LTTD is a process that uses the available temperature gradient between two water bodies. It can also use flow instead and thus evaporate the warmer seawater at low pressures. It then condenses the resulting vapour with the colder seawater to obtain fresh water. Dr Ramana Murthy, a scientist at NIOT told the Indian Science Journal that the 12-13 degree C cold water available at around 400m depth within 600m from the Lakshadweep island is used in the island chain. He further explained that this is achieved along with surface water at about 28 degrees C to produce potable water in the Lakshadweep Islands.
Dr Harsh Vardhan, the minister of the Ministry of Science and Technology and Earth Sciences has told the parliament during question hour that the Ministry of Earth Sciences had three Low-Temperature Thermal Desalination (LTTD) plants with a capacity to generate 1 Lakh litre of drinking water per day. These are functional in Minicoy, Agatti and in the Union territory of Lakshadweep islands at Kavaratti. Six more of the plants at Amini, Androth, Chetlat, Kadamat, Kalpeni and Kiltan Islands and LTTD plant based on Ocean Thermal Energy Conversion at Kavaratti has also been approved.
For the purpose of generating potable drinking water, a similar technology to LTTD has been used by North Chennai Thermal Power Station using the wasted heat.
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The government has also approved a scaled-up experimental plant. It can produce 2 million litres of drinking water. It will be set up at Tuticorin’s Thermal Power Station. A solar-assisted desalination plant, also on an experimental basis, is being set up at Kanyakumari.
The above response was given to an unstarred question asked by Kinjarapu Ram Mohan Naidu, a Member of the parliament in the 17th Lok Sabha from Srikakulam, his Lok Sabha constituency. He had asked whether the Government proposes to develop desalination units to serve the potable water requirements of coastal areas. The response was given on November 22, 2019.