How much CC will a typical MPS dosage (1lb/10,000 gal) treat?

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1 pound per 10,000 gallon of typical non-chlorine shock that is 43% potassium monopersulfate (MPS) is equivalent in oxidizing power to 2.4 ppm Free Chlorine (FC) so figure it would treat roughly that amount of CC -- that is, in the 2-3 ppm range. This assumes that there aren't other organics in the pool to oxidize besides the CC. If there are other substances to oxidize and if they react more quickly with MPS, then it can take more MPS to get rid of the CC. Depending on the nature of the CC, even MPS may not get rid of it.

Forget the 10x rule you've been taught since that only applies to the amount of chlorine needed to oxidize ammonia measured in its own ppm units (ppm Nitrogen). Combined Chlorine (CC) is measured in the same units as Free Chlorine (FC), namely ppm Cl₂ so there is no factor of 5 difference in units of measurement. Also, CC already has one chlorine attached to it (if it's monochloramine) so is already on its way to getting oxidized. Technically, it only requires half the CC as FC, but adding somewhat more to get over the hump for reactions and to have excess due to side reactions makes the practical rule simply 1x.

I know that it is an oxidizer but can you speak to it's ability to sanitize as well?

At pool temperatures, MPS is not a sanitizer -- it's kill times are too slow. It is only EPA-approved as a sanitizer when used with silver ions in hot (104ºF) spas as with that Nature² with MPS system used in residential spas.

["Depending on the nature of the CC, even MPS may not get rid of it."]

Could you explain this a little further.

I am also curious about Medium pressure UV and chloramines.
What exactly are the by-products?

It was long thought that MPS oxidized ammonia before chlorine had a chance to form disinfection by-products or that it would oxidize monochloramine if formed, but then I read this paper that showed that this was not the case for ammonia (see Figures 1 and 2). I wrote to Dupont about this and they confirmed it though noted that there might be catalytic effects in real pool water (since that can contain metal ions). The paper is about activated MPS where it is activated either by cobalt metal ions or by UV. Nevertheless, the paper showed that ammonium ion was not oxidized even by activated MPS in the presence of carbonate buffers -- something that is always found in pools (that's mostly what is measured in TA). Similarly, Figure 4 in the paper showed that MPS alone (i.e. not activated) was very slow to oxidize creatinine. L-arginine, on the other hand, does appear to be oxidized by MPS if one extrapolates what is seen in Figure 5.

Combined Chlorine (CC) is seen from the chlorinated versions of the compounds just mentioned such as monochloramine, chlorocreatinine, chloroarginine. Figure 9 shows that even activated MPS without UV does not oxidize chlorinated creatinine very much though Figure 10 implies at least chlorine consumption with activated MPS in this situation (but that is from chlorine getting used up reacting with sulfate radicals).

In my discussions with Dupont, MPS shows good reactivity with some components of bather load such as amino acids and uric acid, but does not appear to react with urea (again, without metal catalysts). So what is the bottom line with this? It means that MPS is not a panacea for handling the waste from bather load. It oxidizes some chemicals, but not all. It may control some CC, but not all. This may be why indoor pools (or any pools not exposed to sunlight) often use UV to help control chloramines, though I do remember from an NEHA convention a couple of years ago that MPS alone (i.e. without UV) was used effectively in some pools. In theory, the combination of UV and MPS should do a reasonable job.

Outdoor pools, or any exposed to the UV of sunlight, tend to have fewer disinfection by-products for the same bather load. This is probably not only because of the better air circulation to remove volatile compounds, but also the UV breakdown of chlorine produces hydroxyl free radicals that are powerful oxidizers. It also produces chlorine free radicals that might increase some disinfection by-products such as chloroform. Nevertheless, even outdoor high bather-load pools can still use supplemental oxidation (MPS, ozone, UV) as well as coagulation/microflocculation/filtration. As for medium/high-pressure UV, it is shown to significantly reduce some disinfection by-products such as chloramines, but may increase others such as trihalomethanes including chloroform. In terms of CC, it almost always shows a reduction of CC so UV may also help in reducing either urea or chlorourea though that is speculative and the mechanism isn't clear (though might be similar to the hydroxyl free radical production from sunlight breakdown of chlorine).

As for the exact by-products of UV against chloramines and other compounds, only some of this is known. As described in this paper, the final products for UV breakdown of chloramines have been measured to be nitrite, nitrate, nitrous oxide and ammonium. Because the water is chlorinated, the nitrite will be oxidized to nitrate and the ammonium will form more monochloramine (to be recirculated again) so the real end products are nitrate and nitrous oxide. This report implies that cyanogen chloride (which is generally more toxic than THMs) may be produced from medium-pressure UV.