1. The Composition of Air Limits the Maximum DO
Air is roughly 21% oxygen, with the rest mostly nitrogen. When air is diffused into water, only the oxygen fraction contributes to the dissolved oxygen level.
At equilibrium, this means that air-saturated water at 25°C can only hold about 8.3 mg/L (ppm) of dissolved oxygen at sea level. Even if nanobubbles significantly improve gas transfer efficiency, they cannot change the basic physics of the gas mixture. You’re still capped by the partial pressure of oxygen in air, which defines the maximum possible DO under those conditions.
2. Nanobubbles Improve Retention — Not Composition
Nanobubbles, because of their ultra-small size (less than 200 nm), have several unique properties:
They stay suspended in water for days or weeks.
They have high internal pressure and large surface area.
They can continuously release oxygen into the water over time.
This makes them far more efficient at maintaining and stabilizing DO compared to traditional aeration methods.
However, these benefits do not change the fact that the bubbles are still filled with air — only 21% oxygen. Nanobubbles enhance how long oxygen stays available, not how much oxygen the water can hold.
3. Why You Can’t “Force” Higher DO Levels with Air Nanobubbles
Some systems claim to “super-saturate” water with air nanobubbles. In practice, this is only possible up to a modest extent.
Here’s why:
Gas solubility in water is proportional to its partial pressure in the gas phase.
Even if nanobubbles temporarily increase local gas-liquid interfaces, the oxygen fraction is still capped at 21%.
Once the water approaches air saturation, additional nanobubbles contribute diminishing returns.
At best, an air nanobubble generator might push DO to 10–12 mg/L under ideal conditions — but not much beyond that without pure oxygen.
4. Reaching Higher DO Levels Requires Pure Oxygen
If you need DO concentrations of 10, 20, 30, or even 40 mg/L, as required in certain aquaculture, medical, or advanced oxidation applications, you’ll need to move beyond air.
This is where dedicated oxygen generators or oxygen concentrators come in. Our machines produce nearly pure oxygen (typically 90–95%), which drastically increases the oxygen partial pressure and solubility in water. When paired with nanobubble technology, they enable sustained supersaturation of dissolved oxygen far above what air could ever achieve.
5. The Practical Takeaway
System Type | Gas Source | Typical Max DO (mg/L) | Notes |
|---|---|---|---|
Air Diffuser | Air (21% O₂) | 6–8 | Standard saturation at sea level |
Air Nanobubbles | Air (21% O₂) | 10–12 | High stability, but limited by air composition |
Oxygen Nanobubbles | Pure O₂ (~95%) | 12–40+ | For high-performance oxygenation needs |
But if you’re targeting supersaturated levels of dissolved oxygen, you need a dedicated oxygen generator. Only then can nanobubbles unleash their full potential — maintaining ultra-high DO levels without the physical ceiling imposed by air.
