FORGET expensive machinery, the best way to purify water could be hiding in a cactus. It turns out that an extract from the prickly pear cactus is effective at removing sediment and bacteria from dirty water.
Many water purification methods introduced into the developing world are quickly abandoned as people don't know how to use and maintain them, says Norma Alcantar at the University of South Florida in Tampa. So she and her colleagues decided to investigate the prickly pear cactus, Opuntia ficus-indica, which 19th-century Mexican communities used as a water purifier. The cactus is found across the globe.
The team extracted the cactus's mucilage - the thick gum the plant uses to store water. They then mixed this with water to which they had added high levels of either sediment or the bacterium Bacillus cereus.
Alcantar found that the mucilage acted as a flocculant, causing the sediment particles to join together and settle to the bottom of the water samples. The gum also caused the bacteria to combine and settle, allowing 98 per cent of bacteria to be filtered from the water (Environmental Science and Technology, DOI: 10.1021/es9030744). They now intend to test it on natural water.
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