Desalination Process | Civil Engineering Optional Notes for UPSC PDF Download

Desalination

History and Development

• Ancient Methods: Aristotle described evaporation methods used by Greek sailors in the 4th century BCE, and Arab writers in the 8th century CE wrote about distillation.
• 19th Century: With the development of steam navigation, the need for noncorroding water for boilers arose, leading to the first patent for a desalination process in England in 1869.
• 20th Century: The first large-scale water distillation plant was built in Aruba in 1930. By 2019, there were about 18,000 desalination plants worldwide, producing over 95 million cubic meters of potable water per day.

Desalination Plant

Desalination Methods

1. Thermal Processes: Use heat transfer and phase change.

   • Multistage Flash Distillation: Involves a series of closed tanks set at progressively lower pressures. Preheated seawater enters the first stage, flashes into vapor, condenses into fresh water, and is collected.
   • Solar Humidification: Uses intense sunlight to partially vaporize salt water under a transparent cover, with condensed vapor collected for use.
   • Freezing: Freezing salt water to form ice crystals without salt, but requires significant fresh water for washing the saltwater trapped between ice crystals.

2. Membrane Processes:

   • Reverse Osmosis: Salt water is forced against semipermeable membranes under high pressure. Fresh water passes through while mineral salts remain behind.
   • Electrodialysis: Uses electrical potential to drive positive and negative ions of dissolved salts through separate semipermeable membranes, leaving fresh water between the filters.

Global Production and Challenges

• Desalination is used in over 120 countries, with about half of desalted water produced in the Middle East and North Africa.
• Major producers include Saudi Arabia, the United Arab Emirates, Kuwait, and the United States.
• Challenges include high energy requirements, costs, greenhouse gas emissions, and brine wastewater disposal, making it suitable mainly where other water sources are not economically available.

Future Prospects

• Desalination could become increasingly important as a freshwater source, particularly for irrigation in coastal areas.
• Continued research and technological advancements aim to reduce costs and environmental impacts, making desalination more accessible globally.