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Ozone & Cold Water: A Perfect Match

Updated: Jan 23


  • Ozone disinfection is safer than chlorine or bromine, because it degrades into pure oxygen without producing harmful byproducts.

  • Most ozone generators built for hot tubs don't work -- both because the generators themselves are poor quality and because hot water destroys ozone.

  • The arc discharge ozone generator in the Morozko ice bath has been tested using both an oxidation-reduction potential (ORP) meter in the water (for efficacy), and an ozone gas sensor above the water (for safety).

  • Ozone is beneficial when used on your skin, but is harmful when breathed into your lungs. Whenever you smell ozone in the air above your Morozko, you know the disinfection is complete and it is safe to turn off your filtration.

Ozone disinfection protects your ice bath

The most powerful and safe disinfecting agent available for water treatment systems is ozone -- more powerful than chlorine and bromine, and safer because it consists only of pure oxygen. Ozone is a chemical rearrangement of O2, the usual form of oxygen in the atmosphere, into a less stable, more powerful combination of three oxygen atoms, O3. The third oxygen atom is what makes ozone such a strong oxidizing agent. It is the oxidizing power of ozone that destroys pathogenic bacteria and viruses, and cleans the water by attacking other organic compounds like algae, and old skin cells. Ozone even destroys pollutants like benzene, toluene, xylenes (BTX), methyltertbutylether (MTBE), and volatile organochlorinated compounds. It even destroys the deadly ebola virus (Davies 2015).

In short, ozone is terrific for cleaning water, which is why it is used in the most advanced drinking water treatment plants in the world.

So why isn't it used in swimming pools and in your municipal drinking water distribution system? Why do our drinking water engineers and pool health standards till poison us with chlorine, and the byproducts of its use (like toxic trihalomethanes)?

The problem with ozone is its instability. Even without something to react with, ozone as O3 will devolve back to plain O2 oxygen -- sometimes in seconds. So, even where ozone is employed for water disinfection, municipal treatment works will still add chlorine so that the there is always disinfectant in the distribution pipes.

Chlorine is more stable than ozone, and it maintains high concentrations in water for longer. That's also why ozone isn't used in swimming pools, because unless you produce ozone 24 hours a day, 7 days a week, most pools would lose all their ozone to natural degradation less than an hour after the pool pump turns off.

Even with constant production, maintaining ozone levels throughout the entire pool is difficult during the warm summer months, when ozone degrades fastest, because warm water destroys ozone. By contrast, chlorine will last until the pool pump comes back on the next day. In that way, chlorine is safer for warm water. For example, in hot tubs, ozone is insufficient for disinfection because, so it is necessary to add chlorine or bromine disinfectant to ensure the water does not carry dangerous levels of pathogenic bacteria or viruses.

That's why hotel pools and gym hot tubs always smell so bad of chlorine. However, Morozko doesn't want chlorine, because it's poisonous, and isn't compatible with the other materials in the tub. Morozko wants ozone, because ozone is the best for cold water.

Some hot tubs and swimming pools will use ozone, too. In fact, the equipment that we install in the Morozko Forge was originally designed for hot tubs, spas, and swimming pools. We've done little more than test it and adapt it for ice baths.

And it turns out that the cold makes a big difference.

High concentrations of ozone disinfect water very fast. It takes little more than seconds at ozone saturation levels to destroy even the strongest viruses. But in hot water, ozone has two disadvantages:

  1. The saturation concentrations of ozone are much lower, because the hot water temperatures boil the ozone out of solution and into the air.

  2. The heat speeds up the ozone degradation.

Because the Morozko is so cold, the disadvantages of ozone in hot tubs are advantages in the Forge. We get higher saturation concentrations in our ozone contact chamber, and the ozone stays around much longer because it is more stable in the cold. In fact, our measured results show that we maintain a safe, low-level residual concentration of ozone in the Forge whenever the filtration system is running. That's how the water in the Filtered Forge stays super crystal clear and safe, all the time.

The use of ozone in water is not controversial. In fact, ozone therapy is beneficial for the skin. However, ozone in the air can be problematic. The United States Environmental Protection Agency (USEPA) recognizes airborne ozone as a toxic pollutant, because it is such a strong oxidant that in high enough concentrations it attacks the cilia in the throat and membranes in the lungs.

Although ozone in the upper reaches of the atmosphere is protects all life on Earth from the most harmful ultraviolet parts of the sunlight spectrum, ozone in our lungs is a dangerous pollutant. The big difference is that the upper atmosphere ozone, known as the ozone layer, occurs naturally and is essential, whereas ozone in city smog is artificial.

Recently, high doses of ozone have been used as an anti-ageing therapy -- but not by bathing in it, or by breathing it. Ozone therapy, when administered by a qualified doctor, is administered directly to the blood (which is not how the Forge works). Nonetheless, you'll never hear a story about how someone has improved their health or cured their sickness by using chlorine.

Ozone levels in the water are measured indirectly, using an oxidation-reduction potential (ORP) meter that measures the activity of electrons in the water. An ORP meter is a specialized piece of laboratory equipment that is easy to learn, but difficult to interpret. I learned how to use one when I was a graduate student in environmental engineering, studying water chemistry, and that how the disinfection potential in the Morozko are monitored. However, measuring ozone in the air requires a different instrument. In the gas phase, ozone is measured directly using an air monitor.

It turns out that, for most people, their nose is a very sensitive environmental monitoring instrument. We've evolved to detect odors that are both harmful and helpful to our survival, and most noses have low detection limits for certain harmful pollutants.

If you ever smell ozone in the air above your Morozko, then you can be sure that the job of water disinfection is complete. Because there's nothing else in the water for the ozone to work on, it escapes into the air.

That's when you can be sure it's safe to turn off your filtration system.

In most host applications, it's not necessary to run the filtration in your Morozko for more than about 45 minutes a day. If you ever observe a problem with water clarity, then go ahead and run it overnight, but for the most part, you're going to be fine without running it all the time.

In commercial applications, we recommend keeping the ozone on whenever the Forge is open for business. Given the higher bathing loads, it's sensible to use all the disinfection protection that the Morozko provides.


About the Author

Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.

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