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Desalination of Water: The Need and Chal

  Mar 18, 2020

Desalination of Water: The Need and Challenges

What is desalination?

Desalination refers to the removal of salts and minerals from a target substance Saltwater is desalinated to produce water suitable for human consumption or irrigation.  Desalination is used on many seagoing ships and submarines. 

Why do we need it?

Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. 

Is it costly relatively to alternatives?

Due to its energy consumption, desalinating sea water is generally more costly than fresh water from rivers or groundwater, water recycling and water conservation. However, these alternatives are not always available and depletion of reserves is a critical problem worldwide. Desalination processes are usually driven by either thermal (in the case of distillation) or electrical (e.g., photovoltaic or wind power) as the primary energy types.

How much is it in use globally today?

Currently, approximately 1% of the world's population is dependent on desalinated water to meet daily needs, but the UN expects that 14% of the world's population will encounter water scarcity by 2025.

What about India?

In Kavaratti Island, the capital of Union Territory Lakshadweep, finding potable water was a challenge for the islanders. High saline content made groundwater unfit for drinking, and bringing large quantities of water from the mainland was not an option. People tried several measures: open wells, rainwater harvesting etc but of no avail.

In 2005, Chennai-based National Institute of Ocean Technology (NIOT) set up a desalination plant with a capacity of 1,00,000 litres potable water a day.  The NIOT plant provides continuous supply of drinking water to more than 10,000 people in Kavaratti, bringing down incidences of waterborne diseases.

Cases of dysentery have dropped from 200 to 10 a year, and instances of diarrhoea and water-borne hepatitis reduced significantly. The success of the desalination plant prompted NIOT to set up low-temperature thermal desalination (LTTD) plants in Lakshadweep's Agatti and Minicoy Islands too. 

Chennai has acute for water scarcity. To take advantage of the long coast line, the state government is setting up two desalination plants. 

Can desalination address India's growing challenge of supplying fresh water? 

In 2018 July, NITI Aayog's Composite Water Management Index Report revealed that more than 600 million people undergo extreme water stress in India today, while 75 per cent households do not have drinking water on premises.

With increasing population, the country might face extreme levels of water scarcity in the coming years, and the 'water balance figure' - which represents the input and output of water - is estimated to go negative by 2027. To address this, desalination technology is one of the emerging solutions. It can particularly help coastal cities such as Chennai, Mumbai, Kolkata, Surat and Vizag ensure water security.

Desalination plants for industrial and public distribution are currently operating in Tamil Nadu, Maharashtra, Gujarat, Rajasthan and Andhra Pradesh. 

Apart from the advantage that desalination plants hold in coastal areas, they are also an all-weather solution. Many West Asian countries, including Israel, have floated tenders for very large desalination plants.

In 'water stressed zones' India can target at least 25 per cent supply from desalination. 

What are the drawbacks?

Cost and the environmental impact.

Why is it costly?

Desalination plants have drawbacks: high cost (capital expenditure, energy consumption and maintenance).

"For a large SWRO (sea water reverse osmosis) plant incorporating the latest technology, the investment needed is very high. It can take about five years to be fully operational. 

In a desalination plant, energy is needed to push water past a membrane at high pressure to separate the salt. It is energy intensive and thus is very costly.

At present, many desalination plants use coal or diesel. However, technologies are being developed to use energy from renewable sources such as solar, in particular, and wind. 

What is the environmental effects?

A big drawback of desalination plants, however, is the environmental impact. The hyper salty brine water that is pushed back into the water, and which often contains other contaminants and chemicals used for water treatment, poses a significant threat to marine life. The brine has to be discharged around 650 metres into the sea. On an average, for one litre of fresh water generation, desalination plants produce 1.5 litres of brine. If not properly disposed of, the brine might affect the shoreline and marine life.

Brine is also warmer than the normal seawater and contains about 5 per cent salt, which poses a threat to corals and aquatic life. 

Any new technological breakthrough?

Technological advances are seen such as development of graphene membranes which could reduce power consumption.