SWG vs Ozonator vs UV?

[chem geek]

Yea, I understand what you are suggestion - that you can achieve a lower overall FC # with an accordingly lower CYA level. But this doesn't speak to maintaining that FC ratio, which would seem to become correspondingly more expensive the more chlorine is consumed by sanitation/oxidation (and via UV-A, or sunlight).

It's not the FC number that is relevant. Only a very, very small amount of the FC is in the active form of hypochlorous acid (when CYA is present). Roughly speaking, it's about half of the FC/CYA ratio (the other half is hypochlorite ion and the rest, 1-FC/CYA, is chlorine bound to CYA). We have found that a higher CYA level, even with a correspondingly higher FC to keep the FC/CYA ratio constant, results in a lower chlorine loss. This is why we recommend 80 ppm CYA for SWG pools (with an FC of 4 ppm). This usually results in a lower chlorine loss per day.

The lower chlorine loss means less atomic chlorine and hydroxyl radical formation when the chlorine is split by sunlight (and actually it is hypochlorite ion that is more likely to get split into O^-• and Cl•). There are a variety of possible reactions, especially if there is a lot of organic material in the water, but mostly it is plain chloride salt (ion) and oxygen gas that is produced.

 

[chem geek]

UV does reduce chlorine demand, and so does Ozone, because it kills some things while the water passes through it, so less work for chlorine.

Sorry to respond to this so late, but wanted to clarify that the above statement is generally only true when the bather load is high so that there is a lot to oxidize. So in a residential spa that is used every day, ozone can be helpful in reducing chlorine demand. However, in a residential pool where the bather load is typically quite low or in a spa that is only used infrequently, UV and ozone deplete chlorine faster (UV breaks it down ultimately to oxygen gas and chloride ion while ozone oxidizes chlorine to chlorate). We've seen this effect quite clearly on another forum (mostly for spas) where ozone was either helpful or hurtful with respect to chlorine demand based on bather load.

 

[jdskycaster]

chem geek,
I have this problem constantly with my spa. For a few reasons we rarely used our spa this past winter. It was a constant battle to keep a chlorine residual in the tub with no bather load and the ozonator running on regular intervals.

JD

 

[teapot]

Dirk, just read your post, Are the UV companies telling you about the Cyanagen gas reports from chlorinated pools??
http://www.drydenaqua.com/afm/appli...d crypto/uvc_irradiation_and_cryptosporid.htm

There is conflicting information out there. This EPA report would indicate that UV did not create nor change the rate of formation of DPBs. Note that this report is with regard to disinfecting drinking water.

I totally agree Richard, there is conflicting information, thanks for the EPA info. It is the need to clarify this information with specific regard to chlorinated pools. I really like the UV features for disinfection of working surfaces tools and equipment and on that it is obvious, with regard to Dirk's studies, he is just as excited as I was many years ago when studying the subject but as both you and Jason (and hopefully me too) have spelled out it is not needed on a domestic low batherload setup.

http://www.drydenaqua.com/afm/appli...reports/uvc_and_thms/UV and THMs in pools.pdf
More reading Richard, it's not all in Danish don't worry!

If you look at my pool (excuse going slightly off topic) I have experimented with the Cu/Ag and monopersulphate and found with a low batherload and low phosphates with regular microbiological tests to backup the safety that really is all you need to have a healthy swim and that is over more than 5 years of testing. That said to add 0.5ppm chlorine to keep everyone safe is a common sense thing to do in that situation and that is the minimum I will be doing this year. Would I try that on a commercial pool? No Way! No Way!

 

[henry89056]

All - thanks again for the insights. Just to be clear, I always assumed using a residual sanitizer - that was never really the question. The claims I was trying to verify were oriented on whether using UV (and I think we can safely place Ozone into this category) are effective at reducing total chlorine required (either FC and/or chlorine "utilization rate") for general upkeep of a pool.

Effectiveness of a given inline system (or potential future ones) is probably a more complex question than a simple 'yes' or 'no'. I think they could be more/less beneficial depending on a number of variables difficult to factor-in casually. I think there is a reason these systems have garnered widespread adoption at the municipal level, but it is probably safe to say they are always used in conjunction with other sanitizing agents.

I do think chlorine-resistant viral strains have gotten a fair amount of attention in the media (outbreaks of crypto in chlorine treated water) and have influenced decisions to "bolt on" these kinds of solution to facilities performing large-scale water treatment (this would include municipal pools). It would be great to see actual 'controlled' in-context test results to verify/deny the claims of such solutions rather than conjecture (by either proponents or dissenters). We have this kind of data for chemical sanitation - why not for other forms?

Possibly it is because alternatives are less effective than they claim. Possibly because they believe other accepted industry use(s) are sufficient to lay claim to their veracity.

In any case, I'll keep reading and working through the decision process. Ultimately, we will employ some form of chlorine in our pool (whether 'free form', inline or SWG generated). Only need to decide whether 'bolting on' anything else is worthwhile based on the limited data available and the kind opinions presented here.

Will post again when I get more info.

 

[JasonLion]

I think there is a reason these systems have garnered widespread adoption at the municipal level

Yes, it has already been mentioned several times that commercial/municipal pools are very different than residential pools. In a pool with dozens of people, or more, swimming every day, the organic oxidization load is far far higher than it is in a residential pool. In that situation, having a UV or ozone system can be a huge help. There are related, though slightly different, issues for indoor pools which also offer some uses for UV systems.

 

[chem geek]

I do think chlorine-resistant viral strains have gotten a fair amount of attention in the media (outbreaks of crypto in chlorine treated water) and have influenced decisions to "bolt on" these kinds of solution to facilities performing large-scale water treatment (this would include municipal pools).

Just so you know, Cryptosporidium parvum is a protozoan oocyst, not a virus and it isn't a chlorine-resistant "strain". As an oocyst, it has a very chemically-resistant thick outer shell that is very chlorine resistant. This isn't something developed by evolution specifically for chlorine -- this isn't like bacteria becoming resistant to antibiotics. The oocyst probably developed through evolution a very long time ago (long before chlorine use by humans) to survive all kinds of harsh environmental influences so that such oocysts which passed out through diarrhea could survive until ingested by another host where the oocyst releases its contents in the intestine.

You are right that one of the main reasons for the increase in UV use in commercial/public pools is to deal with Crypto since high levels of UV can inactivate it. In addition, better coagulation and filtration are used to remove the oocysts.

I think you need to take a step back and simplify the analysis. If your primary concern is to lower chlorine consumption/usage, then neither UV nor ozone is going to do that in a residential pool because the bather load is simply too low and the UV and ozone will end up consuming more chlorine. They only save on chlorine use (especially with ozone) under high bather load situations. If you want to minimize chlorine consumption/usage, then use a high CYA level to protect chlorine from sunlight and use a mostly opaque pool cover. If you also want to use a lower FC level, then you will need to have a supplemental algaecide at extra cost (or risk of staining) such as weekly PolyQuat 60 or use of copper ions (being careful to monitor concentration and pH to avoid staining) or possibly phosphate removers or even borates. Remember that the chlorine consumption from bather load in a residential pool will be a very minor component.

 

[chem geek]

http://www.drydenaqua.com/afm/appli...reports/uvc_and_thms/UV and THMs in pools.pdf
More reading Richard, it's not all in Danish don't worry!

This report isn't about disinfection by-products (DBPs) from UV specifically, but rather from chlorination. Cyanogen chloride is one of the DBPs also seen this recent paper so that's not a surprise.

I couldn't tell from the Danish paper if the pools were mostly indoor or outdoor -- can you tell me that? Also, the two pools studied would seem to be commercial/public pools due to the high bather load. Can you tell me whether these pools were using any Cyanuric Acid? Were they using German DIN 19643 where the water is filtered through activated carbon thereby removing some DBPs (though producing more chloroform, apparently) and stripping all chloramines and chlorine where chlorine is then reinjected at the end of the filtration process? Were both pools using UV?

The main relevant conclusion that is consistent with virtually every paper I've seen is that the quantity of DBPs is directly related to bather load (total organic content -- TOC) and in the Danish paper the variation in DBP is even seen in a diurnal variation associated with a lag to bather load. Residential pools are at FAR lower risk due to the lower bather loads and possibly also due to the very low active chlorine (hypochlorous acid) concentration when CYA is being used.

 

[henry89056]

chem geek - yes, sorry, was over-simplifying the viral comments (I was not inferring cyrpto is some form of evolutionary adaptation ... though that aside, I don't see why this is necessarily that far fetched).

The other line of thinking is interesting and speaks more to what I'm after. Are there any data to suggest % FC utilization by oxidation vs. UV-A over time. Even rough est. would be nice to have.

 

[chem geek]

Are there any data to suggest % FC utilization by oxidation vs. UV-A over time. Even rough est. would be nice to have.

Unfortunately, I haven't seen any specific data regarding how much chlorine is consumed by the UV sanitation systems. I do have spectral models for sunlight, water absorption, and chlorine (both hypochlorous acid and hypochlorite ion) that show the predicted half-life of chlorine breakdown from the UV in sunlight, but I don't have any of that for actual UV sanitation systems themselves, nor the complication of how much time is spent in the tube or other factors.

Presumably, the UV sanitation systems would have a time-power product that was greater than that of sunlight in an outdoor pool, but the spectrum is different so I can't directly compare. I believe that a pool with CYA will have a lower chlorine loss in the UV sanitation systems for the same reason there is lower loss from the UV in sunlight. My rough completely off-the-cuff guess is that UV sanitation might, at most, double the loss rate compared to sunlight alone. So at a high CYA of around 80 ppm, this may mean a daily chlorine loss of 30-40% instead of 15-20%, but again this is just a guess and it might not be that bad, though mostly that's probably because most residential UV systems for pools are woefully undersized (same with ozone systems). The claims of significant chlorine usage reduction in commercial/public pools when using UV seems suspect -- UV is primarily disinfection and has some oxidation of chloramines, but to oxidize organic precursors generally UV is used in conjunction with ozone or hydrogen peroxide in water treatment where the UV creates free radicals from these (such as hydroxyl radicals and atomic oxygen). For real oxidation supplementation, either ozone or the "advanced oxidation" systems would probably be better though those would certainly oxidize chlorine as well (mostly to chlorate).

There are other techniques that would be better for supplemental oxidation that wouldn't affect chlorine such as the use of enzymes. Unfortunately, chlorine oxidizes enzymes, but some have been developed that last somewhat longer in the presence of chlorine.

Of course, by the time one adds up all of these products trying to reduce chlorine consumption -- enzymes, algaecide, etc. -- one is probably spending a whole lot more than the cost of the chlorine that is saved. This is why such techniques aren't promoted on this forum -- also, using chlorine alone is so much simpler and chlorine is useful as both an oxidizer of bather waste, to disinfect against pathogens AND to prevent algae growth if a sufficient FC/CYA ratio is maintained.

 

[henry89056]

Hey chem geek -

I was actually looking for the est. loss due to UV-A (sunlight). It is my understanding that narrow-band UV-C (like that used for sanitation) does not have a substantive effect on chlorine.

I am working to verify, though that might simply require some isolated indoor testing using one of the units.

 

[Ohm_Boy]

I'm going to design and market an autoclave-based sanitizing system for pool water. I can prove the sanitizing effects of an autoclave, so the sales should be simple. You will still need a small amount of sanitizer, but certainly the savings overall would recoup the thousands and thousands that I'd charge to boil part of the pool water in a continuous batch process...

Sorry. Yes, I am obviously being facetious, and no, I'm not trying to start anything. Just thought it was funny. I'll go back under my rock now.

 

[chem geek]

I was actually looking for the est. loss due to UV-A (sunlight). It is my understanding that narrow-band UV-C (like that used for sanitation) does not have a substantive effect on chlorine.

Sorry I missed that. First, let me finish off the UV lamp discussion. The low-pressure UV lamp produces primarily two lines at 185 nm and 254 nm and is primarily for disinfection and not so much for oxidation while the medium-pressure UV lamp produces many spectral lines that are much broader in spectrum that are both for disinfection and for more oxidation (i.e. for dichloramine and some for nitrogen trichloride). The UV absorption peak for monochloramine is 246 nm while for DNA damage it is 264 nm. See this link for more info, but it looks like there is a decline in Free Chlorine (FC) even at disinfection doses, but it seems to be fairly small at perhaps 10% per pass (turnover), and this is without CYA in the water. So with CYA, the loss may be quite low.

So I was wrong in assuming much higher dosing for UV. If low-pressure UV is used, then one can have fairly low UV doses for disinfection and this minimizes the amount of loss of FC. On the other hand, this sort of UV is for disinfection and will only reduce monochloramine but not the bulk of what chlorine has to deal with which is urea.

Now as far as sunlight is concerned, the half-life of hypochlorous acid in shallow water with no CYA is 2 hours and 10 minutes while with hypochlorite ion it is 20 minutes. Near a pH of 7.5 where the mix is close to 50/50, this is a half-life of 35 minutes. However, lower depths are shielded by the chlorine itself (i.e. the breakdown in the shallow water absorbs photons that don't make it to lower depths) so that near a pH of 7.5 at 4.5 feet in depth the half-life is around 1 hour. Basically, you can figure that without CYA in the water, most pools in direct noontime sun would lose about half the FC every hour. So over a day with equivalent of 6 hours of peak sun (14 hours of daylight total) this is a 98% loss of chlorine so with other fixed non-sunlight losses, it essentially wipes out the chlorine in less than a day. If you're really interested, I can send you a spreadsheet on this with the derivation using spectral curves (PM me your E-mail address).

With CYA in the water, the half-life is significantly extended, but this is where things get pretty dicey since there isn't really good data that is consistent with what we've seen with users on this forum (i.e. the industry data seems to be wrong). For full-day sun on a pool in the summer, the daily FC loss at 30 ppm CYA can be up to 60%. At 50-55 ppm CYA, this can be up to 30-35% while at 80 ppm CYA it gets to around 20% and at 100 ppm CYA it's around 15%. These are very rough estimates and will vary depending on number of hours of sunlight, time of year, latitude, pH, etc. [EDIT] Mark's experiments showed a greater difference where there was a 50% loss at 45 ppm CYA and a 15% loss at 80 ppm CYA. Every situation is a bit different so these are just rough guidelines. [END-EDIT]

 

[frustratedpoolmom]

So um, when can I move this thread to the Deep End?