SAN DIEGO, March 13, 2016 -- Farm-grown fish are an important source of food with significant and worldwide societal and economic benefits, but the fish that come from these recirculating systems can have unpleasant tastes and odors. To clean contaminated water for farmed fish, drinking and other uses, scientists are now turning to an unlikely source -- the mucilage or inner "guts" of cacti.
The researchers present their work today at the 251st National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world's largest scientific society, is holding the meeting here through Thursday. It features more than 12,500 presentations on a wide range of science topics. A brand-new video on the research is available at http://bit.ly/ACSCactus.
"We found there is an attraction between the mucilage of cactus and arsenic," says Norma Alcantar, Ph.D. "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."
The technology grew from century-old knowledge that mucilage from some common cacti can clean drinking water. Alcantar was first introduced to this 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.
In 2006, Alcantar, who is at the University of South Florida (USF), began experimenting with the cleansing properties of cactus. She and her team tried the approach to clean contaminated drinking water following the Haiti earthquake and found it worked well. Common worldwide, cacti are a sustainable product and are not only nontoxic, but are edible and considered a delicacy.
Following the 2010 Deepwater Horizon oil rig disaster, she 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.
Such tanks, Alcantar and Peng say, 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 flavor 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 says.
In a search for alternatives, Peng and Alcantar turned to cactus mucilage. Now, she adds, they are seeking to determine the mechanism that allows mucilage to be such an effective purifier.
Also, the researchers are currently studying the chemical composition of the mucilage, which is made up of carbohydrates and some 60 sugars, with the goal of synthesizing it in a lab. In addition, they are developing a prototype of a recirculating aquaculture system that uses cactus extract as a cleansing agent, and they will conduct a life cycle analysis of the system.
A press conference on this topic will be held Tuesday, March 15, at 11 a.m. Pacific time in the San Diego Convention Center. Reporters may check-in at Room 16B (Mezzanine) in person, or watch live on YouTube http://bit.ly/ACSliveSanDiego. To ask questions online, sign in with a Google account.
Alcantar acknowledges funding from the National Science Foundation (NSF), the NSF Innovation Corps program (I-CorpsTM), the Gulf of Mexico Research Initiative, the Mote Marine Laboratory & Aquarium and the Aquaculture Review Council of the Florida Department of Agriculture and Consumer Services.
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Degradation of Taste and Odor Compounds with Cactus Mucilage Extraction: Applications for Recirculating Aquaculture Systems
Recirculating aquaculture systems (RAS) are gaining popularity due to their water savings compared to conventional aquaculture. In RAS the water is treated and recirculated, reducing fresh water inputs and volume of wastewater discharges. In addition, they provide more environmental control for fish growth, which in turn can result in higher production rates. A disadvantage of RAS is that conditions are created for the production of taste and odor compounds. These compounds, such as (-)-Geosmin (GSM) and 2-methylisoborneol (MIB), are secondary metabolites created by cyanobacteria and some actinomycetes that cause an earthy musty flavor that can be detected in water at extremely low concentrations. The current removal approach for these compounds is to purge them from the fish prior to harvesting which requires large amounts of highly treated water or treating the water onsite. Removal of GSM and MIB can be achieved by conventional adsorption treatment with activated carbon; however, removal efficiency has been inconsistent due to variations in the base of the carbon, adsorption capacity of the media and interactions with natural organic matter (NOM). This research will focus on using cactus mucilage extraction to degrade the taste and odor compounds in the recirculating aquaculture systems.
Cactus mucilage is a biomaterial that is used as food source in some countries and it is renewable, biodegradable, easy access and low cost. Previous research has found mucilage extraction can be used as dispersant in different cases, such as oil. Different concentrations and types of mucilage extraction solution are applied into recirculating aquaculture systems to test their effectiveness for removal of GSM and MIB. During the research, Fourier Transform Infrared Spectroscopy and GC-MS will be performed to monitor the concentration change GSM and MIB during the processes studied. UV-TiO2 photo-catalysis will also be combined with the mucilage extraction solution to further enhance the removal effectiveness of odor compounds.