Bartier Disinfection Index

[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.

[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

[waterbear]

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

Actually, the use of monochloramines for killing algae is not a new practice. Many 'old time' pool guys would add per 20000 gal water 1 gal anhydrous ammonia and 8 gallons of 12..5% hypochloruous acid (50 ppm) to form monochloramines in the water. Filtration is shut off for 24 hours and then an additional 8 gallons of chlorine is added and filtration turned on to destroy the chloramines. This is similar to the use of 'chlorine enhancers' that are based on inorganic ammonia compounds and are used to kill algae. They do create a huge chlorine demand in their aftermath. Perhaps PoolDoc (Ben) would have some more insight into this older practice.

Also, my understanding of MPS is that it will not break down chloramines....this info comes right off the DuPont Oxone website. They work by having a residual in the water to oxidize organics before choramines can form. This is a quote
" Does Oxone® reduce chloramines?
Products containing Oxone® prevent chloramines from forming by oxidizing contaminants. Regular oxidizing with Oxone® keeps contaminant levels to a minimum, so the water remains clear and sparkling, allowing you to enjoy longer periods of uninterrupted swim time. And because Oxone® is chlorine-free, you don't have to worry about high chlorine levels; chloramines; unpleasant odors; or burning, irritated eyes."
Here is the link
http://www.dupont.com/oxone/faq.html#a4

I can understand the benifits of MPS with an indoor pool but the caveat seems to be that a residual of MPS is required in the water at all times for them to be effective in the prevention of the formation of chloramines. I see no real advantage to their use in outdoor pools.

The only other non chlorine shock I am aware of is sodium percarbonate, which from my understanding, is no longer being used because of the effects it had on ORP controllers. It is still employed in limited use with conversion of biguinide to chlorine but I doubt it is really any better than chlorine for that purpose.

[chem geek]

Also, my understanding of MPS is that it will not break down chloramines....

I can understand the benifits of MPS with an indoor pool but the caveat seems to be that a residual of MPS is required in the water at all times for them to be effective in the prevention of the formation of chloramines. I see no real advantage to their use in outdoor pools.

Yikes! I had no idea that MPS didn't oxidize monochloramine, but the Dupont literature certainly implies that MPS only prevents their formation. Ben told me that supercholorination to achieve breakpoint almost never works, especially for indoor pools with poor air circulation. He speculated that sunlight breaks down monochloramines in outdoor pools and I've read literature that suggests the same thing.

So this begs the question of how do you get rid of monochloramines? If a pool has CYA in it, then you need a heck of a lot of chlorine to properly shock it. Originally I was thinking that a small amount of CYA for indoor pools was a good idea to reduce effective chlorine concentrations to minimize exposure to bathers (and their swimsuits), but that would make superchlorination even more difficult. A real catch-22. Why wouldn't you use a constant level of MPS to prevent monochloramine formation? Is this not necessary in outdoor pools due to the breakdown from sunlight?

(NOTE: I have contacted Dupont to ask them if their MSP product, Oxone, will oxidize monochloramine in which case it could be used as a shock and not just as a chloramine preventative. I will let you know their response, if any.)

[chem geek]

Okay, I got a response from DuPont on Oxone, but I'm not sure how to be diplomatic about this since I don't want to burn any bridges. I suppose I will paraphrase the jist of the response.

The response I got was essentially that combined chlorines are always being formed as people go into the pool, swim, and prespire. There is no technology on the market today that gets rid of persistent combined chlorines [I suppose that's by definition of "persistent"]. Using chlorine as a shock will oxidize some contaminants, but it will also lead to an increase in combined chlorine [again, I suppose he's talking about the "persistent" variety of combined chlorines since the shocking would probably dispose of the "easier" combined chlorines]. Since Oxone [MPS] is non-chlorine, it cannot form chloramines [very true]. Also, by eliminating periodic high chlorine doses, one reduces chloramine formation [here it sounds like he's talking again about the more complex organic chloramines, not the simple ammonia-based monochloramine]. In pool water samples, they have seen destruction of the "monochloramine" component of combined chlorine by Oxone. This "monochloramine" component is almost certainly not NH2Cl, but a chloramine species which mimics NH2Cl in the DPD test [again it sounds like this is an organic chloramine]. In fact, NH2Cl cannot exist in actual pool water where there is always a free chlorine residual [I believe he is talking about the breakpoint reaction of chlorine preventing NH2Cl from remaining].

I then wrote back with more details and questions (such as the breakdown of monochloramines by sunlight, the impact of CYA on low HOCl and low breakpoint rates, the differences of outdoor and indoor pools, etc.), but haven't heard back and may not. So what's the bottom line? Using MPS in a preventative dosage will likely prevent chloramines of any type from forming so shocking with chlorine will not be necessary and may not work completely anyway (at least for that purpose -- it would still be needed for killing algae blooms but they shouldn't happen at all if chlorine levels are maintained).

Since I have not seen any significant reports from users of this forum on battling Combined Chlorine when using BBB or other methods that do not use non-chlorine shock, it would appear that the use of MPS may not be necessary in residential outdoor pools (commercial pools with high bather loads might be different). On the other hand, there are frequent reports of problems with indoor pools so perhaps MPS would be quite useful in maintenance doses in that environment. What we don't know for sure is what exactly is the difference between these two environments that is the root cause of the CC difference that makes outdoor pools much easier to manage. Is it the sunlight (UV) breakdown of choramines? Is it the greater air circulation? Is it the use of CYA (doubtful)?

[EDIT] For an alternative point of view based on experience, read Ben's tip. I'm giving the DuPont Oxone a little more credit for possible benefit in indoor pools. I am also one with the heretical idea of using a small amount of CYA (10 ppm or less) in indoor pools to lower the effective chlorine concentration to reduce exposure to clothing and people. However, using CYA means that superchlorinating is much harder, but if the CYA amount is small enough, then you can fairly easily overwhelm the CYA and get lots of pure chlorine in your pool during shocking (e.g. 15-20 ppm chlorine), but that's a topic for another thread (someday)! [END-EDIT]

Richard