Tech Talk: Beyond Superchlorination

More THAN THE BASICS including BREAKPOINT FAILURE IN INDOOR POOLS and REAL VERSES PHANTOM CHLORAMINE

Excerpted from PrP 9 and PrP 10

“Last month we couldn’t achieve breakpoint for tryin’, and the complaints were rampant. Now, finally, we’ve got no eyeburn or odor, but they want to close us for two ppm apparent combined? What gives here!!”

This article is incomplete. It discusses phenomenon beyond the understanding of the collective knowledge of experts in swimming-pool technology. But this editor is compelled to write about it anyway, because superchlorination, a tried and true technique for half a century, has in the recent decade become a superheadache. Primarily in indoor pools, achievement of breakpoint often eludes us, and combined chlorine readings are as often not to be believed. Mysterious and onerous – even of the devil himself – superchlorination can be the biggest water-chemistry problem you’ll face.

Hey, you understand the basics of superchlorination... You just read the breakpoint discussion on page two, or you already knew it all. But the standard stuff just doesn’t seem to apply to you and your problem pool. This wasn’t the case at the last pool you worked at; you just dosed for ten times the combined reading and poof, the water was sweet again. Now this brand-new, state-of-the-art indoor pool makes you wish you were back at that tired pre-war plunge!

The key word here seems to be “new”. Amidst designers’ denials and claims to the contrary, “tight” new pools with “efficient” new air handling systems appear to hold the key to persistent chloramine problems and almost predictable inability to get rid of it! Air handling, by huge, expensive fans, ducts and machinery which turn over and condition the air – filtering out dust, reducing humidity, adding or removing heat, diluting with small amounts of fresh outside air, even recovering energy in the process – can cut costs of heating and dehumidifying the pool in half. And, apparently, it can drive you nuts.

Rather comfort and safety are fundamental to the success of a swimming pool and its program. Eyeburn and other irritation, then, is something to be avoided at all costs. And the costs are often high. We’ve made it clear that superchlorination is the fundamental weapon in the war against red eyes, but if your goggle sales continue to rise, you probably need to look further.

There are two problems that have shown up in the last decade which were rare to non-existent twenty years ago. They may be related, but, while often confused in conversation, appear to be distinctly different. We should, therefore, examine each separately. These two curses are: (1) Highly irritating chloramine presence, measured and experienced, which either refuses to respond to breakpoint efforts or responds partially, then re-establishes itself in a matter of days; or (2) High to very high chloramine readings with DPD #3, without the corresponding irritation and odor.

Stubborn Chloramine readings, failing superchlorination efforts.
First let's re-emphasize that preventing the formation of the common culprit, chloramine, is better and easier than ridding your pool of this annoying ammonia compound or its derivatives. If you are fortunate enough not already to have the problem in your pool, simply maintaining generous chlorine levels (maintaining breakpoint) usually works quite well. If you're a little late (or conditions are otherwise crummy) and amines have developed, however, this doesn't work at all; higher chlorine levels short of breakpoint combine to make additional chloramine, and sometimes even more offensive forms of it.

Here’s where the mystery comes in for indoor pool owners. When air movement/ exchange/ refreshment is inadequate for the normal breakpoint chemistry to occur, the effort produces unusual, even unpleasant results. Stubborn chloramine conditions come about that respond poorly or not at all to your times-ten efforts. Eye irritation may be ever-present, and combined readings - ranging from well over a half part per million before superchlorination to at least a few tenths or more after – linger in your logs, with zero evading you entirely. Programs suffer, and the afflicted operator begins to doubt himself and his training. Take at least this word of comfort – you are not alone!

Their are two kinds of chloramines, organic and inorganic, and they respond differently to high levels of additional chlorine. In cases of heavy people-caused, organic amine, the superchlorination process doesn't always go to completion, especially in indoor pools. Even though the presence of tri-chloramine is somewhat controversial, reliable authorities claim that it is the result of the process of super-chlorination itself! One solution in a water-treatment reference is the maintenance of high-chlorine contact time not for minutes or even hours, but days!

The chemistry of pool water is extremely complex, no matter how we in the teaching business try to simplify it. Virtually all unpleasant or dangerous chemical compounds in chlorinated water are the “products of incomplete oxidation”. It’s a handy catch-all phrase, as nitrogen trichloride, chloroform, monochloro creatin, unspecified trihalomethanes, nitrates, chlorates and so forth develop despite your best efforts. What we think is happening when air replacement at the water’s surface is inadequate is much of the monochloramine is “upgraded” to tri-chloramine (nitrogen trichloride), that steroid-injected form of chloramine which causes eyeburn in deck staff as well as in swimmers. This tri-chloramine gasses off intact, creating the staggering odor and irritation now characteristic of problem pools indoors – and it simply doesn’t yield to common superchlorination.

