Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 5 of 5

Thread: Ozone Claims

  1. Back To Top    #1

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Ozone Claims

    Since the thread Ozone cleaner brought up the topic of ozonators from a manufacturer, I want to analyze some statements made on this website (note that such statements are fairly common to all ozone manufacturers so this is just an example). Let's look at some of these statements individually. Many of them are not outright falsehoods, but when applied to outdoor residential pools they can be misleading.

    Ozone and chlorine differ in how they oxidize other compounds. At pool or spa residual levels, chlorine becomes incorporated into the compound. This chemically alters the compound. In this fashion, chlorine combines with organic compounds in the water. These organic compounds include body oils, suntan lotions, cosmetics, dead algae and bacteria. These reactions consume a lot of chlorine – and chlorine is no longer available to function as a biocide and residual. The altered chlorinated organic compounds (combines) form scum lines and greases that clog filters, (remove) and form layers with calcium carbonated which result in the formation of soft-scale.
    The main flaw in the above reasoning is the implied assumption that the bather load in residential pools is large enough to have a noticeable amount of chlorine reacting with the organic compounds (and ammonia) mentioned. That is simply not true in most cases. The bather-load from the nitrogenous chemicals in sweat and urine along with chlorine reacting with skin and swimsuits is roughly 4 grams of chlorine (as Cl2) per person-hour. In an 18,000 gallon pool this is only (1000 milligrams/gram) * (4 grams) / (68137 liters) = 0.059 mg/L or ppm. I would not call this consuming a lot of chlorine.

    As for suntan lotion, it too does not result in a measurable chlorine demand and I speak from personal experience about this since my wife swims almost every day in our pool and uses sunscreen regularly. The cartridge filter is full of such suntan lotion when cleaned once a year (they are oversized filters) and the chlorine demand does not change at all after an entire season of accumulation vs. after cleaning the filter (at least within 0.2 ppm FC per day which is the resolution of the FAS-DPD chlorine test using a 25 ml sample size). Suntan lotion has many compounds, but only some of the FDA allowable active ingredients are nitrogenous compounds with which chlorine will react.

    As for the chlorinated organic compounds forming scum lines and greases that clog filters and removing and forming layers with calcium carbonate, not only have we not seen this being reported but I don't see the chemistry that makes this happen. Scum lines are typically from a combination of calcium or magnesium with soap forming calcium or magnesium stearate. In pools saturated with calcium carbonate to protect plaster surfaces one can have calcium carbonate scale, but that does not involve chlorine. "Greases" would be greases without chlorine and chlorinated organics would not become more grease-like.

    At operating residual levels, chlorine also combines with nitrogen-containing compounds to form chloramines. Chloramines are less effective biocides than the killing forms of chlorine. Chloramines are responsible for the eye and skin irritations associated with chlorinated water. The formation of chloramines consumes considerable amounts of the free available chlorine. More chlorine needs to be added to establish a sufficient free chlorine residual in the water, a process known as “superchlorination” or “shocking”.
    Again, the amount of chloramines that are formed are a function of bather load and the amount is not "considerable" in a low bather-load pool. Also, with the low active chlorine levels in the Chlorine/CYA Chart, there is less nitrogen trichloride produced. The UV in sunlight also breaks down dichloramine which is a precursor to nitrogen trichloride. Chlorine oxidizes ammonia mostly to nitrogen gas and some nitrate, and very very little nitrogen trichloride when the bather load is low.

    Superchlorination or shocking is not needed if the chlorine level is properly maintained, especially when the bather load is not high. Breakpoint chlorination is continuous. In my own pool, I almost always measure <= 0.2 ppm CC and that is also true for the vast majority of outdoor residential pools that are properly maintained. Furthermore, most of this CC is chlorourea and monochloramine, not dichloramine and nitrogen trichloride. Chlorine reacts very slowly with urea, but ozone also effectively does not react with urea, but ozone does react more with chloroureas so that could be helpful if they built up to high levels, but that doesn't happen in low bather-load pools.

