Journal of Membrane Science (2020): 118984.
Polysaccharides were usually considered as important organic compounds causing organic fouling of reverse osmosis (RO) membranes. In this study, the RO membrane fouling behaviors and mechanisms of 9 polysaccharides with different molecular weights and structures were studied. It was found that not the molecular weight but the molecular structure mainly influenced the fouling behavior. Straight-chain polysaccharides tended to cause slight and slow membrane fouling (final flux decline < 30% in 100 h), while branched-chain polysaccharides led to severe fouling (final flux decline > 50% in 50 h) and formed thicker foulant layers on membrane surfaces. The presence of Ca2+ could double and even triple the flux decline of straight-chain acid polysaccharides, but showed barely effect on branched-chain polysaccharides as well as neutral polysaccharides. The extended Derjaguin-Laudau-Verwey-Overbeek (XDLVO) theory revealed that attractive energy dominated the interaction between branched-chain polysaccharides and membranes. The addition of Ca2+ turned the repulsive interaction between straght-chain acid polysaccharides and membranes into attractive interaction, but showed no significant effect on neutral polysaccharides. The viscosity of straight-chain polysaccharides didn't increase with the polysaccharide concentrations, while that of branched-chain polysaccharides showed a positive relationship with mass concentrations. Ca2+ also enhanced the viscosity of straight-chain acid polysaccharides.
