Ozone Question. (Very Technical)

[Vermonter]

Didn't someone post Vermonter's analysis of ozone not too long ago? I searched for it but didn't find it.

I think that's the most complete dissertation on the +/- of ozonators in hot tubs that I have seen.

Back on July 31st (my first post here) I included three posts on ozone in hot tubs.  I'm not sure how much help they'll be and I'm not too familiar with how to post them here (they were too long for one post), but here's what I had originally included.  

I'd be happy to go into more detail or help with any specific questions (if I can)...

This is from my July 31 post:

I have followed, with interest, a few of the recent threads that deal with the general subject of "ozone".
 
I guess it is appropriate for my first post on this forum to focus on ozone - a topic that I have nearly 30 years of experience with ranging from 3 million gallon per day high purity water systems (semiconductor) to drinking water systems many  times that size to table-top carafes treating a liter at a time to hot tubs.  Regarding hot tubs, one of my first posts on the rhtubs.com site concerned ozone - and, over the years, there have been several dozen on that site that followed that original post.
 
For this post, I wanted to not get into specific applications of ozone to hot tubs; what brand does or doesn't have a contactor, etc.  Rather, I thought I would go through the basics of ozone - both as an oxidizer and as a sanitizer / disinfectant.
 
I should say that the following represents my opinion - backed by a considerable amount of experience and actual testing of ozone in hot tubs.
 
General:
 
First, ozone, like chlorine and bromine, is both an oxidizer and a sanitizer / disinfectant.  Ozone functions first as an oxidant and secondarily as a sanitizer (I will use the term sanitizer vs. disinfectant; while ozone is a disinfectant, its use, in hot tubs, would, under optimum conditions, function as a sanitizer).
 
Ozone as an Oxidizer:  
 
An oxidizer serves to "oxidize" or break down both organic and inorganic "contaminants" in your spa's water.  If you use chlorine, some of the more common contaminants are chloramines - shocking with chlorine or MPS will effectively break down those compounds; theoretically, ozone would do the same.  Other contaminants are from body waste (sweat, skin flakes, etc.), natural contaminants (pollen, insects, dust, etc.), contaminants in your water (both organic carbon as well as inorganic species such as iron, manganese, etc.).  Oxidation breaks these contaminants down into simpler compounds.  In the case of organics, the ultimate breakdown product is likely to be carbon dioxide or some simple form of organic acid.  In the case of inorganics, it will be some oxidized form of the inorganic (i.e. a metal oxide).  
 
If you have a tub with an ozonator installed and, if you have some "clear" tubing downstream of the Mazzei injector site, take a look at the tubing after a few weeks or months of use - most likely it will be reddish colored.   That is the result of the ozone oxidizing the iron in your water from the reduced, ferrous state to the oxidized, ferric (rust) state.  The fact that you see this immediately downstream of you ozonator is a visual representation of what I said above - oxidizers, in this case, ozone, functions first as an oxidizer (hence the color immediately after the ozone is introduced).
 
Part 2 continues with ozone as a sanitizer....and more!

[Vermonter]

Continued from Part 1:
 
Ozone as a Sanitizer:
 
If the oxidative demand of the water in the tub or in the "contact chamber" is met, then, theoretically, ozone can function as a sanitizer.  However, simply "injecting" ozone will not make this happen.  To have ozone act as a sanitizer, you have to have ozone in the dissolved, or aqueous form, vs. the gaseous form that we all equate as "ozone" (i.e. the bubbles that you see and smell).  All hot tub CD ozonators use air as the makeup gas - the ratio of air to ozone coming out of the ozonator is typically well over 95% and well less than 5% ozone.  To get ozone into the water the best approach is to use a venture type of injector - such as the Mazzei (a brand) used in many hot tubs.  This makes use of a pressure drop within the injector to "suck" in the air/ozone gas from the ozonator and to then diffuse it into the water flowing through the infector in an effort to transfer the gas into the liquid.  Ideally, you want very, very small bubbles - so that for a given volume of gas you will have a maximum ratio of surface area of the bubbles to allow the ozone to enter the aqueous form.  To do this effectively requires a long contact chamber and sufficient time for the phase transition to occur.
 
As indicated, once the ozone / air bubble is produced, it has a very limited time to transfer the ozone to the water.  By the time you see bubbles rising in your tub, it is too late.  Anyone who says that you can put a spa blanket on the water and "hold" in the ozone is simply wrong (my opinion).
 
