Purifying Contaminated Water with Cacti?

The latest breakthrough in clean water comes in the form of plants from the driest places on earth—desert cacti. According to a paper presented at the 251^st National Meeting and Exposition of the American Chemical Society, the inner mucilage of cacti is a powerful tool for purifying water—both for making safer drinking water, and for creating fish-farm environments that make fish taste better.

Norma Alcantar, PhD, professor at the University of South Florida’s Department of Chemical & Biomedical Engineering in Tampa, explains, “We have tested mucilage to remove contaminants such as sediments, bacteria, and off-flavor compounds separately. We have also looked at its properties as a dispersant of crude oil in fresh and salt water.”

The mucilage, she says, is an effective “flocculant”—it promotes the clustering of contaminants. According to Dr. Alcantar, the mucilage can be used first to coagulate contaminants, and after that, the remaining water can be filtered with a rough filter. As she explains in the press release announcing the discovery, “We found there is an attraction between the mucilage of cactus and arsenic. The mucilage also attracts sediments, bacteria, and other contaminants. It captures these substances and forms a large mass or ‘floc’ that sort of looks like cotton candy. For sediments, the flocs are large and heavy, which precipitate rapidly after the interaction with mucilage.”

This is a discovery that could have far-reaching effects across the world of water purification—particularly because the key product is easy to reproduce.

“The cactus plants used for our extraction are obtained via sustainable agriculture,” Dr. Alcantar says. “They are abundant, fast growing, and they do not require large amounts of water to survive. It is a plant that can easily grow in desert-like environments. The demand for mucilage can be easily covered with sustained growth/harvesting.”

As well, cactus mucilage can be synthesized using polysaccharides from biomass waste. At the moment, she and her team are studying synthesizing mucilage out of waste products.

Across a variety of water uses, the potential advantage of this discovery is wide. On the commercial end, Dr. Alcantar notes that experimentation with fish-farms has shown an enormous potential for the mucilage used in conjunction with photocatalysis to separate off-flavor compounds.

At the same time, the discovery has a potential humanitarian value. After the 2010 Haiti earthquake, Dr. Alcantar and her team experimented using cactus mucilage to clean contaminated drinking water, and found the results were positive.

“Bacteria and heavy metals are abundant after a disaster like the one in Haiti,” she explains. “We found prickly pear [cactuses] in Haiti, so our recommendation was that communities can work on water purification as small businesses to advance a microeconomic system or as point-of-use applications. However, the intervention of social workers and anthropologists is critical when this technology is ready to be introduced in low income communities.”