USE OF COLD ATMOSPHERIC PLASMA FOR RAS DECONTAMINATION
Introduction
Worldwide arising challenges from antibiotic-resistant bacteria require new decontamination strategies. In this regard, the microbial inactivation via reactive oxygen and nitrogen species, provided by the technology of cold atmospheric plasma (CAP) can be applied in recirculating aquaculture systems (RAS) to prevent future disease outbrakes. The decontamination properties of CAP in RAS showed promising results in the past (Balazinski, Hahn et al. 2025). In addition, toxicity tests performed in-vitro on fish cells confirmed a safe application (Balazinski, Hahn et al. 2026). For the consideration of this technology in real environment, an animal testing setup was performed to obtain in-depth results on fish welfare and impact on the water microbiome.
Materials and Methods
The experimental trial was carried out with two equally equipped RAS setups (Figure 1). Each consisted of two tanks with 90 L each, followed by a drum filter, a biofilter and a decontamination unit which was either ultraviolet radiation (UV) or CAP. Each setup had a total capacity of 580 L. In each tank approximately 70 rainbow trouts were transferred. The experiment ran for three weeks. For the UV setup two UV lamps each of 55 W were operated continuosly. In contrast, CAP was applied daily for 8 h in cycles of 10 min on and 30 min off, corresponding to 2.03 hours of treatment per day. During the experimental trial, water samples were taken at least once a week to determine the microbial load and microbiome in the water, the ionic composition of the water and also the stress of the fish. Standard water parameters, such as oxygen, conductivity, pH and temperature were recorded by a data logger every 15 minutes.
Results
The evaluation of the water samples revealed only negligible deviations between the two setups, resulting in an average microbial load of four orders of magnitude (Table 1). For the microbiome analyses the highest abundance in CAP and UV was given by the phylum Pseudomonadota, with a mean abundance of 32% ± 15% for CAP and 57% ± 2% for UV. Regarding the water composition it is noteworthy, that the pH, conductivity and oxygen values remained stable. Cortisol measurements showed no differences between the two groups.
Discussion
The implementation of CAP in RAS showed, that a sufficient microbial inactivation can be achieved with far shorter treatment periods in contrast to the UV application. In this regards, CAP provides a powerful tool for future RAS decontamination, without affecting major water parameters, such as oxygen, conductivity, pH and temperature. In addition, the composition of the water microbiome was constant, indicating optimal cultivation conditions. However, the experiments were successfully performed with rainbow trout, further testing must be carried out to obtain optimal settings for other species and setups.
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Figure 1: RAS setup with (A) CAP and (B) UV as decontamination unit
Table 1: Comparison of CAP and UV (Average energy consumption [W], Daily device runtime [h], Average microbial load [cfu/mL]), n= 20
Average energy consumption [W]
Daily device runtime [h]
Average microbial load [cfu/mL]
CAP setup
500
2.03
2.16E+04 (±2.66E+04)
UV setup
110
24.00
3.27E+04 (±5.03E+04)
Acknowledgment
Rica Tielebier, Andreas Tielebier, Daniel Genz and Stefan Herper is thanked for technical assistance during animal experiments.
References
Balazinski, M., V. Hahn, R. Wagner, M. Basen, K.-D. Weltmann and J. F. Kolb (2026). "Safety evaluation of physical plasma for water treatment in recirculating aquaculture systems." Aquacultural Engineering (Vol. 112, Issue 102646). https://doi.org/10.1016/j.aquaeng.2025.102646
Balazinski, M., V. Hahn, R. Wagner, M. Schmidt, C. Höhne, G.-M. Arndt, M. Basen, K.-D. Weltmann and J. F. Kolb (2025). "Cold atmospheric plasma and pulsed electric fields as alternative decontamination technologies in recirculating aquaculture systems." Aquacultural Engineering (Vol. 110, Issue 102543). https://doi.org/10.1016/j.aquaeng.2025.102543