Water Management – Institutional Reforms, Conservation Efforts, etc.

Desalination Plants and their Feasibility

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Desalination plants

Mains level : Drinking water scarcity in Urban India

Maharashtra state govt. has announced the setting up of a desalination plant in Mumbai, becoming the fourth state in the country to experiment with the idea.

Try this PYQ:

Q.What is the role of ultraviolet (UV) radiation in the water purification systems?

  1. It inactivates/kills the harmful microorganisms in water.
  2. It removes the entire undesirable odour from the water.
  3. It quickens the sedimentation of solid particles, removes turbidity and improves the clarity of water.

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 and 3 only

(c) 1 and 3 only

(d) 1, 2 and 3

What are Desalination Plants?

  • A desalination plant turns salt water into water that is fit to drink.
  • The most commonly used techniques used for the process is reverse osmosis where external pressure is applied to push solvents from an area of high-solute concentration to an area of low-solute concentration through a membrane.
  • The microscopic pores in the membranes allow water molecules through but leave salt and most other impurities behind, releasing clean water from the other side.
  • These plants are mostly set up in areas that have access to seawater.

How widely is this technology used in India?

  • Desalination has largely been limited to affluent countries in the Middle East and has recently started making inroads in parts of the United States and Australia.
  • In India, Tamil Nadu has been the pioneer in using this technology, setting up two desalination plants near Chennai in 2010 and then 2013, while there are two more to come.

Need for such plant

  • According to the projections, the population of Mumbai is anticipated to touch 1.72 crores by 2041 and accordingly, the projected water demand would be 6424 MLD by then.
  • Currently, BMC supplies 3850 MLD as against the requirement of 4200 MLD each day.

Is it ecologically safe?

  • The high cost of setting up and running a desalination plant is one reason why the Maharashtra government has over the last decade been hesitant in building such a plant.
  • Desalination is an expensive way of generating drinking water as it requires a high amount of energy.
  • The other problem is the disposal of the byproduct — highly concentrated brine (saltwater) — of the desalination process.
  • While in most places brine is pumped back into the sea, there have been rising complaints that it ends up severely damaging the local ecology around the plant.

Back2Basics: Osmosis and Reverse Osmosis

  • Osmosis is a phenomenon where pure water flows from a dilute solution through a semi-permeable membrane to a higher concentrated solution.
  • Semi-permeable means that the membrane will allow small molecules and ions to pass through it but acts as a barrier to larger molecules or dissolved substances.
  • As water passes through the membrane to the salt solution, the level of liquid in the saltwater compartment will rise until enough pressure, caused by the difference in levels between the two compartments, is generated to stop the osmosis.
  • This pressure, equivalent to a force that the osmosis seems to exert in trying to equalize concentrations on both sides of the membrane, is called osmotic pressure.
  • If pressure greater than the osmotic pressure is applied to the high concentration the direction of water flow through the membrane can be reversed.
  • This is called reverse osmosis. Note that this reversed flow produces pure water from the salt solution since the membrane is not permeable to salt.
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