EVALUATION OF ULTRA-VIOLET STERILIZATION TO REDUCE POTENTIAL HUMAN PATHOGENS IN AQUAPONIC SYSTEMS

Food safety is a particular concern in new or emerging industries which often lack the scientific data or history to assess potential risks to consumers. Aquaponics is one such industry. One of the main concerns is that fish culture water is in constant contact with the plants in the system. While pathogens that affect fish are not typically associated with human health issues, other modes of transfer (human contact, birds, rodents, etc.) can introduce pathogens such as coliform bacteria, Salmonella spp., and Listeria spp. Ultraviolet (UV)-sterilization of water is a common tool used to reduce bacteria and viruses in recirculating aquaculture systems (RAS) and might be effective to reduce bacterial loads and contamination in aquaponic systems.

The objective of this research was to determine if in-line UV-sterilization could reduce potential pathogens in aquaponic systems. Six, 500 gallon replicated systems were stocked with approximately 6,000 grams of tilapia (Oreochromis niloticus) and 72 Buttercrunch Bibb lettuce (Lactuca sativa) plants per unit. Three systems were fitted with 27 Watt high-output UV-sterilizers while three were operated without UV and served as Controls. Samples of culture water, edible biomass, and plant roots were collected weekly for microbiological analysis. Samples were plated on selective media to enumerate total coliform counts, Listeria spp., Vibrio spp., and pathogens in the Enterobacteriaceae family. The experiment lasted a total of six weeks over two production cycles of the lettuce.

These data indicate that UV-sterilization of water is an ineffective method to reduce selected bacterial loads in aquaponic systems. Total counts of tested pathogens in water, on plant leaf, and on plant root samples were not significantly reduced (P > 0.05).

As the edible plant portion poses the greatest risk to consumers, enteric bacteria (which encompass a wide spectrum of potential pathogens) is highlighted (Figure 1). It is likely that reduced water clarity in these systems negatively impacts UV transmittance. Future studies will evaluate increased fine solids filtration and probiotic applications to address food safety concerns with aquaponic produce.