Clarification For Decon Recipe

[dlleno]

I'm seeing recommendations here for decon procedures involving 50 ppm for 60 min. other procedures (one I obtained from my local spa store for example) recommend 100ppm for similar time periods.

I was just reading on the US CDC site where I found some very interesting information involving kill concentrations, which are expressed in terms of "ppm times minutes", or the product of FC concentration in PPM times the number of exposure minutes.

http://www.cdc.gov/healthywater/swimming/pools/chlorine-disinfection-timetable.html

The most chlorine resistant parasite, Cryptosporidium (or Crypto) requires some very aggressive treatment:

1ppm for 15,300 minutes (almost 11 days)

20ppm for 765 minutes (12.75 hours)

50ppm for 306 minutes (5.1 hours)

100 ppm for 153 minutes (2.55 hours)

Of course, these numbers assume pH is 7.5 or lower, water temp is 77 degrees F or higher, and NO STABILIZER. these thoughts immediately come to mind:

1. it is now clear to me why, if if is really needed, one must perform superchlorinization AFTER and IN ADDITION to any purge or scrub process, as these procedures are normally performed on "old" water (read: stabilizer present). especially if one is concerned about crypto.

2. How does the higher water temperature of 100 degrees (for example) affect the above kill rates, such that one can de-rate the above CDC numbers? In other words, is 50ppm for 60min really enough to kill Crypto in 100 degree water? on a more technical note -- how does one derive such a extrapolation?

4. we know (see below) that legionella can find protective refuge in biofilms, and this implies that superchlorinating without purging first may not even be effective in some situations -- at least in the case of legionella. Are there other microorganisms besides legionella that can find protection from chlorine inside biofilms?

5. Do we know what the kill concentration (FC PPM times minutes) required for legionella is (assuming biofilms are purged)?

http://www.cdc.gov/healthywater/pdf/swimming/pools/hyperchlorination-to-kill-cryptosporidium.pdf

http://www.cdc.gov/legionella/downloads/hot-tub-disinfection.pdf

[chem geek]

1. it is now clear to me why, if if is really needed, one must perform superchlorinization AFTER and IN ADDITION to any purge or scrub process, as these procedures are normally performed on "old" water (read: stabilizer present). especially if one is concerned about crypto.

Cryptosporidium pavrum is a protozoan oocyst and is very, very, very rare in residential spas because it doesn't just spontaneously appear nor is it pervasive in the air or soil or most water sources, especially not typically treated fill water or well water. Crypto is most commonly introduced by people with diarrhea so is found in commercial/public pools when an infected person uses the facility. It is rare in spas because the water is changed and if for some reason you did have Crypto in your spa a complete and thorough water change should remove it because it does not form biofilms.

You are correct that you should use a biofilm remover such as Ahh-Some® before doing a super-chlorination, but these procedures are primarily to thoroughly remove biofilm and kill the associated bacteria. Planktonic (free-floating) bacteria are mostly very easy to kill -- it is when the form biofilms where chlorine is not very effective at normal concentrations.

2. How does the higher water temperature of 100 degrees (for example) affect the above kill rates, such that one can de-rate the above CDC numbers? In other words, is 50ppm for 60min really enough to kill Crypto in 100 degree water? on a more technical note -- how does one derive such a extrapolation?

Again, don't worry about Crypto as a water change will remove it and it's very unlikely you have any in your spa. Though higher temperature increases kill rates, the CDC has not measured this.

4. we know (see below) that legionella can find protective refuge in biofilms, and this implies that superchlorinating without purging first may not even be effective in some situations -- at least in the case of legionella. Are there other microorganisms besides legionella that can find protection from chlorine inside biofilms?

It's mostly bacteria that are found in biofilms but algae may also be present. Protozoan oocysts and viruses are not reproducing in water so are generally not found in any substantial quantities in biofilm (except for viruses that infect bacteria or viruses, but those aren't ones that infect humans).

5. Do we know what the kill concentration (FC PPM times minutes) required for legionella is (assuming biofilms are purged)?

