This method can easily and efficiently convert brackish water that contains 3,000 mg/L. New membranes are being studied to help make this process better for desalting sea water. Reverse osmosis is the second most common way to desalt water, behind flash distillation. In reverse osmosis, salty water of two different concentrations are separated by a semi permeable membrane. This membrane allows the passage of solvent, but not dissolved substances. Naturally, osmosis will come into play and the two concentrations will start to even out; meaning the dilute side will start to flow to the concentrated side. The difference in pressure between the solutions of different concentration is the osmotic pressure. (Degremont 306) What happens in this reverse osmosis method is that a high pressure, greater than the osmotic pressure, is applied to the membrane and pure water passes through. A major advantage to this method is the rather simple method that is used. .
The most common membranes used in reverse osmosis desalination are made of a treated cellulose acetate. Using this membrane, 98-99% of the original salinity is removed at a rate of 150 to 200 liters per day. New research is concentrated on increasing the flow through the membrane, and increasing the reduction in salinity. Flash distillation is the most widely used method of desalination. It works using evaporation at low pressures. First, hot sea water passes into an area of lower pressure where some of the water evaporates quickly. .
This instantaneous boiling and the generation of vapor without a heat supply is known as flashing. Distillation takes place and the hot sea water is cooled in the process. Further flash steam can be released at a lower pressure and temperature in a series of stages. (How It Works 729) Usually, a flash distillation plant is consisted of a series of chambers that are running at lower temperatures than the previous one.
