Ultrafiltration of polysaccharide-protein mixtures: Elucidation of fouling mechanisms and fouling control by membrane surface modification

This work describes the fouling behavior of polysaccharide-protein mixture solutions by investigation of adsorptive and ultrafiltration fouling. Alginate, dextran, myoglobin and bovine serum albumin were used as model foulants. Three commercial poly(ether sulfone) (PES) ultrafiltration (UF) membranes with nominal cut-off of 10, 30 and 100 kg/mol and a PES-based thin layer hydrogel composite (TLHC) membrane, synthesized by photo-initiated graft copolymerization of poly(ethylene glycol) methacrylate (PEGMA) and having a cut-off of 10 kg/mol were used. The effects of pH, foulant concentration, ionic content and proportion of protein to polysaccharide in the solution on fouling were investigated. The results showed that significant water flux reductions and changes in membrane surface property were observed after static adsorption for PES membranes for all feed solution conditions. This water flux reduction decreased with increasing the pH of the solution. Addition of monovalent ions could either increase or decrease the water flux reduction. Synergistic effects between polysaccharide and protein with respect to forming a mixed fouling layer with stronger reduction of flux than for the individual solutes under the same conditions have also been verified for PES UF membranes. UF experiments using a stirred dead-end UF suggested that both reversible and irreversible fouling have contributed to the overall fouling. The antifouling efficiency of the TLHC membrane with respect to both adsorptive and ultrafiltration fouling has been demonstrated for the strong foulant alginate as well as for polysaccharide-protein mixtures. (c) 2008 Elsevier B.V. All rights reserved.