By Evan E. Koslow, PhD

Summary: In what may be the most exciting news to come from the water treatment industry in some time, a carbon filter has been devised that provides microbiological purification. Here’s a primer on how the idea went from concept to fruition.

Recently, a breakthrough was announced that activated carbon block filters providing comprehensive microbiological reduction would enter the market this year (see “Newsreel”, WC&P, December 2001). This is the first time a product providing high levels of viral, bacterial and protozoan cyst reduction has been certified and approved by the California Department of Health Services (DHS)3 and undergone review by the U.S. Environmental Protection Agency (USEPA). The Connecticut company making the announcement anticipates a second and more powerful wave of products based on a new flat-sheet nanofiber filter medium that will enter the market later this year. The second-generation product has such low-flow resistance that it will operate in gravity-flow applications while providing all of the major health claims normally associated with point-of-use (POU) devices together with essentially comprehensive microbiological reduction capabilities.

Because activated carbon block filters are pervasively sold as consumer POU products, this development opens the door for microbiological reduction to be included in nearly all POU markets. Products for use in appliances (refrigerators), foodservice and retail applications are in various stages of an intensive government certification process by the California DHS and will proceed to market in the near future.

A second Manhattan Project
In 2000, a review of the POU/POE (point-of-use/point-of-entry) industry was carried out. One of the conclusions drawn was consumers have a strong desire for POU products that provide comprehensive microbiological reduction. Focus groups in the United States have a nearly constant 65-70 percent level of interest in POU products with comprehensive microbiological reduction capabilities if the costs are comparable to current conventional products. No other health claim can produce such a high level of consumer appeal. Unfortunately, in 2000, not only were microbiological reduction claims outside the scope of relevant ANSI/NSF standards, but no POU/POE technology short of chemical disinfection, ultraviolet (UV) irradiation or ozone had been previously developed to provide such a claim.

The benchmark, akin to a “gold standard,” for the attainment of a high-performance microbiological filter is the USEPA “Guide Standard for Microbiological Purifiers.” This standard dictates that a device provide >99.99 percent viral, >99.9999 percent bacterial, and >99.95 percent protozoan cyst reduction in not only potable water, but also in water that’s abnormally cold, turbid, and alkaline, or contains excessive total dissolved solids (TDS), organics matter (humic acid), and lies outside the normal range of pH values (see Table 1). The product would need to handle extended stagnation periods as well as long periods of intensive operation at elevated flow rates. To be a practical product, such a device would also need to pass the ANSI/NSF Standards 42 and 53 requirements for chlorine, taste and odor reduction (see Water Matters, WC&P, this issue); health claims such as lead, mercury, volatile organic compounds/total trihalomethanes (VOC/TTHM) and asbestos reduction, and meeting structural integrity and extraction requirements.

A goal was set to achieve these targets for both pressurized and gravity-flow consumer products while sustaining low manufacturing costs. The aim was to create a product that wasn’t a “pesticide” and didn’t rely upon disinfectant chemistry. Instead, microbiological reduction would be accomplished entirely by an interception mechanism that supported high flow rates. At the same time, pressure drop through the product would need to remain consistent with conventional household supply pressure. It was also recognized that there would be no tolerance for a product that didn’t look and fit within standard POU systems. Together, these criteria were very tough to meet.

For such a complex project, a science and engineering organization was assembled with the requisite chemistry, physics, microbiology, chemical engineering and industrial design skills. This complex multi-disciplinary organization developed the laboratory, pilot plant and full-scale manufacturing systems required in bringing the technology to market. The project spanned nearly four years, cost millions of dollars and involved nearly 20 scientists and engineers.

It was also known that at least three of the world’s largest corporations—one Dutch and two U.S.—had launched programs to create such a product. For the consumer water filter industry, it was the equivalent of a race to develop the atomic bomb, complete with the construction of new laboratories, new chemical plants, huge pilot facilities and a scramble to hire numerous talented people to support these efforts. The cumulative investment to date is in the tens of millions of dollars and could approach $100 million within five years.

Problems at the start
Within the first 18 months of the project, a series of fundamental problems were identified. The first was that the best state-of-the-art glass and polymeric fibers were too large to be used in a viral-reduction structure. For a gravity-flow product, the fibers required would need to be nearly an order of magnitude smaller than the smallest commercially available fibers. This meant that the large-scale production of nanofibers would be required, and these nanofibers would need to be extensively modified with chemical treatments.

The production of nanofibers would need to be moved from the laboratory (producing perhaps 10 grams per hour) to a pilot plant (10,000 grams per hour) to a production plant (100,000 grams per hour). The nanofibers would need to be converted into filter media at paper machine speeds, although the capillary forces between the fibers were nearly 50 times greater than those usually encountered. There was no known technology to physically desaturate a web of such fibers, as is typically required during the paper-making process. Hence, the fibers or process needed to be adapted to deal with this problem.

Alternatively, to create carbon block filter elements with these capabilities, the carbon surfaces would need to be modified extensively. This required a new type of chemical reactor and construction of a three-story production tower. To measure the performance of the resulting materials, entirely new laboratories were built to assay the quality of new raw materials and the microbiological performance of the final filter products.

None of these developments solved what was a serious confounding problem. That is, there was no known regulatory mechanism to have such a product approved for sale in the United States. A process needed to be established to obtain regulatory approval for a new type of product never previously approved for sale. As an example, the state of California had never before issued a comprehensive microbiological claim on a consumer water filter product for mechanical reduction (although it has issued such a claim for distiller and UV systems), according to Terry Macaulay, manager of the California DHS Drinking Water Treatment Device Certification Program.

