By P. Regunathan & Gary Hatch
The following is a continuation of a discussion between Gary Hatch and “Regu” P. Regunathan to review the current microbiological standards for the point-of-use/point-of-entry drinking water treatment units (DWTUs) and compare them to a proposal up for adoption. Hatch is the chairman of the Mechanical Device Sub-Task Group of the Microbiological Reduction Standard Development Committee at NSF International’s DWTU Joint Committee. Regunathan serves as a member of several sub-task groups of this effort.—The editors
Regu: Can you tell me what the basic differences are between the U.S. Environmental Protection Agency (USEPA) ceramic candle test protocol and what, at least to date, your task group has come up with?
Gary: Well, I’ll try. So far, it has been a long road, and I think we’re very near the end. Let me give you a general overview of what we want to accomplish and then give you some specific details. First, our general approach was to incorporate as much existing know-how and other standard protocols as possible into the process.
Regu: Such as from the USEPA protocol and existing NSF DWTU standards?
Gary: Precisely. These standards will follow the basic format of the existing NSF/ANSI DWTU standards such as Standards 42 and 53. As a matter of fact, we plan to move the cyst reduction section from Standard 53 into these new mechanical filtration standards. Now, let me fill you in on some of the details of the mechanical reduction standard that are different from the USEPA protocol.
Regu: Good! I’m sure our readers will be interested to learn what those are.
Gary: To start with, we decided to use RO/DI water—which is treated with a reverse osmosis (RO) unit and deionization (DI)—as the base make-up water and add hardness and other salts to provide the background total dissolved solids (TDS) and tannic acid to provide total organic carbon (TOC). It was felt that if labs used local tap water, variables such as TOC or suspended solids would cause premature clogging or other interferences.
The General Test Water contains:
- Hardness (as CaCO3): 40-60 mg/L*
- Sodium chloride: 80-120 mg/L (as NaCl)
- TOC (as tannic acid): 3.0 ±1.0 mg/L
- pH (as adjusted per test)
- Chlorine or other disinfectant: not detected
- Heterotrophic plate count (HPC) bacteria: ≤ 100 cfu/10 ml**
The other main difference is the proposed increase in the length of the test. The current draft calls for a test time of three weeks.
Regu: Why such a long test time? The USEPA protocol for ceramic candles only required 10.5 days!
Gary: Some on the task group were concerned about the phenomenon of “grow-through” and wanted to incorporate enough time into the test to determine whether that would occur with the proposed test organism, which is a coliform bacteria called Klebsiella terrigena. This test is called the “longevity” test. By the way, this is the same bacterium used in the USEPA protocol. The theory is, if grow-through was detected in the units with this organism, it might occur with some other disease-causing bacteria. There are differing opinions on this and some argue that only HPC bacteria will grow through and not disease-causing bacteria. And since HPC aren’t known to be a health concern, this standard does not address HPC removal or control as a requirement.
Regu: Interesting—and I would agree about the HPC issue. What other filter tests are proposed?
Gary: Let’s start from the beginning of the test regimen. The first test is to determine initially if the system is capable of filtering out very small bacteria and we propose using Brevundimonas diminuta, which is about 0.2 microns (µm) in diameter. If the two units pass this initial test, then they proceed to the longevity test with the K. terrigena. But at the same time the K. terrigena are added during the sample points; virus surrogates are added also.
Regu: What are the virus surrogates and are there any special water conditions employed during their testing?
Gary: Here again, we deviated from the USEPA protocol by employing different virus surrogates. We chose to use the coliphages fr,MS2 and PhiX-174. These have been used for quite some time now in research studies demonstrating filtration and disinfection efficiencies. It was concluded these two simulate best the physical size and surface charge properties of many disease-causing viruses, better and more stringent than the two used in the “EPA Guide” in our opinion. Use of these phages also would allow many to do developmental work in their own labs without the fear of using pathogens. And since surface charge is an important factor in mechanical filtration and is affected by pH, we’ve proposed conducting the initial three weeks of testing at three different pHs—one week at pH 9, followed by one week at pH 6, then the last week at pH 7.5.
Regu: Sounds like you’re covering all the bases, but what about when the filter begins to plug and experiences high-pressure differential? How do you test for seal integrity and media integrity during high-pressure differential?
