Bartier Disinfection Index

[chem geek]

I am the user that Ben mentioned who created the spreadsheet that accurately calculates the chlorine species in water including the chlorinated cyanurates.

With regards to the Bartier Disinfection Index, the pH Factor table is reasonably accurate and simply describes the HOCL to OCl- ratio that is independent of CYA (the RATIO is independent of CYA, but the absolute levels are certainly not).

However, simply subtracting the CYA level from the disinfection index is NOT an accurate way of predicting disinfection (assuming disinfection is directly related to the concentration HOCl as appears to be the case). There are two primary problems with the Bartier formula. First is that with no CYA it sets the minimum chlorine levels too high as required for disinfection (see below), though this level and even higher IS required for a reservoir of chlorine. For outdoor pools exposed to sunlight, you'd have to continually add chlorine as half of it could be gone in a half-hour. Second, their formula woefully underestimates the effect of CYA on reducing HOCl concentration (and therefore on reducing disinfection ability).

I won't put in the whole CYA/FC/HOCl table into this post (I'll create a new China Shop forum topic instead) but results from a commercial spas study and HOCl vs. ORP correlation data from a reliable ORP sensor manufacturer indicate that a 0.011 ppm HOCl concentration is the minimum required for disinfection and roughly corresponds to 650 mV ORP (at pH 7.5). Of course, prevention of algae may require more (this is part of what I want to find out from forum users). The "Ideal" Bartier Disinfection Index value of 91 implies the following levels of chlorine at different CYA levels and a pH of 7.5 (and I also show the calculated ppm HOCl):

CYA ..... ppm FC ..... ppm HOCl
.. 0 ....... 1.9 ............ 0.916
. 10 ....... 2.1 ............ 0.109
. 20 ....... 2.3 ............ 0.052
. 30 ....... 2.5 ............ 0.036
. 50 ....... 2.9 ............ 0.024
. 70 ....... 3.4 ............ 0.020
100 ....... 4.0 ............ 0.016

As you can see, a small amount of CYA will store (in chlorinated cyanurates) most of the total chlorine. The Bartier "VERY LOW" level of 50 with a CYA of 100 results in a ppm HOCl of around 0.011 so everything in their table does provide for minimum disinfection (which is good), but their "equivalency" of chlorine levels at varying of CYA is wrong. Also, I suspect that 0.03 or 0.05 ppm HOCl may be needed to prevent algae and if this is the case, the chlorine levels they propose at high CYA would be too low.

Ben's table is a better guide to chlorine requirements vs. CYA since it more closely tracks a minimum level of 0.02 ppm HOCl though the mid-points of the ranges are closer to 0.05 ppm HOCl. It's nice to know that real-world experience has a basis in chemical theory (or vice versa). As Ben mentioned elsewhere (on another forum), the shock values are not as consistent, but we really need more real-world experience to know what minimums are truly required to zap algae at various CYA levels.

Richard (aka "chem geek")

[chem geek]

With regard to HOCl vs. OCl- as a sanitizer, there appears to be valid science to back the notion of HOCl being the more powerful sanitizer for certain kinds of bugs. This is because most pathogens have cell walls that are negatively charged as follows:

1) Gram-Positive bacterial cells (so named due to a positive result from a stain test developed by Hans Christian Gram) have teichoic acids (phosphate groups joined by glycerol or ribitol) that give a negative charge to the outer cell wall.
2) Gram-Negative bacterial cells have lipopolysaccharides that give a negative charge to the outer cell well.
3) Many, but not all, viruses have a net negative electrical charge since their viral envelopes often come from host cells (which have a negative charge on their cell wall). Viruses enter cells at specific binding sites that overcome the electrostatic repulsion.

Since HOCl is neutral, it is more readily able to enter cells than OCl-. Polar molecules and ions generaly only enter cells through specific channels that only allow ions of certain sizes and shapes generally blocking OCl-. On the other hand, algae have different types of cell walls like cellulose that does not appear to be charged. So while HOCl may be a more effective sanitizer for bacteria and viruses, it may not be more effective for algae, but I cannot confirm that.

(See WHO water sanitation document)

Once inside a cell, the mechanism of sanitation appears to come down to two different mechanisms though this appears to be somewhat speculative:

1) Chlorine substitution where the HOCl substitutes its chlorine with hydrogen from an organic compound (a protein, typically an enzyme). This substituion inteferes with the enzyme's function (folding of protein, intereference of active site, etc.).
2) Chlorine oxidation of organics (typically from production of free radical oxygen O• from HOCl or OCl-). This can destroy proteins (including enzymes) as well as DNA (typically during cell division).

