Desalination: The process of removing salts like sodium chloride from the water is known as desalination.
Commonly employed methods for desalination of brackish water are:
i) Electro dialysis
ii) Reverse osmosis
Reverse osmosis. (R.O)
Reverse osmosis is one of the membrane filtration processes. The process is used to remove salts and organic micro pollutants from water.
Principle:
Osmosis: When two solutions of different concentrations are separated by a semi permeable membrane, solvent flows from region of low
concentration to region of high concentration. This is called Osmosis.
The Pressure developed on the membrane is called osmotic pressure.
If the pressure higher than osmotic pressure is applied on the concentrated side, then the solvent flows in reverse direction i.e from higher concentrated region to lower concentrated region. This is called reverse osmosis.
In this process pure solvent (water) is separated from its contaminants, rather than removing contaminants from water. Sometimes it is also called super/hyper filtration.
Method:
Reverse osmosis cell consists of a chamber fitted with a semi permeable membrane above which, sea water or impure water is taken.
Pressure (of the order 15-40 kg cm-2) is applied to the sea water/impure water.
The pure water is forced through the semi permeable membrane.
The membrane consists of very thin films of cellulose acetate/ superior membrane made of polymethacrylate and polyamide polymers, affixed to either side of the perforated tube.
Advantages:
Removes ionic and non-ionic colloidal particles and high molecular weight organic matter.
It removes colloidal silica
The life time of semi permeable membrane is high.
Membrane can be replaced within few minutes.
Low capital and operating cost & high reliability
Tags
waterchemistry