Bartier Disinfection Index

[chem geek]

My understanding is that the 650 mv is an arbitrary selection and have not been able to find anything that explains why this 'magic number' is the level at which sanitation occurs. It is interesting that in a 2005 CPO training handbook that I have seen it talks about 850 mv as being the level of adequite sanitation.

Take a look at page 5 of the following link:

http://www.sbcontrol.com/ppmorp.pdf

The "Commercial Spas Study, Portland, Oregon" shows how the 650 mV ORP cutoff is reasonable for sanitation -- at least for the types of bugs found in those particular spas. There are clearly some bugs that require much higher concentrations of chlorine to get killed, but most bugs die below the 650 mV llevel. On the other hand, I found that the concentration of HOCl was at least as good if not a little better than ORP. I will put this information into the "Pool Water Chemistry" thread so you can see it.

You may also be interested in the following link that gives CT (C for concentration in ppm chlorine and T for time in minutes) values for various pathogens, though the focus is mostly on the ones that are hard to kill (for water treatment). The "easy" bugs (those easier than E. Coli) are not listed. Note that kill time is shortened at higher temperatures and the temps given are rather low.

http://www.who.int/water_sanitation_...treatpath3.pdf
http://anrcatalog.ucdavis.edu/pdf/8149.pdf

On the other hand, bacterial biofilms may require much more chlorine than is ever found in pools, even with shocking without CYA:

http://www.edstrom.com/Resources.cfm?doc_id=145

My understanding is that the algae will actually consume this as a food source as they consume other nitrogeneous compounds, hence the greater effectiveness.

I see you said that in your earlier post. Sorry I missed that the first time. If we try to use monochloramines for killing algae, then that will be a tricky combination of adding chlorine and ammonia. If CYA is present, then after the algae is killed, it will be virtually impossible to shock to breakpoint to get rid of the monochloramine, though it's possible a non-chlorine shock could do the trick.

Thanks for your comments. They are helpful.

Richard