^{NIOT to build India’s first offshore desal plant near Chennai coast}

CHENNAI: Scientists from city-based National Institute of Ocean Technology (NIOT) will build the country’s first offshore desalination plant about 40km from the Chennai coast with a capacity of about 10 million litres of water per day, said the director of the institute Satheesh C Shenoi.
A detailed project report for the plant, which is estimated to cost ?2,000 crore, has been submitted to the Centre for approval.Designed and built by NIOT scientists, the plant will come up off the shores of Ennore.
“Buiding the offshore plant involves a lot of engineering challenges, and the design is complex,” said Shenoi, adding, “The plant can be scaled up for more capacity if required.”
“The design for the offshore plant is ready. The project will be part of the deep ocean mission estimated to cost ?10,000 crore, which will be launched in March 2018,” said M Rajeevan Nair, secretary, ministry of earth sciences on the sidelines of a one-day workshop on harnessing energy from the oceans.
‘Existing plants dump concentrated brine in sea, harm marine life’
At present, Chennai has two desal plants each in Nemmili and Minjur with a combined capacity of 210 MLD and two more are planned with a total capacity of 550 MLD.
The plant will operate on the indigenously developed low temperature thermal desalination (LTTD), a lowcost and environment friendly technology to get potable water. The technology is based on the temperature difference in seawater at different depths.
To begin with, the plant will be diesel powered. But, eventually, scientists are hoping to operate the plant with electricity generated through Ocean Thermal Energy Conversion Technology (OTEC).
The technology will drastically cut down on the operating cost of the plant. OTEC, which generates electricity using the ocean’s thermal gradient, will soon be tested in a desal plant to be built in Kavaratti, Lakshadweep. An OTEC test lab was also launched in NIOT on Monday to optimise the technology.
Scientists said the existing plants in Chennai operate on reverse osmosis tec hnology, which deposits highly concentrated brine in the sea, harming marine life.
The LTTD technology studied by NIOT works on the temperature difference between the surface water and the deep waters of the sea. The warmer surface water is evaporated at a low pressure and the resulting vapour is then condensed using the colder deep sea water to get purified water.
“We have to go 40 km from the coast to find the required depth for intake of deep sea cold water required for the process, since Chennai has shallow waters,” Nair said.
Purnima Jalihal, head, energy and freshwater programme, said, “The capital for the proposed plant is high only because of the offshore component. The aim is to have the desal plant powered by OTEC, which will drastically bring down the cost. We also need not carry diesel from the shore to the plant to operate it.”
NIOT will set up six more desal plants in Amini, Chetlet, Kadamath, Kalpeni, Kiltan and Andrott islands of Lakshadweep apart from the three that are currently operational.