Analysis of BSA, dextran and humic acid fouling during microfiltration, experimental and modeling

Abstract

Fouling caused by natural organic matter like extracellular polymeric substance (EPS) is a major problem in using membranes in MBRs (MBR's) for separation of biomass from water. In this study, membrane fouling caused by a well-known protein (BSA), a humic acid and a well-known polysaccharide (dextran) as representatives of three main constituents of EPS; proteins, humic substances and polysaccharides were investigated. The objective of this study was to develop a fundamental understanding of fouling mechanisms using a combined pore blockage and cake filtration model with respect to hydrophilic nature of membranes and the pre-filtration effect of the foulant deposit layer. These two factors were inserted in a combined pore blockage and cake filtration model and this modification resulted in much better agreement between the modified model predictions and the experimental data. The experimental data were obtained over a range of foulant concentrations and transmembrane pressures. The results showed that the rate of flux decline is proportional to the hydrophilic nature of membrane, i.e. the extent of fouling in hydrophilic membranes with smaller water contact angle is smaller than that in hydrophobic membranes with larger water contact angle. Also, the fouling rate of the foulants with higher pre-filtration effect is smaller, so the foulants with higher resistance of the first deposit layer have smaller fouling rate. In this study, a modified pore blockage-cake filtration model was also developed. The predicted results were in very good agreement with the experimental data.