ozonator worth it or not. circulator pump?

[chem geek]

If you want to use ozone as a residual disinfectant in a hot tub then you need to be running the ozonator and circulation pump 24/7 [EDIT] well, at least not with many-hour gaps without operating [END-EDIT], but there are health risks for doing so if the level of ozone is too high in the water when you are in the spa and such ozone levels also oxidize spa materials (pillows, covers, etc.).  Also, spas generally intentionally turn off their ozonators when spa jets are turned on and the ozonators are designed to not put out too much residual into the spa water.  This is to prevent outgassing of ozone since it is an EPA regulated air pollutant that causes health problems.  So the way ozone is normally used is as an oxidizer for bather waste that passes through the ozonator.  It is not generally used as the bulk-water disinfectant.  That is what an EPA-approved disinfectant is for: chlorine, bromine, Baquacil/biguanide/PHMB, Nature²/MPS.

I kept track of hot tub itch/rash/lung incidents on another forum and the use of an ozonator did not prevent such incidents.  The primary factor causing problems was not using a disinfectant (i.e. using "alternative" systems) or not using enough disinfectant (not adding enough to handle the bather load or not dosing in between soaks if needed).  However, when ozonators were present, they were never run 24/7 so there were definitely times when there was insufficient disinfectant in the water to prevent runaway bacterial growth.  Under ideal conditions, bacteria can double in population every 15-60 minutes so one bacteria can turn into over 4 billion in 8 hours (in practice, the growth isn't this fast, but biofilms can still form in a matter of hours).

[clover]

....Is ozone better suited for larger tubs? And does it work better with bromine or chlorine systems?

Ozonators are used for a wide variation of commercial purification processes including washing the produce we eat, rather than using water based chemicals to wash produce with.  Here it is sized down for Hot Tubs and operates well on any size of Hot Tub.  It is the water it works on, and it is the relationship of ozone reacting with what is in the water, whether it is 250 gallons or 500 gallons, it does not matter.

Ozone, Chlorine, and Bromine are all sanitizers / oxidizers.  Technically, chlorine and bromine become chemical molecules in the water while ozone is an air bubble or gasseous form, O³, and it will take a like atom from that chemical molecule to revert back to 2 molecules of O² going airborne, thus consuming the chemicals you put in the water as well.   

As you can see, there are those that use it, have a working knowledge of it, knows how it works and what it does, while others play the role of the doubting Thomas, challenging what they have not proven to themselves.     Thus, the reason you should rely on your support team. 

While we have put over 3,000 Ozonators into operation over the years, others simply discourage it as they do not fully understand it to sell it and prefer the long standing methods best known to them creating additional sales. 

It is somewhat like the old dog learning new tricks.   

keep in mind, everyone here is trying to provide insight known to them, and time tested in their point of view.  There is no simple answer here, just confusion and contradiction.

[chem geek]

Read Chemistries of Ozone for Municipal Pool and Spa Water Treatment and Decay of Ozone in Water: A Review for facts backed up by science including peer-reviewed papers in respected journals.  Ozone decays in the water so unless your ozonator is running the ozone will get depleted.  At pH 7.5, the half-life of ozone is less than 15 minutes while at pH 8 it's less than 5 minutes (these were at cooler temperatures than spa temps so the decay would be faster, but the presence of carbonates from TA has it slower so is roughly a wash).  If you go for hours without running the ozonator and have no other residual disinfectant then the water will be able to allow bacteria to grow.  Such bacteria can be in films above the waterline and enter into the water.  On the plus side, it takes only a very small amount of ozone to kill bacteria quickly -- even 0.001 ppm will kill fecal bacteria faster than they can reproduce (with a 15 minute half-life, 0.05 ppm ozone will become 0.001 ppm in less than 1-1/2 hours).

The Rice paper also describes how ozone reacts with chlorine so breaks it down thus increasing chlorine demand if there is no bather load (i.e. in between soaks) while with a bromine spa it makes more bromine from the bromide bank.

If you want to promote using only ozone for disinfection in between soaks, then you had better tell users how to properly have the ozonator on frequently enough.  Like I said, there were real users with real health issues because they thought they didn't need a residual disinfectant and their ozonators did not help them when run infrequently.

