Small, solar-powered water treatment plants promise water for world's poorest
Researchers from the Fraunhofer Institute for Solar Energy Systems (ISE) have successfully tested small, decentralised water treatment plants with an autonomous power supply. The researchers are planning to put the plants on the market at some point in summer 2008. The compact plants, developed in the framework of two EU-funded projects, can produce about 120 to 150 litres of pure drinking water per day, transforming either salty seawater or brackish water. The system 'consists of six square metres of thermal solar collectors, a small photovoltaic module to power a pump, and the desalination module itself,' explained engineer Joachim Koschikowski of Fraunhofer ISE. One of the main objectives in their development was to keep the plants as low maintenance as possible, Mr Koschikowski told CORDIS News, as they are intended particularly for the arid and semi-arid regions of Africa and India, where it is growing increasingly difficult to supply drinking water. There, large, industrial desalination plants are not suitable. 'The regions have a very poor infrastructure. Quite often there is no electricity grid, so conventional desalination plants are out of the question,' Mr Koschikowski pointed out. Test plants in Jordan and on Grand Canary have demonstrated that the researchers have achieved their aim: The plant on Grand Canary has been up and running for three years, Mr Koschikowski said. So far, only little things have needed repair, such as the odd cable or the pump that had to be replaced. 'But those are teething problems. In principle, the plant has been designed to be maintenance free.' The desalination system is based on the principle of membrane distillation: 'The salty water is heated up and guided along a microporous, water repellent membrane,' Mr Koschikowski explained. 'Cold drinking water flows through the other side of the membrane. The steam pressure gradient resulting from the temperature difference causes part of the salt water to evaporate and pass through the membrane. The salt is left behind, and the water vapour condenses as it cools down on the other side. It leaves us with clean, germ-free water.' In comparison, other methods such as reverse osmosis or solar water distillation are either too sensitive to impurities in the water or too inefficient. Membrane distillation plants, on the other hand, are rather robust and uncomplicated. In addition, the system recovers the heat after the distillation process, making it more energy-efficient. The Fraunhofer researchers have also developed a dual-circuit system in which several desalination modules are connected, so that the system is more powerful and reaches a greater output of several cubic metres of water treated per day. Even though, compared to this, up to 150 litres of drinking water from the compact plants might seem like a drop in the ocean, Mr Koschikowski said that there is definitely a demand for the small capacity, too. In developing countries, water consumption is much lower than in developed countries. Hence, a small plant can supply drinking water for up to 15 people. The price per 1,000 litres will amount to about €10 as soon as the plants can be mass-produced. 'When you think how much the inhabitants currently have to pay for the same amount of bottled water or soft drinks, the plant will pay off very quickly,' Mr Koschikowski concluded.
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