    Ozone acts as a primary oxidizer, not as a disinfectant or biocide. Disinfection is achieved by maintaining a free available chlorine or bromine residual. Because Ozone is a more powerful oxidizing reagent than chlorine, Ozone reacts with organic or nitrogen containing compounds faster. Ozone does not combine with other compounds; instead, it causes the organic and nitrogen compounds to break apart. The smaller molecules are more water soluble, and some can even gas-off. Amine compounds are altered so that they no longer combine with chlorine. Ozone stops the buildup of chlorinated organic and amine compounds and does not form combines.
    There is a fallacy that just because an oxidation potential is higher, that "ozone is a more powerful oxidizing reagent than chlorine". Oxidation potential is a thermodynamic quantity that says what is possible, not the rate at which it actually happens. Oxygen has an oxidation potential that should be oxidizing the organics in our bodies (or in wood) to carbon dioxide, nitrogen gas and water, but that doesn't happen except at high temperatures (i.e. burning). Whether a reaction actually happens, or happens quickly enough to matter, depends on reaction kinetics which depends on temperature and activation energy, not just on thermodynamics. See Chemistries of Ozone for Municipal Pool and Spa Water Treatment for many such fallacies. It is true that partial oxidation can still be helpful, but ozone does not oxidize that many more compounds than chlorine in pool water. See Use of Ozone in the Treatment
    of Swimming Pools and Spas
    (see Tables 9 - 13).

    When ozone breaks down, which it does more quickly at higher pH, it breaks down into a variety of oxygen species the most powerful of which are hydroxyl radicals, OH•. The thing is that chlorine also breaks down into hydroxyl radicals from the UV in sunlight. The difference is that with ozone this radical production occurs mostly in the contact chamber (if one is used where ozone can remain in contact with pool water for minutes), whereas with chlorine it occurs throughout the pool water (UV penetrates deeply into water, unlike infrared).

    Without Ozone, the homeowner uses much more chlorine to keep a free available residual and requires “superchlorination” or “shocking” compounds and other specialty chemicals to treat problems caused by pool oxidation by chlorine.
    Again, this is simply not true. No weekly or regular superchlorination or shocking is needed in a properly maintained outdoor residential pool. The key is understanding the chlorine/CYA relationship because standard industry recommendations for FC and CYA do not account for the basic science known since at least 1974 as described in this paper. Pools not following the FC/CYA relationship typically have too low an active chlorine level so algae can grow faster than chlorine can kill it. This may not always result in visible algae and may instead result in dull/cloudy water or in a higher chlorine demand. It is in such situations where ozone or any other supplemental systems including algaecides and phosphate removers seem like a miracle, but these extra products or systems wouldn't be needed if the proper FC/CYA levels were maintained in the first place.

    Ozone is very, very useful when the bather-load is higher (many commercial/public pools and spas and high-use residential spas) as it can oxidize the bather waste (and other chemicals) before they build up to high levels, sometimes before chlorine reacts with them while other times afterwards. Ozone is also useful at inactivating the protozoan oocyst Cryptosporidium parvum which is highly chlorine resistant. Ozone also oxidizes bromide to bromine (and some of it to bromate) so is useful in bromine spas.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  2. Back To Top    #2

    In the Industry

    Join Date
    May 2013
    Location
    California
    Posts
    46

    Re: Ozone Claims

    I service about a dozen pools with Ozone systems. I keep the chlorine about where I normally would in a pool without the system. Ozone is released in the water in such a way that it is nearly impossible to keep a residual ozone level. If the Ozone runs into contaminants in the water it will only last for a few seconds. It can last as long a 30 minutes if it doesn't react with anything in the water. So I don't know about keeping the chlorine at 1.0 ppm. I just don't chance it. One thing I do notice is that these Ozone equipped pools get zero algae in them. Very nice for me. However, half the time the system isn't even running when I get there since a lot of them are plumbed in incorrectly. I know some tricks to get them running again but technically they need to be running 24 hours a day to work correctly. I don't argue with a customer who wants to install one of these but I wouldn't invest in one myself. I also agree with all of your feedback posted.

  3. Back To Top    #3

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Ozone Claims

    Quote Originally Posted by mrdgvb1
    I service about a dozen pools with Ozone systems. I keep the chlorine about where I normally would in a pool without the system.
    :
    One thing I do notice is that these Ozone equipped pools get zero algae in them.
    Your "normal" chlorine level, which should really be an FC level relative to the CYA level as per the Chlorine / CYA Chart would have all your pools not have algae using chlorine alone with no ozone so if you had algae in such pools they must not have had the right FC/CYA ratio (and that can be hard to maintain for a pool service that only visits and doses once a week or uses Trichlor which increases CYA levels). That's the point. Very few outdoor residential pools on this forum have ozonators and these pools don't get algae when properly maintained with chlorine. After properly managing the pools with the appropriate FC/CYA ratio, a few users turned off their ozonators and didn't notice any difference. Some others discovered their ozonators were no longer working, but it didn't matter since they were now properly using chlorine alone.

