Principles of forward osmosis

Forward osmosis (FO) is a process driven by differences in osmotic pressure between a feed and draw solution, as opposed to many other membrane processes, such as reverse osmosis (RO), where hydraulic pressure is applied. The FO process needs a semipermeable membrane that segregates the feed solution, with relatively low osmotic pressure and a more concentrated draw solution. As the main operating cost for systems such as RO is the energy needed to pump solutions at high pressure, it is generally expected that FO will have much lowered energy costs. Due to water permeation across the membrane, the concentration of the feed solution will increase over time, whereas the draw solution becomes diluted.