The daunting challenge
By now, most in the international drinking water industry are very familiar with the UN Millennium Development Goal to reduce by half the number of people lacking daily access to safe drinking water by 2015 and that the majority of the world’s 1.1 billion in greatest need are living in developing and under-developed countries.
In some of the developing world’s largest cities, water supply is erratic. Aging, leaky pipes and intermittent power supply can result in tap water flowing only a couple of times per day or even as little as merely two hours a day, even in middle- and upper-class neighborhoods. This is frequently the case, for example, in parts of major cities like Hanoi and throughout India. Common usage of rooftop cisterns provides continuous water supply to households and improves pressure, but often such water is shunned for drinking because it becomes fouled in the seldom-cleaned tanks.
Relying on local or national governments to solve these infrastructure challenges in the near term is not realistic. The connection between poor water quality and disease is proven. Emerging middle-class consumers are increasingly looking for simple, affordable means to take control of water quality in their own households. Clearly, with erratic supply, storing clean water safely is also a must.
Untrained consumer household use in developing world
There are many good technologies for treating water. However, when assessing those most practical for simple household use by an untrained consumer of limited financial means, the list grows short rather quickly. Residual protection after primary disinfection is of great concern when the requirement for safe storage is added, essentially necessitating the use of chemicals (i.e., halogens). Halogens are defined as the column of elements from fluorine to astatine. For the purposes of this article we will only concern ourselves with the most common three: chlorine, bromine and iodine.
Very few look to bromine among halogen options. In part, this is because until recently, the available chemical forms for bromine have not been practical or easily managed.
This article discusses how circumstances have changed and why brominated disinfection media is poised to bring new power and potency to bear on this important consumer need.
For the record, this author in no way wishes to challenge the benefits derived from the use of chlorine and iodine in a wide range of applications. In particular, chlorine is by far the most prevalent water treatment chemical used for disinfection and has arguably saved more lives than antibiotics. Keeping this fully in mind, let us turn our attention pragmatically toward constraints upon applications within impoverished households of the developing world struggling to achieve the UN goals.
Many people turn to chlorine or iodine in their quest for safe drinking water. These chemicals can certainly accomplish primary disinfection and provide residual protection for safe storage, but with some important limitations and trade-offs in the context of what will be readily accepted, properly used and achieve the desired positive health impact in the developing world.
Three major challenges
Three major obstacles stand in the way of finding ‘truly ideal’ means of household drinking water treatment and safe storage in developing nations:
- Uncertainty of dosage and time required for adequate disinfection. In a well-equipped environment, trained personnel can accurately determine well-established dosage and time requirements for the halogen of choice and achieve the desired germicidal affect. However, a mother collecting water from a village well or an urban tap is not prepared to assess water quality variations of turbidity, organic load or temperature and the subsequent impact on chemical requirements.
- Taste and odor criteria for consumer acceptance. Many would like to believe that people can become accustomed to the taste of halogens (most typically chlorine) added to water and that they may even be taught to appreciate the taste by associating it with the knowledge that it represents ‘safety’. The universal fact is that consumers globally prefer little or no chemical taste and odor in their drinking water. That is really the benchmark for a truly ideal solution.
- Safety with long-term daily use/ingestion. There must be safety with daily ingestion over entire lives, inclusive of pregnant women and nursing mothers, infants and those with hyperthyroidism.
With these three obstacles in mind, let us consider the chemical options available for household water treatment and safe storage in the developing world.
The following dosing issue is not unique to chlorine, though it is the most common example encountered in household water treatment in the developing world. The core of the issue has to do with required manual intervention, which suffers from inadequate or improper user compliance.
The most common forms of chlorine for household use in the developing world are liquid chlorine bleach or chlorine tablets as additives to the raw water source. The problem lies in arriving at just the right dose for the needs of sanitation without compromising the qualities of the water that make it acceptable to the consumer.
Manufacturers may provide recommended dosage instructions, but widely varying water conditions and human error can confound reliability of results.
Consumers may assume if a few drops of bleach or a single tablet is good, then twice that much is bound to be better and more reliable. Such over-dosing can result in undrinkable water, reminiscent of aromas associated more with indoor swimming pools than with potable water. Perhaps more likely is the view that less is better in order to stretch the money spent on chlorine in order to treat more than the recommended volume of water. Under-dosing water, particularly when there is high chlorine demand, results in inferior disinfection and compromised safety. Consumers cannot see bacteria and viruses and they are not equipped to adjust chlorine dosing based on water conditions. For example, does the water temperature require a higher dose of chlorine? Another example is water containing high levels of organics (TOC) with oxidation demand that consumes chlorine before all disease-causing organisms are inactivated.
