Ozone/Chlorine combo

JohnT

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Apr 4, 2007
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The ozone only affects the water that is in the ozonator at that instant, so the pool has to be chlorinated just as if it wasn't there. With that, the only benefit of the ozonator might be to reduce shocking. Hardly worth any extra expense since I seldom need to shock anyway.
 

JasonLion

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There is a claim that there are a couple of rather rare nasties that are highly chlorine resistant yet ozone wipes them right out. I suspect this is more hype than real, but it is impossible to tell. In any case ozone is at best useful as a supplement, not a replacement for chlorine.
 

chem geek

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Mar 28, 2007
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Both ozone and UV inactivate some bugs that chlorine doesn't handle very well including Giardia and Cryptosporidium cysts. However, these are typically filtered out through the multiple turnovers in a residential pool and are really more of a concern in public pools where the bather loads are higher so that transmission between people is far more likely. At any rate, ozone is mostly best at oxidizing organics so is great at keeping combined chlorine at zero and breaking down most chlorinated disinfecting by-products. Of course, this is generally unnecessary in an outdoor pool exposed to sunlight, but might be helpful for an indoor pool and is an alternative to using weekly non-chlorine shock (potassium monopersulfate, KMPS). It's also "insurance" to help prevent an algae bloom if you let the chlorine drop too low, but won't stop any algae growth stuck in biofilms on pool surfaces.

The main problem with ozone in a chlorine pool is that the ozone is a more powerful oxidizer than chlorine so ends up breaking down some of the chlorine. So even though the claim is that you can use lower chlorine levels when using an ozone system, you actually end up needing at least as much if not more chlorine to make up for the loss from the ozone destroying chlorine itself!

[EDIT] Technically, an oxidizer such as ozone shouldn't be able to oxidize chlorine, yet the breakdown or greater usage of chlorine when an ozonator is present is seen by virtually everyone with such a system. So I haven't figured out exactly how this breakdown occurs (yet). This is a mystery similar to that of high phosphate levels that some claim breakdown chlorine. Haven't figured that one out either (though it may not be as true). [END-EDIT]
 

TheOne

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Mar 28, 2007
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Houston, TX
I have seen lower chlorine usage not higher by using an ozonator. Now I dont have any science or data to back any claims about an ozonator but again it didnt cost me anything to install it. The whole principle behind it is to offload part of the oxidation tasks from chlorine so you can run lower chlorine levels. There are apparently many different types of ozone systems out there and its hard to get solid independent data about them.
 

chem geek

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Thanks for your feedback. Your situation is what I would normally expect. Ozone breaks down organics so chlorine doesn't have to so in theory should lower chlorine usage. If anything, the ozone could convert some chloride to chlorine (it is known to convert bromide to bromine). I'll have to look at other things going on in such pools/spas to see where the chlorine usage is coming from and have the people turn off their ozonators to see if the chlorine usage drops. Glad to know it works for you.

You know, I just had a thought and that was that some ozone systems use UV to generate the ozone. In that scenario, the UV could break down the chlorine. Do you have any idea how your ozone system works? If it's from corona discharge rather than UV, then perhaps that explains the difference. I would have expected the UV to expose air that created ozone injected into the water and that the water itself would not get exposed to the UV, but perhaps some designs don't do this.
 

KurtV

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Mar 29, 2007
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SE Louisiana
I pulled these statements from a post by Ben Powell (user name: PoolDoc) over at poolforum:

"First, ozone and chlorine mutually destroy each other, when effective levels of both are present.
Second, ozone is more toxic than chlorine, and less soluble."
 

TheOne

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Mar 28, 2007
167
Houston, TX
chem geek said:
Thanks for your feedback. Your situation is what I would normally expect. Ozone breaks down organics so chlorine doesn't have to so in theory should lower chlorine usage. If anything, the ozone could convert some chloride to chlorine (it is known to convert bromide to bromine). I'll have to look at other things going on in such pools/spas to see where the chlorine usage is coming from and have the people turn off their ozonators to see if the chlorine usage drops. Glad to know it works for you.

