Why Is Residual Ozone a Concern in RAS?
Ozone has become an increasingly important tool in modern Recirculating Aquaculture Systems (RAS).
By oxidizing dissolved organic compounds, improving water clarity, and helping control microorganisms, ozone can significantly enhance water quality and support higher stocking densities. As a result, ozone treatment is now widely adopted in salmon farming, shrimp hatcheries, fish nurseries, and commercial RAS facilities worldwide.
However, successful ozone treatment is not only about generating ozone.
A critical question remains:
What Happens to the Ozone After Treatment?
While ozone is highly effective during the treatment process, any residual ozone that remains in the system can create operational and biological risks.
In a well-designed RAS, ozone should perform its intended function and then be removed before treated water returns to fish tanks or biological filtration systems.
Failure to properly control residual ozone may affect both system performance and animal health.
Potential Impact on Fish and Shrimp
Fish and shrimp are highly sensitive to water quality fluctuations.
Because ozone is a powerful oxidant, excessive residual ozone exposure may irritate or damage sensitive tissues such as gills and respiratory surfaces.
Even low levels of residual oxidants over extended periods can create stress conditions that may negatively influence:
- Survival rates
- Feeding behavior
- Growth performance
- Overall animal welfare
For hatcheries and juvenile production facilities, where aquatic organisms are particularly vulnerable, ozone control becomes even more critical.
Impact on Biological Filtration
The biofilter is often considered the heart of a RAS system.
Beneficial nitrifying bacteria convert toxic ammonia into less harmful nitrogen compounds, helping maintain stable water quality.
Residual ozone entering the biofilter may reduce microbial activity and disrupt biological treatment efficiency.
As a result, operators may experience:
- Reduced nitrification performance
- Water quality instability
- Increased operational adjustments
- Longer system recovery times
Protecting the biofilter is one of the primary reasons many RAS designers place significant emphasis on residual ozone management.
Challenges in High-Density Aquaculture
As aquaculture systems become more intensive, the margin for error becomes smaller.
Modern RAS facilities often operate with:
- Higher stocking densities
- Increased feed loading
- Greater water reuse rates
- More automated process control
Under these conditions, a small ozone control issue can potentially affect a large volume of recirculating water.
Therefore, ozone management is no longer viewed as a standalone treatment process—it is an integral part of overall system reliability.
Residual Ozone in Marine RAS
For marine and brackish-water aquaculture systems, ozone application requires additional attention.
Seawater naturally contains bromide ions. During ozone treatment, bromide can participate in oxidation reactions and form secondary oxidizing compounds.
This is one reason why many marine RAS operators closely monitor oxidation levels and incorporate effective de-ozonation strategies into their system designs.
Beyond Ozone Generation: The Importance of De-Ozonation
Many discussions about ozone treatment focus on ozone generators, injection systems, and contact chambers.
However, experienced RAS engineers understand that ozone treatment does not end when ozone is injected into the water.
A complete ozone treatment strategy includes:
Ozone Generation → Oxidation → Monitoring → Residual Ozone Removal
The final step—residual ozone removal—is essential for maintaining a safe and stable aquaculture environment.
How Is Residual Ozone Removed?
Several approaches can be used to reduce residual ozone, depending on the application and system design.
Among them, Ozone Decomposition Catalysts are receiving increasing attention due to their ability to rapidly convert ozone into oxygen under suitable operating conditions.
Catalytic ozone destruction systems can help:
- Reduce residual ozone levels
- Improve operational safety
- Protect biological filtration systems
- Support stable long-term operation
- Enhance overall process reliability
For equipment manufacturers and system integrators, selecting the right ozone destruction technology can be just as important as selecting the ozone generator itself.
A Growing Focus for the Aquaculture Industry
As RAS technology continues to advance, the industry's attention is gradually shifting from simply generating ozone to managing ozone throughout the entire treatment cycle.
The question is no longer:
"How do we produce ozone?"
Increasingly, it is:
"How do we ensure that residual ozone is safely removed before water returns to the culture system?"
For modern aquaculture facilities, effective residual ozone management is not merely a technical detail—it is a key component of fish health, biosecurity, operational stability, and sustainable production.
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