Cold atmospheric plasma and pulsed electric fields as alternative decontamination technologies in recirculating aquaculture systems

Aquaculture, in particular indoor farms that utilize recirculating aquaculture systems (RAS), are an expanding market with significant sustainable potential. These systems allow controlled production of aquatic organisms all year-round. Therefore, filtration units, e.g., with ultraviolet radiation (UV) or ozone are necessary to maintain hygiene but high energy and freshwater costs are incurred. Moreover, an increase of fish-pathogenic microorganisms can lead to disease outbreaks and mortality making decontamination an essential tool to ensure the cultivation of healthy aquatic organisms under sustainable conditions. Novel approaches, such as cold atmospheric plasma (CAP) and pulsed electric fields (PEF) present promising solutions. Both are effective for water decontamination, scalable to industrial volumes and have the potential of an energy-saving operation. The efficacy was evaluated using RAS water from Baltic sturgeon (Acipenser oxyrinchus). Additionally, to improve the reproducibility of conditions, treatments were compared with model aquaculture water, which was designed from analytical results of RAS water. The study evaluated the inactivation of fish-pathogenic microorganisms by CAP and PEF in comparison to UV. CAP reduced Gram-positive and Gram-negative bacteria by logarithmic reduction factors (log₁₀-RF) of up to 2.1 and 5.9, respectively. A similar inactivation was determined for PEF. Furthermore, a technology efficiency coefficient, putting the required energy in relation to the bacterial inactivation of the respective process, was introduced. Our laboratory findings provided relevant parameters towards a novel, improved treatment of water in RAS. Both tested technologies, CAP and PEF may be combined with UV to ensure hygienically safe fish production together with improved fish welfare.