If you succeed in getting ozone into the dissolved or aqueous phase, it doesn't stay there long.  Ozone, in pure water, at a temp of 20'C (68'F) has a half-life of about 22 minutes (estimates vary a bit); meaning that after 22 minutes you have 50% of what you started with, after another 22 minutes you have half of that, etc.  Hot tub water is not "pure water" and it is not at 68'F.  The half-life of ozone in typical hot tub water is likely to be in the single minutes - perhaps even seconds (I have not seen studies on this, but comparable ones for other water types would indicate these numbers to be in the right ball park).
 
Heat is a big enemy of ozone half-life - so under the best of conditions (ozone generator, injector...) you are fighting an uphill battle in hot tubs.  In my HotSpring Grandee (2001), the ozone is "injected" on the heater line - meaning that, if the heater is on, the ozone is being injected into water that is about 120'F - not good at all for efficient introduction of ozone.  There are other problems associated with ozone - including such factors as pH and general water quality.
 
OK, but can ozone work as a sanitizer in a hot tub?  Sure, IF you can achieve a dissolved ozone concentration and if that can be maintained for a long enough time to meet the CT (Concentration x Time)  "kill" factor required for the target microbes.  Ozone is one of the most powerful sanitizers (actually, in this sense, disinfectant and ozone is second only to fluorine) known and is effective, given enough CT, against essentially all microorganisms.  BUT, to get a CT of above "0" you have to have both the C and the T above "0" or the product is "0" and you won't sanitize.  
 
In the past I have challenged anyone to provide defensible results showing that dissolved ozone concentrations are present in EITHER the contact chamber of, more importantly, the main hot tub water.  To do so, the method used must be an ozone-specific method.  Many of the kits sold and "used" are DPD based - and will pick up any type of oxidizer present (chlorine, oxygen, etc.).  There are ozone-specific methods such as indigo trisulfonate.  I have tried measuring ozone myself - in my hot tub, in my contact chamber, in a few other hot tubs and have been unable to get any measurable (my detection level is 0.03 ppm) levels of dissolved ozone.
 
If you don't have a dissolved ozone residual - you will not get any "kill".
 
Best,
 
Vermonter

[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

[Tman122]

Continued from Part 2:
 
 
Vermonter

Thank you Vermonter......finaly you stuck your head and pocket protector in the door.

Good thread.

[Ehizzle]

Thanks a ton for the info Vermonter.

One more question for anyone? Are ppm and grams the same type of messurement. Jacuzzi measures its ozone in grams produced per hour, where as HS measures in ppm. My understanding is that they aren't the same type of measurement.

[hottubdan]

Thanks a ton for the info Vermonter.

One more question for anyone? Are ppm and grams the same type of messurement. Jacuzzi measures its ozone in grams produced per hour, where as HS measures in ppm. My understanding is that they aren't the same type of measurement.

They are different measurements.  And, as Vermonter showed, somewhat irrelevant.

[Vermonter]

They are different measurements.  And, as Vermonter showed, somewhat irrelevant.

They are, indeed, different measurements and have different implications when it comes to ozone applications.

The "grams per hour"  (or weight per unit time - it may be milligrams or even pounds per unit of time) is a measure of the output of the ozone generator.  It has nothing to do with the concentration of ozone in water.  

It is a measure of the "applied" ozone (gaseous form) to the water - but not the concentration of the ozone in the water.  Depending on whether any given generator is run on air or oxygen, the grams per hour output can vary by about 100% (an oxygen fed generator usually puts out about twice as much as the same generator on air).  

The ppm (parts-per-million or milligrams per liter - the are the same) is a measure of the DISSOLVED concentration of ozone in water (the aqueous form I mentioned in the posts above).  Unfotunately, the efficiency of the transfer of the gaseous form of ozone to the dissolved / aqueous form of ozone is very, very inefficient and it is likely that well less than 10% (perhaps closer to 1%) of the applied ozone ever makes it way to dissolved ozone in hot tubs.

The fact that the dissolved ozone concentration (in mg/L) in hot tubs is so low that you can't really detect it (at least I haven't been able to and no manufacturer that I am aware of makes claims as to dissolved concentration in the hot tub itself), this means that ozone is likely too low to function at all as a disinfectant.  Remember (as described earlier), ozone works first as an oxidant and secondarily as a disinfectant - any dissolved ozone (in my opinion) never gets a chance to work as a disinfectant.

Vermonter

[Ehizzle]

Vermonter,
Again thanks. A HS Freshwater 3 sell sheet I have says, and I quote, "The FreshWater III system delivers 600 to 900 ppm of ozone continuously, ensuring the output remains at a level well above the minimum threshold of 250 ppm even with the high heat and humidity in a spa's equipment compartment." Since you said you have a HS I am guessing this is the Ozonator you have. I was curious what your thought are on this.

