Industry Solutions
Ozone in RAS: When to Use It, Where to Dose It and How to Protect Fish and Biofilters
Use ozone in RAS only with controlled contact, monitoring and residual destruction. Protect fish, biofilters and operators from ozone carryover.
Ozone can improve RAS water quality, but it should not be treated as a general-purpose additive for direct fish-tank dosing.
Ozone is a strong oxidant that can react with dissolved organics, color, fine particles and microorganisms.
The process question is:
What water-quality problem is ozone solving, and how will residual ozone be prevented from reaching livestock or biological treatment?
1. Define the Treatment Objective
Possible objectives include water clarity, oxidation of dissolved organics, microorganism control and selected off-flavor management.
Do not add ozone only because a generator is available.
2. Use a Side-Stream Contact Process
Ozone is commonly applied in an external contact loop rather than directly in the culture tank.
A side stream allows control of gas dose, contact time, water flow, residual destruction and off-gas.
3. Protect Fish From Residual Ozone
Residual ozone can be toxic to fish and crustaceans.
The system should include project-appropriate safeguards such as adequate reaction/destruction time, controlled return, monitoring, alarms and automatic shutdown.
Do not rely on smell or visual observation.
4. Protect the Biofilter
Nitrifying bacteria are sensitive to strong oxidants.
Avoid uncontrolled ozone carryover into MBBR or other biological units.
The contact point should be selected as part of the complete RAS process layout.
5. Use ORP as an Indicator, Not a Direct Ozone Meter
ORP measures overall oxidation-reduction potential rather than ozone concentration alone.
It can be affected by ozone, organics, pH, temperature and other oxidants/reductants.
Use ORP as a control indicator with project-specific limits and independent verification where needed.
6. Check Water Chemistry
Ozone behavior changes with salinity, bromide, pH, temperature and organic matter.
Brackish and seawater RAS require additional care because secondary oxidants may form.
7. Provide Controlled Contact
The contactor may be a tank, loop, venturi or other gas-liquid mixing device.
The arrangement should provide reaction time while keeping ozone away from occupied spaces.
8. Handle Off-Gas Safely
Ozone in air is hazardous.
Provide appropriate off-gas collection, destruction, ventilation and leak management.
9. Size the Generator From Ozone Demand
Do not size from total tank volume alone.
Relevant data include side-stream flow, treatment objective, organic load, water chemistry, ORP trend, contact efficiency and operating hours.
10. Check the Oxygen Feed Source
Confirm oxygen purity, pressure, gas drying and generator feed requirements.
Practical RAS Ozone Checklist
Data Group | Information | Purpose |
|---|---|---|
Objective | Clarity, organics, microbes | Process need |
Side Stream | Flow | Contact duty |
Water | Fresh/seawater, pH, temperature | Chemistry |
Organics | COD/UV data where useful | Demand |
ORP | Baseline and trend | Control |
Contactor | Type and volume | Reaction |
Residual Control | Destruction method | Fish safety |
Biofilter | Location and flow | Biomass protection |
Off-Gas | Destruction/ventilation | Operator safety |
Generator | g/h and feed gas | Equipment duty |
Common RAS Ozone Mistakes
Dosing Directly Into the Fish Tank
Residual ozone creates livestock risk.
Using ORP as a Direct Ozone Measurement
It is an indirect oxidation indicator.
Ignoring Seawater Chemistry
Saline systems can behave differently.
Protecting Fish but Not the Biofilter
Biological treatment can also be damaged.
Sizing From System Volume
Ozone demand depends on water quality and objective.
Ignoring Off-Gas
Operator safety is part of process design.
Technical Basis
SRAC guidance describes ozone as being generated on-site and commonly applied in an external contact basin or loop. It also warns that residual ozone entering culture tanks can be toxic and that excess ozone gas requires safe venting.
Aquaculture guidance from the New South Wales Department of Primary Industries describes ORP as a common indirect control method rather than a direct ozone measurement.
The practical rule is:
apply ozone in a controlled side stream, monitor oxidation, destroy residual ozone and protect both fish and biofilters before water returns to production.
Need Help Reviewing Ozone for RAS?
Send HydroNovus the RAS flow, side-stream flow, fish species, freshwater/seawater condition, pH, temperature, ORP, treatment objective, existing ozone equipment, contactor layout and residual-control method.
HydroNovus can provide a preliminary ozone-system integration review and identify the data needed before generator selection.