Reverse osmosis (RO) is a filtration method that removes many types of large molecules and ions from solutions (typically water) by applying pressure to the water when it is on one side of a selective membrane. The result is that the solute (the excess salt and minerals) is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side.
The process is similar to other filtration processes, such asnanofiltration and ultrafiltration. However, there are key differences – the predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Reverse osmosis, however involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure and water flux rate.
