CHENNAI: Water-starved Chennai could earn the distinction of being the first in the world to set up an off-shore desalination plant, for which a deep sea site that is 40 km from the Ennore coast has been finalised. The National Institute of Ocean Technology (NIOT) has already submitted a detailed project report (DPR), which is likely to be considered by the Union government under the Rs 10,000-crore Deep Sea Mission scheduled to be launched in March next year.
Unlike the existing desalination plants in Nemmeli and Minjur that uses reverse osmosis (RO) technology to separate fresh water from seawater, this plant will use indigenously developed low temperature thermal desalination (LTTD), which is an environment-friendly technology.
The LTTD utilises the temperature difference available between surface water and deep sea water. In this methodology, the warmer surface sea water is made to evaporate at low pressures and the vapour obtained is condensed using the colder deep sea water to get potable water.
The current RO-based desalination plants use lots of chemicals and produce highly concentrated brine that is usually sent back into the ocean. This brine is toxic to bottom-dwelling marine life when it settles on the ocean floor, and can also cause hypoxia or oxygen deficiency in the ocean floor area.
Also, ocean scientists are exploring the possibility of powering the proposed desalination plant with electricity generated through ocean thermal energy conversion (OTEC), instead of diesel, which will drastically reduce the operating cost of the plant. This makes the project the first of its kind in the world. The OTEC uses the ocean thermal gradient to produce electricity.
M Rajeevan Nair, secretary, Ministry of Earth Sciences, told Express, on the sidelines of one-day workshop on “Harnessing Energy from the Oceans - A Global Scenario”, that the NIOT had finalised the design and submitted the DPR. It would be a 10-MLD (million litres per day) capacity plant costing an estimated `2,000 crore. “Since Chennai has shallow waters, we have to travel 40 km into the sea to get the kind of depth to take in deep sea cold water needed for the process. It is a great challenge for ocean engineers and complex in design,” Nair said.
Satheeesh C Shenoi, director, NIOT, said the off-shore desalination plant by itself is a first of its kind. “In the DPR submitted, the use of OTEC to power the plant is not included. But, the NIOT is optimising the technology at a laboratory scale for which an OTEC test lab has been commissioned on the NIOT campus on Monday. Next, we will be setting up India’s first OTEC powered desalination plant at Kavaratti in Lakshadweep Islands for which tendering process is on. Then, we will bring the best of technology to the proposed Chennai plant that will go a long way in solving the water crisis of the city,” he said.
Purnima Jalihal, head, Energy and Freshwater Programme, NIOT, said the initial high capital cost was due to building of an off-shore platform. Otherwise, the technology is very economical and environment-friendly. “We are operating three 1 MLD desalination plants in Kavaratti, Minicoy, and Agatti islands of Lakshadweep islands using LTTD technology and six more are planned, each at Amini, Chetlet, Kadamath, Kalpeni, Kiltan and the Andrott islands. The use of OTEC for Chennai plant depends on the budget sanctioned.”
With diminishing freshwater resources, desalination plants will be future sources of drinking water. The Tamil Nadu government is investing heavily in the desalination plants and plans to meet 65% of Chennai’s water requirement through these plants. The government is setting up two more desalination plants with a combined capacity of 550 MLD. This would reduce stress on natural resources like lakes as well as groundwater, said sources in the Tamil Nadu Municipal Administration and Water Supply.
Chennai requires 1,200 MLD of water, of which only 800 MLD is being realised. The State has already two desalination plants at Minjur and Nemmelli having a capacity of 100 MLD each.
Only recently, Finance Minister D Jayakumar submitted proposals to Union Finance Minister Arun Jaitley for Rs 5,300-crore desalination projects to address the drinking water needs of Chennai. Out of the two new proposed plants, one with 150 MLD capacity is being funded by German investment agency KFw and the other with 400 MLD capacity, which would be one of the biggest plants in the world, is being funded by Japan International Cooperation Agency at Perur.
However, environmental issues related to these mega projects are debatable. Marine biologists warn that widespread desalinisation could take a heavy toll on ocean biodiversity. The intake pipes will essentially vacuum up and inadvertently kill millions of sea animals.
M Rajeevan Nair, secretary, Ministry of Earth Sciences,on Monday launched the first Indian wave-powered navigational buoy developed by the NIOT. The buoy was tested at Kamarajar port and proved to be cost-effective and efficient. It will now be moved to the port’s channel for full utility.
A K Gupta, general manager, Kamarajar Port, said that so far, all Indian ports had been importing navigational buoys, which are either solar-powered or battery-operated and which involve high maintenance costs. However, this wave-powered navigational buoy is self-sustaining with minimum fuss.
IEA-OES meet from today
For the first time, India is hosting the executive committee meeting of the International Energy Agency and the Ocean Energy System (IEA-OES). It will be conducted at the NIOT on Tuesday and Wednesday.