Water resources for agricultural production have been declining globally. This is due to an increase in water demand over limited resources and poor quality water, which has a negative impact on crop quality and yield and deteriorates soil properties. Desalination, the process of reducing the salt content in water to an acceptable level, could be an option for improving water quality, increasing water sources, and decreasing competition among various water users. As a result, desalination could improve crop quality, yield, and all year crop production, making it an important tool for effective agricultural water management. This article will explain to you about Desalinization which will be helpful in preparing the Agriculture Syllabus for the UPSC Civil Service exam.

Desalinization Technologies

1. Reverse Osmosis

• Desalination is a technology that uses reverse osmosis to convert salt water to freshwater (RO).
• Osmosis is the natural movement of a solvent (such as water) from a low concentration area to a high concentration area through a membrane.
• A reverse osmosis system uses external pressure to reverse the natural flow of solvent, so seawater or brackish water is pressurised against one surface of the membrane, causing salt-depleted water to move across the membrane and release clean water from the low-pressure side.
• Desalination occurs when a plant pumps in salty or brackish water, filters separate the salt from the water, and the salty water is returned to the sea.

2. Heat Distillation

• Over 60% of the world's desalinated water is produced by distilling fresh water from sea water using heat.
• The distillation process is similar to the natural hydrologic cycle in that sea water is heated, resulting in water vapour, which is then condensed to form fresh water.
• In a desalinization plant, sea water is heated to its boiling point to allow maximum vaporisation.
• To do this economically, the boiling point is lowered by lowering atmospheric pressure.
• The reduction of the boiling point is important for two reasons: it allows for multiple boiling, resulting in lower energy requirements, and it controls the accumulation of carbonate and sulphate scale on the apparatus.

3. Ion Extraction

• Ion extraction is another method of desalinization in which the ionised salts found in sea water are extracted using chemical or electrical means.

4. Ion Exchange

• The chemical process is known as ion exchange.
• Granules of commercially prepared resin are used in this method to remove positive ions from sea water and replace them with ions that are loosely bound in the resin's molecular structure.
• Other resin beds are capable of exchanging negative ions.
• This process, however, is too expensive to be used to desalinate large amounts of sea water.

5. Electrodialysis

• The electric current in electrodialysis pulls the ions through membranes that are only permeable to positive or negative ions.
• Hundreds of alternating positive or negative membranes are bound by a frame and form narrow compartments to trap the ions.
• When a direct electric current is applied, positively charged ions migrate through membranes permeable to positive ions, while negatively charged ions migrate through membranes permeable to negative ions.
• Ions move between compartments and become more concentrated as a result of this process.
• The distance the liquid flows in the compartments, the intensity of the current flow, the permeability of the membranes used, and the distance between the membranes govern electrodialysis efficiency.
• The cost is determined by the salt concentration in the sea water, because the electrical power required varies directly with the number of ions to be removed and their electrochemical properties.
• The electrical power required to separate the ions from the water is typically less expensive than the resin and chemicals used in ion exchange.
• Even so, it is usually so high that only brackish water, which is less salty than sea water, can be economically desalinated for large-scale use by electrodialysis.

6. Freezing Desalinization

• Dissolved salts are naturally excluded from the lattice structure of ice crystals during the freezing process.
• Under controlled conditions, cooling the water to form ice can desalinate sea water.
• The ice is removed and rinsed to remove any salts that have adhered to the ice surface before the entire mass of water has frozen.
• It is then melted to create new water.

7. Solar Humidification

• For some time, direct solar energy has been investigated and used for desalinating sea water.
• Small solar stills were developed for use on life rafts during World War II (from 1939 to 1945).
• These devices mimic the natural hydrologic cycle by heating the sea water, increasing the production of water vapour (humidification).
• The water vapour is then condensed on a cool surface, and the condensate collected as fresh water.
• Although the thermal energy is free, the stills are costly to build, additional energy is required to pump water to and from the facility, vapour can leak from the stills, and careful operation and maintenance are required to prevent scale formation.
• In general, these types of solar humidification units have been used for small-scale desalination of sea water in areas where solar energy is abundant but electricity is scarce.

8. Nanofiltration

• It is a process that uses nanotube membranes that are more permeable than reverse osmosis membranes, allowing more water to be processed in less space and with less energy.
• These membranes are made of sulfonated compounds that, in addition to salt, remove traces of pollutants.

9. Gas Hydrate Formation

• Gas hydrates are solid crystals formed by combining high pressure and low temperature water with a gas, such as propane.
• All of the salts and impurities in the water are removed during the process, and as the temperature rises, the gas can be recovered, leaving only fresh water.

Desalinization - Advantages and Disadvantages

Conclusion

Despite the fact that soil salinity has been a problem for agriculture for thousands of years, significant research has only been conducted in the last 100 years. Desalination technologies have applications that are not limited to seawater. Desalinization, for example, is used to treat groundwater in inland areas that is too salty for drinking or irrigation. Desalinization can also be used to treat sewage treatment plant effluent. To summarise, the future of desalinization looks bright, and this technology will almost certainly play a larger role in countries that can afford to develop it.