Is oxidizing different than removing combined chlorine?

[Cheetiah]

I thought I had a good handle on spa water chemistry until I read this article about MPS from the Medina County Health Department:

http://www.medinahealth.org/images/...ecc84e8f1117/PotassiumMonopersulfate_b0b9.PDF

In particular, this quote has me very confused, "This product is used to eliminate organic contamination. It will NOT remove combined chlorine (CC). Therefore, it is not equivalent to 'Superchlroination'... MPS is mainly used to oxidize organic matter which increases sanitizer efficiency by 'freeing up' more product to be used for disinfection."

I thought "oxidizing organic matter" resulting in "freeing up more product" IS the process of removing combined chlorine from the water. Every other description of MPS I've read seems to indicate that it replaces the use of chlorine as an oxidizer, hence the term "non-chlorine shock", which indicates that its purpose is to oxidize chloramines resulting in reduced combined chlorine. Am I missing something or is this article way off the mark when it claims that MPS "will NOT remove combined chlorine?"

 

[JasonLion]

Welcome to TFP!

There are lots of different things that need oxidizing. Different oxidizers work on these various chemicals at various rates. MPS does oxidize combined chlorines, just not all that quickly. However, MPS oxidizes some other things rather quickly that would otherwise react to chlorine to form combined chlorine. So when used with chlorine it usually has the net effect of lowering the combined chlorine level.

To put that another way, "shocking" with MPS has a similar, but not exactly the same, effect as "shocking" with chlorine. They each react most quickly with different things, so the effects won't be exactly the same.

The document you link to is cautioning people about a specific, and common, problem: high CC levels in indoor pools. Using MPS in those pools can significantly reduce the rate at which CC accumulates, but it is not especially effective at lowering CC that already exists. Since CC levels are often regulated, and commercial pools can be shut down if the CC level gets too high, knowing that MPS isn't at all good at lowering CC that already exists becomes a fairly important thing to know.

 

[woodyp]

Welcome to the forum. Excellent first question post btw!

 

[chem geek]

While people used to think that MPS non-chlorine shock oxidized ammonia and inorganic chloramines, it turns out that it effectively doesn't since it is so slow in doing so that any inorganic chloramines would get oxidized by chlorine first. As Jason noted, MPS does oxidize some chemicals (though not ammonia) before chlorine has a chance to form combined chlorine and it may oxidize some organic chloramines. In general, it is not a replacement for chlorine. At best, it is a supplement most suited to indoor pools though using a UV (or ozone) system in such a situation might be a better choice.

In chemistry, one usually can't use generalizations in talking about chemical reactions, especially those involving chlorine. It's quite complex chemistry where different reactions occur at different rates or not at all.

 

[Cheetiah]

Thank you all. This was very helpful.

 

[chem geek]

I should add that for spas only, due to their hot temperatures, MPS non-chlorine shock may be used in conjunction with silver ions such as in the Nature² system and that this is an EPA-approved disinfectant. One usually still needs to use chlorine once a week or two to keep the water clear.