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Context

• As a part of its ongoing initiative National Institute of Ocean Technology (NIOT) was providing potable water in six islands of Lakshadweep using Low-Temperature Thermal Desalination (LTTD) technology. But now it is working at making this process free of emissions.

Background

• Currently, the desalination plants, each of which provides at least 100,000 litres of potable water everyday, are powered by diesel generator sets — there being no other source of power in the islands.
• LTTD exploits the difference in temperature (nearly 15°C) in ocean water at the surface and at depths of about 600 feet. This cold water condenses water at the surface, that is warmer but whose pressure has been lowered using vacuum pumps. Such de-pressurised water can evaporate even at ambient temperatures and this resulting vapour when condensed is free of salts and contaminants and fit to consume.
• However, the need for diesel power to reduce the water pressure means that the process is not fossil-fuel free and also consumes diesel, a precious commodity in the islands that has to be shipped from the mainland critical for powering the electric grid.
• But now, for the first time in the world, NIOT is setting up a [desalination] plant that will also supply power to the plant.

LTTD

• Low-temperature thermal desalination(LTTD) is a desalination technique that takes advantage of the fact that water evaporates at lower temperatures at low pressures, even as low as ambient temperature.
• The system uses vacuum pumps to create a low pressure, low-temperature environment in which water evaporates even at a temperature gradient of 8 °C (14 °F) between two volumes of water.
• Cooling water is supplied from deep sea depths of as much as 600 metres (2,000 ft). This cold water is pumped through coils to condense the evaporated water vapor. The resulting condensate is purified water.
• The LTTD technology does not require any chemical pre and post-treatment of seawater and thus the pollution problems are minimal and suitable for island territories.
• Since no effluent treatment is required, it gives less operational maintenance problems compared to other desalination processes. The LTTD technology is completely indigenous, robust and environment friendly.

National Institute of Ocean Technology (NIOT)

• The National Institute of Ocean Technology(NIOT) was established in 1993 as an autonomous society under the Ministry of Earth Sciences in India.
• NIOT is managed by a Governing Council and is headed by a director. The institute is based in Chennai.
• The major aim of starting NIOT was to develop reliable indigenous technologies to solve various engineering problems associated with harvesting of non-living and living resources in India's exclusive economic zone, which is about two-thirds of the land area of India.

https://www.thehindu.com/sci-tech/energy-and-environment/national-institute-of-ocean-technology-to-set-up-green-self-powered-desalination-plant-in-lakshadweep/article66627730.ece

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