Forward osmosis concentration of high viscous polysaccharides of Dendrobium officinale: Process optimisation and membrane fouling analysis

Abstract

Polysaccharides of Dendrobium officinale (DOP) need to be dehydrated and concentrated after extraction for further application. They are usually concentrated by thermal evaporation which consumes great energy. However, high viscosity of DOP makes the concentration more difficult even using non-thermal membrane technologies such as nanofiltration (NF) or reverse osmosis (RO). In this study, effects of process conditions, such as membrane orientations, draw solutions and their concentrations, and flowrate on forward osmosis (FO) concentration of viscous DOP were studied. Active layer to feed solution mode, cross flowrate at 240 mL min −1 , and draw solution of 3 M NaCl have been found as the optimal conditions. Foulants on the membrane surface with loose structure could be easily cleaned and removed by hydraulic flushing. DOP concentrated by FO achieved almost 1.3 times at the same time compared with that in NF and RO. DOP could be further concentrated for 1.5 folds at longtime without significant decrease in water flux. In addition, slight reverse solutes in FO process could reduce the viscosity of high viscous DOP, which was good for concentration. Accordingly, FO is a potential technology for concentration of high viscous polysaccharides such as DOP.

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