Ozone Effect On Fc

[cofive]

One issue that has not been clearly discussed here is the effect of ozone on the FC residual so I will ask the question:

What effect does ozone have on the FC residual? If ozone is run 24/7 does it oxidize the chlorine, thereby making a residual difficult to maintain? And if it does, determining a true CD would be virtually impossible for the average D-I-Yer who cannot do the chemical calculations to compensate for the ozone addition.

Ken

[Nitro]

Ozone will destroy FC, and vice-versa. Having an ozonator will also cause more outgassing therefore lowering FC more. However, Ozone will help FC oxidize waste. Given all that, it's difficult to predict the exact effect Ozone will have on CD.

I predict a new ozonator will raise CD more in a clean freshly filled tub, but help keep it lower after the tub starts getting used. e.g. I'd guess on a fresh fill CD would be around 50%, but it will be easier to keep it there after the tub starts getting used.

It would be interesting to find out. If you have an ozonator, and would like to test it for us, feel free. Just test it on a fresh fill in order to get your Baseline. The other thing to keep in mind is that as an ozonator ages, it produces less ozone.

[cofive]

Ozone will destroy FC, and vice-versa. Having an ozonator will also cause more outgassing therefore lowering FC more. However, Ozone will help FC oxidize waste. Given all that, it's difficult to predict the exact effect Ozone will have on CD.

I predict a new ozonator will raise CD more in a clean freshly filled tub, but help keep it lower after the tub starts getting used. e.g. I'd guess on a fresh fill CD would be around 50%, but it will be easier to keep it there after the tub starts getting used.

It would be interesting to find out. If you have an ozonator, and would like to test it for us, feel free. Just test it on a fresh fill in order to get your Baseline. The other thing to keep in mind is that as an ozonator ages, it produces less ozone.

Thanks for the response Nitro. I had been assuming there would be a loss due to the ozone from the informaiton I was gathering here and that it has been nearly impossible to keep much better than a 50% CD. I will attempt, at next water change to get a baseline CD, then every two weeks or so check the CD and report my findings.

But in the mean time I'm guessing that if I add Cl to say 3-5ppm and don't let it fall to zero I should be okay.

Ken

[Nitro]

Thanks for the response Nitro. I had been assuming there would be a loss due to the ozone from the informaiton I was gathering here and that it has been nearly impossible to keep much better than a 50% CD. I will attempt, at next water change to get a baseline CD, then every two weeks or so check the CD and report my findings.

But in the mean time I'm guessing that if I add Cl to say 3-5ppm and don't let it fall to zero I should be okay.

Ken

As long as your FC is maintained above zero (ideally above one) consistently you'll be ok, regardless of your CD level. It's just that the lower your CD the easier it is to maintain your tub.

If your CD is around 50%, that means your FC is dropping by half everyday, without use. So realistically, assuming you start with ~5 ppm FC, you'll have to add chlorine a minimum of every couple days.

[dlzc]

One issue that has not been clearly discussed here is the effect of ozone on the FC residual so I will ask the question:

What effect does ozone have on the FC residual? If ozone is run 24/7 does it oxidize the chlorine, thereby making a residual difficult to maintain? And if it does, determining a true CD would be virtually impossible for the average D-I-Yer who cannot do the chemical calculations to compensate for the ozone addition.

Ken

The ozone generator pushes air-with-ozone into the water. When the bubbles leave solution with less ozone in them, they carry chorine gas (essentially) away with them. The ozone in general does not touch chlorine directly. Bromine, yes, ozone reactivates bromide ion to hypobromous acid. But ozone and chlorine systems are not "synergistic".

You already have good answers, just thought I'd touch this implied "where'd the chlorine go".

[chem geek]

I don't think the loss of chlorine from ozonators is completely from the bubbling effect, though clearly aeration does lead to some amount of chlorine loss as well as a pH rise from carbon dioxide outgassing. Ozone is a stronger oxidizer than both bromine and chlorine. You are correct that ozone can oxidize bromide to bromine, but it can also oxidize both bromine to bromate and chlorine to chlorate. This isn't a fast reaction, but it does occur:

O₃ + 2H⁺ + 2e^- ---> O₂ + H₂O ..... E₀ = +2.076V

HOCl + H₂O ---> HClO₂ + 2H⁺ + 2e^- ..... E₀ = -1.645V

--------------------------------------------------------------------------------------------------

O₃ + HOCl ---> O₂ + HClO₂ ..... E₀ = +0.431V

Ozone + Chlorine (Hypochlorous Acid) ---> Oxygen + Chlorous Acid

O₃ + 2H⁺ + 2e^- ---> O₂ + H₂O ..... E₀ = +2.076V

HClO₂ + H₂O ---> ClO₃^- + 3H⁺ + 2e^- ..... E₀ = -1.214V

--------------------------------------------------------------------------------------------------

O₃ + HClO₂ ---> O₂ + ClO₃^- + H⁺ ..... E₀ = +0.862V

Ozone + Chlorous Acid ---> Oxygen + Chlorate Ion + Hydrogen Ion

See also this link where the half-life of Free Chlorine (FC) in the presence of 1 mg/L (ppm) ozone is about 15 minutes where chlorate is one of the products (chloride being the other). As seen here, the concentration of ozone in the water can be hundreds of ppm for pool systems while it would still be rather high for spas (far more than 1 mg/L).