You know, I just had a thought and that was that some ozone systems use UV to generate the ozone. In that scenario, the UV could break down the chlorine. Do you have any idea how your ozone system works? If it's from corona discharge rather than UV, then perhaps that explains the difference. I would have expected the UV to expose air that created ozone injected into the water and that the water itself would not get exposed to the UV, but perhaps some designs don't do this.
Yes the Paramount ozone system uses a UV bulb to create ozone enriched air which is then injected into the pool water right before the pump. The water itself doesnt pass by the UV bulb. It doesnt inject ozone through a random return to the pool. The process is concentrated at the equipment pad at a specific point in the flow. So the ozone is used to help break down non living wastes between the pump and in the filter. Chlorine is produced later on downstream of the ozonator by the swcg which is the last step prior to returning the water to the pool. Per the Paramount information they say killing living organisms (virus, bacteria, algae) consumes only 20% of chlorine in a pool. Oxidation of non-living waste uses up to 70%. The residual 10% is what is left in the water as a "safety net" to maintain water quality until the water circulates through the equipment again.

Anyway, I'm not trying to say its the greatest thing ever just sharing what information I have about it.
 

JasonLion

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Poolnerd has his facts off in a tricky way. First he says that you have to use chlorine even with ozone, so why not just use chlorine. Then he says that cholrine is a problem because of chloramines (CC). Ozone destroyies the CC, solving the problem, all true enough. However, a properly chlorinated pool will never have any significant level of CC, so his whole argument is misleading. Basically he ends up saying that if you do ozone really well it will be better than if you do chlorine really poorly, which is probably true. But it is so simple to do chlorine well that what he is saying really doesn't make any sense.

The advantage to ozone that I see is as an adjunct to chlorine to wipe out the occasional chlorine resistant nasty. Chlorine alone is quite safe. Ozone alone won't work at all. Chlorine plus ozone is just a little bit safer (and more expensive).
 

chem geek

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In an outdoor pool exposed to sunlight, the CC level is usually very close to zero almost all of the time. Ben thought that sunlight may help break down CCs and I would tend to agree with that though I can't find literature on the specific mechanisms (except for chlorine breakdown, of course). So I agree that ozone and even shocking with chlorine are usually not needed (unless there's an "accident" or unusually high bather load, etc.). However, indoor pools and other pools (or spas) not exposed to sunlight seem to have a much harder time getting rid of CCs. The chlorine alone (without sunlight UV energy) is not enough to complete oxidation for some organics. So in these pools I can see the use for ozone or for non-chlorine shock (potassium monopersulfate) as alternatives to keep CCs near zero.
 

cliff_s

Well-known member
Mar 28, 2007
93
Since most so call ozonators are nothing but a couple of UV tubes next to a clear plastic tube, their effect is much like bright sunlight.
This would tend to destroy any residual chlorine in the water if they are mounted before the salt cell. The UV light would display sanitizing
properties when the water is passed through the UV cell. I suppose the theory is that the UV light reacts with the dissolved oxygen in the
water to form ozone. Since ozone will stay in solution under pressure it will pass through the salt cell. The salt cell will add chlorine to the
water and return it to the pool. I really don't know what happens when current is passed through the water containing ozone and what affect it
has on the ozone.

In an outdoor pool during the summer a great deal of UV light is absorbed by the pool water. The sanitizing effect should be the same as
adding ozone to the system. Interesting is that there is a 10,000,000+ gal. pool, lagoon at a hotel(Videfel) in southern Mexico that uses no
chlorine or added chemicals. They use a series of water falls to sanitize the water. It might be noted that it is a salt water pool.
Saying the above, I really wonder whether adding a UV ozone system is adding anything to an outdoor pool other than destroying the residual
chlorine.

Cliff s
 

chem geek

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Between Cliff and TheOne plus what I've seen on the web, I think we've figured out the issue with ozonators and chlorine. It depends on the ozonator. Not all are just UV tubes next to tubes with water flowing in them. In fact, I wouldn't even call those ozonators, but rather UV disinfection systems and they would degrade chlorine flowing through the tube. Many of the ozonators I looked up had the UV tube exposed to air and this air was injected into the water stream so the UV did not expose the water directly. In this latter system, there shouldn't be any chlorine degradation, at least not from UV. So it would seem that whether chlorine gets degraded or not has a lot to do with the type of ozonator that is used.
 

cliff_s

Well-known member
Mar 28, 2007
93
I might add that the true Ozone generators are rather more expensive than the UV tube ones.