This post shows a table of kill times for chlorine (vs. copper and silver ions) at a concentration of 0.1 ppm FC with no CYA at a pH of 7.5 or equivalently an FC that is around 10% of the CYA level. The kill times are in minutes for a 3-log (99.9%) kill. So you can see that Legionella is 99.9% killed in an hour, but half will be killed every 6 minutes which is faster than it can reproduce (typically 15-60 minutes). So normal chlorine levels in a spa will prevent Legionella from growing. Other bacteria are far easier to kill. A super-chlorination will obviously kill more quickly, but is really unnecessary unless you've let the chlorine get to zero for many hours or this is a new or used spa with a questionable history.

[dlleno]

yes my experimentation has certainly revealed better results with ahh-some compared to Seaklear system flush and I'm using ahh-some exclusively now and highly recommend it. I'm even tempted to perform additional experiments with other products in the same way I compared System Flush with Ahh-some and post results.

I did suspect the crypto risk was low for residential hot tubs, after reading the CDC site, so thanks for that information, esp. that this guy does not grow/multiply in the tub. That is really good to know. But this raises the question regarding the decontamination recipe of 50ppm FC for 60 min (3000 ppm-minutes). AT 77 degrees F, this is clearly not enough to handle Crypto (which requires over five times that figure). However, 3,000 ppm-minutes is more than 60 times the exposure required to kill Giardia, which the CDC lists as the next most chlorine tolerant bug associated with hot tubs. Accordingly, 50 ppm for 60 min seems like an overkill of grand proportions to me, suggesting that I must be missing something regarding how the 3,000 ppm-minute figure was obtained. I'll study the link you posted to see if there is a clear answer

[chem geek]

The 50 or 100 ppm chlorine are primarily to try and remove biofilms, most especially if you don't use a biofilm removal product. Originally before we found such products, decontamination with high chlorine levels was all there was. So you need to look at the super-chlorination as not being disinfecting of planktonic organisms nor really for Crypto, but of getting rid of biofilm. When you use a biofilm removal product, then super-chlorination is just an extra safety factor in case there is still some biofilm left over. It may be overkill, but you should only need to do it once if you properly maintain your spa thereafter. If you want to use a biofilm remover and then just do a regular shock chlorine level (say, for Legionella), then that's fine.

Also note that when you add 50 or 100 ppm chlorine using Dichlor or bleach, you don't get particularly high HOCl concentrations that are the primary disinfectant. Let's use 50 ppm FC as an example. If I assume an initial 80 ppm TA and 7.8 pH of the fill water, then adding bleach has the pH rise to 8.5 so that the HOCl concentration is only 4.6 ppm so equivalent to roughly 9 ppm FC at pH 7.5 with no CYA. Likewise if you add Dichlor, then the pH drops to 7.5 but the CYA rises to 45 ppm and the HOCl concentration is only 4.5 ppm so again equivalent to the same 9 ppm FC. So 50 ppm isn't as high as it sounds in practice given the reality of what occurs. In equivalent CT terms considering only HOCl and using a pH of 7.5 as a reference, it's really 9*60 = 540 for CT value. That's still pretty high and again is because this isn't so much about disinfection as for thorough biofilm removal.

Now in the bleach case, the OCl^- concentration is 45 ppm while in the Dichlor case it's 4.5 ppm so to the extent that some chemicals are oxidized by hypochlorite ion then the bleach may be more effective, but for disinfection HOCl is at least 20 times if not 50 or more times effective than OCl^- because HOCl "look like" water and is uncharged so gets into cells more readily.

And yes, we could tell people to add less bleach and then acid to lower the pH back down, but that gets more complicated.

[dlleno]

makes sense. I just noted that nitro's decon procedure included an enzyme purge step as well, prior to the 50ppm FC dose. the implication, then, is that these enzyme based materials are not really biofilm removal products at all, at least not to the extent as the ahh-some product appears to be. There's probably still some confusion around what a "biofilm removal" product is.

[chem geek]

I think the Ahh-Some type of product is fine for both removing biofilms AND greases. It is not an enzyme so will not break down such greases, but it will dislodge them just as it does with biofilm. The powerful surfactants break up and dislodge these items so that you physically remove them with a water change. So an enzyme may not be needed and you are correct that enzyme products aren't usually considered to be biofilm removal products. They are normally associated with being able to oxidize chemicals chlorine has trouble with such as skin oils, suntan lotion, greases, etc. So if you use them at all, it's usually ongoing and not for a decontamination procedure with a water change.