WQA 2010 Summer Webinars - Asked Questions - Webinar 1
Webinar 1: Disinfection and Sanitation of Water Treatment Equipment
Presented May 20, 2010 Presenter: Larry Zinser, Master Water Conditioning, Corp.
- Questions asked during the webinar
- Questions asked during Virtual Office Hours (VO)
Questions Asked During the Webinar:
Q1: What is the difference between initial and irreversible attachment [in biofilm]?
A: The initial attachment is when the bacteria first adheres to the side of the pipe or whatever surface it’s on. That’s before it develops the [protective] polysaccharide layer. You may have recalled when we were first talking about some of the bacteria we talked about one in particular that had that produced [a colony]. Its outer cell was actually the polysaccharide. Once it’s formed a polysaccharide layer, then it’s termed irreversible because now it repels many of the attempts to remove it.
Q2: Can biofilm actually grow in the reservoir of a filtration unit?
A: It can, but obviously it only attaches to surfaces. Any surface that’s exposed to water with bacteria can form biofilm. It is amazing within some of the high purity water applications how quickly biofilm can form. I’m particularly familiar with the dialysis business where even very, very pure water that’s circulating bacteria can establish itself within the pipes. [Given] any hard surface, it can form.
Q3: Will UV treatment effectively kill or detour [biofilm] growth from occurring?
A: No, it won’t. [Later in the webinar] we are going to address how we tackle biofilm, but ultraviolet light is not effective against biofilm.
Q4: Can biofilm grow in the reservoir of a POU filtration device?
A: [By] “in the reservoir of a point of use filtration device”, I assume you mean something like a storage tank for an RO or maybe a media tank for a water softener or a filter and the answer to that is yes. It can actually form on the resin beads themselves. Once again it’s very insidious….
Q5: On a relaxed membrane how long do we have before we need to start worrying about bacteria growth?
A: I think the question refers to growth of bacteria through membranes….There are no hard and fast rules here. We’ll say that in dialysis business, the business that I was familiar with we would establish a three month period as maximum to wait until you run a disinfection process on that. But I’m not sure that there’s a standard time for that on how quickly it takes for bacteria to start going through membranes, but I know it’s insidious. I think sometimes it just comes down to trial and error.
Q6: Is biofilm caused by non-pathogenic bacteria? And if so, why is it an issue in potable supplies apart from nuisance?
A: Biofilm that’s formed from non-pathogenic bacteria is not really an issue of itself. But the bacteria and [its] remains can produce food for pathogenic bacteria. But obviously what we’re concerned about are pathogens. I guess part of it also refers to the whole purpose of water that’s being used. This becomes true for residential use; we’re only concerned about [bacteria] that are specifically pathogenic. If we were in an industrial environment, or as I mentioned, dialysis, or in pharmaceutical use, or some area where even bacteria that’s generally not pathogenic in everyday use might become dangerous in other applications, in that case, non-pathogenic biofilm would be a danger. But, your inference is correct, if it’s not pathogenic then it’s not specifically dangerous within a residential environment, other than the fact that it does create food and environment for pathogenic bacteria to grow.
Q7: If you have no colony forming after UV what is causing an increase in HPC counts in holding tanks that are re-circulated with 0.5 ml to 1.0 ml of NSF [approved] bleach [for disinfection]?
A: Bacteria can get through ultraviolet light and still be viable. There’s nothing that’s 100%. And if a bacterium happens to get through ultraviolet light it is then free to do whatever it is intent on doing….There are some species that are resistant to chlorine but I think I’d have to know [more about the application to be able to provide an accurate answer.]
Q8: If UV light disables the formation of bacteria colonies can biofilm then form within a storage device with constant UV light applied?
A: If the UV light is in the tank, and I’ve seen this, it’s not too prevalent now, it used to be quite prevalent previously. Just because there’s an ultra violet light does not mean that you’re killing the bacteria. The dosage level is particularly important and it has to do with the intensity of light that’s emanating from the UV bulb. That’s why the UV lights themselves have a specific diameter, because the intensity has to be effective at the outside of the inside of that container. If you make a larger container for example, you take a UV light that’s 6 in. in diameter and you put that UV light into a container that’s 20 in. in diameter, then the outer areas of that container are not going to have effective UV light. Because it takes a certain amount of intensity and time in order to dose the bacteria properly. To go back to your question, if you had a container you would have to insure yourself that at the outer limits of that container you have a proper dose of ultra violet light. You can do that with an ultra violet light sensitivity monitor, which will actually give you the intensity of the UV light at the outer layers so to speak of that container.
