Caption template - NEHA
Hello everyone and welcome to the presentation "Advanced Chemistry and Its Impact on Disinfection." To ask questions about this presentation, please join the presenter in the networking lounge at the designated time listed on the agenda. I would now like to introduce Roy Vore, Technology Manager at BioLab Inc.
Good day everybody. This here is going to be a very interesting year for us. This will be the third time we get together to talk about the Model Aquatic Health Code this fall. A lot of us are looking at our pool codes on a routine basis anyway, but this year is very important. And as we go into this year, and I know a lot of us are very active in the Model Aquatic Health Code, I've got some ideas that I want to just shine the waters with to get us thinking about what we should be doing.
Let's talk about swimming pools for a little bit. The modern pools, as we envision them here in the United States, really started in the more early 1900s. And historically speaking, a few things have changed in American cultures and rural cultures since the 1900s. When we look at swimming pools, the filtration systems have changed in more ways than most of us recognize. In the early days, we looked at chlorination as simply a way to oxidize components in the water and keep the water clear. Now we focus on disinfection. But more recently, now we've started looking at the chlorination of things like pharmaceuticals and cosmeceuticals, what kind of infection byproducts.
So our thought of chlorination has changed. The way we've tested our chlorine has changed. The list of pathogens in the last few years has gotten much longer. The concentration of chlorine that we use has gone way up, and then kind of come back down a little bit. Our water balance parameters over the last 60 years have actually narrowed in North America. And as many of us know, we've got the Model Aquatic Health Code. And so here in the United States and impacts outside of that, and particularly in Canada, we've got a platform where we can discuss all the parameters, how should we be operating our pools and our spas, what is the correct procedure, what are the best practices that we can adopt and standardize in our own local codes.
So, with that thought, are we happy with our latest version in the Model Aquatic Health Code or should we be making some adjustments? Well, I'm going to give you kind of a myopic view. And usually I'm an optimist, but in some areas I'm a little bit of a pessimist because some of us that travel a little bit, have been in a lot of hotels and a lot of health clubs, and it's like we look at the way our pools are operated around here, and our pool operators, particularly in the hotels and health clubs, they're working on the water fountains, they're fixing the broken locks, they're replacing the doorknobs when they break, they're working in the showers that are leaking, the toilets that are backed up, and the last thing on their mind a lot of times is keeping the pools operating. No wonder we're having outbreaks on weekends.
Our inspectors, many of you on the phone are inspectors, in the winter you're running around looking at restaurants, looking at nail salons, looking at pedicure baths, we're looking at tattoo parlors. And surprise, surprise, the summer comes along, that work doesn't go away and now you have to look at swimming pools in addition to that. Is it any wonder that all of us go to the simplified method and we just go through the checklist? If this is on the checklist, I'm going to look at it; if it's not, I'm not going to look at it.
So let's ask a few questions as we're going into this review cycle on the Model Aquatic Health Code. Here's a couple things I'd like to ask. What lessons from the past have we lost? And are some of those basic assumptions that we made and built into our Model Aquatic Health Code and all of our local codes, are they a little bit more restrictive than they need to be based upon science? So there are three areas that I'd like to talk to us about today. Let's talk about the filters, how they've changed. Let's talk about recreational water illnesses. Do we have the right list of pathogens and are we focusing on them in the correct way? Let's look at the water balance parameters and how they really impact disinfection. And right toward the end I'm going to throw in a little on bromine in here because we did have a historic year of 2016 of crypto outbreaks, including in bromine pools.
So let's start off talking about filtration. Let's look at it from an historical viewpoint. In the early 1900s, we started out with what was called slow rate sand filters. And the basic design of this filter goes back to the Roman time periods. It's a gravity flow system. You've got very fine sand on top. You've got mid-grade sand in the middle. You've got gravel on the bottom. Sometimes you've got charcoal or anthracite coal down there. It's a very slow trickling filter system in there. And in the early days these pools were always -- these filtrations systems were always operated with ammoniated alum.
Right there in the middle of the left-hand block on there you see a little word that's called schmutzdecke. My German's not very good, but what that translates is "slime layer." These filters were designed to operate with a biologically active slime layer across the top, and that is what removes the organics from the water. This system is still used in potable water in parts of the world today. It's very good about removing organics. But systems moved on.
