Reverse Osmosis

Reverse osmosis (RO) is a water purification method that uses a semipermeable membrane to remove ions, molecules, and sediments from water to make it drinkable. In reverse osmosis process, pressure applied with pump to overcome osmotic pressure. Reverse osmosis can remove many types of dissolved and suspended particles or species from water, including bacteria, sediments etc. and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurised side of the membrane and the pure solvent is allowed to pass to the other side of the membrane. To be selective, this membrane should not allow large molecules or ions through the pores or holes, but should allow smaller components of the solution such as solvent molecules to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration or high water potential through a membrane, to an area of high solute concentration or low water potential. The driving force for the movement of the solvent is the reduction in the free energy of the system when the difference in solvent concentration on either side of a membrane is reduced, generating osmotic pressure due to the solvent moving into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, key differences are found between reverse osmosis and filtration. Reverse osmosis also involves diffusion, making the process dependent on pressure, flow rate, and other conditions. Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and other effluent materials from the water molecules.