Gary: Good question! Actually, this is partially confirmed all during the longevity test with on-off cycling every day during the week’s run and is also confirmed at the end of the longevity test by plugging the unit with test dust to 75 percent of its initial flow rate, then challenging with pH 9 test water again containing both the virus surrogates and the small B. diminuta bacteria.
Regu: You haven’t mentioned anything about stagnation periods. The USEPA protocol includes a stagnation test. Is this incorporated into the protocol?
Gary: Ah, yes, I forgot to tell you that at the end of each five-day week, on-off cycling test run, the units are challenged with the K. terrigena and then left to stagnate for at least a 56-hour period. Following each stagnation period, the first flush from the units will be analyzed to determine if bacteria grow through the barrier media in the units.
Regu: What about claims and the microbial reduction requirements? Can a manufacturer claim just bacteria reduction or just virus reduction?
Gary: After considerable debate and urging from the DWTU Joint Committee, it was decided to change from the initially proposed 2-log (99 percent) virus reduction and 3-log (99.9 percent) bacteria reduction to mirror the USEPA protocol’s 4-log and 6-log—99.99 percent and 99.9999 percent—reduction requirements for virus and bacteria, respectively. Cyst reduction will stay at 3.3-log (99.95 percent), somewhat higher than the “EPA Guide” requirement. Also, initially, it was desired by some to be able to claim only bacteria reduction; but, again, most thought that wouldn’t be conservative enough since, in many cases of bacteria contamination, there also is—or could likely be—virus contamination. So, only a combined claim of bacteria and virus reduction can be made. And, if the units pass for both bacteria and virus reduction, cyst reduction can be claimed without conducting the cyst test.
Regu: Well, this sounds like a very comprehensive standard and one that could benefit the DWTU industry by providing guidance to manufacturers for helping them to develop reliable and effective microbiological water treatment devices that can protect consumers.
Gary: Right, but we’re not done yet! There are other task groups working on standards that would utilize other antimicrobial technologies.
Regu: What are these other standards and technologies, and what about UV? The USEPA protocol included UV. Is UV included in these other standards?
Gary: There’s another standard that’s also very close to completion and it covers the use of halogens such as chlorine, iodine and iodinated resins. But you would have to talk to the chairman of that task group, Tom O’Brien, of CUNO Inc., to find out details on it. Regarding UV, after the USEPA protocol was developed NSF did eventually develop NSF/ANSI Standard 55, which covers microbiological water treatment. As I recall, you were very instrumental in the development of that standard.
Regu: Right! And that was quite a battle, but we got it through and it has since gone through several revisions for improvements.
Gary: Well, the Microbiological Standards Committee has decided to leave Standard 55 “as is” and so it stands on its own as a microbiological water treatment standard. It’s similar in many ways to the protocol for UV in the “EPA Guide.” But that’s probably a subject for discussion for the next time we meet.
Regu: I agree! I’ve enjoyed talking with you and look forward to another discussion soon on other subjects that are important to the DWTU industry. Talk to you soon!
We hope you’ve enjoyed this more informal give and take between two respected technical experts in the POU/POE drinking water device market. They felt the format was more appropriate to explain the intricacies and rationale for them in proposals to integrate microbiological claims within NSF/ANSI DWTU Standards.—The editors
About the authors
Gary L. Hatch, Ph.D., is director of research and development for Pentair/Plymouth Products in Sheboygan, Wis., manufacturer of Pentek™ brand water filtration products. He’s responsible for new product R&D for residential and commercial POU/POE markets. Hatch graduated from Kansas State University with a doctorate degree in analytical-inorganic chemistry and has been actively involved in water treatment for the past 30 years. He can be reached at (920) 451-9353, (920) 451-9384 (fax), email: [email protected] or the web: www.pentekfiltration.com
P. Regunathan, Ph.D., is president of ReguNathan & Associates Inc. He works as a consultant to NSF International and the Water Quality Association in addition to other clients. He was formerly senior vice president of Science & Technology at Culligan International, as well as president of Everpure Inc. He received his doctorate degree in environmental engineering from Iowa State University and worked in the POU/POE industry for 35 years. He can be reached at (630) 653-0387 or email: [email protected]