electrostatic repulsion or the promotion of specific ion interactions under these conditions. A linear correlation was observed between J96 h and the square of zeta potential of BSA (ζ2), suggesting that ζ2 can be potentially a good indicator for predicting the long term fouling behavior.