Comment from participant: Microbes are known to repair their DNA after UV storage that is why UV should not be followed by storage. Answer from presenter:That is a fair comment and that is exactly right.
Q9: Do you suggest sanitizing the whole RO system or just the membrane and how would you go about sanitizing the systems such as the storage tank, housing, and membrane and the pressure?
A: [At the time of installation of the system] the membranes themselves generally do not require disinfection as they have a disinfectant within [the package]. You can run a mild disinfectant through the system. [Typically] a filter housing that would be installed prior to the RO [would have] the disinfectant added [to] the housing and then water [would be run] through there. Each of the membrane housings themselves should be individually disinfected and then once all those components are disinfected, the membranes [are placed] inside [the system]and then flush[ed]. Because you have to flush the membranes themselves, you’ll also at the same time be flushing out any residual disinfectant you put in. Regarding the RO the storage tank [I would suggest] the same thing but it [involves] running the disinfectant into a storage system and then afterwards flushing it out.
Q10: How can ozone remove biofilm? It is also a point disinfection and dissipates pretty quickly.
A: Yeah, it does. In fact I’ve been involved in the process of removing biofilm with this process. First, you have to be very careful [when working with ozone] because ozone can be harmful. There are OSHA standards that you should use.…The real difficulty is at the end of the piping system: lets’ say it’s a length of pipe we’re disinfecting with ozone, [then] at the end of the pipe, that’s where you measure the ozone dosage, and depending on what dosage you’ve selected to remove the biofilm, that dosage must be maintained. What will happen is - in fact it’s really interesting to watch this take place – [when] the ozone… goes through the piping system, [it] will be consumed by its oxidation of the polysaccharide and the bacterial material inside the pipes. [If you’re maintaining the ozone dosage at the end of the pipe] all of a sudden you see your dosage [measurement] going up. That’s the key. At that point that’s when you’ve been effective because now the ozone going through the system [with nothing to react with] as long as your generation [of ozone] remains constant …. After the organic matter has been consumed then… you’ll have a spike in the ozone [concentration] at the end of the pipe because it is no longer being used to oxidize organic material.
Q11: In the shop we use some of our heavily ozonated product water freshly dispensed to spray onto water cooler surfaces, please comment on this as a practice.
Comment from another attendee : Ozonated water itself is not a disinfectant.
A: The ozone within the water is what does the action. The same way as [when] removing biofilm. The ozone travels in the water. I would believe that if the ozone concentration is strong enough that if there is enough contact time the water with the surface that the process would take place. But the ozone in the water, when it’s exposed to bacteria it will destroy the bacteria by decomposing it.
Q12: How would you know if you had a biofilm problem would it be by color or case change in the water?
A: The best way to tell biofilm [is present], first of all you can feel it. If you ever have a system that has unions on it and you open the unions, you can feel the slime just like plaque on your teeth. The way it’s done industrially is they measure bacteria at certain sample points....You establish a pattern [for]bacterial levels whatever the bacterial levels [may be]. [If you get] spike[s], [that is] you get a very high reading one day and you’re back to a small reading the next and you get another spike, those spikes tell you that you have biofilm. Because, what you’re measuring… is the dispersion rays of biofilm. So typically, [in industrial applications] to determine biofilm is spikes in bacteria [levels]. If you don’t have that level of sophistication, the best way is feeling the inside [surfaces] you can tell [when] there’s a slimy surface there’s biofilm. You don’t know what species it is, but there’s biofilm.
Q13: In reference to drinking water, typically, [is] biofilm associated with taste and odor, or just the presence of bacteria in general.
A: I’ve always determined that’s a presence of bacteria. For example, a well sample that has that musty odor it’s just generally bacteria. I’ve never looked at whether biofilm could create that same thing. Even in the times I’ve been dealing with biofilm I’ve never noticed a musty smell. I imagine you could get it depending on the layer of polysaccharide over the bacterial layer.
Follow up comment: So, typically musty taste and odor is more an indication of bacterial presence.
Presenter’s Answer: Yes bacterial presence; not necessarily biofilm.
Q14: How would you sanitize a water softener that has been contaminated?
A: Typically, with [a] chemical [disinfectant]. Chlorine is used periodically. We all know chlorine is dangerous for water softening resin because it can break it down. Industrially I’ve used hydrogen peroxide. Hydrogen peroxide is used with softening resin at an industrial level but chlorine or any chemical disinfectant as long as it’s [approved for the application]. I don’t know off the top of my head what [dosage] is prescribed, but I can look that up.