The dependence of Oxidation-Reduction Potential (ORP) on pH that follows the concentration of HOCl plus my analysis of the commerical spas study (Oregon) data using HOCl lead me to believe that HOCl is indeed the effective sanitizer against bacteria. I couldn't find scientifically valid information on algae to know whether HOCl or OCl- is more effective, but in any event I would doubt that OCl- is more effective than HOCl even for algae (though it might be about equally effective -- I just don't know).

[waterbear]

There is one other factor to look at with pH when killing algae. If the pH is on the high side it will favor the formation of monochloramine when the chlorine combines with ammonia in the water. Chloramines are nitrogenous compounds and the algae will consume them as food. It is by this mechanism that 'chlorine enhancers' (inorganic ammonia based) are supposed to work. This makes the situation a bit more complex than just looking at the ratio of HOCL to OCl- based on pH since other reactions and substances become involved and are also pH dependant.

[chem geek]

Evan (waterbear),

Thanks for the info on chloramines and their use in killing algae. I did read something about this in some non-scientific articles, but couldn't find good data on algae kill levels (for different algae types) for either chlorine (HOCl) or chloramines (NH2Cl) except for an EPA report that essentially said that 0.1 ppm chlorine (in sea water, so chloramines certainly were formed) killed most marine plankton. On the "Save Swimming with Elevated Chlorine" forum you mentioned that there were studies showing the relationship of ORP to different types of algae that grew in that environment -- I would appreciate links to those studies or a summary of results and whether there was ammonia present (so that chloramines would have formed), what the pH was, etc. I can roughly translate ORP to ppm HOCl at least to get an idea, both for maintenance and shocking.

You also commented on the other forum (if I should respond there instead, let me know) about the use of ORP sensors and how these measure oxidation potential which is not the same as disinfection capability. I believe you are right about this, though there is some correlation since the primary oxidizer in pool waters is chlorine (HOCl) which dominates the ORP reading. So in some sense, ORP acts as a proxy for HOCl. You are right, however, that it also has other pH dependencies and the actual reactions that are being measured appear to be close to 1 electron instead of the 2 one would expect with HOCl oxidation. I've had numerous discussions about this with several ORP sensor manufacturers which led me down the path towards comparing calculated ppm HOCl against the Oregon Commercial Spas study where I found that calculated (not even real-time) HOCl concentration was at least as good if not slightly better than real-time ORP (with one exception at low chlorine and zero CYA that was very, very strange).

I plan to start two new threads in the China Shop. One will be non-technical and will be focussed on getting more real-world information from users who are battling algae (maybe some will even be willing to try some experiments) -- perhaps Ben will move this out of the China Shop, but I'll leave that up to him. The other new thread will be technical and will address the issues I described above regarding ppm HOCl and ORP, giving you graphs, spreadsheets, etc.

Richard

[waterbear]

Evan (waterbear),

Thanks for the info on chloramines and their use in killing algae. I did read something about this in some non-scientific articles, but couldn't find good data on algae kill levels (for different algae types) for either chlorine (HOCl) or chloramines (NH2Cl) except for an EPA report that essentially said that 0.1 ppm chlorine (in sea water, so chloramines certainly were formed) killed most marine plankton. On the "Save Swimming with Elevated Chlorine" forum you mentioned that there were studies showing the relationship of ORP to different types of algae that grew in that environment -- I would appreciate links to those studies or a summary of results and whether there was ammonia present (so that chloramines would have formed), what the pH was, etc. I can roughly translate ORP to ppm HOCl at least to get an idea, both for maintenance and shocking.

The studies I cited come from various books and articles from the 70's when ORP controllers for marine aquarims were being first employed freqently with ozone and foam fractionalization (protien skimmers). I would not know where to begin looking today! (I experimented back then, found it viable, and just continued to use the procedures. Today they are pretty much standard practices in the hobby) As far as whether ammonia is present or not...ammonia is one of the biggest problems in marine or frehwater aquariums since the waste products of the livestock are nitrogeneous compounds. This is the reason biological filtration is used to convert ammonia first to nitrites and then to nitrates which are much less toxic. The buildup of nitrates is still problematic in reef tanks so ozne and foam fractionalization is used to reduce the initial loading of ammonia and then anerobic denitrification is used to reduce the remaining nitrates formed by aerobic nitrification (along with dilution). Also green algae is used to consume the nitrates and then harvested and removed from the tank to further reduce nitrate levels. If I am not mistaken the 450 mv reading of a 'healty tank' comes from the ability of the tank to oxidize the ammonia that is generated and it has a direct bearing on the type of algae that can grow. Foam fractionalization and ozone both will raise the mv reading in a tank and both lower the amount of ammonia present in the water. I have found from my own experiments that the type of lighting in the tank also has a bearing on the ORP readings...Actinic (440 angstom peak but quite a bit of the UVA spectrum) and metal halide (strong UVA/UVB component) tend to produce a higher mv reading than the same tank with daylight or wide spectrum lighing. I don't know of any studies that have been done on this but there might be. I attribute it to the UVA/UVB components of the lighting destroying the ammonia and related compounds in much the way sunlight would and therefore raising the redox potential of the water system. This is supposition on my part and the actual mechanism might be completely different.

