Isolation of LC-OCD-quantified biopolymers from surface water: Significant differences between real biopolymers and model biopolymers

Abstract

High molecular weight biopolymers quantified by a liquid chromatography with organic carbon detection (LC-OCD) system have been recognized as major players in fouling that occurs in microfiltratrion (MF) and ultrafiltration (UF) of surface water. Although detailed investigation of biopolymers is important, there have been few studies in which real biopolymers isolated with sufficient purities and high recoveries were used. In this study, cross-flow UF using membranes with a molecular weight cut-off (MWCO) of 13,000 was performed to isolate biopolymers from surface water. Merely carrying out UF, however, did not result in a high purity of biopolymers in the isolated product: significant contamination by humics became a problem. Adjustments of electric conductivity and calcium concentration during UF were found to be effective. With the optimized conditions, humics could be eliminated almost completely and the isolated biopolymers were obtained with a high recovery rate (67–85%). Isolated biopolymers were compared with model biopolymers such as alginate. Fouling potentials and physical-chemical properties of the isolated biopolymers were considerably different from those of model compounds. The results obtained in this study give rise to an important question of whether common biopolymers such as alginate should be blindly used for fouling studies: they might not represent fouling caused by real biopolymers.