The foregoing is all too common and underscores the unpredictability of simply adding chlorine to achieve reliable results, while still maintaining acceptable taste and odor.
Iodine is another commonly used halogen for small-scale in-home or personal water treatment. It can also be administered in tablets or as a liquid from concentrate derived by soaking iodine crystals in water. In the last few decades, iodinated resins have been developed for passing water across beads to leach iodine residual in the range of 0.5 ppm to 2.5 ppm or higher.
Iodine left in the water is more foul-tasting and smelling than chlorine, often described as fishy or medicinal by consumers and it leaves an unpleasant, lingering metallic after-taste. Years ago, the US Marine Corps abandoned the use of iodine tablets as troops were dehydrating rather than drinking iodinated water.
Iodinated resins were developed in an effort to regulate dosage and increase performance reliability when used by consumers. They are typically used in drinking water treatment devices that include sediment and carbon prefiltration. The idea is to clean up incoming water quality in order to get more predictable water conditions prior to passing through a chamber filled with iodinated resin beads. A dwell chamber typically follows to give the iodine residual leaching from the beads adequate time to kill bacteria and virus. However, because iodinated resin relies on leaching and the iodine residual declines over the life of the cartridge, the dwell time (contact time) requirements increase over time, in order to maintain performance. One must, therefore, engineer an iodinated resin system with a dwell chamber of adequate size for the lowest level of residual delivered at the end of cartridge’s rated capacity.
Like chlorine, performance is affected by cold temperatures, variations in pH and/or salinity. Hot weather, high TOC levels, increased salinity or pH above 8.9 can cause increased spikes in iodine residual that can overwhelm polishing or scavenging carbon, raising the residual to highly undesirable levels.
Most important, certain people are cautioned against excessive iodine/iodide intake; these include individuals who are iodine-sensitive, have over-active thyroids or are pregnant or nursing mothers. As a result, iodine-based systems should have a good surplus of scavenger carbon to remove iodine and a strong base anion resin to remove iodine for long-term daily use. An alternate, though less desirable option is to use a good silvered carbon with a surplus of positively charged silver ions (not negatively charged silver oxide or ground-state silver) to precipitate insoluble silver-iodide to be filtered by the carbon. However, these scavenging measures eliminate the desired benefits of having residual disinfectant iodine in the water.
Many readers are probably already saying to themselves, “What about bromate?” or “What about the nasty reddish-brown liquid that is hazardous to handle?” If those are your reactions, much has changed over the years and the information you have is likely out of date. Look at the timeline (page 64) describing the use of bromine in drinking water treatment to see the evolutionary track.
Bromine (Br) usage in drinking water treatment is certainly not new. A quick scan of the literature will confirm that elemental bromine is a strong oxidizer and much more effective against many pathogens than chlorine, even though classified as less active than chlorine, but more active than iodine. This is because of bromine’s different mode of killing action from chlorine in attacking pathogens. Its proven record of potency and the tolerance of Br-mediated disinfection to a wider range of pH and temperature than other halogens makes bromine look attractive for drinking water treatment.
There are additional advantages: bromine does not affect the thyroid gland like iodine and is better tolerated in terms of taste and odor than chlorine, often being described as sweet, instead of sharp or biting, like chlorine. Of the three halogens, bromine is favored in consumer opinion as determined in blind taste testing. This enables one to leave a meaningful bromine residual in treated water for safe storage and still remain below taste and odor thresholds of detectability for most people. This is beginning to sound like the ideal chemical in some ways, right? So why is it not more commonly used?
There are really two reasons traditional bromine has seen limited usage:
- Bromine’s form
- Disinfection byproducts (DBPs)
Historically, bromine has been handled as a liquid. According to sources at the American Chemical Society and the CRC Handbook of Chemistry and Physics, it is the only nonmetallic liquid element. It is a heavy, mobile, reddish-brown liquid, volatizing readily at room temperature to a red vapor with a strong disagreeable odor, resembling chlorine. It is a strong irritant and in concentrated form, produces painful blisters on exposed skin and especially mucous membranes. Even low concentrations of bromine vapor (10 ppm or above) can affect breathing and inhalation of significant amounts of bromine can seriously damage the respiratory system. Accordingly, one should always wear safety goggles and ensure adequate ventilation when handling bromine. This certainly does NOT sound like a user-friendly option for household water purification.
The US Navy favors the use of bromine aboard naval vessels for safety reasons associated with fire hazard and has used bromine for drinking water treatment for the last 30-40 years. At least two companies have developed a means to facilitate handling elemental bromine. Porous beads are soaked like sponges in concentrated solutions of elemental bromine and then encapsulated in cartridges (polybromide resins). These cartridges serve as delivery mechanisms, whereby water is pumped in a split stream manner. Then the two streams (one containing a concentrated amount of bromine) are blended to achieve a desired level of residual bromine of two ppm. In contrast to practical limitations of household use in developing countries, the foregoing setup entails excessively sophisticated plumbing and engineering management by trained technicians.
Advances in bromine technology
The latest advances in bromine technology address both forms and DBP limitations of traditional elemental bromine usage while preserving the advantages over chlorine and iodine.
In 1996, Dr. S. Davis Worley at Auburn University developed a patented means of stably bonding bromine onto modified polystyrene that essentially avoids the elution of bromine into product water so as to eliminate the need for split-stream metering and blending. This development is commonly referred to as ‘N-halamine’ chemistry, meaning that there is a compound containing one or more nitrogen-halogen covalent bonds and for which the bond polarization leaves the halogen with a positive oxidation state. Specific to germicidal use in treating drinking water, it can be more narrowly defined as a ‘cyclic organic’ compound with the same properties just mentioned. The latter cyclic organic specification is a more narrowly defined type of N-halamine referred to as an ‘N-halamide’ which is more stable in water than, for example, inorganic N-halamines such as NH2Cl, NHCl2, or NCl3 that are also biocidal but unstable in water.
The stable brominated N-halamide-based medium is a contact biocide, most recently developed in the convenient form of spherical, macroporous beads, with which to form reproducible, uniform beds with highly consistent physical and chemical properties. The brominated beads can be safely handled without skin irritation and with no need for the special safety equipment associated with liquid bromine.
Brominated beads can be enclosed in a water treatment device in a cartridge having only a few seconds of contact time, followed by a relatively short dwell time, in order to achieve complete disinfection of bacteria and virus, meeting US Environmental Protection Agency (US EPA) purification requirements. Consequently, water is only exposed to a high concentration of a stably bound-bromine in the bead cartridge for a few seconds followed by very low levels of residual bromine in the product water.
Often people in the water industry immediately associate bromine with concern over bromate or brominated DBPs. The US EPA regulates these chemicals since it is quite common for naturally occurring bromide in untreated water to be converted into bromate and/or brominated DBPs once oxidized during treatment. US EPA maximum contaminant levels (MCL) are quite low, established at 0.01 ppm for bromate, 0.08 ppm for total trihalomethanes (TTHMs) and 0.06 ppm for haloacetic acids (HAAs). Note that the US EPA is concerned with total intake of disinfection byproducts regardless of origin and therefore the limits for TTHMs and HAAs combine both brominated and chlorinated DBPs. Commercial-grade bleach can contain low levels of bromide from raw materials. As a naturally occurring element, some source waters may also contain bromide. When bromide ion is in the presence of a strong oxidizer, such as ozone or hydrogen peroxide, bromate is formed, as illustrated below.
O3 + Br- → O2 + OBr-
2O3 (or OH-) + OBr- → 2O2 + BrO3–
Powerful oxidizers are commonly used in municipal treatment plants and bottled water operations. Much publicity has been generated recently, especially over the discovery of bromate in some bottled waters and product recalls have resulted.
In the context of household use in the developing world where brominated N-halamine technology may be deployed, there is certainly no reasonable expectation for residual bromine or bromide exposure to ozone or hydrogen peroxide to provide sufficient oxidation potential to form bromate. Using laboratory equipment of great sensitivity has repeatedly resulted in bromate levels downstream of brominated N-halamine beads as ‘non-detectable’.
The two most important factors associated with germicidal use of any halogen are dosage concentration and time. The greater the dosage, the less time is required for germicidal effect. The lower the dosage, the more time is required for the same effect. Similar principles apply to formation of DBPs associated with the use of any of the halogens.
Three characteristics of N-halamine chemistry work together to minimize DBP formation compared to freely dosing any of the halogens into solution for water disinfection. First, exposure or contact time is typically limited to only a few seconds for water flowing through a bead-filled cartridge where a concentration of bromine is found. Second, the involvement of bromine on the beads is bound onto nitrogen and is thus in the form of ‘bromamine’ rather than free aqueous elemental bromine or other bromine species. Third, downstream of the cartridge the dosage or concentration of residual bromine is very, very low, often in the range of 0.1 to 0.2 ppm. All three of these factors favorably work together limiting the formation of DBPs.
Safety with long-term use
WHO has established Acceptable Daily Intake (ADI) levels of bromine ranging from zero to one mg/kg of body weight. With the extremely low discharge of bromine/bromide from N-halamine beads, an average adult male might have to consume more than 30 liters of water a day to approach this recommended limit.
Ideal for household use?