We moved on to a rapid rate sand filter beginning in about the 1920s and to about the 1960s in most cases. They look a lot like the gravity drain systems. They're smaller and you still have the multi-layers and the fine gravel and the fine sand on top, the little coarser sand mid-level, the gravel toward the bottom, but if you look at that left-hand picture again, you see that point layer on top, that is a very dense layer of alum, not ammoniated alum, just regular alum. And these systems are very good at removing particulate matter because of that alum layer on top.
And then, starting in the 1950s, we started seeing our modern designs, our high rate sand filters, the third generations. This is a vertical system that we see here on the left-hand picture. There are horizontal, larger systems out there. Many of our larger facilities have horizontal, but they operate in the same way. Flow rates have gone from gravity speed, very slow, to almost 20 gallons per minute per square foot of the surface area, very high grade compared to the rapid rate sand filters. Uniform sand throughout. Flocculants are not generally used with these kind of systems. Filter aids are only used when necessary. Really radical change. But let's summarize those changes in one slide so we can see.
Going from left to right in historical developments, gravity feed, a little bit faster flow, to a very fast flow that we have today. Multi-layers, multi-layers, single uniform layered sand. Drop down there to the next to the bottom down there, gone from ammoniated alum to alum to not using flocculants. We used to recognize in the first two generations that we had a biologically active system. The modern, high rate sand filters were not really considered biologically active. Should we? What do we really know about filtration systems?
Well, we know that our modern filters work better when they're just a little bit dirty. In a standard practice, we used to add flocculent to them. We also know that when you pop one of these filters open, and you do it in microbiology, and I am a microbial physiologist and an ecologist on here, and so I've done this an awful lot, on a well-maintained sand filter you're going to get between ten-to-the-sixth and ten-to-the-eighth bacteria per gram of sand. In other words, you've got a few billion bacteria in a well-maintained sand filter. In water treatment, we would call one of these filters a fixed-bed bioreactor. And we use these fixed-bed bioreactors to remove organics from wastewater streams.
We also know that chlorinated organics do not get digested as easily as non -- chlorinated organics are not as easy to digest as the non-chlorinated ones. So what should we thinking about? Well, let me just put a couple thoughts out here. Would a slow rate sand filter on a side stream help us to reduce some of the disinfection byproducts, because a lot of the organics are suspended in the water? They're filterable. Now, we've got that kind of organic buildup there on a filter, and we're not putting much chlorine through it, but are we going to get growth, things like pseudomonas? Now, we know we get this at a point of use potable water filtration system. So are we going to get the wrong kind of growth in there? I don't know. Maybe.
So would we then have to post-chlorinate the side stream coming up? I don't know. We'd have to do some research on them. But, bottom line, could we slightly change our practice on our filtration systems and increase our removal of the disinfection byproducts? Would we end up with healthier water if we changed our filtration practices? And everything on that bottom third of the slide we're looking at right now is exactly what they're doing in Europe and the Province of Alberta today.
All right. Let's move on to the next topic. Let's talk about the pathogens we've got. Let's talk about the evolution of the pathogens and the list that we've got. So where have the list of organisms that we're concerned about come from? Well, they've come from practical experience. In the early days, when we started talking about the pathogens in pools in the 1930s and '40s, we were really concerned about coliforms and the enterococci, the same organisms that we were concerned about in drinking water, because we were using these as indicators of water quality.
In the 1950s, in the Handbook of Chlorination -- and if you're in the recreation water business I'd strongly suggest you get a copy of the Handbook of Chlorination from 1972 because a lot of background information is in there. But we started getting concerned about Staphylococcus aureus. And I've run an awful lot of microbiology under an awful lot of swimming pools, and I can tell you if you've got a high school pool with a lot of kids in there, you're going to get Staphylococcus aureus in a swimming pool. It's there. It's there in large numbers.