[clover]

To Chem and other advisors,  I do not dispute, or debate, what you say, or what the paper reports.  Admittedly, the report does not specifically apply to spa water and that seems to be the bone of contention with ozone adversaries choosing to support the use of chemicals, without a full understanding or application of ozone.  One does not profit in that interest.

Please be aware, I have made no assertions that ozone should be used as an exclusive sanitizer, in the absence of chemicals.  Even though, my own personal experience leads me to differ.  I do not support one method over the other, but give them both equal time for evaluation.  I am only trying to be the voice of reason and understanding, while trying to clarify the confusion for those that ask the questions.  I am not her to debate the doc, or others who prefer to be the devils advocate on this subject.

As for your first point,

.....Ozone decays in the water so unless your ozonator is running the ozone will get depleted.....

It actually breaks down while interacting with bacteria, virus, mineral and nutrient molecules.  This interaction happens within seconds, as is indicated in the article.  But then, so do chemicals break down, but chemicals leave behind an accumulation of undissolved solids requiring more frequent water changes. 

At pH 7.5, the  half-life of ozone is less than 15 minutes while at pH 8 it's less than 5 minutes (these were at cooler temperatures than spa temps so the decay would be faster, but the presence of carbonates from TA has it slower so is roughly a wash). 

When water properties change, so does everything else.  I believe the ozone lifetime is measured in seconds as it interacts with other molecules like a magnet seeking a like atom which is spontaneous, and is typically accomplished within the water mix in seconds.  If nothing provides that like atom, then the water is clean, and the ozone continues it's quest looking for a like atom eventually going airborne.

.....If you go for hours without running the ozonator and have no other residual disinfectant then the water will be able to allow bacteria to grow....On the plus side, it takes only a very small amount of ozone to kill bacteria quickly -- even 0.001 ppm will kill fecal bacteria faster than they can reproduce.

This is absolutely correct, but you should be running your ozone in concert with your circulation, filtration system.  But, this statement applies also to the absence of chemicals as well, and thus requires a support team to understand the differences.

.....also describes how ozone reacts with chlorine so breaks it down thus increasing chlorine demand if there is no bather load (i.e. in between soaks) while with a bromine spa it makes more bromine from the bromide bank.

Chlorine and Ozone are competitors and are consumed by each other, benefiting no one other than the chlorine seller.  Thus, my repeated statement to rely on their "support team".

If you want to promote using only ozone for disinfection in between soaks, then you had better tell users how to properly have the ozonator on frequently enough.  Like I said, there were real users with real health issues because they thought they didn't need a residual disinfectant and their Ozonators did not help them when run infrequently.

Between soaks, you will always need more ozone, chlorine, or bromine.  I am not opposing the use of residual disinfectants, I am only suggesting that ozone works quite well, and it needs to be understood before it can be relied upon.  As for health problems, well I don't really want to inhale ozone, nor do I want to inhale chlorine, or bromine gasses.  There are a long list of issues that occur with almost anything in this world, one that comes to mind for chemicals is "life guard lung" and “green hair”, not to mention its attack on the skin, so where ever we go, there will always remain to be 2 sides to every coin.  Or in this case, the bright side of the moon, and the dark side.  Ying, Yang, in every case.

In the interest of answering Mowin's question, I am only trying to represent my perspective on ozone, and the need for a support team to call upon.  I am totally confident, that if you and I were to work together, we would both learn new things from each other that could change our point of view on things we believe.  But, then this calls for an open mind, with a willingness to learn.

A proven fact: "one does not know it all"

[chem geek]

I don't believe you read the papers I linked to thoroughly since some of what you wrote is simply not true.  Let me clarify below.

Admittedly, the report does not specifically apply to spa water and that seems to be the bone of contention with ozone adversaries choosing to support the use of chemicals, without a full understanding or application of ozone.

The title of the first paper was "Chemistries of Ozone for Municipal Pool and Spa Water Treatment" and the word "spa" is used over 80 times in the text of that paper.  It is true that the paper "Decay of Ozone in Water: A Review" does not specifically refer to pools and spas but that is because it it defining the pure science of ozone decay in water generally, not just in pools and spas.  Nevertheless, it does consider the effect not only of parameters such as pH and temperature, but of inorganic and organic carbon compounds as well, such as may be found in spa water.

