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Thu 26 Nov, 2020

Why in News ?

  • Recently, Maharashtra announced the setting up of a desalination plant in Mumbai.
  • The plant will process 200 million litres of water daily (MLD), and will help in overcoming the water shortage faced by Mumbai in the months of May and June.
  • Maharashtra will be the fourth state to experiment with Desalination Plants.


  • Osmosis : Osmosis is a biophysical process occurring commonly in biological systems where solvent molecules move across a semi-permeable membrane towards a region of high solute concentration.

·  What is Reverse Osmosis?

  • Reverse osmosis is the process in which pressure is applied to overcome colligative property and osmotic pressure that is directed by a thermodynamic parameter and a chemical difference of a solvent.
  • This application is mainly applied in the production of potable water in water plants and in industries. The end result will be the solute. It happens when the pure solvent is allowed to follow to one end of the membrane thus allowing a solute to retain in a permissible side of a membrane. Reverse osmosis removes suspended and types of dissolved species from water including bacteria.

Reverse Osmosis Principle

  • Reverse osmosis works by reversing the principle of osmosis.  The salt solution is subjected to pressure and pressed against the semi-permeable membrane. Here, the applied pressure is greater than the osmotic pressure. Thus, the molecules move from a highly concentrated solution to a less concentrated solution.
Osmosis Reverse Osmosis
This is the process by which the molecules of a solvent pass through the semi-permeable membrane from a region of lower concentration to a higher concentration. This is the process by which the molecules of a solvent pass through the semi-permeable from a region of higher concentration to lower concentration when pressure greater than the osmotic pressure is applied.
It is a natural process. It is an artificial process.
Occurs along the potential gradient. Occurs against the potential gradient.
This is observed during the opening of stomata and absorption of water from the soil by the roots. This is used in water purification systems.