1969 was the first time they recognized that shigella was a pathogen. In 1978, pseudomonas became recognized as a pathogen, particularly Pseudomonas aeruginosa. After 1978, the literature about Staphylococcus aureus being a pathogen disappeared. All the concerns we had about dermal rashes were probably misplaced about staph. It was pseudomonas we were really concerned about, but we didn't recognize it until 1978.
Then, in 1981, just five years after the famous outbreak of legionella in Philadelphia, we get our first major outbreak of legionella in a hot tub. Think about it, legionella likes water, it likes warm water, it likes organics, and it likes to be spread in droplets. You cannot engineer a better system than a spa for dissipating legionella into the breeding zone of humans. It's a perfectly engineered system.
Giardia was recognized in 1985. And then the one that I remember distinctly was in 1998 when we had our first outbreak of what are Shiga toxin-producing E. coli, or O157s, in a water park just to the west side of Atlanta. We always wondered where this was coming from, and now we recognize this is a very acid-resistant organism with a very low infectious dose. One person contaminating a facility if they don't have the right chlorine and we could have a major outbreak if somebody's swallowing the water. Then in 1992, cryptosporidium, the 800-pound gorilla that we now all face.
Yes, there are viruses. There are a lot of viruses in there, but the amount of information that we can gather on the concentration of viruses and diseases that are caused by it is really not very well-documented in scientific literature. So we need to focus on cryptosporidium and those organisms above it. But before we go on, let's look at that E. coli, the giardia, the legionella, the pseudomonas, the shigella. All those are very chlorine-sensitive. If there is adequate chlorine in there, we shouldn't be seeing these organisms. Cryptosporidium, highly chlorine-resistant. Two different categories, chlorine-sensitive, chlorine-resistant. That's a key factor in designing our disinfection systems.
So what do we really know about the pathogens? We know, based upon CDC reports, that if you've got one PPM or more of free chlorine, as measured by DPD, you do not have a documented case of E. coli, shigella, giardia, pseudomonas, or legionella. Let me repeat that. If we have one PPM or more of free chlorine by DPD, we do not have outbreaks of E. coli, shigella, pseudomonas, legionella, or giardia. Further, in 1984, the Australians did a very wonderful cross-functional study, they had pool operators, they had environmental health, they had microbiologists that went out and verified that, with one PPM free chlorine, you have a 99% chance of having a well-maintained pool with no E. coli, shigella, pseudomonas, legionella, or giardia. 99% confidence level.
All right. But let's think about cryptosporidium. For the last couple years, our primary tool in solving cryptosporidium has been with education. Do not swim for two weeks after you've had diarrhea. How well is it working? Well, let's look at some other things we do. We tell people not to drive and drink. We tell people not to use their cell phones while they're driving the car. We tell people not to use drugs. We tell people to buckle their seat belts. Education in situations like this is not tremendously effectively. And clearly since 2016 is going to come out to be our highest number of outbreaks of cryptosporidium ever, education isn't working. So now we have to fall back, in most facilities, hyper-chlorination. Well, it's pretty hard to do. It's reactive. Most of the time, we don't even know we need to do it until we're in the middle of an outbreak and we've already got tens, if not hundreds of people sick.
So what should we be thinking about? Well, for the chlorine-sensitive ones, we know these outbreaks occur, one, when somebody didn't add chlorine to the pool, or the equipment broke. Failing to add chlorine to the pool is usually a result of training issues. Equipment breaking is because somebody wasn't monitoring it. So are we ready yet to require a full-time CPO at every facility during its hour of operations or at least requiring remote sensing? So if the CPO isn't present at the facility, at least to get a text on the phone or an email, "Hey, heater broke, we're low on chlorine. pH is out of range. Come fix it." Right now, a lot of our outbreaks are occurring on Saturday nights and Sunday nights at hotels because the operator isn't there on the weekends. If we've been in hotels recently, you know exactly what I'm talking about. So that's it for the chlorine-sensitive box.
Cryptosporidium, presently in the Model Aquatic Health Code we require a secondary disinfection system on increased risk facilities. Are we ready yet to require a secondary disinfection system on every facility? So, at least in this case, somebody might have a diarrheal accident and introduce a large bolus of crypto, but with secondary disinfection that outbreak will be over by the time the facility opens tomorrow morning. Instead of infecting hundreds of people, we at least have a chance of infecting maybe a few dozen or even less.
