Clean Tech

One problem, many solutions

M Ramesh | Updated on July 30, 2019

A look at the options to tackle Chennai’s — and the world’s — drinking water shortage

A sardonic refrain going around Chennai is that the city’s residents may not have water to drink but can take heart from the fact that the water problem has made the city internationally famous. It now has the unenviable distinction of being bracketed with Cape Town, when people talk about scarcity of drinking water.

But more Indian cities and towns are set to follow Chennai’s footsteps. NITI Aayog, the Centre’s think tank, has warned that half the country’s cities will run out of drinking water in a decade in a business-as-usual scenario.

The threat of drinking water shortage looms over the country (and other parts of the world), but it is not without solutions, so, we can be reasonably assured that we won’t die of parched throats. Often, what is vexing is not a want of solutions but the means to implement them. Take, for instance, Minister Nitin Gadkari’s answer to Chennai’s water problems — bring it to the city from where it is plentifully available, to wit, the Godavari river, some 600 km north. Only, bring it in pipes, and not through canals. Canals are costly as you’d need to buy lands to run them through and cement blocks to line them up. Pipes are cheaper. How cheap? Just ₹60,000 crore!

This might well happen, who knows, but there are other solutions on the horizon. For example, Denmark-headquartered pumps manufacturer Grundfos says it can provide solar-powered water pumps to suck out the stuff from deep underground. Krishna Ranganath, Managing Director of Grundfos’ Indo Region, says that for ₹3 lakh, you can put up a system that can pump 10,000 to 25,000 litres of water from as deep as 200 metres (650 feet).

The solution is not new — 35,000 such systems are providing water to 7.5 million Indians, says Ranganath.

Another option is, obviously, desalination, especially for coastal areas. Take sea water, remove the salt and you are in business. But the trick is in removing the salt. Now, when you soak a raisin in a cup of water, it bulges because it absorbs water —water flows through its skin to its interiors, where the liquid is denser. This is called ‘osmosis’. The opposite happens in ‘reverse osmosis’, where you make a liquid flow from a denser regime to a less dense regime. You do that by forcing the dense (sea water) liquid through a membrane — as only pure water can pass through the membrane, you end up with the cool stuff. This act of ‘forcing’ calls for energy (electricity). This messes up both the plant and the economics a bit — but sea-water desalination is a working method of producing drinking water.

Using the power of waves

But can there be a simpler and cheaper way? Sure, says an American company called Resolute Marine. Instead of using electricity to push sea water through the membrane, use the power of waves — which is immense and never-ending. The company’s website has a graphic on how much ‘push’ (or energy, in terms of kW) you get per metre of wave-front. It says its technology works well with 10 kW; India is shown to have 14 kW. Resolute Marine is aware of the “well publicised water security issue” in India. “We have been told that the best opportunities in India might lie in the Kerala province because the wave energy resource there is quite strong and consistent,” Co-Founder and CEO, Bill Staby, told BusinessLine via email. Its standard commercial plant can produce 4 million litres of potable water a day — too small for a city like Chennai but you can scale it up. Scrap sheet workings show the cost to be a rupee a litre.

Moving on, we come to machines that suck water out of the air, by the simple process of condensation. But the problem, again, is that they are knock-out expensive. To illustrate, a Chennai-based company, Swelect, is marketing American solar-powered water machines that cost ₹2 lakh a piece — they produce 5 litres of water a day. Soldiers in a desert or mountain might find it useful, but a regular household is bound to find it a wallet-bleeder. However, there are ideas to bring such ‘water out of the air’ contrivances within reach. For instance, Dr LR Chary, a marine technologist who has worked with Shipping Corporation of India, has come up with a concept. If you have a source of not-so-pure water, first vaporise the water in a chamber using solar heat, then have water-from-air machines pull out the water from the vaporous air. Chary is convinced the system will provide cheap water.

Another idea of Chary, who has long been a strong advocate of offshore wind farms, is to put up wind turbines on retired oil platforms out in the sea and use the electricity to desalinate water.

A variant of the idea is to use the wind turbines on the platforms to produce compressed air, which could be used to push sea water through a membrane to produce fresh water on the other side.

So, it is one problem, many solutions. The world might need all of them. The World Resources Institute has warned of severe water stress, and ‘climate change’ is exacerbating the problem. And, do not forget, we are adding 80 million people to the planet every year.

Published on July 30, 2019

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