Tri-chloramine can theoretically be neutralized by simply allowing the chlorine to fade to zero. That process usually takes too much time in an indoor pool, so de-chlorination with sodium thiosulfate is the only quick option. A carefully calculated dosage of “thio” will reduce the chlorine residual to zero thereby reducing all chloramines to zero as well. Ammonia remains, however, so re-chlorinating re-establishes monochloramine – the easy stuff to superchlorinate out. When the residual rises to a typical one-to-two-ppm residual, the chloramine can again be measured, then superchlorination can be calculated and performed. With any luck, breakpoint will be achieved, eliminating the monochloramine that comprised virtually all the ammonia compounds present. When this technique works, you’ve finally eliminated the un-eliminatable bad guys, and only HOCl remains.

It doesn’t always work, however, as the conditions that allowed the chloramine to build and which resisted the original efforts to superchlorinate still exist. Air must be moved and exchanged. Doors and windows must be opened. Rent or buy box fans, floor fans, turbo fans... Do whatever it takes to blow fresh air across the surface of the pool. You’ll improve your odds greatly.

Some indoor pool operators have had good luck with potassium mono-persufate (one of the non-chlorine oxidizers or "oxy”-named products). When using the oxy-stuff, according to the manufacturer's recommendations, a more complete oxidation may occur and the persistent chloramine just might go away. To add to the confusion, however, potassium mono show up on the test kit as the very stuff you’re trying to get rid of – combined chlorine! (A discriminating test is now being developed by one of the big test-kit manufacturers.)

As your ace in the hole, activated carbon – or kiln-dried charcoal – is the ultimate water cleaner. It has a tremendous appetite for many and various compounds and contaminants in water, including dissolved gasses and odors. It handles chloramines with ease. Some operators have loaded a layer of it in the pool's filter, letting it go to work for a half-dozen turnovers. The object here is to present your pool water to this carbon without getting the carbon in the pool and making a big mess, so check your filter for leaks or channelization with a small dose first. It'll work in the pool as well as in your filter; it's just a lot harder to clean up.

Locating a source for this material is probably more difficult than putting it to use; try your local industrial chemical supplier first. Powdered rather than granular or chunk carbon works best, mostly because you can rid your filter of it through backwashing. Figure one to two pounds of this jet-black powder per thousand gallons of pool water, pre-wet it (not easy) and pour it into the skimmers, surge pit or wherever you can in order to coat the filters.

Chlorinate the pool by hand, directly, to preclude an algae bloom. (Let's not create another problem here...) Your chlorine won't make it through the carbon-laden filter; you'll have to add more regularly throughout the process.

At the end of all this effort, you should end up with really "clean" water in your pool. Backwash the carbon from your filters thoroughly, and return to normal procedures. (If some carbon made it through your filters and ends up in the pool, let it settle and vacuum it up. At least you know something more about your filters now...) The pool's saturation index will be unaffected by all this, so you're back to fastidious maintenance of pH and chlorine, hopefully with enough residual this time to preclude the return engagement of problem water.

Why don't we use carbon in our filters full time? If it weren't for carbon's hunger for chlorine, we would. In Europe, an activated carbon "bypass filter" is used specifically for chloramine management, where five to ten percent of the circulation water is constantly being passed through this chamber. (Yes, carbon does get saturated and consumed, requiring additions and eventual changing. It can be rinsed and reactivated in a hot oven, where contaminants are driven off as gasses - but it’s hardly worth the effort...)

Phantom Chloramine.
This is the least understood problem of them all – highly elevated total chlorine readings, often many times that of the free reading, without the symptoms associated with high chloramine. Those so afflicted call this phenomenon “phantom chloramine”. Pools have been closed by health inspectors and operators have stayed up nights trying serial superchlorinations when the DPD #3 or other total-chlorine reagent darkens through the roof. No odor and no eyeburn accompanies this phantom curse, just staggering readings that make you consider binge drinking.

Those of us who have observed this phenomenon have concluded that either the free reading is depressed or the combined reading artificially elevated. All brands of kits have been faked out, including titration types. All the test-kit companies have denied this possibility, alluding to operator error or simple misunderstanding of the problem. Yes, we don’t understand the problem, but this consultant believes it’s a constituent of the water causing reading errors. We know that potassium monopursulfate will elevate total readings, why not something else?

Another factor always is present – the phantom shows up only in those newer, indoor pools with efficient, tight air handling systems. Technicians with as much as thirty years’ experience seem to agree; we didn’t have this problem a decade ago...

As the jury is still out on this one, your PrP staff and PPOA technical-board advisors are anxious to hear from the field. What have you heard and what do you know about the phantom. It appears to do no harm, like Casper the ghost, but it is a most difficult concept to shrug off when the health inspector has her red pen poised over the clipboard.

