Article: Is Superchlorinating The Best Way?
- Thread starter CaOCl2
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An interesting article where they STILL do not acknowledge that the 10x rule is wrong even for inorganic chloramines if the 10x is against CC as opposed to ammonia concentration. There main focus in the article is on organic chloramines though interestingly they talk about creatinine and not urea even though urea is by far the largest nitrogenous component in sweat and urine and builds up the most in pool water as it is slow to oxidize from chlorine (in indoor pools where there is no UV in sunlight; it seems to be oxidized more in outdoor pools). They do seem to acknowledge the higher nitrogen trichloride when using higher chlorine levels.
So this is an improvement over what has been said before, but I really wish someone would just come clean with the fact that CC is measured in ppm Cl2 units and not ppm N units so that the 10x rule for inorganic chloramines was simply wrong. Also, the breakpoint curve is misleading since pool water already has chlorine in it and nitrogenous compounds are introduced into it -- not the other way around which is what the breakpoint curve shows.
So this is an improvement over what has been said before, but I really wish someone would just come clean with the fact that CC is measured in ppm Cl2 units and not ppm N units so that the 10x rule for inorganic chloramines was simply wrong. Also, the breakpoint curve is misleading since pool water already has chlorine in it and nitrogenous compounds are introduced into it -- not the other way around which is what the breakpoint curve shows.
Interesting. They point out a problem, but they don't have any solution for it. It seems to me that they are being alarmist to no purpose.
Keep in mind that most of what they say only applies to indoor public pools. The volatile chlorination byproducts are essentially a non-issue in outdoor residential pools as they start at far lower levels to begin with and then blow away very quickly.
Keep in mind that most of what they say only applies to indoor public pools. The volatile chlorination byproducts are essentially a non-issue in outdoor residential pools as they start at far lower levels to begin with and then blow away very quickly.
Any opinions on the DuPont Non-Chlorine Shock Oxidizer that is vaguely mentioned in the article?
Quick Google and I found the MSDS for Oxone, which is what DuPont calls it..I hope it's OK to post the link...?
http://www.carricoaquatics.com/uploads/ ... ulfate.pdf
Quick Google and I found the MSDS for Oxone, which is what DuPont calls it..I hope it's OK to post the link...?
http://www.carricoaquatics.com/uploads/ ... ulfate.pdf
I responded to that article since they are still missing some critical points. Yes it is true that in high bather load pools, especially indoors, there can be a buildup of Combined Chlorine (CC) that will not get oxidized readily by superchlorination. However, that isn't necessarily a real problem. The current commercial/public pool standards of <= 0.2 ppm CC are based on the presumption that higher CC levels mean more volatile and irritating disinfection by-products such as nitrogen trichloride or more volatile and carcinogenic disinfection by-products such as chloroform (and other trihalomethanes). However, that assumption is not correct, at least for nitrogen trichloride, since one can measure higher CC and yet have lower nitrogen trichloride because the active chlorine level is lower. The tradeoff is that other intermediates such as monochloramine, dichloroamine and chlorourea will be higher, but these are less problematic (i.e. less volatile, higher odor thresholds, not carcinogenic, etc.).
As for reduction of disinfection by-products, there are ways of reducing them and their precursors without having to resort only to water dilution. One can use supplemental oxidation IF such oxidizers actually break down the precursors and don't create worse by-products in doing so -- sunlight seems to work well for outdoor pools since it creates hydroxyl free radicals when it breaks down chlorine and these are very powerful oxidizers. One can also use coagulation/filtration techniques though that only works well with certain types of chemical compounds. The German DIN 19643 standard has a heavy emphasis on coagulation/filtration.
The Dupont Oxone product, which is the non-chlorine shock product we call MPS (short for potassium monopersulfate), is a selective oxidizer similar to chlorine but selective in different ways. It is good at oxidizing ammonia and can do so before chlorine so can avoid the inorganic chloramines. It has some oxidation ability against monochloramine, though not as much. It apparently is not much of an oxidizer for urea which is unfortunate though Dupont didn't look at actual pool water so it might have some reactivity via catalytic pathways (i.e. in the presence of metals). MPS does react with amino acids and other compounds. The good news is that it does seem to react to many compounds that chlorine reacts with, but does so more quickly so it can prevent at least some of the disinfection by-products, but mostly as a preventative being present in the water along with chlorine. To use it after the fact when DBPs are already present is not as effective.
