(410e) Fouling of RO and NF Membranes by Proteins - the Role of Hydrodynamic Conditions and Solution Chemistry

Reverse osmosis (RO) and nanofiltration (NF) processes are increasingly used in wastewater reclamation. Organic fouling by effluent organic matter (EfOM) is one of the major limitations of such applications. In the study, bovine serum albumin (BSA) and lysozyme (LYZ) were used as a model foulants. The effect of feed solution chemistry (pH, ionic strength, and divalent ions concentration) and hydrodynamic conditions (crossflow velocity and initial flux) were systematically investigated through flux performance to study protein fouling mechanisms. A limiting flux behavior was observed for BSA fouling ? while high initial flux accelerated the rate of flux decline, the stable flux at a longer fouling duration had little dependence on the applied pressure (or initial flux). Membrane properties played little role on the stable flux behavior, with RO and NF membrane fluxes all converged into an identical value. Crossflow fouling experiments also demonstrated that fouling was more significant at pHs close to isoelectric point (IEP) of BSA, at high ionic strength and/or in the presence of divalent ions such as Ca2+ and Mg2+, likely due to the reduced electrostatic repulsion between foulant-membrane and foulant-foulant under these conditions. Compared to BSA fouling, flux decline due to membrane fouling by lysozyme was much milder. However, the mixture of BSA and LYZ showed detrimental effect on membrane flux, which was likely due to the electrostatic attraction between the negatively charged BSA and positively charged LYZ.