What are Desalination plants?

On 23 November 2020, Uddhav Thackeray led Maharashtra Government gave a go-ahead to the Brihanmumbai Municipal Corporation (BMC) for setting up of a desalination plant in Mumbai's Manori to overcome the water crisis in Mumbai. The proposed desalination plant is expected to process 200 million litres of water daily (MLD). 

The Chief Minister of Maharashtra, Uddhav Thackeray stated, “If the project is implemented on solar energy, the production cost will also be reduced. Government land is available at Manori and roads are also available. As there is no urban settlement in this place, the project will be completed without any interruption.”

Details about the project

1- The proposed project will be set up on 25-30 acres of land at Manori, Mumbai. 

2- It is expected to process 200 million litres of water daily (MLD).

3- The project is expected to be completed by the year 2025, as per the officials. 

4- The projected cost of the desalination plant is Rs. 1,600 crores. 

5- The construction cost is expected to be 3-4 paise per litre. 

6- The process for this project will be through the Swiss Challenge Method. 

Need to set up a desalination plant in Mumbai

As per the BMC's projection, the population of Mumbai is expected to touch 1.72 crores by the year 2041, which in turn will raise the water demand to 6424 MLD. 

At present, BMC supplies 3850 MLD against the requirement of 4200 MLD per day. The desalination project is expected to provide relief to the residents of Mumbai in tackling 10-15% water cut. It is to be noted that the residents of Mumbai go through water cut every year due to the delayed monsoons. 

In 2007, a state government-appointed high-level committee suggested setting up desalination plants in Mumbai. The suggestion was scraped by the BMC quoting that setting up 100 MLD desalination plant will cost around Rs 1000 crore and will require large amounts of energy, specialised expensive infrastructure.  

In the year 2016, the BMC called off the proposal for setting up a desalination plant citing 'high cost and lack of land'. 

Desalination Plants in India

The Indian State of Tamil Nadu has two desalination plant near the capital, Chennai. One was set up in 2010 while the other in 2013. The two of them supply 100 MLD each to Chennai. 

Gujarat has also announced to set up 100 MLD RO plant at the Jodiya coast in Jamnagar district. Other proposed desalination plants in the state are in the coastal areas-- Dwarka, Kutch, Dahej, Somnath, Bhavnagar, and Pipavav. 

Andhra Pradesh is also planning to set up a desalination plant. 

What is Desalination?

The process through which mineral components are separated from saline water to make it fit for drinking is known as desalination. 

Is desalinated water fit for drinking?

The saline water which undergoes this process is monitored and tested in the same way as water from a filtration plant. 

How does this process work?

There are two commonly used methods for desalination of water. These are as follows:

1- Distillation: In this method, desalination occurs naturally through evaporation, where salty water is boiled and the steam is condensed. 

2- Reverse Osmosis: In this method, external pressure is applied to push solvents from an area of high solute concentration to an area of low solute concentration through a membrane. The membrane is so tiny that only water can pass through them, leaving behind salt and other impurities. 

At present, desalination accounts for 1% of the world's drinking water and is prevalent in countries located in the Middle East and North Africa region. It is also an important source of water for small island nations and developing countries. The disposal of the byproduct (highly concentrated brine) in desalination technology is a major problem. In many places, the brine is pumped back into the sea but it severely damages the local ecology around the plant. 

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