    Also, if one wants some form of insurance against algae because they are unable or unwilling to maintain a proper FC/CYA level, there are many ways to prevent algae growth that are less expensive than using an ozonator (amortizing its cost) -- Polyquat 60 weekly, for example.

    If the ozonators in the pools you describe truly prevented algae and that no ozone residual existed in the bulk pool water, then such algae would be free-floating because any algae not circulating would not get exposed to any ozone.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  4. Back To Top    #4

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Ozone Claims

    I should add that some pool builders/designers who promote ozone systems are using Trichlor in inline chlorinators but do not manage the FC/CYA relationship. So normally as the CYA level rises, the chlorine demand goes up as algae grows because the FC level is not proportionately raised as the CYA level climbs. Adding any product or system that even partially handles the algae growth will be seen as a benefit. So free-floating algae gets killed by ozone, but it would also be killed by an algaecide or limited by a phosphate remover and those would also handle algae that is not free-floating. In other words, the ozone is really being used as a supplemental algae control system, not really so much for supplemental oxidation. The claims that in outdoor residential pools it is handling bather load are not what is really going on.

    The same "use less chlorine" claim and actual observations are seen with a variety or products such as those promoting copper algaecides or phosphate removers. It would be more appropriate for those promoting ozone systems for outdoor residential pools with low bather load to describe them as partial algae control at extra cost. They are not necessary if one manages the appropriate FC/CYA levels. The trade-off is the cost savings from lower chlorine usage (mostly loss from sunlight) by having lower chlorine levels vs. the cost increase of the supplemental systems or products and the side effects or limitations of those systems and products.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  5. Back To Top    #5

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Ozone Claims

    I am updating this thread with a calculation for the number of hydroxyl radicals produced in a swimming pool exposed to sunlight so that this can be compared to the amount of hydroxyl radicals produced from ozone via an ozonator. One of the claims from ozone manufacturers and distributors/sellers of ozone systems is that these are advanced oxidation processes largely due to the hydroxyl radicals that are produced. Let's see how a chlorinated outdoor pool exposed to sunlight compares to the typical ozonator.

    Let's take the example of an SWG pool where we recommend an FC that is roughly 5% of the CYA level and let's assume a pH of 7.5 and a 10,000 gallon pool which is 0.04 ppm of unbound chlorine (hypochlorous acid and hypochlorite ion in a 50/50 mix at pH 7.5). During noontime sun, roughly half of the unbound chlorine is broken down from sunlight every 35 minutes where the rate at a maintained level is 120% per hour so 1.2*0.04 = 0.048 ppm FC per hour (there may be more loss than this from sunlight perhaps from some chlorine bound to CYA but I'm being conservative). Chlorine breaks down in sunlight to form hydroxyl radicals as described in this paper. 10,000 gallons is 35854 liters so this is (0.048 mg/L/hr Cl2) * ((17.01 g/mole OH•) / (70.906 g/mole Cl2)) * (35843 liters) / (1000 mg/g) = 0.4127 g/hr OH• per hour.

    The following net reaction is how ozone produces hydroxyl radicals and I will assume that is all it produces (see this post for how chlorine produces hydroxyl radicals).

    3O3 + H2O ---> 4O2 + 2OH•

    So the equivalent amount of ozone necessary to produce the same amount of hydroxyl radicals as from the breakdown of chlorine is (0.4127 g/hr OH•) * (3 O3 / 2 OH•) * (48.00 g/mole O3) / (17.01 g/mole OH•) = 1.75 g/hr O3 (for every 10,000 gallons of pool volume).

    Most residential pool ozonators are far lower in output per 10,000 gallons than this. UltraPure UPP50 is 0.435 g/hr that they recommend for pools up to 50,000 gallons for $645 (so only 0.087 g/hr per 10,000 gallons), Del Ozone Eclipse-40 is 1.0 g/hr for pools up to 100,000 gallons for $750 (so only 0.1 g/hr per 10,000 gallons), Pool Ozone Systems PZ2-4V is 2.0 g/hr for pools up to 100,000 gallons for $1664 (so only 0.2 g/hr per 10,000 gallons). One could, of course, significantly oversize their ozonator but that would be expensive. Commercial units such as the Absolute Ozone Atlas 30 outputs 30 g/hr but is nearly $5000.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •