N-halamine Technology for Developing Nations: Providing Clean Water 50 Impoverished Homes
By D. Duane Dunk and Jeffrey F. Williams, Ph.D.
Summary: For underdeveloped countries around the world, one treatment is gaining wider acceptance for supplying purified water to their residents. Using chlorine as an antimicrobial agent, N-halamine technology has many advantages going for it, as this article indicates.
With high mortality rates from inadequate water sanitation in developing countries, the promise of inexpensive and effective water purification methods holds endless opportunities to improve public health and living standards. For more than a billion people forced to use contaminated water, diseases such as cholera, typhoid, chronic dysentery and rotavirus diarrhea are constant problems that debilitate economic development and quality of life.
The enormous cost of implementing municipal water purification and distribution systems consistently hampers efforts to provide clean drinking water, and the lack of safe supplies perpetuates and aggravates the relentless cycle of poverty and disease. To truly advance the crusade to provide clean, potable water, a solution that’s effective, inexpensive and simple to operate is necessary.
The solution may reside in a novel use of N-halamine technology. N-halamine chlorinated resin beads, an emerging water purification application, use antimicrobial properties of chlorine to safely purify drinking water supplies at the point-of-use (POU) without electrical power. N-halamine compounds harness chlorine atoms by linking them covalently onto polymeric water filtration beads with halogen receptors. Washing the beads periodically with chlorine bleach recharges and greatly prolongs the antimicrobial power, even in a heavily contaminated water source.
The N-halamine chlorinated beads kill the same broad spectrum of pathogenic microorganisms without adding high concentrations of free chlorine to water flow, maintaining quality and taste while decreasing the generation of trihalomethane (THM) by-products from organics in water. As a result, it’s become possible and affordable to bring safe, clean water to impoverished consumers throughout the world.
Harnessing chlorine power
Continuous chlorination of drinking water began in the early 1900s in Great Britain, where its application sharply reduced typhoid deaths. Today, more than 98 percent of drinking water disinfection systems in the United States use chlorine for its germicidal potency, economy, safety and efficiency.1
N-halamine beads provide the same wide-ranging spectrum as the conventional deployment of free chlorine, efficiently controlling waterborne bacteria, viruses and some protozoa. It’s also effective in broad pH and temperature ranges for all water qualities. N-halamine compounds work by bonding chlorine atoms directly to the surface of polystyrene resin beads similar to those regularly used in water softeners. These N-halamine receptors charge the bead resin, creating a biocidal surface that’s lethal to many microbes on contact. Once contaminated water begins to exhaust the biocidal chlorine atoms, the resin is easily recharged with a rinse of dilute hypochlorite solution, or household bleach.
The biocidal beads effectively attack chlorine-susceptible target sites on bacteria and viruses, rapidly killing or deactivating microbes in the same manner as free chlorine in municipal drinking water or household bleach; however, because chlorine atoms are so tightly bound to the N-halamine beads, the process releases less than 0.2 parts per million (ppm) of free chlorine to the water flow, far below the amount left by decontamination processes with free chlorine alone2 (see Figure 1).
Challenges with biocide dosing
Chlorine is very safe, and dosage requirements for efficacy haven’t increased during the last 100 years because bacteria are unable to mutate and become chlorine-resistant. Still, traditional dosing with chlorine or other halogens—chloramines, chlorine dioxide, iodine and bromine—can be impractical, costly, and difficult to regulate for households or other small-scale applications.
In the early 1970s, efficient and practical dosing of biocides in drinking water was approached with iodinated resins, particularly for point-of-use (POU) devices.3 While researchers made important advances for relatively controlled dosage, several drawbacks remain.
The typical bonding mechanism for iodinated resins is weaker than the N-chlorine covalent bond, so iodine-leaching rates are much higher than chlorine elution from N-halamine resins. Initial leach rates with some iodinated resins can far exceed 6 ppm. Though high quality resins are more often in the 2-4 ppm range and some maintain a reasonable effluent range for long periods, dosing with iodinated resins is often an unpredictable option.
Because of taste and odor issues as well as iodine sensitivity affecting thyroid functions, both residual iodine and iodide must be removed by silver impregnated carbon or a combination of carbon and a strong-base anion resin. This eliminates residual protection and increases colonization on downstream surfaces in unprotected water and generation of high levels of heterotrophic bacterial contaminants. These aren’t necessarily health threats in potable water, but they may impart bad taste and smell and are increasingly subject to regulatory agencies in the Western world.
An emerging solution
N-halamine technology eliminates the need to add high concentrations of free chlorine or iodine, decreasing the possibility of generating THM by-products from organics in the water, reducing the amount of disinfectant compound consumed by those drinking the water, and keeping system operating costs affordable.
Like other chlorine-based disinfectants, N-halamines provide an effective residual in distribution systems, which is an important part of the multi-barrier approach to preventing waterborne disease; however, the downside associated with municipal delivery system—demands for greater dosages of free chlorine, longer exposure times, and increased possibility of forming THMs—isn’t a danger with N-halamine technology.
N-halamine chlorinated beads provide an extremely constant 0.1 to 0.2 ppm effluent chlorine level throughout its useful life, only giving a temporary chlorine spike in a liter or two of rinse water right after the beads are rinsed with bleach to recharge their biocidal efficacy. With this low elution rate and brief contact time in the media bed, the beads show much less tendency to generate THM by-products from organics in water than free chlorine.4
The insolubility of N-halamines also eliminates the inherent disadvantage of other methods that result in people consuming the disinfectant compounds, such as iodinated resins and free chlorine. Segments of the population with iodine sensitivity—those with over-active thyroids, pregnant women and nursing mothers—need not be concerned when drinking water that contains only 0.1 to 0.2 ppm of chlorine residuals.4
Finally, purifying drinking water with N-halamines costs much less than other methods, thus making it a viable alternative for poverty-stricken areas.
Several factors contribute to the affordability of N-halamine resins:
- Scavenging and polishing media aren’t required downstream, reducing cost and conserving space in compact systems for other media.
- The rate of effluent discharge of chlorine is one-tenth of the typical 2 ppm effluent discharge of iodinated resins.
- The resin beads last longer and are more economical.
- Deploying chlorine in POU devices with the beads is more cost effective than small-scale dosing or shocking with surplus free chlorine because N-halamines eliminate overdosing and associated costs. In fact, chlorine use is so efficient with N-halamines that the cost-per-gallon for a small POU system is comparable to large municipal systems, which buy chlorine—with their massive economies of scale—at bulk rates and then overdose the water.
- Consumers can easily recharge the beads, dramatically lowering the cost of long-term use. The resin can be regenerated more than 100 times.
In the developing world
N-halamine technology operates principally as a contact biocide component of purification devices. It works best when system or cartridge design maximizes the number of “hits” as chlorine atoms contact and kill contaminants in the flow path of the media bed.
Normally, extremely low doses of chlorine have little or no killing effect on most healthy pathogenic microorganisms, even with extended contact time; however, in systems designed with product water dwell time reservoirs or chambers, the N-halamine chlorine residual 0.1 ppm allows for the media bed to be minimized while increasing efficacy against hard-to-kill organisms such as poliovirus (see Figure 2).
For POU systems, these resins are best used in the form of a durable spherical bead of controllable size to encourage maximum flow in water treatment applications without creating pressure build-ups. Greater chlorine loading offers increased usage between recharges, and the stability and durability of the beads make it possible to rely on consistent flow rates without the shedding of bead fragments or “fines.”
Typical home POU devices designed to remove excessive chlorine taste and odor can become breeding grounds for heterotrophic bacteria. Biocidal N-halamine technology solves this problem as a heterotrophic barrier when positioned as the final process media. In this case, it encourages system compliance with Western drinking water standards and contributes to the provision of safe water in less developed areas.
Currently, the technology has passed extractable toxicology testing for process media conducted by St. Paul, Minn.-based Spectrum Labs (see Newsreel this issue) to ANSI/NSF Standard 61 protocol, and manufacturing has been increased to commercial levels.
While there’s great demand for affordable purified water in developing nations, the need for POU water treatment isn’t limited to poverty-stricken regions. Aging infrastructure and improved detection of emerging pathogens are growing issues globally, even for Western treatment methods. Regulatory issues are driving heightened concern over heterotrophic plate count (HPC) levels that may be effectively addressed with N-halamine chlorinated technology. The resin beads are also effective in handheld water purification units for portable use. Whether pressurized or gravity-fed, POU or point-of-entry, domestic or industrial/commercial, there are many conceivable applications for these and other N-halamine-bonded rechargeable surfaces.
Solid phase, contact-biocidal N-halamines offer boundless opportunities to bring sophisticated water purification to impoverished areas throughout the world. The technology harnesses the proven, reliable, safe antimicrobial power of chlorine for potable water treatment. It’s easily recharged, decreases THM by-products and disinfectant effluents in the water, and reduces operating costs compared to other POU methods. These factors make it possible to deploy this effective chemical treatment in developing nations.
- “Groundwater Disinfection: Chlorine’s Role in Public Health,” Nov. 3, 1997, Chlorine Chemistry Council, June 21, 2002: http://c3.org/chlorine_knowledge_center/groundisinfect.html
- Worley, S.D., and G. Sun, “Biocidal Polymers,” Trends in Polymer Science, 4,364, 1996.
- Eknoian, M.W., and S.D. Worley, “New N-halamine Biocidal Polymers,” Journal of Bioactive Compatibile Polymers, 13, 303, 1998.
- Worley, S.D., and J.F. Williams, “Disinfection of Water by N-halamine Biocidal Polymers,” WC&P, July 1997.
- Panagala, V.S., et al., “Inactivation of Rotavirus by New Polymeric Water Disinfectants,” Journal of Virology Methods, Vol. 66, pp. 263-268, July 1997.
About the authors
Duane Dunk is vice president and general manager of the Water Treatment Division at Vanson HaloSource, of Redmond, Wash. He has more than 10 years of manufacturing and product development experience in the drinking water treatment and environmental industries. Dunk joined HaloSource in 2001 after serving as managing director for Marathon Ceramics. There he led development, manufacturing and commercialization efforts in ceramic filtration for water treatment, including patented diatomaceous earth ceramic filter extrusion technology recognized by the American Ceramics Society as one of the top innovations in the last 100 years.
Jeffrey Williams is the innovator behind development of commercialized N-halamine technology. Before serving as co-founder and former CEO of HaloSource and now the senior vice president and chief technical officer at Vanson HaloSource, Williams spent 26 years as a microbiology professor at Michigan State University. In that time, he served as principal investigator in a series of internationally renowned research programs in infectious diseases, including interdisciplinary biomedical research projects funded primarily by the National Institutes of Health and World Health Organization.