Researcher Uses Cactus Mucilage to Clean Water

TAMPA, Fla. (Oct. 31, 2008) – The ‘prickly pear’ cactus, sporting wide, flat, teardrop lobes shaped like tennis rackets, is especially plentiful in rural northern Mexico. True to its common name, the prickly pear cactus (Optunia ficus indica to scientists) is studded with little spikes. However it’s what’s inside the lobes –a thick, gooey mucilage – that is helping residents of rural Mexico clean their drinking water, thanks to a University of South Florida chemical engineer and her research team. There are tremendous global implications.

“The World Health Organization recognizes a need for developing low-cost ways of cleaning water for household use,” says Norma A. Alcantar, an assistant professor in the USF Department of Chemical and Biomedical Engineering. “Consistent with that need, and to be able to clean water by removing heavy chemicals such as arsenic through a natural and inexpensive process, is the focus of our research.”

The process of using cactus mucilage is quite old, something Alcantar learned from her grandmother. But now the process has been validated by, and improved by, science.

Here’s how it works:

‘Mucilage,’ a thick, gum-like substance in the cactus pads, helps the cactus retain water in the dry climate and can be extracted by boiling the pads. When mucilage is added to dirty water it binds to the dirt and the larger dirt particles settle out of the water due to the high molecular weight of the gum-like mucilage when it swells in water.

Alcantar’s research has shown that the mucilage can bind to and starve bacteria as well as form a complex with arsenic, a known carcinogen that occurs naturally in the soil or comes from industrial or agricultural pollution. Arsenic is removed when it binds to the natural sugars in the mucilage and the combination is drawn through a sand or membrane filter. The amount of arsenic removed depends on several variables, such as the source and pH values of the water to be treated.

Even trace amounts of arsenic can cause serious health problems when consumed over long periods of time. Alcantar and her team are also assessing whether the cactus mucilage can be as effective in removing other dangerous heavy metals, such as selenium, chromium and cadmium, from water.

The site of their investigations is the small town of Temamatla, Mexico, 25 miles southeast of Mexico City. “Ours is a complex interdisciplinary, international research project merging engineering principles, scientific explorations and socio-cultural investigations,” says Alcantar. “Temamatla was chosen for study because of its multiple water contamination problems of both arsenic and suspended solids from volcanic sources as well as debris from a suspected collapsed well.”

Because varieties of the prickly pear cactus grow from western Canada to the tip of South America, the process may have wide spread application in rural communities where getting clean drinking water is a problem and the cacti are plentiful. Alcantar speculates that the success of the research may spur a ‘green technology’ industry in which harvesting the cactus will help depressed economic areas, providing a financial boost when the ‘cash crop’ can be used for wastewater treatment on a large scale.

The University of South Florida is one of the nation's top 63 public research universities and one of 39 community-engaged, four-year public universities as designated by the Carnegie Foundation for the Advancement of Teaching. USF was awarded more than $360 million in research contracts and grants in FY 2007/2008. The university offers 219 degree programs at the undergraduate, graduate, specialist and doctoral levels, including the doctor of medicine. The university has a $1.8 billion annual budget, an annual economic impact of $3.2 billion, and serves more than 46,000 students on campuses in Tampa, St. Petersburg, Sarasota-Manatee and Lakeland. USF is a member of the Big East Athletic Conference.

– USF –