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[THIRUVANANTHAPURAM] Evaporating and condensing sea water at low temperatures to remove salt offers the best way to provide drinking water in India’s coastal areas, says a new study.

In 2005, India's National Institute of Ocean Technology (NIOT), Chennai, set up the world's first low temperature thermal desalination (LTTD) plant at Kavaratti in the largely coral Lakshadweep islands off the coast of Kerala state in the Arabian Sea. 
LTTD technology is based on the fact that water at the surface of the sea is warmer than water drawn from deeper down. Warmer surface sea water is subjected to vacuum pressure to hasten evaporation and then condensed by cooling with cold water pumped up from the sea depths. 
The study published last month (February) in Current Science compares LTTD with reverse osmosis (RO), a desalination method that passes brackish water through a porous membrane to remove dissolved salts. In India, RO technology is used in small household units as well as at industrial scales. 
LTTD is suitable for use in coastal areas where sea water at different temperatures is available. About 600 metres off the Kavaratti coast water at a depth of 350 metres is cooler than surface waters by as much as 15 degrees Celsius.
The study by R. Venkatesan, head of the industry division at the National Council of Applied Economic Research, compares the economic as well as ecological and environmental costs of LTTD and RO technologies.
In general, LTTD plants are costlier than RO units and need more energy to operate. On the other hand, LTTD plants have minimal ecological impact, according to the study.
“As far as energy efficiency is concerned, RO scores over existing seawater desalination processes,” P. K. Tewari, head of the desalination division at Bhabha Atomic Research Centre, Mumbai, tells SciDev.Net.
A survey at Kavaratti showed that people were happy with the LTTD plant installed there because it does not disturb fisheries and has lowered the prevalence of water-borne diseases by improving access to potable water. 
“The use of heat at low temperatures could greatly decrease the energy footprint of desalination,” says Corrado Sommariva, president of the International Desalination Association. “I believe that this technique has a lot of potential to offer to the international desalination scenario”.
“LTTD is the way forward on coral islands because it is ecologically friendly,” says Venkatesan.
Link to article in Current Science

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