Low-dose ozone has become a powerful tool in advanced water treatment, particularly in recirculating aquaculture systems (RAS), where even modest oxidation can lead to measurable gains in clarity, contaminant control, and aquatic health.
But ozone, while incredibly effective, is not forgiving. Applying it at low concentrations, typically below 1.0 mg/L, requires engineering precision, tight process control, and a clear understanding of gas transfer dynamics, materials compatibility, and biological thresholds.
At Pinnacle Ozone Solutions, we’ve spent years developing ozone systems capable of ultra-precise operation. Informed by field studies like those from the Freshwater Institute, this blog explores how to engineer low-dose ozone systems that are both safe and highly effective, not only in aquaculture, but in reuse, industrial cooling, and environmental polishing.
Why Low-Dose Ozone?
In systems like RAS, the goal of ozone isn’t disinfection or high-dose oxidation. Instead, it’s used to:
- Oxidize dissolved metals (e.g., Fe, Mn, Cu)
- Break down nitrite (NO2–) into less toxic nitrate (NO3–)
- Improve water clarity by reducing suspended solids
- Enhance filter performance and reduce backwash frequency
- Reduce biochemical oxygen demand (BOD)
- Support better growth rates and lower stress in aquatic species
These benefits can be achieved with ozone doses as low as 0.1–0.5 mg/L, provided transfer and reaction conditions are carefully controlled.
Engineering Low-Dose Ozone: Critical Elements
Ozone Generation and Feed Gas
Use oxygen-fed ozone systems to ensure high concentration output and minimal contamination. Since many RAS facilities already use oxygen for aeration, this infrastructure can often be shared for ozone generation.
Pinnacle’s QuadBlock® ozone systems operate efficiently under oxygen-fed conditions, providing stable low-dose generation down to sub-gram levels with tight output control.
Gas Transfer Strategy
The RASTECH article highlights two methods:
- Continuous ozone generation with gas directed via solenoid valves
- On/off ozone generation controlled by ORP or timer-based systems
In both cases, ozone is introduced into a low-head oxygenator (LHO), allowing gas-liquid contact before the water reenters the culture system.
At Pinnacle, we go further by designing pressurized contact systems or optimized gas diffusers that achieve >95% mass transfer efficiency, even at low flow and dose rates. This ensures:
- Minimal off-gas loss
- Predictable reaction completion
- Faster system response to setpoint changes
Contact Time and Decomposition Zone
Key to low-dose application is ensuring ozone reacts fully before reaching sensitive biological zones. Contact time depends on:
- Ozone demand (ORP, TOC, nitrite, metals)
- Temperature (ozone half-life decreases with rising temperature)
- pH (which affects decomposition rates and speciation)
For instance, in cooler RAS water (10–15 °C), ozone decomposes more slowly, extending its oxidizing presence, requiring careful CT modeling and possibly smaller doses.
Monitoring and Control (ORP ≠ Residual Ozone)
ORP (oxidation-reduction potential) is commonly used as an indirect proxy for ozone presence. While it’s not a direct measurement, it’s useful when calibrated and maintained correctly.
Typical setpoints:
- Target ORP: 290–320 mV
- Alarm ORP: >350 mV
- Toxic thresholds (for fish): 0.002–0.005 mg/L dissolved ozone
We recommend:
- Dual ORP and dissolved ozone sensors for validation
- Alarm systems tied to ozone generators and fans
- Automated shutdown on probe failure or exceeded thresholds
Materials and Compatibility
Ozone is corrosive and chemically aggressive, even at low concentrations. Failures often stem from:
- Non-ozone-rated valve seals (EPDM, Buna-N)
- Incompatible fiberglass resins (leading to microcracking)
- Brass, mild steel, or PVC in high-contact zones
Pinnacle systems use:
- 316L stainless steel, PVDF, and PTFE components
- Short gas path lengths to reduce hold-up volume
- Fully destructed off-gas streams via catalytic destructors
Safety in Low-Dose Ozone Systems
Even at low output, ozone leaks pose a risk to staff and livestock. Engineering best practices include:
- Audible gas alarms near distribution plates and off-gas zones
- Venting off-gas through destruct units and out of the facility
- Emergency shutdown tied to ORP alarms and ozone detectors
- Portable ozone sniffers for safe reentry
- Redundant control on solenoids and valves (spring return, fail-close)
OSHA exposure limits:
- 0.3 ppm (15-minute exposure)
- 0.1 ppm (8-hour TWA)
Pinnacle offers integrated alarm/control packages that trigger exhaust fans and shutdown commands based on monitored gas-phase levels.
Applications Beyond Aquaculture
The principles outlined in the Freshwater Institute’s work apply well beyond fish farms. Low-dose ozone is being used in:
- Industrial cooling systems (to control biofilm without over-oxidizing metallurgy)
- Closed-loop reuse systems (greywater, wastewater polishing)
- Drinking water (for color removal, DBP precursor control)
- Food wash systems (low ozone residuals for microbial control)
Low-dose ≠ low-performance. With proper design, low-dose ozone systems can outperform higher-dose chemical systems, with lower operating cost and improved safety.
Conclusion
Low-dose ozone, when applied correctly, is one of the most precise, controllable, and effective oxidation tools in water treatment. But it’s not forgiving, a single failed seal, stuck valve, or misread ORP probe can compromise the entire system.
At Pinnacle Ozone Solutions, we bring deep expertise in designing low-dose ozone systems that work under pressure, literally and figuratively.
We engineer:
- Accurate gas delivery
- High-efficiency contactors
- Fail-safe automation and alarms
- Systems that protect people, processes, and aquatic life
If you’re looking to integrate low-dose ozone into your aquaculture or industrial process, our team is ready to design a system you can trust.
References
- Crouse, C. (2025). Fresh Tips: A Quick Guide to Effective Low-Dose Ozone Application. RASTECH Magazine.
- Timmons, M.B., Ebeling, J.M. (2013). Recirculating Aquaculture.
- von Gunten, U. (2003). Ozonation of Water: Kinetics and By-products. Water Research.
- Pinnacle Ozone Solutions: Field Design Data & Contact Modeling (2021–2024)
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