It is interecting that CYA is a nitrogeneous compound and it is known to lower ORP readings in pool (as does combined chloramines). I am not really sure what the correlation between the level of nitrogen compounds and the ORP reading really means but it poses a lot of questions to me concerning actual sanitation vs. oxidation potential. A marine aquarium is NOT a sterile enviroment (although attempts have been make with sterile systems using UV and micron filtration with varying degrees of success) yet oxidative processes are necessary for the health of the system.

You also commented on the other forum (if I should respond there instead, let me know) about the use of ORP sensors and how these measure oxidation potential which is not the same as disinfection capability. I believe you are right about this, though there is some correlation since the primary oxidizer in pool waters is chlorine (HOCl) which dominates the ORP reading. So in some sense, ORP acts as a proxy for HOCl. You are right, however, that it also has other pH dependencies and the actual reactions that are being measured appear to be close to 1 electron instead of the 2 one would expect with HOCl oxidation. I've had numerous discussions about this with several ORP sensor manufacturers which led me down the path towards comparing calculated ppm HOCl against the Oregon Commercial Spas study where I found that calculated (not even real-time) HOCl concentration was at least as good if not slightly better than real-time ORP (with one exception at low chlorine and zero CYA that was very, very strange).

I plan to start two new threads in the China Shop. One will be non-technical and will be focussed on getting more real-world information from users who are battling algae (maybe some will even be willing to try some experiments) -- perhaps Ben will move this out of the China Shop, but I'll leave that up to him. The other new thread will be technical and will address the issues I described above regarding ppm HOCl and ORP, giving you graphs, spreadsheets, etc.

Richard

I look forward to your threads. I have a strong chemisty background and previous (a very long time ago!) research laboratory experience but am not a chemist and have been a serious marine aquarium hobbiest for over 30 years now. I hope that I can add something to your threads with my limited understanding of the concepts involved (although my understanding probably excedes that of the average non-technical person).

[chem geek]

I look forward to your threads. I have a strong chemisty background and previous (a very long time ago!) research laboratory experience but am not a chemist and have been a serious marine aquarium hobbiest for over 30 years now. I hope that I can add something to your threads with my limited understanding of the concepts involved (although my understanding probably excedes that of the average non-technical person).

You had mentioned various ORP levels that inhibited algae and all of these were quite low relative to the 650 mV level for sanitation. Maybe the level of HOCl to inhibit algae is below that for sanitation and it is only after algae is established (and forms a biofilm) that chlorine is not effective (except at "shock" concentrations)??? Or perhaps the lower ORP levels reflect monochloramine and that virtually no HOCl is present.

I have read that monochloramine is more effective against established algae since it reacts more slowly (weakly) than HOCl so it doesn't get "used up" by the biofilm layer and is therefore able to penetrate more deeply. If you have any way of figuring out what it takes to suppress algae and to kill algae, please let me know. We know from the experience on this forum that large amounts of chlorine will kill algae, but I'd like to quantify this further in light of our knowledge of HOCl concentration.

I've posted the technical thread in the China Shop called "Pool Water Chemistry". After I get that stable, I'll post another non-technical thread to ask for real-world algae experience.

Richard

[waterbear]

You had mentioned various ORP levels that inhibited algae and all of these were quite low relative to the 650 mV level for sanitation. Maybe the level of HOCl to inhibit algae is below that for sanitation and it is only after algae is established (and forms a biofilm) that chlorine is not effective (except at "shock" concentrations)??? Or perhaps the lower ORP levels reflect monochloramine and that virtually no HOCl is present.
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.
I have read that monochloramine is more effective against established algae since it reacts more slowly (weakly) than HOCl so it doesn't get "used up" by the biofilm layer and is therefore able to penetrate more deeply.
My understanding is that the algae will actually consume this as a food source as they consume other nitrogeneous compounds, hence the greater effectiveness.
If you have any way of figuring out what it takes to suppress algae and to kill algae, please let me know. We know from the experience on this forum that large amounts of chlorine will kill algae, but I'd like to quantify this further in light of our knowledge of HOCl concentration.

I've posted the technical thread in the China Shop called "Pool Water Chemistry". After I get that stable, I'll post another non-technical thread to ask for real-world algae experience.

Richard

Hope this is helpful.