All right. Let's talk about chorine disinfection. What concentrations of chlorine are we using, how did we get here, and are we using the right concentrations of chlorine? We need to focus, at this point, on the chlorine-sensitive ones, because it doesn't matter what we do with chlorine for cryptosporidium. And the normal concentrations for using it in pools, we are not killing crypto. We need secondary disinfection if we want to maintain cryptosporidium outbreaks.
So let's talk about disinfection for a few minutes. I mentioned George Clifford White's Handbook of Chlorination 1972. It's a really good description of some of the historical developments in here. So this is a summary table of how we got to where we are today, historical from left to right. If we look at, you know, pre-World War II, 1941 and before, White described the chlorination patterns there as really token chlorination. He really doesn't have a lot of good things to say about how we used to operate pools in there. We measured it by O-T or O-T-O, depending on how you want to call it on here. And this is when we were using the ammoniated alum, as we talked about in the filtration section just a minute ago.
Typical total chlorine was less than one PPM. Monochloramine was the primary -- well, we know monochloramine is a disinfectant, because we used it in our drinking water, but the rate of kill is very slow compared to hypochlorous acid versus chlorine. What really killed the system off was really World War II. A lot of the ammonia was being pulled out of the water system and being used for the production of explosives. So it phased out in World War II, as well as the understanding of break points in our nation. Then, after the World War II, when the pool industry started picking back up again, they went into a period that White described as high pre-residual. And, again, we were measuring it with the O-T, O-T-O systems in there, but we talk about high pre-residuals.
Look at the total chlorine in there. It's three to five PPM of total chlorine with free chlorine of one to two. That necessarily means the combined chlorine was between one and four PPM of combined chlorine. White makes a very subtle comment in here as these pools required frequent super chlorination. Yeah, right. You know how many rashes we had to be having in here? Oh, by the way, when you look at the historical literature, it is full of discussions about rashes during this time period. That's when they were talking about the Staphylococcus aureus all the time. It probably wasn't staph that we're referring to; it was the combined chlorine that was causing the rashes.
And this was phased out really when two things happened: one, we recognized that O-T-O was a carcinogen and we didn't want to be handling it, and two, we recognized, hey, if we switch over to this other method called DPD, which we use now, we can measure free chlorine effectively and distinguish free chlorine and combined chlorine and give us better control. And that started phasing in the U.S. operations in about 1969, mid-year. And we're into our current operating systems now where most facilities are operating in the one to four, one to five PPM of free chlorine, trying to keep our combined chlorines as low as possible. There's a few states that are still sub one PPM; we'll explain why that in a minute. But our current Model Aquatic Health Code, we're one to ten PPM free chlorine without CYA, and two to ten PPM with CYA.
So how did we get to this approximate one PPM? Well, that's kind of a long story in itself. Let's look at it. The first thing, you make the assumption is how do we want to disinfect our pools? Number one, we want a broad spectrum thing that kills any of the pathogens that could be in there, and we want it in the water at all times because we don't want to build up anything.
Well, in the early 1960's, before the EPA was even created, pesticides in the United States were regulated by the U.S. Department of Agriculture. And there were two microbiologists and chemists there, working in there, it was Ortenzio and Stuart. And they came up with a way to estimate how effective a treatment system was, and they used indicator organisms that they were familiar with in potable water, E. coli and enterococcus. They formalized the method. They published it in 1964, and today we call AOAC 965.13. It hasn't been updated since 1970. And that method, today, is still cited by the U.S. EPA. It's officially called OCSPP 1810.2600, in other words, the presumptive efficacy test for disinfectants used in swimming pools in the United States.
Now, I'm a microbiologist and I've run this system a few times, and I've given talks like this probably for the last 20 years. I've rarely run across anybody that's ever really run into doing this test. So let me give you a little background. I kind of like the test in some ways, but let's understand what we're doing in here. When you take the glassware, you wash it first, and then you rinse it in chromic acid, triple rinse it in distilled water, and bake it for 180 degrees and two hours. We grow your bacteria on solid lawns, as specified in the test protocol, relatively simplified media. You flood the media, wash the bacteria, filter off the organics, float the bacteria back up, centrifuge them, collect the pellets of bacteria, discard the organics, then you come up with a very pure solution of bacteria and sterile distilled water.
