REVERSE OSMOSIS-----WATER TECHNOLOGY---CY2111 183101 –ENGINEERING CHEMISTRY –I Lecture Notes

Reverse Osmosis Method: (Desalination)
1.Removal of common salt (NaCl) from water is called ‘ Desalination’.  Fresh water contains dissolved solids less than 1000ppm.  Brackish water 1000 to 35000ppm .
Sea water contains greater than 35000ppm.  Reverse osmosis is used to convert sea and brackish  water to fresh water.
2.Osmosis:  When two different concentrated solutions are separated by a semi permeable membrane, due to osmotic pressure, low concentrated solvent flows to higher one. This is known as osmosis.
3.But when we apply an excess and opposite Hydrostatic pressure to overcome the osmotic pressure, then higher concentrated solvent will flow to the lower one.  This is known as reverse osmosis.
4.During this RO process , only the water flows across the membrane and it prevents the salt migration.  So, this method is also called as ‘ Super filtration’.  The membrane is madeup of cellulose acetate or cellulose butyrate.
Advantages of Reverse Osmosis:  
1.High life time 
 2.Removes ionic, non-ionic and colloidal impurities.
3. Low capital cost.
 4.  Simple operational procedure.

Diagram:




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