Superchlorination follow-up, from PrP 10

PrP has heard from a small number of our members concerning the “phantom chloramine” discussion, and a few more experiencing the un-breakable combined-chlorine phenomenon. Most have commented on the existence of the problem rather than the solution.

Investigation with technical advisors of test-kit companies yielded less than desirable results, with one exception. Dr. Neil Lowrey, our PPOA Canadian Advisor from Toronto who represents Taylor Chemical Company in Canada, commiserates; he’s recommending a change in testing procedures and test kits. He tends to agree with us that the colorometric comparitors are harder to read with accuracy and repeatability, the related reagents aren’t really as compound specific as we’d like them to be, and, especially with bromine, the color precipitants we view in the dosed sample tend to develop (change) over time. Using the relatively new FAS (that’s ferros ammonium sulfate) titration kits, many of these problems are overcome. Here we measure a value by counting drops needed for a color shift or a bleaching, rather than trying to match a color’s hue or its intensity. Each drop can represent .2 ppm or .5 ppm, accurate even for higher residuals. Especially for these higher values – like two, three, even five or more parts per million where small color variations and intensity shifts are impossible to discern – the drop-counting pool operator has a renewed confidence in his residual values.

No one has yet put her or his finger on the elevated but non-offensive “phantom” chloramine. We know that potassium monopersulfate will elevate DPD #3 artificially, showing up as the very thing that oxy-stuff is being used to eliminate. And sodium persulfate, also in the non-chlorine-shock family, fakes out the test kit similarly. (But, as it doesn’t activate sodium bromide, it is less common in public pools.) Otherwise – while we suspect there is something – no other constituent of treated water has the reputation of pretending to be chloramine. Test kits, again, are more suspect than chemicals, showing depressed free or elevated combined readings.

Now that most of our busy pools are automated, scrutinizing and demanding more hair-splitting “precision” (you know about precision, don’t you...), maybe a leading-edge test kit is the answer.

So what does this “FAS” kit solve? It appears that “free” and total values of chlorine will be more accurate, tending therefore to make the combined calculation equally more real. You’ll then become more confident in your superchlorination targets. And, following the reasoning and procedures described in PrP #9, you indoor pool guys might actually get breakpoint chlorination to “break”! You’ll recall that falling short of reaching that magic point on the initial attempt is the primary cause for making it very much more difficult on the next. It behooves us to get it done right on the first shot!

Reviewing a bit more, failed superchlorination actually creates those nasty compounds – products of incomplete oxidation – which don’t succumb to our simplistic times-ten rules. These compounds, most of which are lumped under the name trihalomethanes or haloforms, are the chloro-unmentionables which are both more offensive and so much more difficult to get rid of. TTHMs, “total trihalomethanes”, are organic, dominated by chloroform (see PrP #5 and PrP #7) which can be absorbed through the skin. While many THMs are unavoidable to a small degree, is ever so much better to do everything you can to keep them down than allowing conditions which create THMs – then having to get rid of them!

We so often discuss chloramines as a single family of like chemical compounds; however they are quite complex and exists both as inorganic and organic matter. The inorganic chloramines are easy to superchlorinate out, the organic ones are not. These organics are the result of decomposition of proteins in bather pollution, pretty much a function of bather density. Compounds called monochloro creatinines, for example, are found in urine. Ammonia, formed from the breakdown of urea, develops slowly, creating amines all along. The resulting chlorinated organic amines contribute significantly to our stubborn combined residual. It’s a Catch 22. Here may be a case for ozonation or even carbon filtration, as described in PrP #9.

If superchlorination seems not to work, even with accurate targeting and copious air flushing, you may well need to begin a dilution process as a last resort. Common in Europe, routine “blowdown” of indoor pool water may find its way into our practice in the US – especially now that pool loading is up and air handling is tighter than ever.

Preferring to know cause, effect and remedy rather than a lot of technical and chemical talk leading to no fix – most of us eventually say “just tell me what to do to make it all go away!” It’s boiling down to this: Cause: too many swimmers,,, Effect: Organic chloramines that won’t go away... Remedy: Careful testing, generous superchlorination, maybe dilution...

As a postscript, there may yet be a chemical answer. Dr. Lowry tells PrP of a “new” Austrian two-part product... The first additive, a poly-aluminum chloride (PAC) called Hydrosan, is used before the filter as a microfloc of organic products. Water returning to the pool is then treated with a chemical called Hydroxsan, which apparently produces ClO2 (chlorine dioxide). This powerful oxidizer/sanitizer, unlike HOCl, “does not chlorinate organic molecules” (make chlorinated organic amines). ClO2, heretofore somewhat risky to generate on site, promises to help us avoid those pesky chloramines...

The process of routine and continuous dilution will be discussed in detail next PrP. Look for a feature called “The Solution to Pollution is Dilution?”!

~kw