If the reccomended concentration of active chlorine for a rezidential pool is arround 0.1 ppm why the reccomended level of bromine are 2-4 ppm and not 0.2 ppm?
Bromine sanitation
- Thread starter Tepelus
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Recommended free chlorine levels for a residential pool will ALWAYS be higher than 0.1 ppm.
- May 23, 2015
- 24,405
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I think chemgeek can probably answer this question the best but what you must realize is that the value you are quoting for chlorine is for pool water with NO CYA in it. If you have pool water with 0ppm CYA, then an FC of 0.1ppm at a pH of 7.5 will give you a hypochlorous acid (active chlorine) level of ~ 0.048ppm. That level is well above the disinfection minimum (0.01ppm hypochlorous acid) and just at the borderline for algae prevention (0.05ppm hypochlorous acid). The problem is, there is no way one can reliably maintain an FC that low throughout the water column of the pool as most residential pools have dead spots in circulation and localized regions of low FC can easily develop.
Where are you quoting those standards from? Please provide a link. They sound like European pool water standards which, like US EPA standards, only apply to commercial/public pools.
Bromine sanitation requires higher concentrations of bromine relative to chlorine in absolute terms but I'm not entirely sure how the total bromine concentration relates to the formation of hypobromous acid which is the active bromine sanitizer. Getting to the appropriate level (disinfection limit) of hypobromous acid might require higher concentrations of bromine as compared to chlorine/hypochlorous acid equilibrium. Bromine is not widely used in residential pools in the US because it is more expensive than chlorine and the halogenated organics of bromine oxidation are more toxic than their chlorinated halogen counterparts. Of course, if one refrains from drinking brominated pool water, then the hazard is minimal since skin absorption is quite low. As well, bromine requires an additional oxidizer such as chlorine, MPS or an SWG in order to convert the bromide into bromine.
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Where are you quoting those standards from? Please provide a link. They sound like European pool water standards which, like US EPA standards, only apply to commercial/public pools.
Bromine sanitation requires higher concentrations of bromine relative to chlorine in absolute terms but I'm not entirely sure how the total bromine concentration relates to the formation of hypobromous acid which is the active bromine sanitizer. Getting to the appropriate level (disinfection limit) of hypobromous acid might require higher concentrations of bromine as compared to chlorine/hypochlorous acid equilibrium. Bromine is not widely used in residential pools in the US because it is more expensive than chlorine and the halogenated organics of bromine oxidation are more toxic than their chlorinated halogen counterparts. Of course, if one refrains from drinking brominated pool water, then the hazard is minimal since skin absorption is quite low. As well, bromine requires an additional oxidizer such as chlorine, MPS or an SWG in order to convert the bromide into bromine.
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From the Chlorine-CYA chart one can see that 0.11 FC with 0 CYA has the same effect like 1.2 Chlorine with 10ppm CYA and like 2.4 ppm Chlorine with 20 ppm CYA, etc. It can be concluded that if one has 20ppm CYA only 0.11ppm is actually active chlorine and the rest is bound to CYA making just a reserve. It is also stated that at low CYA levels, it is recommended to have 2ppm chlorine just to have a reserve. The german norm is 0.3ppm chlorine (0.2 if ozone is used). So, for a residential pool 2ppm bromine is an overkill since even in case some bromine is used, the resulting bromamines are still efficient sanitizers while the chloramines are not. It seems to me that 0.5ppm bromine should the targeted level.
- May 23, 2015
- 24,405
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Agreed
Yes, most of the chlorine is bound to the CYA. BUT, as soon as the free available active chlorine (hypochlorous acid) reacts with and kills a pathogen or oxidizes an organic, the chlorine bound to the CYA is released. The reaction rates for chlorine-CYA equilibrium are very fast, less then 1/4 of second. So even though the chlorine is "bound" to the CYA, it is still very much available for disinfection and oxidation.
This is necessary because, as I stated previously, it is next to impossible to maintain low levels of FC evenly throughout the water volume of a residential pool. There are physical flow rate and mixing limitations that make it impossible to completely homogenize a pool water volume. Therefore, if the residual sanitizer levels are low, "dead" spots with little to no chlorine can form and allow for pathogen growth.
This is because the German standard does not allow for the use of CYA in commercial/public swimming pools. As well, filtration and delivery systems are optimized for precise, rapid mixing and homogenization of the pool water volume with multiple stages of carbon filtration, coagulants, secondary sanitizer sources (UV/Ozone system), etc being deployed and used. Finally, chlorine is mixed into the water flow just prior to return of the water to the pool.
This level of filtration and sanitation would be impossible and/or prohibitively costly to replicate in a residential pool.