Time will tell, but quite possibly, brominated beads may prove to be the most ideal means of meeting the dire need in the developing world.
1) Uncertainty of dosage and time can be resolved with proper design of a simple combination of sediment and carbon prefiltration, brominated contact biocidal beads and a dwell chamber for completion of the purification process.
2) Taste and odor are typically below detectability thresholds for enthusiastic consumer acceptance. This means that residual bromine does not have to be scavenged or polished from the product water for taste acceptability at the expense of residual protection for safe storage. Rather, safe storage can be achieved without objectionable taste and odor.
3) Safety requirements are met through verification of extractability toxicology to NSF standards, establishing DBPs and residual bromide levels well below international guidelines.
Furthermore, subsequent to discovery at Auburn University, the N-halamine chemistry has been licensed, scaled up for commercial production, further refined and advanced and is now being commercialized throughout the Indian subcontinent. Consumer acceptance by the emerging Indian middle-class has reinforced the belief that this may be the best fit for developing world needs at the household level. Bromine technology development is not standing still, either. Rather than have users discard exhausted cartridges of brominated N-halamine media, a user-friendly method of sustaining the biocidal charge on the beads has been developed. Patented, consumer-friendly, safe-to-handle tablets have been developed that continuously maintain the biocidal activity of the brominated beads. Residual bromine levels remain at or below levels of consumer detectability and bead cartridge life can be extended for years without costly recurring disposal of beads and plastic housings.
Reduced cartridge disposal is good for the environment, but more important, it is good for consumers who can more readily afford weekly or monthly tablets to sustain their home water purification, rather than having to pay for periodic replacement of cartridges. Effectively, these ultra-slow-dissolving bromine tablets enable consumer financing of household drinking water purification with more frequent, but smaller expenditures. This also coincides with normal lifestyle habits of frequent purchases in small portions. Consumers are not asked to dose each batch of water to be treated, as this would suffer from low compliance and these tablets would dissolve much too slow to be adequate for disinfection by themselves without the use a of brominated N-halamine bead cartridge downstream of the tablet.
The consumer cost for bacteria and virus disinfection is estimated to be as little as US $0.001 per liter. To put this in perspective, it is four times higher than simply adding chlorine bleach, but with the added benefits previously discussed that come with a passive-contact biocide system and a non-offensive low residual for safe storage. The cost of these ultra-slow dissolving bromine tablets for continuously charging brominated N-halamine beads is estimated to be approximately 20 percent of the cost of boiling using kerosene or CNG fuel. Filtration cost must be considered in addition to the disinfection costs referenced above. Filtration cost can vary widely depending upon type of filter and water conditions.
Complete filter systems, either iodine or chlorine-based with no residual protection after scavenging media, operate in the range of US $0.004 to $0.005 per liter. Complete filter systems in India utilizing brominated N-halamine technology in disposable cartridges operate in the range of $0.003 to $0.004 per liter. Using slow-release tablet technology to sustain cartridges, eliminating their frequent disposal, may cut total filtration system operating cost in half.
An additional benefit of charge-sustaining tablet usage is that it can serve as a substitute for an end-of-life indicator or meter. The user simply looks to see if a tablet is present. If so, the system is fully charged and disinfecting properly. If the tablet disappears, it is time to insert a new one. One would no longer have to speculate on the amount of water treated versus the claimed cartridge capacity.
As this latest development becomes commercially available, as expected brominated N-halamine chemistry will become much more widely recognized for its utility in addressing the global problem of daily access to safe drinking water. As the developing world awakens to the efficacy of brominated contact biocides without major safety issues, perhaps a sleeping giant has been uncovered with bromine; something that has been largely ignored for over a quarter century in the drinking water industry.
About the author
Director of Drinking Water Systems Duane Dunk has been with HaloSource Inc. for over six years and in the drinking water treatment industry for 14 years. His primary focus continues to be business development through establishing business partnerships and translating market requirements into product development guidance for household consumer devices. Contact him at HaloSource Inc., 1631 220th Street SE, Suite 100, Bothell, WA 98021 or via email firstname.lastname@example.org
HaloSource Inc. holds global exclusive licenses for N-halamine chemistry in drinking water treatment from Auburn University and has branded this chemistry as HaloPure. HaloSource has partnered with Eureka Forbes Ltd. in India for nationwide distribution of HaloPure in an expanding family of products for household use. Additional HaloSource brands are HaloShield textile and surface coating solutions that harness the antimicrobial power of chlorine, SeaKlear water treatments to maintain clean and clear water in pools and spas and StormKlear natural erosion and sediment control for treating and decontaminating storm and waste water. More information is available at the company’s website, www.halosource.com.