Osmosis is the flow of solvent through a semi-permeable membrane, from a dilute solution to a concentrated solution.
This flow results from the driving force created by the difference in pressure between the two solutions. Osmotic pressure is the pressure that must be added to the concentrated solution side in order to stop the solvent flow through the membrane. Reverse osmosis is the process of reversing the flow, forcing water through a membrane from a concentrated solution to a dilute solution to produce filtered water. Reverse osmosis is created when sufficient pressure is applied to the concentrated solution to overcome the osmotic pressure. This pressure is provided by feed water pumps. Concentrated contaminants (brine) are reduced from the high-pressure side of the RO membrane, and filtered water (permeate) is reduced from the low-pressure side. Membrane modules may be staged in various design configurations, producing the highest-quality permeate with the least amount of waste. Typically, 95% of dissolved salts are reduced from the brine. All particulates are removed. However, due to their molecular porosity, RO membranes do not remove dissolved gases, such as Cl2, CO2, and O2. RO Membranes. The two most common RO membranes used in industrial water treatment are cellulose acetate (CA) and polyamide (PA) composite. Currently, most membranes are spiral wound; however, hollow fibre configurations are available. In the spiral wound configuration, a flat sheet membrane and spacers are wound around the permeate collection tube to produce flow channels for permeate and feed water. This design maximizes flow while minimizing the membrane module size