The test water you actually run is sterilized distilled water with a phosphate buffering and it has zero chlorine demand. For this test to be accepted to quality control parameters so you can start at time zero, at 0.6 PPM free chlorine, and at ten minutes you'll have to have 0.4 PPM of free chlorine, and that's measured by a thiosulfate titration. Your positive controls at 30 seconds you have to have six logs of kill of E. coli. And the other organism is Enterococcus faecium, you need six log of kills in two minutes or less. All right. This is where the six log, 30-second, less than one PPM standard came from that is still in some of our codes. This is a laboratory test.
Is this applicable in the real world? Let me ask you a couple of questions before you get into that, before you want to make that the gold standard. At the end of the day, do you drain all the pools in your jurisdiction? Get all the water out, scrub all the surfaces out with chromic acid. This includes, by the way, the plumbing and the filtration system. Now, I'm not going to get really obnoxious and make you bake your pool at 180 degrees C for two hours, but you could.
Are the bacteria that are being introduced in their pure solutions, are they being introduced by swapping skin cells and vomit and diarrhea with a large bolus of organic material that is depleting the chlorine? Is your pool outdoors? Is any soil ever getting blown into it? Do any of your bathers sweat, urinate in the water? Is any sunscreen going into the pool? In other words, are you running a pool in a laboratory or are you running the pool in the real world? And before you cite that 30 seconds is a mandatory requirement, the standard says E. coli is killed at 30 seconds, but enterococcus is killed in two minutes. Are you still certain that you want to use this laboratory test at your basis of writing a code in your jurisdiction? Just some food for thought.
All right. Where are we today? Well, there's a variety of different codes out there available. There's guidelines. Let's just look at a few of them. Now, I work for BioLab right now and we're a pretty big chemical manufacturer. So if you call me up and you ask me, "Roy, how much chlorine should I use in my pool," I'm going to look you right straight in the face and I'm going to say "You should use one to four PPM of chlorine in your pool, and you should maintain your pH between 7.2 and 7.8." And I'm going to tell you that for one reason, because all of our products and all of the chlorine products used in the United States are registered by the United States Environmental Protection Agency. That first little paragraph on the back that says "Directions for Use," right underneath that there's a little sentence in there, and it says "It is a violation of federal law to use this product in a manner inconsistent with its label."
So if you ask me how much chlorine you're going to use, I'm going to cite the U.S. EPA because I'm not going to try to violate too much federal law, and I'm going to say you use one to four PPM. Scientifically, I got to give you a different answer, but if you ask me professionally, I've got the answer I've got to give you. It's a little frustrating, but that's the world we live in sometimes. All right. So that's where the EPA guidelines came from. All of us that make chemicals and sell them out in the industry, we live by the EPA.
The Model Aquatic Health Code, which I've got several years of my life in helping write the disinfection module on here, for guidelines there's one to ten with no cyanuric acid, two to ten with cyanuric acid, keep or combine chlorine low, or pH that's 7.2 to 7.8 -- that was a rough one for me to write, but we did it and we'll talk about that in a minute. Nova Scotia looks an awful lot like a cross between the U.S. EPA and the Model Aquatic Health Code. That was because when Carey Frazier [ph] was writing this several years ago, Nova Scotia didn't have a code, she did a cross between the Canadian labels and the Model Aquatic Health Code, and she wrote a new guideline for Nova Scotia. So, Model Aquatic Health Code is being read outside the United States and this is one example.
But there's an entirely different school of thought about operating pools, and that's in Europe. And on the far right-hand column is the British standard, which is a guideline, it’s not really a code requirement in England. It's very similar to the German DIN standard we've all heard about. And I'm citing the British standard because I'm very fluent in reading that, as opposed to the German standard on here. But look at the pH range on the British standard on the far right. It's 6.8 to 7.6. Your chlorine is a little bit lower. The most current code that I can find that's quite a little bit different is the Alberta code. And this is really an outgrowth of specific operational parameters that's come out of Germany. The amount of chlorine that you use in Alberta depends on the temperature.
