Pb2Au said:
Wow. That is great. I am sure glad to know that chloroform, dibromochloroform, haloacetonitriles, cyanogen halides, halopicrins, haloacetic acids, chloral hydrates and haloacetones are all destroyed by additinal chlorine. Also the 186 nitrogenous componds that can combine with chlorine that are in sweat and urine.
Pb2Au,
Welcome to TFP!
That's not what Jason is saying. He is saying that the chlorinated organics (and volatile inorganic chloramines) that are not fully oxidized are a very small fraction of the total amount of chlorine that is consumed so is normally not even measurable in our test kits. It's not that they are all destroyed with additional chlorine but that the quantity created of these compounds is very small.
For example, in a pool where the FC is roughly 10% of the CYA level so the hypochlorous acid level is roughly 0.05 ppm, then for ammonia the oxidation is mostly complete with the amount of nitrogen trichloride being around 2 ppb (that's 0.002 ppm) that will eventually outgas since it is fairly volatile (it doesn't build up to a higher level because it reacts with dichloramine to produce nitrogen gas). There is more produced from urea, but even there it's still low at < 10 ppb (that's 0.01 ppm) and these amounts are low because the active chlorine level is low. As for the trihalomethanes, the largest amount is chloroform where the quantity varies but is usually in the range of 50-100 ppb (when fill water has around 30 ppb) as a steady-state in most pools but is produced at a low rate, mostly because the active chlorine level is so low.
The vast majority of chlorine loss in residential pools is from sunlight as is obvious by comparing the loss during the day (usually 1.5-2.5 ppm) vs. at night (usually < 1 ppm; often < 0.5 ppm) and also by comparing an uncovered pool vs. one with an opaque cover during the day. The next largest loss is from oxidation of organics where the largest component of sweat and urine (by far) is urea. Urea very slowly combines with chlorine to form N-chlorourea (probably mostly monochlorourea) and is mostly oxidized to nitrogen gas and carbon dioxide gas with the chlorine becoming chloride ion. Even Ernest "Chip" Blatchley's experiments (see
this paper) at very high chlorine and urea concentrations have most of the chlorine consumption result in chloride ion, though nitrogen trichloride gets up to 0.45 ppm in the more extreme experiments. However, the nitrogen trichloride level is proportional to the hypochlorous acid concentration which in our pools is about 1/70th the concentration used in some of his experiments at around 7 ppm FC with no CYA.
In residential pools with low bather load, there is probably more loss of chlorine from oxidation of organics that are not from bather load, such as from pollen, leaves, and pool surfaces and components themselves. There is also some outgassing of chlorine itself, though that is fairly minimal.
Again, it's not the number of different chlorinated organic compounds that matters, but their quantity. As described in
this WHO document, the proportion of nitrogenous compounds (those that would most likely react with chlorine) are the following concentrations and relative percentages:
......................................
Sweat ........................................
Urine
Compound ........
mg/L ..
% of total Nitrogen ......
mg/L ..
% of total Nitrogen
Urea ..................... 680 ............ 68 ..................... 10,240 .......... 84
Ammonia ............. 180 ............ 18 .......................... 560 ............ 5
Amino acids ........... 45 .............. 5 .......................... 280 ............ 2
Creatinine ................ 7 .............. 1 .......................... 640 ............ 5
Other compounds .. 80 .............. 8 .......................... 500 ............ 4
------------------------------------------------------------------
Total nitrogen ...... 992 ........... 100 .................... 12,220 ......... 100
The chlorine bound to organics would mostly register as Combined Chlorine (CC), but that is almost always <= 0.2 ppm in most outdoor residential pools and most of what does register as CC is likely to be monochlorourea since it is very slow to form (so urea builds up in pools) and slow to oxidize so builds up as an intermediate (and is not volatile). In outdoor pools, the UV from sunlight creates hydroxyl radicals from the breakdown of chlorine that likely help to more readily oxidize both urea and N-chlorourea intermediates as well as other organic compounds.
Pb2Au said:
The chloride loss can also come from HOCl combining with an organic contaminant or ammonia in the water. We call this combined chlorine but they can also be trihalomethanes (THMs), disinfection byproducts (DBPs) and others. Whenever HOCl combines with anything in the water, the chloride will not revert back.
I would qualify this to say that whenever HOCl combines with anything in the water AND that compound does not get further oxidized, then the chloride will not revert back. Chlorine combining with ammonia to form monochloramine is not permanently lost. More chlorine combines with monochloramine to form dichloramine and again to form nitrogen trichloride that then reacts with dichloramine and water to form nitrogen gas, hypochlorous acid, hydrogen ion and chloride ion (see
this post for more details). Urea is more complex, but also results in chloramines that go through a similar substitution followed by oxidation process.
The bottom line is that most chlorine reverts back to chloride. It is water dilution (splash-out, carry-out, backwashing, rain overflow) that is the primary source of chloride (salt) reduction. I can tell you from my own measurements in my pool over several seasons that the salt level rises over the summer swim season in accordance with the chlorine and acid additions with nothing lost beyond the small amount removed from dilution. I have a mostly opaque pool cover so increase from evaporation/refill is minimal and I have an oversized cartridge filter that is only cleaned once a year so there are no backwashing losses. The pool is used almost every day so there is some splash-out and carry-out, but that's about it for dilution until the winter when I use winter rains to dilute the water. Salt (chloride) measurements at the start and end of the summer season confirm that there is minimal chlorine/chloride loss from volatile compounds or permanently combined chlorine (even if not measured as CC in that test). In fact, one of the main reasons I use winter rains for water dilution is to keep the salt levels in check.