Q15: Does too high of a flow rate allow bacteria to pass through a point to sub micron filter on a re-circulating loop?
A: Yes it would. Once again it’s a matter of degree. What I would refer to is the manufacturer’s [information]. Surface type [filters] all have a flow chart which gives the range of flow that is prescribed for that particular cartridge. And typically with a cartridge filter you want to select a gallon per minute range that’s in the middle of that chart. For example, [a filter with a range] that goes from 0 up to 10 gallons per minute …. You would want to run that particular filter …at [no more than] the 10 gallon per minute limit, certainly not over that, because then the manufacturer is saying all bets are off essentially. You want to choose a flow rate that’s towards the center of that prescribed chart for flow rate.
Q16: What is your opinion of using hydrogen peroxide as a sanitizer?
A: I think it’s great. It’s very effective. The positive thing about it is that it doesn’t create disinfection byproducts, it doesn’t create chlorine residuals, it [dissociates] into water and oxygen so it dissipates very freely. However, it is not as effective as chlorine and you have to maintain it at a certain level because if you leave it in an open container it will lose its potency. The very interesting thing, I learned a hard knock lesson a time ago when I was working using peroxide as disinfection, I also had ultra violet lights in the stream that’s a no-no, which I found out at the time because the hydrogen peroxide will form bubbles [that coat the lamp] sleeve and essentially you’re losing the effectiveness of the ultra violet light. So in general, hydrogen peroxide is a great product the peracetic acid, which includes acetic acid and hydrogen peroxide, is extremely effective and very popular. I’ve seen the popularity of that grow quite a bit.
Questions Asked During Virtual Office Hours (VO):
Q1 VO:When sanitizing DI recirculation loops (with storage tank) using ozone, what is a good ORP mV value to achieve and how long should you maintain that value before considering the loop sanitized and taking bacteria samples? 700 mV seems to be the standard, but would a lower value (say 550 mV) for 1 hour might be adequate?
A: My experience with ozone has been in two application types: organic oxidation (of Thimersol) and biofilm removal. In both cases my goal was +600 mV with an injection of 0.5 mg/L ozone. In both cases—both contained an abundance of COD—the initial ORP at the outlet was quite low (below 300 mV), but eventually rose to a steady reading near 600 mV. That was my indication of COD removal. Neither of these was considered a “routine” disinfection protocol, but rather a corrective action. However, regarding your application of preventive maintenance, I would believe that 1 hour would be quite satisfactory unless your outlet ORP is low.(I have been taught that a consistent outlet ORP of 600 mV means complete disinfection.)
Q2 VO:Problems with recurring spikes of bacteria counts after water softeners in hospitals:
As President of the Technical Committee of the French trade association (UAE) I am currently facing reports from one of our members of recurring spikes of bacteria counts after water softeners in Hospitals.
From what I understand the units are disinfected once every 3 weeks without end, but the bacteria come back.
This in turn is leading some voices in France to suggest that softeners should be banned from hospitals because they increase bacteria proliferation and cannot be sanitized properly.
So I am in search for arguments that confirm that:
1. Softeners do not pose a health risk as long as they are properly maintained/operated.
2. In the event of an accidental pathogenic throughput (and biofilm build-up) they can be sanitized properly to prevent recurrence.
Finally I would be interested in any experience of sanitizing softeners in hospitals.
1. Unfortunately, I do not know of any study results which prove that properly maintained softeners do not pose a health risk. One of the reasons for this is that much will depend upon the character of the influent water, the water-use profile and the regeneration frequency. Influent water with no disinfectant residual, for example, will present an entirely different situation than water that has one. Any surface area—and softening resin has a lot of it—will provide the foundation for the formation of biofilm. Water sitting in distribution pipes can pose a health risk, especially if there is no residual. Additionally, as we have discussed in the webinar, idle water increases the likelihood of biofilm formation. The more idle time, the greater the risk. Salt-based regeneration on its own has no specific bactericidal function, but when delivered with a high pH additive such as sodium hydroxide, there is such an effect. Depending upon the nature of the influent water, the use of a disinfection protocol (such as UV) prior to the softener would certainly deter the formation of biofilm within the softener. The first step in working on this application should be to fully analyze the influent water. One of the lessons I have learned with bacteria is that if there is a problem, solve it (destroy bacteria) as close to the point-of-entry as possible.
