Ozone and hot tubs - some basics. Part 3 - Long!

[Vermonter]

Continued from Part 2:

Why don't hot tub manufacturers make powerful enough units?  I'll admit, it's been a couple of years since I've really looked into this and it is possible that someone has.   But the age-old problem is that since the transfer process of the ozone from the gas (bubble) phase to the aqueous (dissolved) phase is so poor that to get any ozone in the water you would generate so much off-gas that the units would fail federal limits.  I have read of some "off-gas destruct" units that would theoretically take care of some of this - but I have yet to see any manufacture of tub or ozonator publish defensible, empirically generated data on dissolved ozone concentrations in tubs.  A couple of years ago, my personal communication with a very, very large tub manufacturer and the largest manufacturer of ozone generators for factory installed units (in hot tubs) confirmed that it is "unlikely" to be able to achieve and measurable ozone level in the hot tub water itself.  That may have changed and I would welcome any input on that.

But, keep in mind, even if you get a residual in the contact chamber and, after satisfying the oxidative demand, you get some antimicrobial (killing) action going on, since you don't  have anything close to "plug-flow" in a tub, there is no way that the residual will be able to be maintained in the main tub or that all the contents of the main tub will be exposed to the contact chamber before being "recontaminated" (keep in mind the half-life and temperature related problems).

Bottom Line:

There is much, much more I could write on ozone - but my goal was to give basic information on what ozone is, how it works, how it is applied to hot tubs and to hopefully give a basic understanding of what it would take for ozone to work as a sanitizer in hot tubs.

Ozone is widely used in the drinking water, food, semiconductor and other industries as a sanitizer / disinfectant.  It is a popular option for many hot tubs and, in my opinion, functions as an oxidizer and, as a result, may slightly reduce the need for your normal oxidizer / sanitizer.  I have yet to see any data to support any claim that ozone can function as a stand-alone sanitizer in hot tubs or, for that matter, that it can exert any "killing" effect on microbes in hot tubs.

Do I have it on my hot tub?  Yes!  Will I keep it?  Yes!  Is there any scientific reason for that?  No - at least not based on any numbers I have been able to generate or that I have seen in the literature!  But I enjoy watching the bubbles!

Best,

Vermonter

[cooltoy2000]

 But I enjoy watching the bubbles!

BINGO!!!

[Dr. Spa™ Ret.]

Hey V-man, long time, hope things are well with you.

Couple questions to "get this party started". I think I understand you to say that until everything in the water is oxidized, the ozone wont begin to sanitize. Correct?

2. With regards to "contact chambers"... They all pretty much seem to consist of a long piece of horizontal pipe (as opposed to a true mixing chamber). Aren't the little bubbles of ozone going to rise rather quickly to the TOP of the pipe, combining into one big ole bubble, thereby no longer being able to be absorbed into the water (and the slower the water is moving, i.e. circ pump, the less turbidity there will be allowing for a faster rise of the bubbles)?

Hottubman made an interesting comment in another thread, suspecting that the real purpose of a contact chamber was to give the ozone enough time to revert back to 02 thereby reducing off-gassing.

[SerjicalStrike]

I am not sure if other companies do this, but on Sundance spas there is an actual "chamber" that breaks the bubbles down as they are passing through.  

Vermonter, very nice posts.

[Chas]

2. With regards to "contact chambers"... They all pretty much seem to consist of a long piece of horizontal pipe (as opposed to a true mixing chamber). Aren't the little bubbles of ozone going to rise rather quickly to the TOP of the pipe, combining into one big ole bubble, thereby no longer being able to be absorbed into the water (and the slower the water is moving, i.e. circ pump, the less turbidity there will be allowing for a faster rise of the bubbles)?

HS uses spa flex - which has a slight spiral built in. I know they try to keep the tubing absolutey level as it makes it's rounds to avoid the bubbles clumping and getting noisey as well, but I guess that's what we would call a "pipe dream" - pun intended.

