EVALUATION OF THE USE OF HIGH FREQUENCY ACOUSTIC CAVITATION TO IMPROVE WATER QUALITY IN COMMERCIAL CATFISH OPERATIONS

The use of ultrasound has been investigated in several USDA funded projects, including pasteurization of fruit and vegetable juices, as well as the deactivation of enzymes in milk. The combination of ultrasound and chemical preservatives has been investigated as an alternative to pasteurization for apple cider and orange juice. While these efforts have focused on food products, ultrasound has been touted as a replacement for antimicrobial wash treatments on produce (fruits and vegetables) that usually use chlorine. Ultrasound is also currently being touted as a cleaning technology for both algae in ponds and wastewater disinfection. Sonication, an application of high amplitude ultrasound, has also been identified as a means to split the cell walls of microorganisms in sewage sludge. The work presented here extends these previous projects and investigates the application of sonication to improve water quality in commercial catfish operations.  Samples of water from catfish ponds have been collected and subjected to  treatments of sonication at various durations and amplitudes, and the results on total coliform and E. coli bacteria were analyzed using a defined substrate method to determine the change in Most Probable Number (MPS) of bacteria present before and after sonication.

Initial results with off the shelf equipment show promise with a reduction in the count of bacteria from 244,600 MPN/100mL to 131,400 MPN/100mL, a 46.3 % reduction, on treated samples at a 1:1000 dilution. Ongoing testing is meant to determine the minimum treatment needed and where the technology may best help the industry. Potential application sites include the cold water wash in processing plants, tank based systems, and effluent streams. It is unclear at the moment if the reduction in bacteria is due to mechanical means, including shock waves and bubble collapse in the water or at the cell wall membrane, or via chemical changes at the bubble wall interface (sonochemistry). Additional tests planned are the intentional injection of microbubbles during sonication to induce additional cavitation nucleation sites, as well as the combination of ultrasound with reduced levels of chemical treatments. These latter tests will help determine if ultrasound may allow for a reduced level of disinfection chemicals if it is unable to clean the water solely.