The prickly pear cactus removed 98% of sediment and bacteria from water.

Flickr/ ah zut

[MEXICO CITY] Scientists have worked out how a common, edible cactus purifies water, paving the way for its use in developing countries.

The nopal (or prickly pear) cactus, Opuntia ficus-indica, is native to the United States and grown widely on the African continent, Mexico and other developing countries. It could now become a sustainable and affordable water purification method in the rural communities of developing countries, say the scientists.

Scientists have known that prickly pear cleans water but their understanding of the mechanism was poor.

They tested two types of mucilage — a gelatinous substance produced by the cactus — in contaminated water. The cactus removed 98 per cent of bacteria within 15 minutes by clumping sediment and bacteria into small 'flocs' — clumps of particles floating in water — that could easily be filtered out.

These findings pave the way for guidelines on how much cactus is needed to purify water, say the researchers. Guidelines already exist for the moringa seed, another natural water purifier (see Poor missing out on moringa seeds' water-purifying powers).

"We envision that communities would be able to use the cactus to feed themselves, and at the same time to clean their water," Norma Alcantar, lead author of the study, from the University of Florida, United States, told SciDev.Net.

When she tested the cactus in a Mexican rural community "people were all open to the idea of using the cactus," she said.

But Alejandra Martín, head of the Water Potabilization Program at The Mexican Institute of Water Technology (IMTA), believes the greatest challenge is educating people about importance of purifying water.

"It's a necessity from our point of view, but not from theirs," she told SciDev.Net.

"Some indigenous communities don't purify water," Daniel Murillo, head of the Social Participation Program, at IMTA, told SciDev.Net. "Stomach and intestinal infections are considered a way of cleansing the body, and are not conceived as diseases."

Alcantar's team is now working on educational programmes with non-profit organisations and universities in Mexico. She is expecting to start a similar project in June to help with water problems caused by the recent earthquake in Haiti (see Geologists survey Haiti quake aftermath).

Adrian Rennie, a materials physicist at Uppsala University, Sweden, whose research includes water purification by moringa seeds, said it was good to see more detailed studies on natural polymers for water purification as different settings suit different bio-polymers.

Link to paper abstract in Environmental Science & Technology