But then look at the middle section in there in the ORP, the oxidation reduction potential value. In Alberta, in certain facilities, they have these very sophisticated filtration systems with low flow and flocculants, and they're able to maintain incredibly pure water and maintain a very high oxidation reduction potential with small amounts of chlorine. Look at the very bottom line. They are following the efficacy by mandatory microbiology testing. This is entirely different than what we use in the United States and most of Canada, but it's an outgrowth of what we're seeing in Europe, and they're following the microbiology. It's the same microbiology we'd be worried about in the United States.
All right. There's also a whole bunch of trade guidelines out there, and these look an awful lot like variations on what you'd expect from the U.S. EPA or the chemical manufacturers. They're out there. They're not nearly as sophisticated as the Model Aquatic Health Code in some parameters or that Alberta code. All right.
So let's just stop for a minute and let's do a hypothetical example here. Let's see what happens if we just play with some of these chemistry parameters. So let's take a hypothetic pool, outdoor pool. We're going to say we're going to disinfect our pool with bleach, and we're going to use an HCl acid to control the pH on here. It's an automatic control system. We're going to measure our free chlorine by DPD. You've two PPM of -- two PPM of free chlorine by DPD. Very low concentration of combined chlorine. Our pH probe was calibrated an hour ago. Our ORP probe was counted an hour ago. Temperature is 77. Don't have any cyanuric acid. This is a very well-run pool.
So let's just play with the chemistry for just a minute. Let's focus for a minute on the green section across the middle of the slide. This is where we're going to start from time zero. Two PPM free chlorine by DPD, 7.5 pH. We know that free chlorine in a swimming pool consists of two components, hypochlorous acid, HOCl, and hypochloride, and that these two are in an equilibrium constant. And the pK of that reaction is slightly above 7.5. So we're always going to bind components of HOCl and OCl in every swimming pool. Our primary disinfectant is not free chlorine but it's HOCl, because laboratory studies have confirmed that HOCl is approximately 100 times more efficacious than OCl-. In other words, OCl is there, it's really not contributing to the disinfection rates.
But let's just play with our pH for a minute. Let's say that our pH probe goes a little bit ahead and we start feeding a little bit too much HCl into there and our acid starts dropping. Then our pH drops to 7.2, then it drops to 7.9. Let's just stop it right there for a minute at 6.9. We're now at pH 6.9, second line from the top. By DPD, we still have two PPM pre-chlorine, pH 6.9. We can calculate that we now have 1.58 DPM of HOCl, and 0.42 PPM of OCl-. We've increased the concentration of the disinfectant simply by lowering the pH. Simultaneously, if you look at the far right-hand column, the ORP value has gone from about 793 up to about 833. This is just a result of the Nernst equation, for every one unit change in pH, you get a 59 millivolt change in ORP. We all did this in German [ph] chemistry many years ago, probably trying to forget it, but it's come back to haunt us at this point. All right. So if we lower the pH, we increase the HOCl.
All right. So now our automated system kicks back in, realized that our pH is too low, and we start feeding bleach back in there to neutralize the system, and our pH is climbing and climbing and climbing and climbing, and we get back to 7.5, we go to 7.8, and now our pH stabilizes at 8.1. But we've now hit a plateau. Our DPD reading is still 2.0 at this point. We've just bounced our pH back up a little bit. We calculate how much HOCl we've got. We've only got 0.39 PPM of HOCl; that's our primary disinfectant. We've got a lot of that OCl-, which isn't that great as a disinfectant. And our ORP value has dropped. Totally different environment, whether you lower the pH or increase the pH.
Summarize that for just a second. As pH goes down, HOCl and millivolt increased, and the rate of kill increases with warning. We kill faster at a low pH. The exact opposite is true as pH goes up. HOCl decreases, millivolt decreases, and the rate of kill decreases. This is why the Europeans push toward a 6.8 pH. Let's think about it a little bit different. This is a little bit complicated, but this is a really what we want to be thinking about. If we decide that HOCl is our target, how do we get there?
