Forward (Direct) Osmosis: A Novel and Prospective Process for Brine Control

This paper reports the study of a novel process - Forward (Direct) Osmosis (FO) that potentially can be used for brine control. The driving force in the described FO process is provided by a draw solution comprising highly concentrated ammonium bicarbonate or fructose solution. Using a commercially available FO membrane, experiments conducted using a crossflow, flat-sheet membrane cell yielded water fluxes ranging from 0.3 to 6.5 gal·ft−2·d−1 for a wide range of draw and feed solution concentrations. It was found, however, that the experimental water fluxes were lower than expected due to internal and external concentration polarizations (CP). SEM images of the FO membrane showed that it has a loose fabric porous support layer, which caused internal CP to a large extent. Explanations were given for the transport phenomena in the FO membrane. The dense selective layer of a common cellulose acetate RO membrane was split from the supporting layer and tested. The result confirmed our conclusion that an ideal FO membrane should be one with a thin dense selective layer without loose fabric support layer. This study also suggests that applying the FO process to concentrate brine to simplify its handling is feasible when using an ideal FO membrane and a suitable draw solution, which require further research.