The spiral induces a swirling motion which seems to keep the bubbles small and mixes them. I have not seen this in action with a pipe camera or anything, so I can't verify that it is doing a perfect job, and the spiral is very minor, nothing more than all spa flex has. But the bubbles emerging from the botton fitting are still pretty small - especially on the newer tubs - so I have to think they are staying well suspended during transit through the chamber.

[Dr. Spa™ Ret.]

"I know they try to keep the tubing absolutey level as it makes it's rounds to avoid the bubbles clumping and getting noisey"

You said it right there. Little tiny bubbles only make a hissing noise. Gergling is only from large bubbles.

I also find it rather unlikely that the natural twist of flex PVC will cause anough agitation to keep the tiny bubble from rising, especially with a small circ pump moving little water.

Real life story... About 15 years ago we installed a hot tub and the equipment, which included an ozonator (BIG dual 28" UV lamps), a mazzie injector and mixing chamber was about 60' away. The piping ran flat and level on top of a concrete wall footing, straight from the equipment to the tub. You could hear the big fat bubbles inside the pipe not very far after the injector/mixer.

It took a bit of playing with the plumbing and orientation of the jet, but we finally got it so the jet was "rearrosoling" the big bubbles back into tiny bubbles as the water shot out into the tub.

[Vermonter]

Hey V-man, long time, hope things are well with you.

Hi Doc - yes, long-time.  Things are going well - I'll try to catch up with you by email!

Couple questions to "get this party started". I think I understand you to say that until everything in the water is oxidized, the ozone wont begin to sanitize. Correct?

That is correct - to the best of my knowledge.

2. With regards to "contact chambers"... They all pretty much seem to consist of a long piece of horizontal pipe (as opposed to a true mixing chamber). Aren't the little bubbles of ozone going to rise rather quickly to the TOP of the pipe, combining into one big ole bubble, thereby no longer being able to be absorbed into the water (and the slower the water is moving, i.e. circ pump, the less turbidity there will be allowing for a faster rise of the bubbles)?

I think the flow, even at a HS 4 - 6 gpm in the circulating pump / ozone injection line, is fast enough to prevent many from "clumping" on the top of the pipe.  An improvement, in my opinion, would be to install a Kenics (or equivalent) static mixer immediately downstream (allowing for manufacturer's recommendations for straight pipe length in and out of the mixer.  This allows highly efficient mixing of two phases (e.g. gas and water) and would help the mass transfer process.

A few years back, I tried modifying my "contactor" on my HS and added a coil of approximately 75 feet of 3/4 " I.D. tubing figuring that this would give an "ultimate" (well, not quite) contact chamber and ozone transfer to the dissolved state.  Unfortunately, the back pressure resulting from the combination dropped the flow rate below the minimum for the Mazzei injector installed in my Grandee so suction / injection was no longer occurring.  I haven't gone back to try some half-way measure.

Hottubman made an interesting comment in another thread, suspecting that the real purpose of a contact chamber was to give the ozone enough time to revert back to 02 thereby reducing off-gassing.

That is an interesting thought.  

Two immediate thoughts:  

First, the logic of that happening would assume that, ideally, the half-life is less than or equal to the residence time in the contact chamber.   I don't recall what the ID is on the tubing coming out of my HS Mazzei injector (I think it is smaller than the 3/4" I used as mentioned above).  If it is 1/2", then the volume per linear foot is about 0.04 liters or about 0.1 gallons.  In 10 feet, you would therefore have about 1 gallon.  If you are flowing at 4 - 6 gpm, then the residence time in that section would be 10 - 15 seconds - so I'm not sure that you would see much benefit.  

Second, since the vast majority of ozone is still going to be contained in the non-dissolved bubbles (probably about 90% but I don't know the exact %) being carried the length of the contactor, and since the half-life of ozone in the gaseous state (i.e. what is in the bubbles) is much longer than in the dissolved state in "unpure" tub water, I think the majority of the ozone would still be carried out into the tub (undissolved) in the bubble form and rise to the surface only to then release the ozone / air mix.

I hope to get back to your board again...

