Low-temperature thermal desalination technology

The Chennai-based National Institute of Ocean Technology (NIOT) is working on making an ongoing initiative of providing potable water in six islands of Lakshadweep using a Low-Temperature Thermal Desalination (LTTD) technology process free of emissions.

About Low-temperature thermal desalination Technology –

• The LTTD is a process under which the warm surface seawater is flash evaporated at low pressure and the vapour is condensed with cold deep seawater.
• The LTTD technology does not require any chemical pre and post-treatment of seawater and thus the pollution problems are minimal and suitable for island territories.
• This technique works on the principle that water in the ocean 1,000 or 2,000 feet below is about 4º C to 8º C colder than surface water. So, salty surface water is collected in a tank and subject to high pressure (via an external power source).
• The pressured water vaporises and is trapped in tubes or a chamber. Cold water plumbed from the ocean depths is passed over these tubes and the vapour condenses into fresh water and the resulting salt is diverted away.
• Currently, the desalination plants, each of which provides at least 100,000 litres of potable water every day, are powered by diesel generator sets — there being no other source of power in the islands.
• Currently there are five desalination plants in operation in the Lakshadweep islands. Four more were expected to be functioning in the coming months. The proposed self-sustaining plant — the 10th — is expected to be ready later this year.

Is RO water good for health?

• Earlier, there were concerns that desalinated water was devoid of vital minerals such as calcium, magnesium, zinc, sodium, potassium and carbonates, referred to as TDS.
• Highly desalinated water has a TDS of less than 50 milligrams per litre, which is pure, but does not taste like water. However, anything from 100 mg/l to 600 mg/l is considered as good quality potable water.
• In today’s times, most RO plants put the water through a ‘post-treatment’ process whereby salts are added to make TDS around 300 mg/l.
• Several of the home-RO systems that are common in affluent Indian homes also employ post-treatment and add salts to water.

About National Institute of Ocean Technology (NIOT) –

• The NIOT was established in 1993 as an autonomous society under the Ministry of Earth Sciences.
• Objective — To develop reliable indigenous technologies to solve various engineering problems associated with harvesting of non-living and living resources in the Indian Exclusive Economic Zone (EEZ) which is about two-thirds of the land area of India.
• Headquarters – Chennai, Tamil Nadu