2. Regarding sanitization, I will refer you to an article from ResinTech, Inc. The article addresses both chlorine and hydrogen peroxide use. Please pay particular attention to the dangers of iron salts in the resin and to the need for ventilation. Additionally, the WQA has an excellent section in its Guidelines for Disinfection and Sanitation of Water Treatment Equipment. This text also encourages attention to the salt used for regeneration. I would also recommend an article by P. Regunathan and W.H. Beauman (“A Comparison of point-of-Use Disinfection Methods”) which was presented by the WQA in their 2008 WQA Educational Kit.
3. My only experience with resin disinfection was in an electronics industry application with 40-cubic foot mixed bed resin tanks. The resin was virgin (no iron danger), and each of the resin tanks had a pressure relief valve. We used 10% hydrogen peroxide, and maintained less than 1% solution for about 30 minutes each tank. Thereafter, we routinely took (heterotrophic) plate counts every two weeks.
Q3 VO:Comparison of disinfecting strength of various concentration hydrogen peroxide (H2O2) solutions, sodium metabisulfite, sodium hydrosulfite, and chlorine:
1. How does a 7% solution of H2O2 compare to a 12% solution of Chlorine in terms of contact time needed, and concentration needed?
2. How do sodium metabisulfite and sodium hydrosulfite (ban iron) compare as sanitizers to H2O2 and chlorine? And what are the effects on the body if consumed?
A: 1. Please see the WQA publication: Guidelines for Disinfection and Sanitation of Water Treatment Equipment, page 33 for useful comparison of sanitizers and contact times. Generally speaking, for 0.0005% chlorine solution (50 ppm) the contact time is 2 minutes, while for 30% hydrogen peroxide (30,000 ppm) the contact time is 180 minutes. (The pH should be between 5 and 6 for the chlorine and a bit over 7 for hydrogen peroxide. The temperature should be over 50 deg F) It should also be noted that Hydrogen Peroxide will not be dependable against virus or cysts, and that chlorine is not dependable against cysts. The situation changes, however, when the chemicals are used as oxidizers.
2. I use sodium metabisulfite as a preservative and disinfectant for the membranes we market. It is an antioxidant that removes oxygen from the water. It is very stable (compared to chlorine or especially hydrogen peroxide), and it is typically used at 1% w/w concentration. Currently, potassium metabisulfite (similar chemical and biological effects) is more available because it is preferred by the winemaking industry (winemakers prefer the potassium ion to the “dreaded” sodium ion.)
3. Sodium metabisulfite should not be ingested (induces vomiting). It readily releases sulfur dioxide which forms sulfurous acid. It can be fatal. If the powder form (or the sulfur dioxide) is inhaled, it can be quite irritable. (I learned this the hard way.) I am including a typical MSDS for your review.
Q4 VO:Sanitization with citric acid.
We are looking for an option to give consumers to keep the device clean and hygienic without having to use chemicals such as chlorine, paracetic acid or ozone. Citric acid is a rather safe chemical to use and can be made readily available.
1. What is your opinion and experience by applying citric acid for this purpose?
2. Can you recommend how to best apply it? 3. Is there any (scientific) literature and/or standard to your knowledge that describes sanitizing POU equipment in a consumer friendly manner?
1. According to the research I’ve seen, bacteria, including the E. coli families, will survive for at least several hours at a pH of 2 (1 ounce citric plus 1 quart water). Most bacteria are considered “neutrophiles”, preferring a pH of 6 to 8. The low pH will impede their ability of bacteria to grow and to reproduce, so over time, the species will die out.
2. If you intend to use only citric acid, relying only on pH as your agent, I would suggest the above solution (1 oz dry citric acid to 1 quart water) since this gives a consistent pH less than 3. However, as per the discussions above, contact time may be an issue for you. On pg 58-59 of his book, High Purity Water Preparation, Theodore Meltzer discusses pH as an anti-bacteria agent. Of course we have to be aware of the potential dangers to the consumers who are to use any disinfectant, even citric acid. The individual Material Safety Data Sheet (MSDS) for that and any disinfectant must be understood. However, we must also be aware of the potential dangers of disinfection failure and the subsequent infection of the consumer. This may be much more consequential, not only for the consumer himself but to his family as well. In some situations the answer may include the education of the consumer so that he can safely employ more effective measures against infection.
3. Again, you may consider the procedures outlined in WQA’s Guidelines for Disinfection and Sanitation of Water Treatment Equipment, or you may consider the outline that we at Master Water Conditioning, Corp. use for consumers.
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