Delivering water to thirsty crops and thirsty people

Sensemaking / Delivering water to thirsty crops and thirsty people

From solar-powered purification plants to the humble jerrycan, Jon Turney explores the promise of technology to improve water supply in dry climates.

By Jon Turney / 05 Dec 2012

From solar-powered purification plants to the humble jerrycan, Jon Turney explores the promise of technology to improve water supply in dry climates.

Wherever people live, they will get water somehow. The question is how hard they must work to get it, and whether it is good to drink. People in arid regions have found many ingenious ways of securing supplies. Bringing safe water to those without easy supply – perhaps 800 million, mostly living in rural areas – depends, above all, on money. But an array of technologies may improve returns on investment.

These need not be new. There is inspiration in ancient systems like the underground tunnels for groundwater irrigation, known as 'aflaj', in Oman. They need not be high-tech. The plastic jerrycan has revolutionised water collection and distribution in many developing countries over the last 30 years, helping erode the division of labour that confined water-carrying to women. But they need to be robust, reliable, and tailored to local geography, climate and culture.

Energy is the key to many efforts to guarantee water supply

Energy is the key to many efforts to guarantee water supply. Pumping needs power. In coastal areas, or where groundwater is brackish, desalination is energy intensive. Water supply and sanitation are always linked, and one simple way to make water contaminated with bacteria safe is heating it – often to boiling point.

Arid conditions often go with hot climates, so solar power is a good match for many water projects' energy needs. It is reliable, getting cheaper, and easy to operate in small-scale, local schemes which are widely distributed. Installation costs are higher than for diesel generation, but running costs are lower.

Electricity from solar panels readily powers pumps or drives distillation, and many combinations of power and mechanism are on trial. One nearing wider use is a solar pump drive, developed in Switzerland and now manufactured by AMRO Technology in Bangalore, India. A brushless motor (originally developed at Bern University in the 1980s for solar-powered car competitions) has been adapted to operate a solar-powered unit which can be fitted to most types of existing hand or treadle pumps. The marriage with existing installations may make them an easier sell, and users have the reassurance they can revert to human power if the solar electricity fails. The latest version of the unit is now being tested in seven countries including Bangladesh, Nepal, Ghana and Haiti, with results due in next year.

Solar power is also an option for cleansing drinking water. It can be used for direct heating, or converted to electricity and stored for later use.

Purification which does not rely on high temperature is also possible, by filtration – which can save money, fuel and carbon emissions. One of the most impressive initiatives is the Lifestraw project (left), which has provided nearly 900,000 households in Western Kenya with a free water filter that removes micro-organisms. Each filter lasts three years, and cleans enough drinking water for a family of five. The project, launched in 2011, includes training for householders and for staff in 31 service centres where faulty filters will be repaired or replaced for ten years. The upfront costs were met by the manufacturer, Verstergaard Frandsen. They say they will recoup the $25 million investment through carbon credits, awarded by ClimateCare's Climate and Development scheme, and others.

Soil solutions

And what about thirsty crops? In areas where rainfall is likely to be adversely affected by climate change, more complex arrays of technology may be needed to ensure crop irrigation can go on. Drip-fed irrigation systems, which target plant roots and save water, are catching on fast. They use less than half as much water as traditional irrigation channels, and save labour while increasing yields. Their original developer, Israeli scientist Dr Daniel Hillel, received the World Food Prize this year, and since he pioneered the method in the 1950s has seen it used on millions of hectares of crops: 2 million in India alone.

More recently, simple drip-fed systems have been updated with the latest in sensors and communications to allow more precise adjustments to water delivery. In California's San Joaquin Valley, some fruit and vegetable farmers are getting used to wireless monitoring and control of automated drip feed systems. A farmer can now check water pressures and flow rates in distant fields from an iPad or phone.

Drip irrigation began in the Negev desert in southern Israel, one of the driest regions on the planet. The Negev is also a centre of research into desalination. Making salt water usable for crops, or even for drinking, can be achieved using a range of technologies, but requires a lot of energy, and is therefore expensive. At the moment, desalination is mainly used to furnish drinking water in countries with plenty of energy, and finds some agricultural use in Spain, the United Arab Emirates and Israel.

New refinements in one of the most-used desalination techniques, reverse osmosis, promise increased efficiency, and may allow much wider use of the method in less developed countries.

The physical chemistry of reverse osmosis is complex. Osmosis describes the movement of solvent molecules from water with low particle content towards more dense climes. If the vessels are joined by a semi-permeable membrane, which has pores small enough to block some particles but still allow water molecules through, water passes from the weaker to the stronger solution, moved by osmotic pressure. However, if a strong enough external pressure is applied, it can force water the other way: hence reverse osmosis. The result is pure water on one side of the membrane, and unwanted chemicals concentrated on the other.

There have been many experiments with reverse osmosis for small-scale operations in remote, rural areas. One way to improve the process is to achieve finer control of the membrane. This is the key to a system now being tested in Israel's Arava Valley, an arid region that nevertheless produces fresh vegetables for export. An 'engineered oasis', developed by the Ben-Gurion University in the nearby Negev, desalinates the brackish groundwater drawn from aquifers using less energy than conventional systems – thanks to nanofiltration membranes, which can operate at lower pressures.

Test seasons in 2010 and 2011 saw the new desalination plant performing as theory predicted, at a pressure 45% lower than a comparable standard reverse osmosis membrane, and using 40% less energy. Moreover, the water resulting from this purification technique is less brackish, and so can be more easily taken up by crops, which means farmers can reduce their consumption. The trials even showed some increases in yield.

The ultimate aim of the project is to prove a system which will be easy to install, maintain and finance on small farms in other countries where there are large areas with no easy access to water or electricity. The nanofiltration option is also good for crops because it does not deliver water completely depleted of ions, such as calcium and magnesium, which are essential for crop growth. As membrane technology develops further, there is the potential bonus of fine-tuning exactly which dissolved chemicals are removed from the water, and which remain. This should allow water content to be modified to suit particular crop plants.

Further improvements in membrane performance are supported by lab work on the new material graphene – a layer of carbon only one atom thick. Researchers at MIT have calculated that graphene pores could be between a hundred and a thousand times easier for water to pass through than current membranes, while still retaining dissolved ions. If it works, the latest nanotechnology will offer more answers to humankind's oldest need.

Jon Turney is a science writer, and author of 'The Rough Guide to the Future'.

Photo: Vestergaard Frandsen, Goodshot/ Thinkstock

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