The true Ozone generators either use a form of electric arc or a special tube to generate
the Ozone then inject it into the water.

Cliff s
 

chem geek

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I forgot to post this update to this thread (it's been posted elsewhere), but waterbear and I figured out how Ozone can breakdown chlorine. Chlorine can be reduced by a strong oxidizer such as ozone as follows:

O3 + H2O + 2e- --> O2 + 2OH- .... Eo = +1.24 V
OCl- + 2OH- --> ClO2- + H2O + 2e- .... Eo = -0.66 V
-------------------------------------------------------------
O3 + OCl- --> O2 + ClO2- .... Eo = +0.58 V
Ozone + Hypochlorite Ion --> Oxygen + Chlorite Ion

and then

O3 + H2O + 2e- --> O2 + 2OH- .... Eo = +1.24 V
ClO2- + 2OH- --> ClO3- + H2O + 2e- .... Eo = -0.33 V
--------------------------------------------------------------
O3 + ClO2- --> O2 + ClO3- .... Eo = +0.91V
Ozone + Chlorite Ion --> Oxygen + Chlorate Ion

So the net result is:

2O3 + OCl- --> 2O2 + ClO3- .... Eo = +1.49V
Ozone + Hypochlorite Ion --> Oxygen + Chlorate Ion

So a powerful ozonator will break down chlorine and this defeats the purpose of running at lower chlorine levels since you'll have to add chlorine more frequently to make up for this loss and probably have to have a higher level at times to make up for this loss.
 

learthur

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Sep 9, 2008
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The Woodlands, Texas, USA
I recommended a friend of mine install the Triopure by Delozone. Here is his experience.

He has a 16000 gal pool near Houston TX.
He has 3 kids plus adults plus neighbor kids using the pool several hours every day in the summer.
The area has a lit of organic matter in the form of leaves from trees and meldew/ mold.

Before the TrioPure install, his pool was generating a lot of combined chloramines and ancesotally the kids were sick more ( but kids do get sick...). Also more algae because the high bather load used more chlorine and the pool boy only corrected it once a week.

This unit generates ozone from a corona discharge cell.

After the install we observed these benefits:
1. Chloramines eliminated.
2. SWG feature very convenient
3. Unit has it's own pump, so money was saved from running pool filter pump less.
4. Chlorine levels extremely stable with the constantly running pump.
5. Water has a very clear sparkle to it.
6. Coloform screening tests passed ( important with kids).
7. The continous circulation gets the most effectiveness out of the small amount of ozone produced.
8. Some people have told us that the ozone helps retard mineral buildup on the SWG cell but don't know yet on that.
9. I don't care which sanitizers you use in your pool. But strong evidence suggests that 2 sanitizers is better than 1. They have a synergistic kill effect.

After 1 year of use the unit has been problem free.

I will say that the plumbing in of such a device can be the most difficult part ( the planning that is). But everyones plumbing is different.
 

JasonLion

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learthur, nearly all of those benefits (except for 3, 7, and 9) would be true of any SWG. The extra pump is a cool idea. On #9, sure two sanitizers will keep the water cleaner than one, but they are also more expensive and more work. Chlorine done well works just fine in an outdoor pool and it is not difficult to do chlorine well, particularly with a SWG.

Indoors is a different issue. Some supplement to chlorine can help a great deal indoors. However ozone frequently causes air quality issues indoors, so it wouldn't be my first choice.
 

budster

In The Industry
Dec 19, 2008
272
Savannah Historic District
You guys are really good! The only "old school" thing I could add is that the ozone generator (either UV or CD) will destroy things "at the point the water passes through the unit", and then that sanitized water goes back into the mix. So, turnover rates are important. Also, the "old" issue was that the ozone gasses out of the water pretty quickly, whereas the chlorine stays in, so in large bodies of water (pools, as opposed to portable spas, where ozone is almost standard equipment), ozone was pretty ineffective. 8)
 

learthur

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When I Added ozone to my pool (CD type not UV), the water became noticsbly clearer. I thought my water quality was great to start with, but this made a clear improvement. It also increased my ORP.