Air & Water Purification: Battling Bugs
June 1, 2006
The market for point-of-use water purification products is expected to grow by leaps and bounds, as consumers want to take more control over the quality of the water they use. They don't just don't water to taste good, they want to be sure it is safe, as in free of contaminants and harmful microorganisms. In some cases, the reason may be a distrust of their municipal water treatment or fear of bio-terrorism. Or perhaps they just want to cut back on the amount of money they spend on bottled water. In any case, there are a number of new technologies emerging that allow consumers to take charge of their water supply.
One such device is the Vortex Water Machine, which launches an all-out, multi-step assault on water.
- Ozone. At the beginning of the process, the machine uses UV light to create ozone, a well-established, powerful oxidant that attacks microorganisms and organic compounds. The ozone is siphoned and mixed with the incoming water.
- UV light. The water is then subjected to high intensity UV light, which also has an established capacity to destroy microorganisms.
- Photo-oxidation. The combination of the UV light and ozone initiates another process called photo-oxidation, in which the UV light causes a rapid conversion of the ozone (O3) back into oxygen (O2), leaving a high concentration of free radicals that further attack microorganisms and organic compounds with an effectiveness many times greater than either the ozone or the UV light by themselves.
- Filtration. The water then passes through a 2-micron activated carbon filter with lead adsorption media that removes particulates, lead, parasitic cysts, chlorine and other contaminants.
- More UV. After leaving the filter, the water is given a parting shot of high-intensity UV light.
Vortex says that this last step is critical because of studies that have revealed the colonization of bacteria on and around granular carbon filters. Vortex says that one study found such filters discharging water with more bacteria than the unfiltered water entering it.
The company says its system prevents this problem by zapping the water with UV light both before it enters the filter and after it leaves the filter. Effectiveness of the unit's purification process can be seen in figure 1.
As the photo on the previous page illustrates, a lot of industrial design went into the unit, as well as technology. The transparent, glowing chamber with swirling water makes some of the process visible, in effect, putting on a show for the consumer, and enhancing the products visual appeal.
The unit is easily installed on a countertop, on the wall, or under the counter. It produces clean water from almost any source for less than 7 cents a gallon for up to 1/2 gal. per minute of flow.
The UV light has a lifetime of 10,000 on/off cycles or about three years of normal household use, while filter life is 500 gal., or six months of normal household use. The unit weighs in at just 5 lbs.
A portable solar-powered or battery-powered Vortex Voyager system is available for emergency situations. It can quickly produce clean drinking water from many sources including muddy streams, stagnant ponds, lakes, mud holes, livestock water holes and holding tanks.
Formidable filterWhile high-tech approaches to water purification may be a good fit for affluent households looking to cut back on the fancy bottled water, more cost-effective methods may need to be employed in order to achieve wider penetration of point-of-use devices. This will be especially true in the larger, global market. There are many areas of the world where the need for clean water is great, where the water quality is low, but incomes are also low.
Simple filtration with carbon filters has always been the simplest and most cost-effective approach for treating water at point of use, but these traditional methods exhibited a shortcoming in their inability to intercept microorganisms. A few years ago, KX Industries, Orange, Conn., attacked that problem head on by unveiling a breakthrough carbon block filter that provided comprehensive microbiological reduction.
The company then took the technology a step further by developing an inexpensive, chemically coated paper filter flat-sheet medium possessing similar microbiological reduction capabilities, permitting the design of extremely effective point-of-use purification devices that don't require ozone, UV light or chemical disinfectants. Importantly, this new filter media has almost no resistance to water flow, so that even with only gravity as a force, the filter functions effectively. This feature allows the design of purification devices that won't require water pressure to function, further expanding design possibilities for the market.
The filter removes chemical contaminants such as chlorine, taste and odors, and can be arranged to remove specific ion contaminants, such as mercury and lead. The filter additionally removes fine particulate matter, including microorganisms such as bacteria, viruses and cysts with a >99.99-percent interception rate of virus and >99.9999 percent reduction rate of bacteria, in line with the U.S. Environmental Protection Agency criterion.
The fiber is a composite consisting of a low-cost nanofiber and particulate ingredients, such as an activated carbon and zeolites. The activated carbon intercepts the chemical contaminants, while the nanofibers help to intercept even very fine particulates.
The nanofiber alone, however, does not provide for the ability to intercept virus particles (sometimes as small as 25 nm.), so the nanofiber is chemically treated with a high molecular weight polymer that works almost like a "molecular pico-fiber."
The particles are pulled down to the surface of the nanofibers by the polymer, which extends into the surrounding fluid. The chemistry of the surface treatment additionally includes silver, which over a period of hours, kills the microbiological contaminants that accumulate within the filter medium.
Many state governments not only require that water purification products demonstrate microbiological interception efficacy in any quality of water against any organism, but also mandate that the product be intrinsically safe. To meet this intrinsic safety requirement, KX Industries added one additional, but critical, feature to its product.
The chemistry of the surface treatment monitors the amount and quality of water that is sent through the filter, and it shuts down the flow of water after the filter's useful life is completed. This chemical shut down of the filter ensures that the filter either passes microbiologically safe water or no water at all. This feature must be demonstrated during the product's testing and registration for sale, and ensures the consumer's security, according to KX Industries.
Sidebar: Protecting PartsIt seems counter-intuitive, but water purification devices themselves can occasionally be sources of water contamination. Filters can be breeding grounds for microbes because of their complex and hard-to-clean structures, which are continually wetted. Tubing, orifices and valves can develop bio-films.
One way makers of such components can prevent that problem is by using antimicrobial compounds that are either embedded in the component materials or as a coating over the materials. An example is a silver-based technology from AgION, Wakefield, Mass., that has been shown to provide long-lasting antimicrobial protection in a variety of commercial, consumer, and medical applications.
The compound, which is comprised of naturally occurring silver ions and a ceramic material called zeolite, has been proven effective against a broad range of microorganisms including bacteria and mold.
Cleaning components with a disinfectant provides a quick, "instant kill" approach that is briefly effective. But in a wet environment, microbes can quickly reestablish themselves. By contrast, components that are fabricated with or coated with an antimicrobial compound deliver enduring protection.
The AgION compound provides continuous protection against microbes by releasing silver ions at a slow and steady rate. This continuous protection prevents the build-up of bacteria, mold and other microbes on filters, decreasing the frequency at which filters require maintenance, or must be cleaned or replaced.
A multifaceted crystal carrier combats microbes in three ways - interrupting cell metabolism, inhibiting membrane transport processes and preventing cell multiplication.
In its ion exchange process, zeolite crystals containing silver ions are randomly oriented and distributed through the surface of a polymer or coating. In conditions that support bacterial growth, the sodium ions, in ambient moisture, exchange with silver ions at reversible bonding sites on the zeolite.
The most significant difference between silver antimicrobials and chemical antimicrobials is the method of attack. Chemical and man-made antimicrobials generally interact with one specific site on a microbe. Silver-based antimicrobials interact with several sites on a microbe, using multiple methods of attack, essentially suffocating the organism.
This difference is significant as it relates to the issue of antibiotic resistance, which occurs when microbes find ways to counteract antibiotic attack. If a microbe develops resistance to an antimicrobial that uses a mechanism of attack that is similar to the method used by an antibiotic, resistance to that antimicrobial is likely.
Chemical antimicrobials are often ineffective against common groups of bacteria, while inorganic antimicrobials, such as silver, can kill a wide variety of microbes. Since silver antimicrobials use very different mechanisms than those used by antibiotics, it is unlikely that any resistance to these antimicrobials will translate to resistance to chemical antimicrobials, according to AgION.