History repeats itself in amazing ways. In 19th century rural Mexico, people used boiled prickly pear cactus to clean dirty water. The sediment sank and the water at the top became potable. Norma Alcantar, PhD, who is at the University of South Florida learned this method from her grandmother and is now experimenting with the cleansing properties of cactus in drinking water and aquaculture.
We found that there is an attraction between the mucilage of cactus and arsenic. The mucilage 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.
Mucilage are the inner guts of the cacti. With over one billion people in the world lacking access to clean drinking water, the commonly found cactus may offer a solution. Alcantar and her colleagues tested this approach successfully following the earthquake in Haiti. They also experimented with this technique after the 2010 Deepwater Horizon oilrig disaster and spill, exploring the use of cacti to clean oil-contaminated seawater and finding it to be an effective dispersant.
At the recent 251st National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society, Alcantar presented her latest findings on using cacti to purify fish tanks used in aquaculture.
Alcantar and graduate research assistant Tunan Peng were approached by representatives from the Mote Marine Laboratory in Sarasota, Florida to investigate whether cactus extract could clean recirculating aquarium water and water in aquaculture tanks and ponds. Such tanks breed bacteria resulting in unpleasant smells in the water housing the fish. The current practice of replacing the tanks with fresh water takes a large amount of water, months of time and stresses the fish. Cactus mucilage seemed like a sound alternative.
Alcantar and Peng are taking on the challenge to find a mechanism using mucilage as an effective purifier for these applications. One study is to determine the chemical composition of the mucilage in order to synthesize it in the lab. A prototype of a recirculating aquaculture system, using cactus extract as a cleansing agent, is also being pursued. These findings can revolutionize aquaculture.
Even in science the adage of “grandmother knows best” applies.