Data regarding protection from UV by CyA

[Knetsel]

Hello,
Still interested in the theory and consequences of chlorine protection from UV by CyA, I'm looking for data published in scientific or technical papers relating to measurements concerning this protection.
I have seen, here and there, mentions of such papers as well as curves "based" on measurement results but I haven't been able yet to find and read those reports and the corresponding data.
If you read this post and that you know of such references, would you be so kind so as to let me know where and how to get them ?

Thank you in advance and best wishes to all for the starting new year.

 

[mknauss]

CYA - Further Reading

www.troublefreepool.com

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

 

[JamesW]

The main cause of chlorine being lost to UV is when a UV photons hit the electrons in the valence shell of an oxygen atom in hypochlorite, the electrons can be excited into a higher energy state and this makes it easier for the chlorine to take the electrons.

2OCl^- + 2UV --> O₂ + 2CL^-.

When you have CYA in the water, most of the chlorine is bound to the CYA and not in the form of hypochlorite or hypochlorous acid.

So, the protection will be comparable to the equilibrium of the species.

 

[JoyfulNoise]

Lots of great reading materials here -

JSPSI – Pool Help

Most of the articles contain extensive reference sections with references to the original O’Brien paper (1974) on the equilibrium chemistry of cyanuric acid and chlorine.

 

[mas985]

Here is some testing that I have done:

CYA Testing Update

I thought I would give those who are interested an update on some testing that I have been doing regarding CYA levels and chlorine. First a summary of the testing that I did in this thread. - Running my spa with the SWG at CYA levels from 45-80 ppm showed no change in chlorine production. -...

www.troublefreepool.com

CYA vs UV Chlorine Loss Test Update

Many years ago, I did a test of chlorine loss vs CYA level and published the results here: https://www.troublefreepool.com/threads/cya-testing-update.2984/ There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now...

www.troublefreepool.com

 

[Knetsel]

Thank you very much for all this information.
Re-readng the reports concerning CyA and OCl photolysis to which I have access, the best (?) data I have been able to find are those from Nelson (Monsanto report 6862) and Canelli (1974) which have been reproduced and used under graphical format by Wojtowicz, Pickens and Wahmann for instance
From what I understand of these experiments, various quantities of CyA were added to water originally containing 2,5 ppm FC. The corresponding samples of water were then xeposed to sunlight and remaining FC measured at different time intervals.
pH was 7 and temperature was ~ 29-32 °C (84-90 °.F).

 

[JoyfulNoise]

This paper might be interesting to you -

 

[Knetsel]

Thank you very much JoyfulNoise for this paper.

I already had a copy of it and found it most interesting especially for what concerns disinfection by UV-C (It mainly deals with 254 nm UV when sunlight UV reaching earth have a wave length over ~ 280 nm).
However there are some considerations regarding quantum yield as well as photolysis modeling which I found very interesting which I intend to investigate a bit further.
For instance, it looks like as if the rate of dissociation of OCl- for low concentrations is proportional to concentration. This would lead , in the absence of CyA, to an exponential variation of concentration with time in line with the proposal of Pickers based on reaction kinetics.

If you know of a possible access to :

Nelson, G. D. “Special Report No. 6862 –
Swimming Pool Disinfection with Chlorinated–s–triazinetrione Products.”,
Monsanto Chemical Co., St. Louis, Missouri,
March 1967.

I would be very happy.

 

[Knetsel]

Hello,
To mas85 : did you measure pH as well as Cl and CyA ?

 

[mas985]

Hello,
To mas85 : did you measure pH as well as Cl and CyA ?

Do you mean between the dilution samples? No but I did log PH for the pool and described it here:

CYA vs UV Chlorine Loss Test Update

Many years ago, I did a test of chlorine loss vs CYA level and published the results here: https://www.troublefreepool.com/threads/cya-testing-update.2984/ There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now...

www.troublefreepool.com

But anecdotally, multiple times I have seen a distinct jump in FC levels shortly after adding CYA to the pool while keeping the SWG setting the same. This is what prompted me to do the testing initially. I was attempting to see if what I was experiencing was real or not. Everything I have seen to date, makes me think the extinction rate decreases faster than the CYA level increases making higher CYA level more CL efficient.

 

[JamesW]

It would be interesting to test the opacity of the water to different wavelengths of UV at different levels of CYA.

You would need a UV generator with the ability to select different wavelengths and a detector to detect the intensity of the UV that passes through the water.

 

[ringi]

Is the CYA reducing the light algae get and hence the amount of chlorine used up killing algea?

 

[mas985]

It would probably be more related to the fact that CYA will absorb UV light at specific wavelengths which then prevents those wavelengths from destroying the CL. Based on the following data, which I have not vetted, it would protect ClO more than HOCl but since they are in equilibrium, it would affect both.