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Thread: chloramine question

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    chloramine question

    My municipal water uses chloramines due to their longer action to sanitize our water supply. If I test my tap water I usually get 1.5 CC.

    As I understand it these are formed by combining chlorine with ammonia. Assuming I fill my pool with this water and immediately shock it (so I know all measured CC is from the fill water and not organics) with the end result being only a FC reading with no CC, where does the ammonia go?

    Thanks

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    Re: chloramine question

    Into the air.
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    Re: chloramine question

    And then where does it go?

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    Re: chloramine question

    England?
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    Re: chloramine question


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    Re: chloramine question

    Chlorine quickly combines with ammonia to form monochloramine which registers as Combined Chlorine (CC). If additional chlorine is added, then the monochloramine is more slowly (over hours, with CYA in the water) oxidized and becomes nitrogen gas and goes into the air (then straight to England!).
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    Re: chloramine question

    Yes it's the Nitrous oxide you send us that gives us our sense of humour

    http://www.texasep.org/html/air/air_2std_nox.html

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    Re: chloramine question

    Quote Originally Posted by chem geek
    Chlorine quickly combines with ammonia to form monochloramine which registers as Combined Chlorine (CC). If additional chlorine is added, then the monochloramine is more slowly (over hours, with CYA in the water) oxidized and becomes nitrogen gas and goes into the air (then straight to England!).
    This may have been addressed before but how much FC does it take to covert 1 ppm of CC (monochloramine) to 0 ppm? And what is the absolute chlorine level required to do so (i.e. breakpoint)? 10:1 seems to be a common recommendation for the breakpoint but I haven't seen any data on the amount of chlorine actually used during the conversion.
    Mark
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    Re: chloramine question

    The 10:1 rule is wrong for two reasons. First off, it is a rough rule of how much chlorine (in ppm Cl2) it takes to oxidize ammonia (in ppm N) and not monochloramine. Second, is that the units for Combined Chlorine (CC), which is monochloramine for this discussion, is the same as for Free Chlorine, namely ppm Cl2. There is a conversion factor between ammonia and chlorine units of 5 that does not apply when looking at monochloramine. Technically from the chemistry it only takes half the CC as FC to get rid of it, but due to some side reactions it in practice takes a little more, perhaps 60-70% of the CC level.

    Of course, this is the amount that actually gets used up, but using a higher level makes the reaction go faster and forces it closer to completion. If you use just the minimum amount, it will take longer and will slow down as the chlorine and monochloramine levels drop.

    Most of sweat and urine (after water) is urea. No one knows the actual mechanism of oxidation of urea but one proposal that appears to be consistent with observation is that chlorine combines with urea to form various combined compounds and eventually a quadchlorourea is formed where additional chlorine produces dichloramine and nitrogen trichloride that then go through normal breakpoint to nitrogen gas. If the combined chlorine (CC) measurement is mostly of monochlorourea, then it takes between 2-3x times the CC level as FC to oxidize this.
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    Re: chloramine question

    A few follow ups:

    So is monochlorourea more/less common than monochlorime? I assume the first is created from urea?

    Also, when I look at a breakpoint graph such as this, it implies that the chloromines are increasing with increasing chlorine dose until the breakpoint at which point the chloromines are broken down. Is this because not all of the ammonia has been converted to chloromines so they keep increasing until the breakpoint?

    Also, this graph would imply that to reduce the chloromines from 3 ppm to 1 ppm would require about 2 ppm of additional chlorine which is pretty much what you had indicated. Am I reading this correctly?

    Thanks
    Mark
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    Re: chloramine question

    (Can't say I'm really following but it is interesting.)
    --paulr
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    Re: chloramine question

    Based on some MEMS measurements made by Dr. Ernest "Chip" Blatchley, it does look like most of what is measured as Combined Chlorine (CC) is organic chloramine, presumably monochlorourea (his lab experiments showing volatile disinfection by-products from chlorination of urea showed DPD CC measurement with virtually no MEMS measurement of volatile inorganic chloramine). And yes, this comes from urea. There are other components of sweat and urine, but urea is the largest by far, followed by ammonia (see Table 4.1 in this file).

    Yes, you read the graph correctly, which implies a roughly 1:1 requirement of the amount of FC to get rid of CC -- it's somewhat less than that, but order of magnitude correct. The breakpoint graph shows what happens when you add smaller amounts of chlorine to a large amount of ammonia, and adding more and more chlorine. That is, initially chlorine combines with ammonia to from monochloramine and this occurs very quickly. After all of the ammonia has been converted to monochloramine, then additional chlorine starts the breakpoint reaction, moving monochloramine to dichloramine and dichloramine to nitrogen trichloride and then these to nitrogen gas (this latter combination is fast so nitrogen trichloride remains low in concentration). Since multiple reactions can occur at once, it's not completely a step-by-step process as the steps overlap as concentrations of various species come and go, but generally speaking it's as I described. This post describes the core reactions of the breakpoint chlorination process.

    The above is not exactly what happens in a pool because the amount of chlorine is generally much higher than the amount of ammonia (i.e. you are adding ammonia to an excess of chlorine, not the other way around) so in practice one is oxidizing ammonia to nitrogen gas somewhat continuously. There is some buildup of monochloramine if the bather load is high enough since the latter steps take a few hours to mostly complete, but in most residential pools this isn't even noticeable. If one has a pool party, then one can usually detect some jump in CC and, of course, if anyone pees in the pool then that increases the chlorine demand considerably and would register a lot more CC for a while.

    Finally, the oxidation of urea is far slower, but it is very temperature dependent and it might be catalyzed by UV though this is pure speculation on my part. This would be consistent with why CCs are generally a lot higher in indoor pools than outdoor pools, though there are many different factors at play in addition to sunlight, such as air circulation and use of CYA.

    Richard
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    Re: chloramine question

    New word for today is "quadchlorourea"

    It starts with the letter "Q"

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    Re: chloramine question

    Quote Originally Posted by duraleigh
    England?
    hahahahaahaha
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    Re: chloramine question

    "Splash" That was the sound of this thread landing in The Deep End.
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