Retep,
You're running around in circles here. ORP roughly correlates with the hypochorous acid level -- it's just that it doesn't correlate consistently in an absolute sense and that it is affected by other factors, but in a relative sense there is a correlation. So obviously ANY experiment showing kill times or oxidation rates is going to show a correlation with ORP. However, NONE of these studies on ORP bothered to look at the hypochlorous acid concentration directly, even calculating it from the FC and CYA levels (along with pH and temperature). If they had done that, they would have found that calculated HOCl correlates at least as well if not better with disinfection and oxidation rates.
This link (which is in the CPO post I keep referring you to) actually measured hypochlorous acid concentration and found the correlation to it directly. And of course, I've already shown you
this post that shows that ORP roughly correlates to HOCl though not perfectly and there is
this paper that showed ORP correlating to FC (with no CYA), again all links that are in the
CPO post.
Again, no one said that ORP wasn't useful for process control since it does roughly correlate with hypochlorous acid concentration and one can create a setpoint against actual FC (and CYA) measurements. It's that it is not useful in an absolute sense the same way that the actual hypochlorous acid concentration would be. Obviously, if you specify a "high ORP" then odds are it will be more sanitized water, but it would be better to know the actual hypochlorous acid concentration, even calculated from knowing FC, CYA, pH and temperature, than it would be to know the ORP level. One manufacturer's "650 mV" is not the same as another manufacturer's and even with one manufacturer 650 mV varies too much by pH and hydrogen gas concentration so again, it's not as good as an absolute standard as actual hypochorous acid concentration. Why would one continue to push a proxy that is only approximate and is affected by other parameters when one can calculate the REAL THING that oxidizes and disinfects? If one is going to use a sensor, then use an HOCl sensor since you are at least measuring the relevant disinfectant directly. This would at least handle situations where there may be CYA-like molecules that bind to chlorine but measure as FC and not as CC (just as the chlorinated cyanurates do). ORP will also catch this situation, but since the absolute ORP level isn't definitive, one can't really know the true HOCl level -- again, one really needs a direct HOCl measurement as is done with the selective-membrane HOCl sensors.
I'm really missing the point you are trying to make with these references. What are you saying? We never said ORP didn't correlate at least in a relative sense with HOCl and its associated disinfection and oxidation rates and we never said that ORP wasn't useful for process control if you have a setpoint and control for external factors (pH, dissolved hydrogen gas). I've only said that ORP is useless as an absolute reading (except at extremes) since it varies so much by sensor and external influences not related proportionately to disinfection or oxidation. The 770 mV "standard" you quoted is arbitrary and will be inconsistent depending on the manufacturer's sensor and the pool being tested where a saltwater chlorine generator pool can readily fool the ORP sensor into thinking the ORP is too low and then overshoot the FC level to be too high -- something that has been reported to happen in real pools.
770 mV for Chemtrol at pH 7.5 would be 0.6 ppm FC with no CYA, but for Oakton it would be 1.1 ppm FC with no CYA while for Aquarius it would be 1.3 ppm FC and for Sensorex it would be 1.5 ppm FC. So what about the German DIN 19643 standard that allows down to 0.3 ppm FC? That's only 730 mV for Chemtrol, 697 mV for Oakton, 654 mV for Aquarius, 556 mV for Sensorex (if one believes their tables). You can see how ridiculous it is to just say that a certain mV ORP level is THE STANDARD. Of course, that doesn't stop people from saying it and even 19643 quotes 700 to 770 mV as a range though it is the ppm FC level of 0.3 to 0.6 (0.2 to 0.5 if ozone is used) is the definitive measurement.
Richard