Furthermore, the first paper that does refer to spas says the following: "Over the past 15 years, Hoigne and his coworkers have defined the decomposition products of ozone in water, in the absence and presence of inorganic and organic materials with which ozone reacts."  What did you think the "decomposition products of ozone in water" meant?  It doesn't mean that the ozone survives as ozone -- the ozone decomposes and it does so "in the absence" of "inorganic and organic materials", not just in their "presence".

It actually breaks down while interacting with bacteria, virus, mineral and nutrient molecules.  This interaction happens within seconds, as is indicated in the article.  But then, so do chemicals break down, but chemicals leave behind an accumulation of undissolved solids requiring more frequent water changes. 
:
When water properties change, so does everything else.  I believe the ozone lifetime is measured in seconds as it interacts with other molecules like a magnet seeking a like atom which is spontaneous, and is typically accomplished within the water mix in seconds.  If nothing provides that like atom, then the water is clean, and the ozone continues it's quest looking for a like atom eventually going airborne.

You are only partially correct here because you are implying that ozone only breaks down in the presence of other items in the water, and by "nutrient molecules" I presume you mean organics and ammonia.  However, what you are missing and what is described in detail in the second paper, "Decay of Ozone in Water: A Review", is that ozone decays in pure water without any "bacteria, virus, mineral and nutrient molecules".  You are absolutely and completely wrong with your belief that ozone won't decay if "the water is clean".  That is a partially true statement for chlorine (whose decay at low concentrations is very slow), but it is not true for ozone.

As noted in the peer-reviewed scientific paper that was a review (summary) of the scientific literature with 85 referenced peer-reviewed papers in respected scientific journals, ozone decays with water itself, or more specifically with hydroxide ions that are always in equilibrium with water and is why such decay is faster at higher pH because the concentration of hydroxide ions is higher at higher pH.  In actual spa water that is clean, there are also other ions in the water since one does not use distilled water, but tap water, and there is a buildup of some minerals as well.  The only minerals in spa water that are relevant to ozone decay are inorganic carbon aka the carbonates.  These are scavengers for hydroxyl radicals that are part of the ozone breakdown process and that promote that process so having TA in the water slows down the ozone decay.  I accounted for this using an 80 ppm TA level that corresponds to 1.6 mM of alkalinity.  So even without any organic carbon (bather waste, bacteria, etc.), ozone decays in water.

This is why ozone does not leave a residual in the water, even when the water is clean.  It doesn't just outgas nor does it require anything in the water to react with -- it breaks down on its own with the components of water itself.

As for the "undissolved solids" left over from chemical oxidation, they also are leftover from ozone oxidation as well.  As noted in the first paper, "FALLACY#3 Ozone will oxidize all pool and spa organic materials totally to carbon dioxide and water."  Both chlorine and ozone oxidize most organics only partially, if at all, and they both tend to make the chemicals more polar so microflocculation can have them get caught in the filter.  It is true that when chlorine fully reacts it becomes chloride salt, but it takes a long time for that salt level to build up requiring a water change.  Nevertheless, it is true that you should be able to go longer between water changes when using ozone -- probably around twice as long as compared to chlorine alone using the Dichlor-then-bleach method and four times as long compared to Dichlor-only.  It is also true that when ozone decomposes it produces hydroxyl radicals that are powerful oxidizers (chlorine does this as well with the UV from sunlight, but that occurs in outdoor pools, not in spas not exposed to sunlight).

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[chem geek]

(...continued from previous post)

.....If you go for hours without running the ozonator and have no other residual disinfectant then the water will be able to allow bacteria to grow....On the plus side, it takes only a very small amount of ozone to kill bacteria quickly -- even 0.001 ppm will kill fecal bacteria faster than they can reproduce.

This is absolutely correct, but you should be running your ozone in concert with your circulation, filtration system.  But, this statement applies also to the absence of chemicals as well, and thus requires a support team to understand the differences.

