Jack Losso, Ng, Chilton, Marshall, Wayne, Rao, Ramu M. | 6/14/2005 7:03:29 PM
Chilton Ng, Jack Losso, Wayne E. Marshall and Ramu M. Rao
Off-flavor in pond-cultivated catfish is a problem for Louisiana catfish producers. One of the compounds most commonly cited as responsible for earthy and musty tastes and odors in water and the cause of off-flavor in catfish is geosmin, which is a substance produced by blue-green algae and bacteria. Although it is not a health hazard, geosmin in water can be absorbed in fish tissue, making fish taste bad and impossible to sell.
Conventional separation techniques for removing geosmin have been unsuccessful, because it is an extremely stable compound. It resists chemical oxidation and heat and is not significantly affected by chlorination. Consequently, the most common water treatment processes have little effect on it. Coal-based powdered activated carbon has been used at water treatment plants to remove geosmin, but this process can be a significant added expense when used continuously.
LSU AgCenter research has found that sugarcane bagasse and pecan shell-based granular-activated carbons (GACs) hold promise as lower cost replacements for coal-based commercial carbons. Laboratory experiments were conducted in which the physical and chemical properties of pecan-based GACs and bagasse-based GACs were compared with a commercially available coal-based product. See Table 1. The pecan shell-based material that was steam-activated matched most closely to the commercial carbon, Filtrasorb 400.
In 2001, 16 million pounds of pecans were grown in Louisiana. This resulted in the generation of an estimated 8 million pounds of pecan shells as byproducts with little economic value to the Louisiana economy. Using this agricultural byproduct as feedstock for activated carbon production, besides solving an environmental problem, would turn it into a valuable commodity. Furthermore, using nutshells to produce granular-activated carbons provides a less expensive raw material than coal.
On the basis of the physical, chemical and adsorptive properties of GAC, LSU AgCenter research indicates that pecan shell-based carbons prepared with steam hold promise as a replacement for commercial coal-based carbons in the removal of geosmin from water. The experimental results have shown the effectiveness of byproduct-based GACs in adsorbing geosmin in a laboratory environment. It was assumed that off-flavor in pond-raised catfish could be reduced by removing geosmin from the pond water. Further studies are warranted to test these carbons as part of filtration units designed to recycle catfish pond water to remove geosmin.
(This article appeared in the winter 2003 issue of Louisiana Agriculture.)