All other considerations aside...

Pound for pound, which is the more efficient oxidizer between chlorine and monopersulfate?

If you literally need a pound per pound reference, think 73% cal-hypo.

as an oxidizer it would be chlorine.
the redox potential of chlorine is 1.36 while the redox potential for all forms of oxygen, including ozone are 1.24 or less. The active oxidizer in KMPS is oxygen. The higher the number the more effective the oxidizer. Nothing to do with pound for pound at all. It's an absolute.

Nice!

Now throw some dichlor in my eyes and disappear in a mist!

Internet pool ninja masters =/.

It's just stuff I learned working in a pool store

In terms of quantity of oxidizer needed (as opposed to oxidation potential), 10 ppm FC in 10,000 gallons is the same as 207 fluid ounces of 6% bleach, 102 fluid ounces of 12.5% chlorinating liquid, 18 ounces weight of Cal-Hypo 73%, 15 ounces weight of Trichlor, 24 ounces weight of Dichlor, 67 ounces weight of MPS non-chlorine shock.

So when you factor in how MPS is already more expensive for the same weight and that it needs more weight than other solid forms of chlorine, it's quite expensive. It's a strong but kinetically selective oxidizer so will oxidize some things chlorine won't. It is effective at oxidizing reduced sulfur and nitrogen compounds along with epoxidation of olefins (that is, turning a double-bond between carbons into a single bond with an oxygen "bridge" between them).

As shown in this Technical Bulletin from Dupont on Oxone which is the MPS in virtually all products sold in the U.S., the standard electrode potential is +1.85V which is higher than the standard electrode potential for chlorine which is +1.611V (see here for example -- the 1.36V you quoted is for chlorine gas, not hypochlorous acid). However, as Dupont noted, the reactions are kinetically selective so just because something has a higher electrode potential doesn't mean the reaction will occur. After all, according to thermodynamics, many of the chemicals in our body should decompose from oxygen in the air or in our blood, but in practice this doesn't happen because it is so slow (due to the high activation energy hurdle). Enzymes or higher temperature (including fire) can overcome such limits.

Richard

chem geek, their is an article in pool and spa news about the use of non chlorine shock in indoor pools, it seemed to conclude that that was safer for air quality than break point chlorination. If you can find it let me know what you think. Im not sure when I saw it but it wasnt too long ago.

I imagine they had a CYA level of zero. The results might be different if the CYA level was 20.

Surely that's more like 206 ounces of 6%?
--paulr

That was a typo -- it should have been 207. Thanks for catching that and I've edited my post to correct it.

They generally have been comparing against indoor pools with no CYA so such pools are basically over-chlorinated by factors of 5-10 or more. This produces around that same factor increase in nitrogen trichloride. I've written more about this here.

Now it is true that if the MPS oxidizes ammonia and especially urea from bather waste before chlorine can get to it, then that would completely prevent the formation of chlormaines and other chlorinated disinfection by-products. It's not that it wouldn't be effective, but that it may not be the only way to minimize the DBPs.

Unfortunately, no experiment has been made in indoor pools to see if a small amount of CYA would help reduce nitrogen trichloride levels. This patent from BioLab (now Chemtura) describes in "EXAMPLE 4" how glycoluril (similar to CYA in being a chlorine buffer but binds even more strongly to chlorine) reduces the volatility of chlorine, inorganic chloramines, and inhibits (slows down) the formation of trihalomethanes (THMs) from humic acid.

Richard

So, in keeping with the MPS line of questioning, what would be the effect of a dosing of MPS to a pool which relied upon ORP sensing to maintain a chlorine-sanitized pool? Say hypothetically that someone was visiting a neighborhood pool, or maybe a hotel pool, and really didn't trust the sanitization there? Just curious, mind you...

MPS would affect the ORP readings and mess things up. It would raise the ORP but not really sanitize.

So it makes the controller 'see' a higher level of chlorine than is really present, and thus won't replenish the chlorine supply until the MPS is gone.
Continuing the vein, if MPS oxidizes the organics, less chlorine will get 'used' for oxidization, and should be available for sanitization.

No chance that those two assumptions cancel each other out, eh?

Nope, chlorine goes low for too long and bad things generally happen.

Bad things! (Maybe even finding Freddy, Jason, and Michael Meyers having a pool party in the pool!)




(sorry, couldn't resist!)

Hi. New here and wondering why they use monopersulfate instead of dipersulfate? Dipersulfate is sold as 99% sodium persulfate. Monopersulfate (Oxone) is only 43% and has got a lot of other salts in it like potassium sulfate, potassium bisulfate, and magnesium carbonate. Oxone costs more than dipersulfate too.

Sodium Peroxydisulfate (Na₂S₂O₈) is very irritating and even the small amount of it in Oxone is what causes most of the irritation (to skin and eyes) that people complain about. So it's not generally suitable for use as a shock where people can go in swimming in 30 minutes or so. It is a strong oxidizer and doesn't last long because of that (assuming there are things to oxidize). [EDIT] As shown in the Oxone MSDS, it has 3% potassium peroxydisulfate. [END-EDIT]

If one wanted to super-shock a pool and would not be using it for a day or two and could ensure getting rid of any remaining peroxydisulfate, then that could be a use. Generally speaking, chlorine alone works well as the primary oxidizer.

Thanks. Interesting answer.

Do the sulfates stay in the water until removed by waste/draining and backwashing?
Or do they combine with other stuff which can be filtered out?
Or do they eventually gas out?
Will they impart a "smell" -- like sulphur dioxide?

Since I have a fairly strong ozonator, will that oxidize the sulfates, making sulphur dioxide?

Yes, the sulfates stay in the water until physically removed by water dilution as you indicated. They do not evaporate or outgas (no ions do that and there is no neutral sulfate compound in pool water). They do not combine with other stuff except in a small amount they form calcium sulfate ion pairs so with high enough sulfates they can make the saturation index more negative (for example, 200 ppm sulfates lowers the saturation index by 0.1 units). They do not smell.

Sulfates are somewhat like chlorides in terms of being relatively innocuous, but like anything else, too high a concentration can lead to issues. The problem is that we don't know exactly what level of sulfates becomes serious. The general TFP rule is to not add anything to the water that you do not need and non-chlorine shock fits into that category -- plus it's pretty darn expensive.