It requires a support team that understands the basic fundamentals of the chemistry of ozone.  You give no indication of how many hours the circulation pump is off and therefore the ozonator is off during the days in between soaks.  If you were cycling to have sufficient ozone output every hour or so, then that should be OK, but if you have cycles of many hours with no circulation and no ozone, then that is a risk if there is no other residual disinfectant such as chlorine.  Since chlorine and ozone react with each other, this makes it difficult to properly disinfect a spa with days in between soaks when using chlorine or ozone and is the primary reason why bromine is used in such situations since not only can bromine tabs be used in a floating feeder for dosing, but bromine is produced from oxidation of bromide ions by ozone.

Chlorine and Ozone are competitors and are consumed by each other, benefiting no one other than the chlorine seller.  Thus, my repeated statement to rely on their "support team".

Yes, chlorine and ozone react with each other, but ozone also reacts with the organic compounds from bather waste and does so more rapidly than chlorine (except for chlorine reacting with ammonia to form monochloramine).  What this means is that using ozone in a chlorine spa LOWERS the amount of chlorine needed if the bather load is high such as in a residential spa used every day.  Since you do not want to be using ozone while bathers are in the spa, especially if spa jets are used, then you need to have chlorine in the spa to prevent person-to-person transmission of disease.  The only time where ozone increases chlorine demand is in between soaks so in spas that are not used frequently such as those used only on weekends.  As a very rough rule-of-thumb, though it clearly depends on the strength of the ozonator and how long it runs, the use of ozone in a high-bather load chlorine spa cuts down chlorine demand roughly in half while it's use in a low-bather load chlorine spa roughly doubles chlorine demand in between soaks (i.e. daily chlorine loss goes from 15-25% to 50% or more).

So if you want to manage this using chlorine and ozone and don't want to dose with chlorine frequently in between soaks in a low bather-load spa, then do the following: add a low dose of chlorine before a soak since the chlorine level will be zero from reacting with the ozone, add a larger dose after the soak to handle some of the bather waste (but about half as much as would be needed if ozone were not used), then cycle the circulation pump and ozonator during the mid-week with no soaks to make sure some ozone is always present in the water so that means short cycles, not many hours in between.

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[chem geek]

(...continued from previous post)

Between soaks, you will always need more ozone, chlorine, or bromine.  I am not opposing the use of residual disinfectants, I am only suggesting that ozone works quite well, and it needs to be understood before it can be relied upon.  As for health problems, well I don't really want to inhale ozone, nor do I want to inhale chlorine, or bromine gasses.  There are a long list of issues that occur with almost anything in this world, one that comes to mind for chemicals is "life guard lung" and “green hair”, not to mention its attack on the skin, so where ever we go, there will always remain to be 2 sides to every coin.  Or in this case, the bright side of the moon, and the dark side.  Ying, Yang, in every case.

"green hair" has nothing to do with either ozone or chlorine.  It has everything to do with copper.  It is true that chlorine can make hair more receptive to getting green from copper ions, but chlorine alone will not cause green hair.  This paper goes into details about this.

If you want to minimize disinfection products as well as chlorine outgassing, then you need to understand the chlorine / Cyanuric Acid relationship.  This is known science since at least 1974 as described in this paper.  There are absolutely ways of managing a spa for balancing between a pleasant experience, minimizing maintenance, preventing pathogen growth or transmission, and reducing disinfection by-products, but one cannot rely on whatever baloney is touted around the industry or made up from one's own personal limited experience.  There is a movement afoot by consumers to no longer take for granted what is told by some pool and spa dealers.  It's not just this forum, but others as well.  There is one primarily for swimming pools with over 60,000 members and over half a million visitors every month during peak summer whose information is based on sound chemistry and has debunked a number of myths or inaccuracies commonly touted in the industry.  Such sites are growing by 20-30% each year.  Just let that sink in for a moment -- there are only around 10 million swimming pools in the U.S.  If the pool and spa industry doesn't start doing a better job educating its dealers with truthful information, more and more people will look elsewhere for valid information.  Fortunately, there are spa and pool dealers who do want to be educated and there are forums such as this one that are able to sort out the difference.