We've seen some reports on this forum with spas where the ozonator was still bubbling (injecting air) but without ozone. The pH tended to rise, but the chlorine didn't seem to be getting used up that much faster compared to systems where the ozonator was working and powerful. That's very anecdotal and not proof, but it's better than nothing.

Richard

[dlzc]

I don't think the loss of chlorine from ozonators is completely from the bubbling effect, though clearly aeration does lead to some amount of chlorine loss as well as a pH rise from carbon dioxide outgassing. Ozone is a stronger oxidizer than both bromine and chlorine. You are correct that ozone can oxidize bromide to bromine, but it can also oxidize both bromine to bromate and chlorine to chlorate. This isn't a fast reaction, but it does occur:

O₃ + 2H⁺ + 2e^- ---> O₂ + H₂O ..... E₀ = +2.076V

HOCl + H₂O ---> HClO₂ + 2H⁺ + 2e^- ..... E₀ = -1.645V

--------------------------------------------------------------------------------------------------

O₃ + HOCl ---> O₂ + HClO₂ ..... E₀ = +0.431V

Ozone + Chlorine (Hypochlorous Acid) ---> Oxygen + Chlorous Acid

O₃ + 2H⁺ + 2e^- ---> O₂ + H₂O ..... E₀ = +2.076V

HClO₂ + H₂O ---> ClO₃^- + 3H⁺ + 2e^- ..... E₀ = -1.214V

--------------------------------------------------------------------------------------------------

O₃ + HClO₂ ---> O₂ + ClO₃^- + H⁺ ..... E₀ = +0.862V

Ozone + Chlorous Acid ---> Oxygen + Chlorate Ion + Hydrogen Ion

See also this link where the half-life of Free Chlorine (FC) in the presence of 1 mg/L (ppm) ozone is about 15 minutes where chlorate is one of the products (chloride being the other). As seen here, the concentration of ozone in the water can be hundreds of ppm for pool systems while it would still be rather high for spas (far more than 1 mg/L).

We've seen some reports on this forum with spas where the ozonator was still bubbling (injecting air) but without ozone. The pH tended to rise, but the chlorine didn't seem to be getting used up that much faster compared to systems where the ozonator was working and powerful. That's very anecdotal and not proof, but it's better than nothing.

Richard

Thanks for those references, those are good, especially the decay of free chlorine.

Bromate / chlorate formation is hardly an issue, since ozone is typically (or shoudl be) applied just prior to a filter, where the C*T is then very low. And "no one" drinks this water routinely...

Ozone and chlorine is contraindicated, but ozone and bromine works.

[chem geek]

Thanks for those references, those are good, especially the decay of free chlorine.

Bromate / chlorate formation is hardly an issue, since ozone is typically (or shoudl be) applied just prior to a filter, where the C*T is then very low. And "no one" drinks this water routinely...

Ozone and chlorine is contraindicated, but ozone and bromine works.

My point wasn't about any hazards due to chlorates or bromates but rather that they are another path of increased chlorine consumption by ozone. As you point out, ozone and chlorine aren't the best mix, but ozone and bromine is reasonable as it reactivates the bromide to bromine. The bromate production is a potential side-effect risk that isn't quantified (probably small).

[cofive]

Ozone will destroy FC, and vice-versa. Having an ozonator will also cause more outgassing therefore lowering FC more. However, Ozone will help FC oxidize waste. Given all that, it's difficult to predict the exact effect Ozone will have on CD.

I predict a new ozonator will raise CD more in a clean freshly filled tub, but help keep it lower after the tub starts getting used. e.g. I'd guess on a fresh fill CD would be around 50%, but it will be easier to keep it there after the tub starts getting used.

It would be interesting to find out. If you have an ozonator, and would like to test it for us, feel free. Just test it on a fresh fill in order to get your Baseline. The other thing to keep in mind is that as an ozonator ages, it produces less ozone.

Finally, finished a fresh fill. Superchlorinated to 13.5ppm and let sit 24 hours. Next reading was 9ppm for a CD of 33%. So I'm guessing if a non-ozonated tub may baseline out at 25% then the ozone may be depleting my FC by about 8%.

Ken

[Nitro]

Finally, finished a fresh fill. Superchlorinated to 13.5ppm and let sit 24 hours. Next reading was 9ppm for a CD of 33%. So I'm guessing if a non-ozonated tub may baseline out at 25% then the ozone may be depleting my FC by about 8%.

Interesting! That's lower then I expected. Is your Ozonator fairly new? Assuming it it's new and in good working order, that's actually good news. That means the ozonator doesn't have as much effect on FC as I thought. Assuming you keep your CD low, If you were to shock to 12 ppm, you should be able to safely leave the tub for 5-6 days, and still have 1 ppm FC upon returning.

It would be interesting to get more data from other tubs with ozonators, but at least we have some idea of the effects of ozone on FC. Thanks for taking the time to experiment for us.