Introduction
The development of new technologies for decontamination in Recirculating Aquaculture Systems (RAS) is a challenging task. Devices generating ozone or UV radiation are commonly used to reduce the amount of pathogens, to ensure an appropriate water quality and to guarantee the welfare of fish (Stiller, Kolarevic et al. 2020). Though these technologies are well established and well known, they have disadvantages concerning costs (Engle, Kumar et al. 2020). Previous studies confirmed the antimicrobial efficacy of cold atmospheric plasma (CAP) and pulsed electric fields (PEF) in water treatments (Banaschik, Burchhardt et al. 2016, Schmidt, Hahn et al. 2019). Our aim was to develop and test system models operated for the treatment of larger volumes on the on-site use.
Materials and methods
Experiments with the developed plasma source and PEF device were carried out using model aquaculture water with the addition of Vibrio cholerae DSM 100200 as fish pathogen. To determine the inactivation of Vibrio cholerae, treatment parameters as flow rate and treatment time were varied for the total volume of 90 L. Next to the detection of the antibacterial efficacy, water analyses were carried out by ion chromatography and determination of pH, conductivity as well as temperature.
Results
For the experimental setting an initial concentration of 105 colony-forming units/mL of Vibrio cholerae, a flow rate of 150 L/h and a total treatment time of 480 minutes was adjusted. A 270 minutes continuous treatment resulted in an inactivation to the detection limit for plasma, whereas an inactivation of 1.9 orders of magnitude was achieved with PEF. Furthermore, the low resulting increase of conductivity (plasma: +200 µS/cm, PEF: + 80 µS/cm) and temperature (plasma/PEF: 22°C up to 30°C) confirm the suitability of the system model for utilization in RAS and will probably not affect the fish welfare.
Conclusion
The decontamination results of the treatments by using this system models are promising for further research and development, especially for larger scale experiments. The system models will further be optimized regarding to the antimicrobial efficacy and energy consumption to establish plasma and PEF treatments as a sustainable decontamination technology in aquaculture.
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