Oh, and by the way, when we shock the pool on this forum when there is CC, we have CYA in the water where the shock level of an FC that is 40% of the CYA level is equivalent to 0.6 ppm FC with no CYA. So it isn't going to be producing as many disinfection by-products as quickly as most indoor pools that have a higher FC and no CYA. Our shocking usually doesn't result in CC persisting, but that's largely because the pools are outdoors so the sunlight helps in producing hydroxyl free radicals. In fact, the shocking raises the pH and it is hypochlorite ion that is more sensitive to chlorine breakdown and that level goes way up sort of like super-charging oxidation. So while we wouldn't want the pH to get excessively high for killing algae or for creating scale, the higher pH is good for oxidation if the pool is exposed to sunlight.
As for reduction of disinfection by-products, there are ways of reducing them and their precursors without having to resort only to water dilution. One can use supplemental oxidation IF such oxidizers actually break down the precursors and don't create worse by-products in doing so -- sunlight seems to work well for outdoor pools since it creates hydroxyl free radicals when it breaks down chlorine and these are very powerful oxidizers. One can also use coagulation/filtration techniques though that only works well with certain types of chemical compounds. The German DIN 19643 standard has a heavy emphasis on coagulation/filtration.
The Dupont Oxone product, which is the non-chlorine shock product we call MPS (short for potassium monopersulfate), is a selective oxidizer similar to chlorine but selective in different ways. It is good at oxidizing ammonia and can do so before chlorine so can avoid the inorganic chloramines. It has some oxidation ability against monochloramine, though not as much. It apparently is not much of an oxidizer for urea which is unfortunate though Dupont didn't look at actual pool water so it might have some reactivity via catalytic pathways (i.e. in the presence of metals). MPS does react with amino acids and other compounds. The good news is that it does seem to react to many compounds that chlorine reacts with, but does so more quickly so it can prevent at least some of the disinfection by-products, but mostly as a preventative being present in the water along with chlorine. To use it after the fact when DBPs are already present is not as effective.
Oh, and by the way, when we shock the pool on this forum when there is CC, we have CYA in the water where the shock level of an FC that is 40% of the CYA level is equivalent to 0.6 ppm FC with no CYA. So it isn't going to be producing as many disinfection by-products as quickly as most indoor pools that have a higher FC and no CYA. Our shocking usually doesn't result in CC persisting, but that's largely because the pools are outdoors so the sunlight helps in producing hydroxyl free radicals. In fact, the shocking raises the pH and it is hypochlorite ion that is more sensitive to chlorine breakdown and that level goes way up sort of like super-charging oxidation. So while we wouldn't want the pH to get excessively high for killing algae or for creating scale, the higher pH is good for oxidation if the pool is exposed to sunlight.
If you have high ammonia could you use MPS to knock it out first rather than the high CL process you described in a different post?
Yes you could, but it would be at least twice as expensive to do so. The only advantage would be in not producing the disinfection by-products so perhaps for an indoor pool this would be reasonable to do, but for an outdoor pool it's not really necessary. When I used chlorine in my own pool to get rid of a lot of ammonia and partially oxidized CYA, it never even really smelled like a poorly managed indoor pool and had no eye irritation or other effects though it definitely smelled. I just didn't hang around it for very long and didn't need to. Just went out, tested, added chlorine, went back inside, etc. When the process was complete, there were no measurable disinfection by-products remaining. Monochloramine and dichloramine get fully oxidized while the nitrogen trichloride is fairly volatile. I'm sure there were nitrates leftover, but they are similar to phosphates and not a problem (they are nutrients for algae, but chlorine controls algae).
Ahh that's some expensive (relatively speaking) stuff then eh?
Will nitrates get oxidized over time due to UV or CL or do they just hang around indefinitely like phosphates?
Will nitrates get oxidized over time due to UV or CL or do they just hang around indefinitely like phosphates?
Nitrates are the endpoint chemical. They do not get oxidized further. Yes, they just hang around like phosphates. Nitrates are like phosphates in that they are an essential nutrient for algae (and bacteria) growth, but some bacteria can use nitrogen gas instead (nitrogen-fixing bacteria). Chlorine can kill both bacteria and algae regardless of nitrate and phosphate levels since their growth is ultimately limited by temperature and, for algae, by sunlight.
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