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Last Update: 2007-03-29   Source: Star Projects
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Solar-powered disinfection

One of the main challenges facing us is solving a widespread water crisis, namely the lack of clean drinking water. European researchers are introducing a simple and practical method to disinfect water of bacteria and disease, using a reliable and convenient source: the Sun.

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Gladys and her neighbour are helped by their children in the daily chore of collecting water. Due to a healthy rainfall the next nearby source is 2.5 km from their village, otherwise it would be 8 km. But it is not clean drinkable water that they collect, rather muddy water containing small animals, insect larvae and bacteria. It is a one hour walk from the small Maasai community, situated near the border between Kenya and Tanzania. The water is put into plastic bottles and placed on the roofs of the huts for 4 to 6 hours. The heat and the ultraviolet rays from the Sun deactivate the bacteria inside. Now the water is ready for drinking with far less risk of infection. Gladys has used these solar bottles for the last 11 years. She claims that not having to boil the water not only saves her time, the bottled water even tastes better than boiled water.

The solar disinfection method is good for various reasons: chlorination costs money for tablets, filtration costs money for filters, and boiling is very laborious (and in some areas of developing countries the collection of wood is not allowed for environmental reasons). A plastic bottle is a sustainable resource with an insignificant cost.

The water must then be consumed within 24 to 48 hours, otherwise surviving bacteria could reactivate. But this method has already proven to be most effective, particularly since the villagers do not possess the means required for chlorination or filtration. Local doctors confirm a drastic reduction in waterborne diseases amongst the villagers. After the first three years, diarrhoea cases were down by 20%; the figure is now 70%.

Dr. Mike Meegan is a cofounder of ICROSS, the organisation that introduced this technique to Kenya more than decade ago. His hopes are set on the implementation of the solar disinfection technique around the world on a bigger and more sophisticated scale. However, more than plastic bottles are required for very large communities. The technology and method must be developed so that it can be distributed and given cost-free to the people. The trick is to achieve this as a sustainable system at a low cost.

The world’s biggest solar research compound (CIEMAT-PSA) is in Almeria, southern Spain. European researchers continue to refine how solar radiation can be used to disinfect water carrying bacteria. They are working as part of a €2 million project funded by the European Union, called SODISWATER. The SODISWATER coordinator Dr. Kevin McGuigan explains how the UV photons sterilise the water by damaging the bacteria cell membranes and the DNA within the cells. As a convenient side-effect, the ability of the cell to counter the damaging effect of the UV rays weakens as the water temperature rises in the sunlight.

Spanish researchers have developed a 1 m2 water reactor, capable of sterilising 50 litres at a time. The reactor is more complex and expensive than a plastic bottle, but it drastically reduces processing time while using the solar rays more efficiently. 90 minutes is enough to deactivate E. coli, a bacterium causing gastroenteritis.

Around 40 000 people in Kenya use solar exposure for water disinfection. The technique is currently being spread to Zimbabwe and South Africa, and trials are about to begin in Cambodia. It could also be applicable in situations involving refugees, disaster zones and war zones. Through the work of those like ICROSS and SODISWATER the solar disinfection of water is realising its enormous potential, improving the public health of those in countries where only the lucky few have access to clean drinking water.


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