So we establish a target. And in this situation, we want one PPM HOCl at pH 7.5. And get there, our DPD has to say 2.05. We would then have 1.05 HOCl and there are available readings [inaudible] millivolts. If we maintain 1.0 PPM HOCl constantly, we can calculate what our reading for DPD must be. If our reading or pH is low, we need a lower reading by DPD. If our pH is high, say 8.1, we need five PPM by DPD to give us that one PPM of HOCl.
This is what we indirectly are doing. This is probably the first time you might have ever seen this kind of table. Our real goal is to maintain HOCl at some predetermined level. One PPM is probably a little bit high, but this is for illustration purposes. We can calculate these numbers. HOCl is our dominant factor. You can't measure HOCl directly because it' a rather complex equation. But you can estimate it and you can work indirectly and calculate what your disinfectant should be if you understand the chemistry.
Now, I want to give credit to the previous slide, this slide, and the next two slides to Richard Falk, who did some of the calculations for me on here. He's working with several of us on the Model Aquatic Health Code and we are working on this kind of calculations and will be published later in 2017. All right. So, if there is a correlation between pre-chlorine and oxidation reduction potential, we ought to be able to graph it; right? All right. So, Richard and Jeff Luedeman went out and got real-world data and graphed it. And they looked at the free chlorine versus ORP, and this is the real-world data, and that's a linear regression plot.
Down there in the lower right-hand corner, that you can't read, there's a little text in there. Let me blow that up for you. Linear regression on this is 0.109. It's not a very good linear regression. We cannot arbitrarily use free chlorine versus ORP across the board in every facility. We must calibrate our ORP probes if we are using free chlorine against valid readings. But let's advance that just a little bit.
If we consider the disinfectant as HOCl and not free chlorine, that's what this graph is. And to the right side of the graph, the kind of little darker purple things in there, this is up in the range where we operate our pools. Look at the data scattered around that linear regression line. Look to the far left, these are really, really, really low concentrations of HOCl, probably we would be closing all these facilities down there anyway. But to the far right we have a very good correlation between HOCl and ORP. There is a very strong correlation in this case in disinfection. Let me blow up that little box down there in the lower right-hand corner for you. Correlation coefficient is now 7.36. So, HOCl and ORP are highly correlated compared to free chlorine.
Overall view of disinfection. We know that HOCl is the only primary disinfectant in a swimming pool. And we try to go back and look at old studies and there's a task force that several of us are working on in the Model Aquatic Health Code, and it's a cross-function with numerous companies and several academics on there. And the old studies, they've got some O-T-O studies in them. They've got some thiosulfate. They've got some DPD. They're a mixed bag and it's very difficult to pull some of this information out. What we do know that disinfectant concentration HOCl is impacted by a lot of parameters, including sunlight, temperature, pH, and organics in there. We know that HOCl is a little bit difficult to measure, but we can calculate it.
Going forward, knowing this and understanding chemistry better than we ever have in the past, could we think about focusing on HOCl rather than DPD? Can we come up with a simplified system that makes it easy for operators as well as inspectors to focus on what we should be doing? And if we do that, have we backed ourselves into the corner, do we necessarily have to shut a pool down if it's pH 1 but it's got chemical chlorine in it, and is it the same threat as the pool where it's 7.9? Data says no. Data says it's a different ball altogether in low pH.
All right. Let me finish up here for the next few minutes. As I mentioned earlier, 2016 is going down as the biggest outbreak of cryptosporidium because of multiple outbreaks of cryptosporidium we've seen to-date. And one of the things that happened just north of Columbus, it was a brominated pool, and I got involved in some of the guidance on what to do in a brominated pool, and I realized just how complicated it is. And so what do we do with crypto in a bromine pool? Well, let's look at the chemistry of bromine for just a minute.
There's really four different ways you can generate bromine in a swimming pool. We start with BCDMH, bromochlorodimethylhydantoin; or you could start with sodium bromide, you could oxidize it with bleach or "calified" bone [ph], you could oxidize it with potassium monopersulfate, that's the third one; or you could oxidize it with an ozone. In all cases, what you end up with is hypobromous acid, which is the brominated equivalent of HOCl. All right.