The committee
By last year, it was clear that while the technology was going to produce products with extremely robust capabilities, the federal and state regulatory agencies required significant time and effort to examine the new technology and approve the new products, especially in the absence of ANSI/NSF standards to provide guidance. Although NSF International, of Ann Arbor, Mich., had already started work on development of a microbiological reduction standard, the performance criteria initially sought by NSF were well below standards demanded by regulatory authorities, and it didn’t appear these differences would be easily resolved. In addition, extremely severe performance criteria were met using the new technology. Because there was no need to compromise on performance standards, the Connecticut company elected to support the strictest set of criteria—the USEPA Guide Standard levels of viral and bacterial removal in essentially any quality of challenge water.

The company, therefore, decided to break away from the ANSI/NSF process to develop a microbial purifier standard at NSF. Instead, an independent committee of leading scientists were systematically briefed about the new technology. This committee then developed a new test protocol for microbiological purifiers—basically a modernization of the original USEPA Guide Standard. The protocol and acceptance criteria recommendations developed by this committee were then submitted to the regulatory agencies—USEPA and California DHS—for review together with a detailed description of the technology and how it functions. These agencies then further reviewed and modified the proposed protocol and California DHS approved it, but only for the testing and performance evaluation of products built using the technology (see Microbial Interceptor). That is, it’s a technology-specific protocol certified for the evaluation of only one technology. It is not approved by the California DHS to register other products with alternative technologies.

The pathfinders
By this time, a series of discussions between the technology’s primary developer and a small group of “pathfinder” companies within the consumer water filtration industry had commenced. Generally, a pathfinder company—one from each major segment of the industry: appliance, food service, and consumer products—was to develop new product specifications amend-ed to include the new microbiological capability. This product would be jointly developed, tested and submitted for approval.

By now, a wide range of products are in various phases of required performance testing for the new regulatory protocol. This includes filters to fit refrigerator water/ice systems, standard food service products suitable for use in restaurants and hotels, and retail products for end-of-tap, countertop and undersink applications.

One of the challenges here is that the regulatory agencies don’t have established rules and criteria of how to regulate mass marketing of filters with these new capabilities. This includes how the claims should be described to the public—i.e., literature requirements—and what limits should be imposed upon how those claims are stated. While microbiological purifiers, often based upon disinfectant technologies, have been previously approved for emergency or backpacking applications, the general release of products with purifier claims (and without significant operational limitations) requires that each retailer work closely with individual state and federal agencies to ensure a measured presentation to the consumer. Standardized wording of microbiological health claims should be established over time as the various regulatory agencies deal with the first products now entering the market.

Future markets for filters
As mentioned above, focus groups consistently identify microbiological threats as a major concern, and consumers have a high degree of interest in POU filters that can reliably control such threats. Carbon block and nanofiber-based products have the potential to address these concerns without significantly altering the economic cost of POU/POE systems. Certainly, they’re inexpensive compared to UV purifiers or ultrafilter modules. Still, the new technology may prove difficult to retrofit into existing filtration systems because of new regulatory demands for high integrity seals as well as accurate flow and pressure regulation.

In the highly competitive field of consumer POU/POE products, rapid implementation of this new technology is expected. The pace of product approvals is expected to roughly double starting this year and product introductions are expected to commence by March. Consumer interest in the new technology is expected to be intense, especially within an environment compounded by water security concerns in a post-9/11 world.

While the market for these new filters may be extensive in North America, potential markets are profound in South America, Asia, Micronesia, Africa, and other regions of the world where millions die and billions suffer as a result of waterborne pathogens and more variable source water quality available in the home or work environment. The technology has a demonstrated capability to operate in essentially any quality water including water that would be outside the range considered potable.

President Bush recently proposed a $15 billion foreign aid program for Africa. It’s estimated that malaria, AIDS, and waterborne pathogens pose the greatest health threats to Africans. POU/POE microbiological interception technology could be a viable candidate for use in those regions where conventional water distribution infrastructure cannot be provided economically.

One POU product, currently under development, will produce microbiologically safe water for a family of four at a cost of approximately a penny per day. To put this in perspective, it would cost approximately $400 million to distribute this capability to every person in Africa. What’s especially exciting about this product is that the user simply pours water into the device and allows it to pass under the influence of gravity through the filter—no chemicals, no mixing, no waiting and no complexity. The company expects to have the ability to produce hundreds of millions of the required gravity-flow filters by the end of this year, and will work with a wide range of organizations to bring this capability to people who desperately need this technology.


  1. “KX launches certified filters; new line hits market in 2004,” WC&P, Newsreel, December 2003.
  2. Koslow, E.E., S.C. Nielsen and M.J. Rook, “Carbon: The Quest for the Holy Grail—Microbiological Carbon Block Filters,” WC&P, August 2002.
  3. California Department of Health Services, Certificate No. 03-1543, DHS Drinking Water Treatment Device Certification Program, September 2003.

About the author
Dr. Evan E. Koslow is chief executive officer of KX Industries, of Orange, Conn., and a member of the WC&P Technical Review Committee. He’s written over 100 articles and papers and holds over 35 patents. Koslow can be reached at (203) 799-9000, (203) 799-7000 (fax), email: [email protected] or website:


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