Vermonter

[Vermonter]

hmmm...my apologies...

I seem to be having a problem with this "reply" feature.  Sorry about that - some of my response is in the blue box and some not!

Vermonter

[Spatech_tuo]

hmmm...my apologies...

I seem to be having a problem with this "reply" feature.  Sorry about that - some of my response is in the blue box and some not!

Vermonter

The nice thing is you can go back and modify the post.

If you want to show his quote, answer and then show another quote and answer you'll have to arrange the quote brackets (beginning and ending) around each one of his quotes.

[In Canada eh]

Vermonter

 Isn't te real idea behind adding ozone to a tub is to get the "bugs" that are resistant to chlorine.  Since chlorine is the principal sanitizer, ozone should only have to target those resistant "bugs".  I know that it will effect everything in its path but since chlorine has no effect on some bugs, isn't that all your asking ozone to do?

[Vermonter]

 Isn't te real idea behind adding ozone to a tub is to get the "bugs" that are resistant to chlorine.  Since chlorine is the principal sanitizer, ozone should only have to target those resistant "bugs".  I know that it will effect everything in its path but since chlorine has no effect on some bugs, isn't that all your asking ozone to do?

Hi Northern Neighbor,

My personal answer to your question is "no".   Given a proper dichlor regimen, there are no bacteria or viruses that I am aware of that would make it through chlorine treatment (applied correctly).  Ozone, while more efficient in some respects than free chlorine, has to be present at some measurable levels for some period of time to be effective on even some of the simpler gram negative and gram positive bacteria.  My testing, and my research, has not demonstrated to me that any hot tub / ozonator combination is able to produce and maintain a dissolved ozone residual in the main hot tub and, as a result, it cannot be relied on as a primary sanitizer in hot tubs (drinking water and other applications are different).

The only microbes that are classically viewed as chlorine resistant are some of the spore formers and mycobacteria, along with the protozoan Cryptosporidium.  Even then, with proper pH and sufficient chlorine CT, they are able to be inactivated or killed.

If a dissolved ozone residual could reliable be produced and maintained in the main hot tub (so far, I have seen no peer-reviewed research to suggest that it can) then it could claim to be a primary sanitizer and would go a long way toward a much more "chemical free" treatment regiment than any of the more traditional approaches.

Vermonter

[In Canada eh]

Hi Northern Neighbor,

My personal answer to your question is "no".   Given a proper dichlor regimen, there are no bacteria or viruses that I am aware of that would make it through chlorine treatment (applied correctly).

The only microbes that are classically viewed as chlorine resistant are some of the spore formers and mycobacteria, along with the protozoan Cryptosporidium.  Even then, with proper pH and sufficient chlorine CT, they are able to be inactivated or killed.

This may be false info that I have been given, you have much more experience that I.  The drinking water industry has started to use ozone for the treatment of cyrpto and giardia due to thier resistance to chlorine.  I know the chances of either occuring in your hot tub are very slim, but if ozone can get them I,m happy it there.


 Its fantastic to be able to "pick your brain" on this subject

[Vermonter]

 The drinking water industry has started to use ozone for the treatment of cyrpto and giardia due to thier resistance to chlorine.  I know the chances of either occuring in your hot tub are very slim, but if ozone can get them I,m happy it there.

By Golly,

You are correct about Crypto's (and to a lesser extent, Giardia's)  resistance to chlorine and that ozone works better.  But, check out the CT requirements of ozone for Crypto (I can dig out a reference if you need) - and if ozone in hot tubs can't produce and maintain a measurable dissolved residual, then ozone's effectiveness doesn't apply (you HAVE to have a residual).

I have nothing against ozone - actually I think it is a great disinfectant.  But, I do not like the implications or claims that manufacturers make that it functions as a sanitizer in hot tubs and then those same groups cannot produce solid test data supporting that claim.

Best,

Vermonter

[In Canada eh]

EXCELLENT INFORMATION !!!!

[In Canada eh]

Your right ozone and crypto CT is I believe 2.5