Reverse osmosis

  Today, I am going to talk about reverse osmosis. It is actually a filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a membrane. The solute will then be retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. Here is a diagram of how it works:

Uses of reverse osmosis:
-drinking water purification
-water and wastewater purification
-food industry
-reef aquariums

The membranes used in reverse osmosis have a dense barrier layer in the polymer matrix where most seperation occurs. The membrane is designed to allow only water to pass through this dense layer, and solutes such as salt ions are prevented from passing through. This process requires a high pressure to be exerted on the high concentration side of the membrane, usually 2-17 bar(bar is a unit of pressure roughly equal to the atmospheric pressure on Earth at sea level) for fresh and bracksh water, and 40-70 bar for seawater.