Recirculating Aquaculture Systems (RAS) are becoming increasingly popular for sustainable fish farming. These closed-loop systems require careful management to maintain water quality. A crucial element is the biofilter, a haven for nitrifying bacteria that convert harmful ammonia excreted by fish into less toxic nitrate. However, maintaining fish health sometimes requires the use of disinfectants, raising concerns about disrupting this delicate microbial balance.
A new study published by scientists from The Conservation Fund Freshwater Institute (USA) and Nofima (Norway) explores the impact of peracetic acid (PAA), a common disinfectant, on nitrifying biofilters in RAS. PAA works by killing microbes, but can it inadvertently harm the beneficial bacteria essential for nitrification?
Why PAA is Interesting for Aquaculture
Peracetic acid is effective against a wide range of pathogens such as bacteria, fungi, viruses, and yeasts; it rapidly breaks down into harmless components like acetic acid, hydrogen peroxide, and water, minimizing environmental impact. PAA has been identified as an effective alternative to common disinfectants used in aquaculture facilities to reduce pathogen loads.
Studies suggest that low-dose treatments with peracetic acid are safe for fish (rainbow trout and Atlantic salmon) at various life stages.
Concern: Effect of PAA on Nitrifying Bacteria
Biofilters with nitrifying bacteria are crucial in RAS to convert harmful ammonia from fish waste into less toxic nitrates.
However, the main concern for scientists is whether the broad-spectrum antimicrobial properties of PAA could potentially harm these beneficial bacteria.
The Experiment: Testing PAA on Biofilters
Researchers used 12 replicated biofilters to test different methods of applying peracetic acid. Their goal was to use low doses (1.0-2.5 mg/l) typically used to eliminate opportunistic pathogens. Two application methods were compared:
- Pulse Dosing: A single high dose of PAA added every two days for five days.
- Continuous Dosing: Smaller doses of PAA added every five minutes for four hours.
The researchers monitored the breakdown of peracetic acid and measured water quality before and after application.
Results: PAA with Minimal Disruption
The good news: adding PAA, regardless of concentration or application method, did not significantly disrupt the nitrification processes of the biofilters.
Similar to previous research, the study’s results showed that even the highest concentration of PAA only caused a slight increase in nitrite production, without hindering overall biofiltration.
Additionally, the researchers reported that the efficiency of TAN (total ammonia nitrogen) removal remained near 100% in all treatments, suggesting that PAA could be a viable option for disinfecting RAS water without compromising the vital role of biofilters.
Conclusion: A Promising Approach, but More Research Needed
This study provides promising evidence that PAA can be used for disinfection in RAS without harming nitrification. However, more research is needed to refine the safest and most effective application protocols, considering the species being raised, stocking density, biofilter type, and other factors that could affect peracetic acid efficiency.
Benefits of Safe PAA Use in RAS
- Improved fish health through pathogen control.
- Effective water disinfection.
- Minimal disruption of biofiltration processes.
- Reduced risk of bioaccumulation: Unlike some disinfectants, PAA is unlikely to accumulate in fish tissues.
The future of RAS disinfection could involve targeted use of PAA along with optimized application methods, ensuring a healthy balance for both fish and the beneficial bacteria that keep their environment clean.
The study was funded by the Centre for Closed-Containment Aquaculture (CtrlAQUA).
Contact
Christine Lepine
The Conservation Fund Freshwater Institute
1098 Turner Road, Shepherdstown, WV 25443, USA
Email: clepine@conservationfund.org
Reference (open access)
Lepine, C., Redman, N., Murray, M., Lazado, C. C., Johansen, H., Espmark, Å. M., Davidson, J., & Good, C. (2023). Assessing Peracetic Acid Application Methodology and Impacts on Fluidized Sand Biofilter Performance. Aquaculture Research, 2023(1), 6294325. https://doi.org/10.1155/2023/6294325
