Clean Tech

Desalination is here to stay — you don’t have to take it with a pinch of salt

M Ramesh | Updated on February 12, 2020 Published on February 12, 2020

The Nemmeli desalination plant near Chennai (file photo> B Jothi Ramalinga   -  B Jothi Ramalingam

Water-stressed regions now have a viable solution at hand

The greens may not like it, but by the looks of it, desalination is here to stay. With climate change getting out of hand and the inevitability of mankind to have to live with its wrath, desalination has a big and growing role to play in the provision of water.

This is particularly true for India. Take any illustration showing water-stressed regions of the world, you’ll find India pretty much in the red.

It was only last summer when the metropolis of Chennai came into severe water shortage and got bad press the world over. The city managed by wheeling water on trucks and railway rakes until, fortunately, the rains came and saved the city from slipping into a Cape Town kind of major crisis.

However, Chennai may not face such a severe problem — at least not in the near future. Guess why? Desalination. The city today has two sea water desalination plants of 100 million litres per day capacity each, and another 150 MLD plant is under construction. And, there is a decent chance that the city’s plan for another 450 MLD plant will get past the legal gauntlet. (If and) When these two plants come up, the city will be able to meet roughly half of its daily requirement of 1,590 MLD from the largesse of the seas.

Chennai is perhaps a standing flagpost of things to come. Mankind, in all probability, is going to have to rely substantially on this source of water.

Proven technology

Today, the world has some 16,000 desalination plants that produce a little over 90 billion litres of water to meet 5 per cent of the world’s fresh water needs, according to the International Desalination Association (IDA). Sea water reverse osmosis plants produce account for a good three-fourths of it.

BusinessLine’s chat with multiple stakeholders reveals some interesting insights.

First, most experts, including those in the industry — such as Syed Amir Basha, Chief Technical Officer of VA Tech Wabag, a Chennai-based water company — stress that it is necessary that desalination should be taken up after exhausting other measures for provision of water, such as, for instance, increasing the capacity of a region to store rain water.

Second, water from desalination is inexpensive, and could be even cheaper if cheaper electricity is supplied. For instance, the cost of production of water from the 100 MLD Nemmeli plant in Chennai, run by VA Tech Wabag, works out to ₹38 for 1,000 litres (around ₹55 including finance costs, depreciation and transportation); cost of electricity alone accounts for 70 per cent of it. The plant buys electricity at ₹6.35 a kWhr. Compare this with the national average power purchase cost, which is ₹3.60/kWhr or the Tamil Nadu’s utility’s average power purchase cost of ₹4.29, you will see how much cheaper electricity a desalination plant could buy power.

Improvements in technology have made desal (desalination) water cheaper. Basha says that in the 1980s, a desalination plant used to consume 9 kWhr of electricity to produce thousand litres of water. Now it has come down to 3.8 kWhr, because of systems that recover energy from the pressure of the discharge water. Power costs — and consequently cost of water — could further come down if electricity is made available to these plants cheaper. If a solar power plant is linked to a desalination unit and wheeling charges are waived, the cost of water would drastically come down, says Basha.

Third, it is a myth that putting the highly salty water (brine) from the RO plants back into the sea is harmful to marine life — only, it has to be done right. Pre-dilute it, use proper diffusers. West Asia, for decades, been getting almost all of its water needs from desalination of sea water, no environmental issue is seen in the Gulf. On the contrary, in December 2019, research conducted by Professor Brendan Kelaher of the National Marine Science Center of Australia’s Southern Cross University, found that the hypersaline water pumped into the sea by Sydney’s desalination plant had actually increased fish life by 279 per cent.

The local press quoted Dr Kelaher as saying that he thought his research would show there was no negative impact, but “we were really surprised to find such strong positive effects.”

A white paper produced by the IDA on the effects of brine discharge concludes that the discharge is fully safe and does not result in negative impacts on the marine habitat.

Fourth, desalination technology is improving fast. Today, ‘forward osmosis’ plants are coming up, which when used in combination with ‘reverse osmosis’ (or other processes such as multi flash or multi effect desalination), vastly improves the plant economics. Then there are upcoming technologies such as ‘membrane distillation’ (a thermal process where only vapour molecules pass through hydrophobic membranes), ‘humidification-de-humidification' (a process that uses sea water to humidify air so that it water could be extracted from it.) And there are experiments going on with using the energy of the waves to force sea water through the membranes.

Finally, there is more promise on the horizon in terms of metal recovery from brine. Sea water has many useful metals—Sodium, Magnesium and Lithium—but in such small quantities as would make their recovery uneconomical. But research is going on in various parts of the world, including at Institute of Minerals and Metals Technology, Bhubhaneshwar, to discover viable processes for metal recovery from sea water. When there is a breakthrough here, brine from desalination plans would become a very valuable commodity.

The world is moving towards a water crisis today and this is forcing attention on to these technologies. The industry is moving into it faster. For example, Pankaj Kumar, CEO of Sterlite Copper says when the Tuticorin plant would double its capacity to 800 tonnes a year, the entire additional water requirements would be met by desalination. A lot more activity can be expected to be seen under the head ‘desalination’ in the next decade than ever before. Welcome.

Published on February 12, 2020
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