Cacti 'guts' clean contaminated water, say researchers
The inner guts of cacti can be used to purify contaminated water for drinking and other uses, according to researchers at the University of South Florida (USF).
Norma Alcantar, associate professor of chemical engineering at USF, said there is an attraction between the mucilage of cactus and arsenic. It also attracts sediments, bacteria and other contaminants.
“It captures these substances and forms a large mass or 'floc' that looks like cotton candy. For sediments, the flocs are large and heavy, which precipitate rapidly after the interaction with mucilage,” she said.
Alcantar was first introduced to the process by her Mexican grandmother who described using boiled prickly pear cactus to capture particles in sediment-laced dirty water. The sediments sank, and the water at the top of the bucket became clear and drinkable.
She and her team tried the approach to clean contaminated drinking water following the Haiti earthquake and found it worked well. Following the 2010 Deepwater Horizon oil rig disaster, Alcantar and her USF team began to explore the ability of cacti to clean up oil contaminated seawater. While the research program never moved beyond bench scale, she says, cactus mucilage was found to be an effective oil dispersant.
More recently, Alcantar and Tunan Peng, a graduate research assistant in her lab, were approached by representatives from the Mote Marine Laboratory in Sarasota, Florida, who asked them to investigate whether cactus extract could clean recirculating aquarium water, as well as water in aquaculture tanks and ponds.
The tanks create conditions that encourage bacterial growth that in turn develops unpleasant smelly compounds, such as 2-methylisoborneol (known as MIB) and geosmin. These compounds result in the musty, earthy flavour that is sometimes in the water and the fish that live in it. At harvest, the current practice is to purge the fish and tanks with fresh water, which takes months, uses large amounts of water and stresses the fish, Alcantar said.
In a search for alternatives, Peng and Alcantar turned to cactus mucilage. They are seeking to determine the mechanism that allows mucilage to be such an effective purifier.
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