Drinking Water from Arabian Sea, Lakshadweep Isle

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The island, Kavaratti in Lakshadweep, made by coral reefs, slopes

down to 350 metres depth at a distance of about 400 metres from the

shore and does not have a regular source of fresh water. This

environment friendly, low cost technology, which is relatively easy

to maintain, will be a boon not only to the local islanders but also

in other water deficient islands and coastal areas around the

tropics.

31 May 2005

Drinking Water from Arabian Sea

By Sitanshu Kar*

For centuries, inhabitants of the picturesque coral island of

Kavaratti in Lakshadweep have lived with an existential paradox- they

have woken up every morning to the sight of the vast expanse of the

Arabian sea but have never had enough potable water from local

sources to sustain themselves. Various methods e.g., rain water

harvesting, setting up of reverse osmosis plants have been tried but

none so successful.

 

The situation, however, changed on May 23, 2005 when a 100,000 litres

per day capacity Low Temperature Thermal Desalination (LTTD) Plant

was dedicated to the people of the island by the Minister for Power,

Shri P.M. Sayeed and the Minister for Science and Technology and

Ocean Development, Shri. Kapil Sibal. Built at a cost of about Rs. 5

crores, the Plant was designed and set up by the National Institute

of Ocean Technology (NIOT), a Chennai based R & D institute under the

Department of Ocean Development in a record time of 90 days.

 

The inhabitants were a little wary, going by their past experiences,

as two reverse osmosis plants set up to convert sea water to potable

water had shut down. The emphatic assurance about the longevity of

the new Plant, came from Mr Sibal who said that the LLTD technology

is based on sound scientific principles and the Plant will be there

to serve the community for a long time to come. "The Plant will use

only 1% of the incoming warm water for `boiling' and the rest will be

discharged to the sea, thereby, precluding the possibility of higher

concentration of salts in the discharged water", says Dr. S.

Kathiroli, Director of NIOT.

 

Indeed, history of sorts was made when this plant became operational.

It is the first of its type in the world. The LLTD process uses a

combination of warm sea water at about 28-30 degrees Celsius and deep

sea cold water of about 13 degrees Celsius, pumped from a depth of

350 metres. Warm saline water is made to boil at room temperature in

a specially designed vacuum flash chamber. The resultant water

vapours are then condensed using cold deep-sea water to produce safe

fresh water confirming to BIS/WHO standards. The water thus produced

is so clean that some minerals are added to make it potable. With a

population of about 11, 000 in the island, the Plant will be able to

provide about 10 litres per capita of potable water to the people.

 

This technology was first tested under laboratory conditions at NIOT

by developing a 5000 litre/day capacity pilot plant. During February

this year, the scientists used actual deep-sea cold water for the

first time and produced fresh water on a barge mounted desalination

plant, off Tuticorin in Tamilnadu.

 

The cold water was also tested for air conditioning the barge.

Kavaratti island provides an ideal setting for this technology where

cold sea water is available to the coast. The island, made by coral

reefs, slopes down to 350 metres depth at a distance of about 400

metres from the shore and does not have a regular source of fresh

water. This environment friendly, low cost technology, which is

relatively easy to maintain, will be a boon not only to the local

islanders but also in other water deficient islands and coastal areas

around the tropics.

 

The technology is also relatively clean from environment point of

view as it does not require any pre-treatment of feed water and

produces no chemical or thermal pollutants, thereby, making it most

suitable for islands having fragile eco-systems. As the cold deep sea

water is rich in nutrients, it will attract marine organisms and

fishes. Thus, `mariculture' can be an additional economic byproduct

of this technology apart from using cold water as an eco-friendly

coolant for air conditioning in hot and humid tropics.

 

India's coastline stretches to about 6,500 km and there are two

island territories. Coastal urban areas where safe drinking water is

in short supply and required sea-depth is not available, may use such

desalination plants with a million litre/day capacity. The production

cost, which is about 25 paise per litre in case of Kavaratti plant,

can be further brought down to about 14 paise per litre if the

capacity is increased to 2 lakh litres. Higher capacity desalination

Plants such as 10 million litres per day capacity floating moored

ones can be set up for coastal urban areas, where production cost

will come down to as low as 3-6 paise per litre. That's the way the

Department of Ocean Development is going to address the problem of

acute shortage of water in the rest of the inhabited islands of

Lakshadweep as also in the Andaman & Nicobar islands and in the

coastal areas in the coming days.

Original Source : *Director of Public Relations of the Ministry of

Science & Technology and Ocean Development