[Dr. Spa™ Ret.]

"Delivers", as I read that only means that the air, as it exits the oozonator contains 600 ppm of ozone.

[Vermonter]

Vermonter,
I was curious what your thought are on this.

Well...I guess I'd have to call HS and ask them exactly what they mean...but I think I know...

Note, that they say "delivered" which is analagous to my term of "applied" (in my posts above).  It does not, I'm positive, equate to concentration of dissolved ozone in a hot tub.  My guess is that HS is trying to market their "superior" generator by trying to maximize numbers figuring that many will not understand or catch the difference between ppm and, say, another manufacturer's grams per hour rating or between the terms "applied" and "dissolved".

Theoretically, you can convert the weight per unit volume measurement (e.g. grams per hour) to ppm as long as it's understood that you are using some constants in terms of the weight of, say, 1 liter of air at STP (standard temperature and pressure) that the generator is putting the ozone into.  Then, assuming you know the mg / min (or hour) output of your generator, you can then readily calculate the concentration (in ppm or mg/L) of ozone for the total mass of air that is flowing through the generator.   This is the "applied" or "delivered" value and, assuming I am interpreting them correctly, it really has nothing, whatsoever, to do with the concentration of ozone in your tub water.  It pertains to the "concentration" in the air flow through the generator and that's it.  There may be other factors that are involved in calculating "delivered" ozone - such as the molecular weight of the ozone molecule (approx. 48) vs. the corresponding weight (or volume) of the air that, again, is going through the generator in a specific period of time.

Confusing?  Yes, and I apologize.   Put another way (simpler, I hope), ppm is an expression of concentration.  If you put one gallon of "bleach" in 1,000,000 gallons of water, you have a concentration of 1 ppm.  So if HS says they are "delivering" up to 900 ppm of ozone, this (in my opinion) does not apply to the concentration in the tub at all but rather to the concentration of ozone in the air flow through the generator.  Their reference to 250 ppm is puzzling but notice it refers to the equipment cabinet and not the water in the tub.  Again, perhaps a bit of misdirection.  They (HS) may have established some minimum gaseous ozone concentration (i.e. 250 ppm) as a minimum for tub applications (perhaps it is some industry spec?) and want to show that their unit can produce "gaseous" ozone concentrations well above this minimum.

I know that about 5 years ago (when I became a HS tub owner) I spoke with the head of their "ozone application" group and, at that time (Freshwater III) had agreement from him that it would be unlikely that there could be any measurable level of dissolved ozone in the main hot tub and perhaps none in the contact chamber.  

While I am a HS fan (I particularly like their no-bypass filtration), I think that these numbers you reference have absolutely no direct relevance to ozone in hot tubs other than to give some yardstick by which the OUTPUT of competitive ozone generators can be compared.  It does not equate to dissolved ozone concentration in the tub's water.  (Keep in mind that drinking water ozone plants typically raise dissolved ozone levels to a maximum of a few ppm (or less) at the time of treatment to effectively kill most types of microbes in the water you drink.) You also simply cannot get 900 ppm of dissolved ozone in water.

Vermonter

[Jacuzzi Jim]

While I think this thread is facinating.

 It seems as if we are beating a so called dead horse.

[Repeat_Offender]

I don't think it's beating a dead horse at all. I think it's refreshing to get an honest, scientific, factual answer, rather than some manufacturers double talk or shill salesperson speak that's meant to mislead rather than educate.

[Ehizzle]

I agree. I think we have heard some real information that we maybe haven't covered on the topic before. I can't thing of anything else that needs to be added now though.

[Reese]

I don't think it's beating a dead horse at all. I think it's refreshing to get an honest, scientific, factual answer, rather than some manufacturers double talk or shill salesperson speak that's meant to mislead rather than educate.

I agree.  It would be a shame if this info got buried in the dead horse category.  As a matter of fact, it would be nice if the Vermonter posts could be pinned up at the top along with the forum rules, so we don't have to go through the "Tastes Great/ Less Filling" debate every few months.

Thank you Vermonter, for taking the time to drop-by and rehash this topic for us.

[Jacuzzi Jim]

I agree. I think we have heard some real information that we maybe haven't covered on the topic before. I can't thing of anything else that needs to be added now though.

   Pretty much what I ment.   I dont mind, it can go on longer but I am not sure how much more info can be added??  

  Other than filtraition and thats another horse.