Forward (Direct) osmosis: A prospective membrane process

Abstract

Forward (direct) osmosis (FO) process utilizes an osmotic pressure gradient generated by a highly concentrated solution (known as b drawb solution) to allow water to diffuse through a semi-permeable membrane from a saline feedwater, which has a relatively lower concentration. Transport phenomena were proposed to explain the experimental results and it was found that internal concentration polarization happened within membrane loose support layer severely deteriorates the performance. New FO membrane with only a thin dense selective layer was fabricated and results indicated that this membrane structure may be ideal in the FO process. Various draw solutes such as: NH4HCO3, glucose, fructose and NH4Cl were tested and requirements for an ideal draw solute was proposed. A low-pressurized FO process was developed and a better performance was achieved. Study also showed that FO can be applied to reclaim brine with a high water recovery.