So, now we've got a brominated pool, and it's like, what happens to the bromine? Oops, looks like my [indiscernible] is kind of trying to get away from me there in hypobromous acid in there. Sorry about that. Anyway, so we threw bromine in a pool, throw a [indiscernible] in the pool, we get a little bit of perspiration there, some organics in there, some of that suntan lotion, and you form a bromide again. You form oxidized products and you form inorganic and organic combined bromines. Bromide is there. Bromide is not going away. The only way you can eliminate the bromide is to completely drain the pool. So you've got bromide in the water. It's there.
But now you've got crypto outbreak and you decide you're going to hyper chlorinate the pool. So let's throw a whole bunch of chlorine into the pool, and the chlorine reacts with the bromide and it oxidizes the bromide to hyperbromous acid, and you get chloride ions left over. Well, the problem with that is this reaction is almost instantaneously, and there's a lot of bromide in there. There is somewhere between 60 and several hundred PPM of bromide in there. And the reaction goes until all of the bromide is converted over. But doing so you deplete all of the chlorine you just added.
You've now effectively hyperbrominated a pool, not hyperchlorinated a pool. That wasn't what you wanted to do. Now you got to figure out exactly how you're going to measure it. All right. The problem there is the DPD cannot tell the difference between hyperbromous acid, combined chlorine, or combined bromines. But you need to measure what you did. So how do you decide that you've achieved the target value on a brominated pool? You can't. It's just that simple. Using current test kits in conventional methodology, there is no way to achieve the hyperchlorination in a bromine pool and demonstrate it. Now we're stuck.
So, with crypto in a bromine pool, you've got two options, drain it, complete drain, because you've got to get rid of the bromide, or you've got to do reduce the crypto to a minimum concentration, or you have to install a secondary disinfection system. That's it. Those are the only two options that I can come up with.
All right. In closing, I want to leave you with five thoughts. Don't have any answers here, just things I'd like you think about. Number one, if someone walked into your shop and they wanted to put in a new filtration system, and they had demonstrated and they've got pretty convincing data that, you know, they can reduce the disinfection byproducts with this new designed system, would you consider it? What if it's a little bit unconventional, but they've got data? I, again, repeat, I am not selling filters. I have no financial interest in it. I'm looking at this as a scientist. Would you consider an unconventional filtration system? Kind of like they did in Alberta, you know, got really good water quality.
All right. Let's go out and inspect a pool. Let's walk into a pool. It's well-operated. You walk into the pool. There's no smell. The water is beautiful. It's very clear, but the pH is 6.6. There's zero chlorine. The water is balanced. And by our DPD test kit, which we run ourselves, not the operator, we're running it, we've got 1.1 PPM free chlorine. There are no eye and skin complaints. Should the pool be shut down? If so, why? Do you shut it down for a health reason? Now, we demonstrated earlier that this is a well-disinfected pool and it's got at least one PPM of HOCl under these conditions. This is a disinfected pool and there are no other health concerns because this is exactly the way they're running pools in Europe. So do we shut the pool down or not?
All right. Let's go down the street and inspect another pool. Pool looks great. No smell, no odor, but the pH is 8.1. Again, there's no cyanuric acid. The water is balanced. Our test kit shows you've got 5.2 PPM free chlorine by DPD. Calculate it back, you've got one PPM HOCl, which is your primary disinfectant. Statistically speaking, this is a very well-disinfected pool. Do you shut it down? Under what basis do you shut it down? Is it because it's outside of our convention code or is it a health issue? Just a thought.
All right. It's now 2017. We've got a crypto outbreak in a bromine pool. How are we going to do it? One last question for us. What if number two or three or four were at a splash pad with a properly designed and well operating UV system, would you be concerned or as concerned under these conditions? As I said at the beginning of it, I'm not giving any information here. I'm just evoking some thoughts. How do we want to run our pools going forward? And my sources of information are right here. Thank you.
Thank you, Roy. And thank you everyone for attending today's webinar, "Advanced Chemistry and Its Impact on Disinfection." On behalf of the National Environmental Health Association and our presenters, thank you for joining us today and have a great rest of your day.
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