In residential pools, bromine, with no buffering, will exists mostly as hyprobromous acid at a pH of 7.5 (94% HOBr / 6% OBr-). One would have to add enough sodium bromide to create a "bromide bank" (~30-50ppm bromide) and then tailor oxidation additions (chlorine, MPS or ozone) to create the necessary amount of bromine. Also, one would likely use some DBDMH (1,3-Dibromo-5,5-dimethylhydantoin) as a source of bromine and dimethylhydantoin (DMH) as the DMH plays a similar buffering role for Br as CYA does for Cl. However, while CYA is very good at buffering Cl and modulating it's strength, DMH is a less effective buffer for Br. Another problem is, DMH has no UV shielding effect like CYA does for chlorine. Therefore, bromine in an outdoor swimming pool will not be as effectively stabilized as chlorine is.
I don't have good data on this, but I am willing to bet the bromine loss rate in an outdoor pool is harder to control than the chlorine loss rate. It's hard to make a complete comparison because one almost always uses CYA with chlorine in an outdoor pool and it is not clear how much DMH is needed to achieve a similar result in an outdoor bromine pool or even if a similar effect can be achieved given that DMH has no UV protective quality.
So with that said, one probably needs to maintain the higher residual Br level of 2ppm (with DMH buffering) simply to ensure that there is sufficient sanitizer (HOBr) in the water. This article by Wojtowicz has a review of standard pool sanitation methods including bromine.
While this true that brominated THM's have, for some pathogens, faster kill rates (CT inactivation, compare Table 11.21 on pg. 521 with Table 11.24 on pg. 523 in this link) than their chlorinated counterparts, brominated THMs are much more toxic as well as carcinogenic and mutagenic than chlorinated THM's. The brominated THM's also tend to remain in pool water longer as chlorinated THM's are more volatile.
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Also note that dmh will reduce the level of hypobromous acid in a similar way to how cya affects fc. Therefore, a higher level is needed to compensate.
- May 23, 2015
- 24,405
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
I tried scouring TFP for information but have not looked at the JSPSI papers yet. Is there a source of info for how DMH buffers bromine similar to the Cl-CYA relationship? I'm curious now about advance bromine chemistry.
Thanks.
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There's not a lot of good information about the br/dmh chemistry. How much it affects the effects of UV and sanitation I don't know.
Mostly, it seems to be anecdotal evidence. There are limits in some jurisdictions for dmh.
In any case, I would try to limit the levels of dmh and to proportionally increase the br as the dmh increases.
Mostly, it seems to be anecdotal evidence. There are limits in some jurisdictions for dmh.
In any case, I would try to limit the levels of dmh and to proportionally increase the br as the dmh increases.
Ignoring DMH for a moment, with bromine not moderated in its strength, one can't readily maintain a very low bromine amount in a pool or spa (i.e. one doesn't have CYA which is a hypochlorous acid buffer for chlorine). It's hard to test that low and hard to maintain through the volume of water. Also, bromine isn't as strong an oxidizer nor disinfectant as chlorine so somewhat higher levels are needed, but I agree that the more typical 2-4 ppm recommendation might be too high in terms of consistency, but then again if we're talking maintaining between soaks it's hard to maintain low levels. If one can do it, they are free to do so -- I just think it will be difficult for the same reason that trying to maintain 0.5 ppm FC or lower is difficult (in U.S. style pools with typically inconsistent non-idea circulation and not-very-responsive dosing systems).
As for DMH, we don't have a paper like the O'Brien paper for CYA that is very definitive. DMH levels should probably be limited and one source says that above 200 ppm is a problem but we don't really know.
As for combined bromines, it is ONLY monobromamine that is still a disinfectant probably due to formation of monobromammonium ion that produces ammonia and a positive bromine reactive atom (see this post). So I wouldn't count on this reliably and the total bromine test will include brominated organics as well. Because bromine isn't as strong an oxidizer, it may not substitute as readily on organics, so this might not be as much of a problem as I described, but we don't really know -- there isn't as much info on bromine as on chlorine at least in terms of its reactivity with organics.
Finally, given that the brominated organics are worse disinfection by-products than the chlorinated organics, some day I think bromine will be eliminated just as iodine was. Once there are enough automation devices for chlorine (for maintaining chlorine between soaks), particularly for spas where bromine is more common, then there will be less need for bromine.
As for DMH, we don't have a paper like the O'Brien paper for CYA that is very definitive. DMH levels should probably be limited and one source says that above 200 ppm is a problem but we don't really know.
As for combined bromines, it is ONLY monobromamine that is still a disinfectant probably due to formation of monobromammonium ion that produces ammonia and a positive bromine reactive atom (see this post). So I wouldn't count on this reliably and the total bromine test will include brominated organics as well. Because bromine isn't as strong an oxidizer, it may not substitute as readily on organics, so this might not be as much of a problem as I described, but we don't really know -- there isn't as much info on bromine as on chlorine at least in terms of its reactivity with organics.
Finally, given that the brominated organics are worse disinfection by-products than the chlorinated organics, some day I think bromine will be eliminated just as iodine was. Once there are enough automation devices for chlorine (for maintaining chlorine between soaks), particularly for spas where bromine is more common, then there will be less need for bromine.
