UV-based purification technology promises total bacteria knock-out
10/01/2004
BY CAROLYN MATHAS
Montreal, P.Q.—An ultraviolet-based air purification system that kills deadly microorganisms at first contact is making its way into biotech cleanrooms.
The Sanuvox (www.sanuvox.com) UV Bio-Wall Air Purifier is designed to fit into the center of a cleanroom air duct, integrating five 19-mm high-intensity ultraviolet (UV) quartz lamps attached to five anodized parabolic reflectors. When properly installed, Sanuvox guarantees a 99.99-percent first-time purification rate.
"The Bio-Wall is not a filter, it's strictly a UV purifier, able to destroy the chemicals in the air, or bacteria virus in mold—it's a killer, but it doesn't do anything for dust or dirt," says Aaron Engel, director of marketing.
Installation variables include how much fresh air is moving through the duct, the duct size, and air velocity. Offered in 40-, 50- and 60-foot lengths, two units of Bio-Wall are recommended to achieve sufficient UV dwell time when dealing with very large ductwork.
Purifying with UV
Ultraviolet light has four main wavelengths, UV-A, UV-B, UV-C and UV-V.
UV-C wavelengths are used to destroy bacteria and other microorganisms, destroying a cell's DNA. By mutating the DNA, viruses, bacteria, and mold are rendered benign by the biological destructive capabilities of short-wave UV radiation in the "C" band (UV-C) between 200 and 280 nanometers. UV-V, in comparison, is an oxidizing wavelength, destroying chemical contaminants and other volatile organic compounds (VOCs) that are so small, they travel right through a filter.
Sanuvox air purifiers incorporate both UV-C and UV-V light. Together, the wavelengths clean by attacking microorganisms on a molecular level. The company's air purifiers destroy biological and chemical contaminants such as odors, mold, mildew, smoke, formaldehyde, and cleaning solvents.
"Most cleanrooms try to keep contaminants out," says Paul Pinelli, project executive for DPR Construction (Redwood City, Calif.)—a national general contractor and one of the country's largest pharmaceutical and laboratory building companies. "In contrast, in these [bio-safety level] facilities, we're trying to keep whatever is being manufactured from getting out."
"I can definitely see higher bio-levels requiring this type of UV technology," agrees Sumner Tison, associate director of engineering at Biogen IDEC (Cambridge, Mass.). "Usually, a carbon filter is used to pull organics out of the air. What we are concerned with as we make biotech drugs is not so much the safety of our employee (as contaminants we work with are contained and are not released into the cleanroom air); our concern is to keep contaminants inside the facility and not expose the surrounding environment."
A broad spectrum of UV light
Air purification systems typically fall into two categories: coil and UV air purifiers. Although both use UV light, they treat air differently. If an air conditioning coil develops mold, for example, an entire cleanroom will become infected with either volatile organic compounds or mold spores. When a UV light is placed over the coil, however, mold growth is arrested, and it begins to reverse.
But if other contaminants are traveling within the air stream—for example, a return duct located over a chemical source that's pulling air in, or a contaminant in the air from a sneeze or cough—UV light over a coil doesn't address the problem. For these situations, UV in-duct air purification is necessary.
The UV Bio-Wall delivers a high amount of UV intensity over a great distance. It fits into a duct, cleaning five or six feet deep and destroying any microbial contaminants traveling through it. Because Bio-Wall is thorough in destroying contaminants in the air stream, Sanuvox says a coil cleaner upstream of the coil is not necessary. In essence, the Bio-Wall is designed to starve any mold that would be on the coil.
Another Sanuvox cleanroom solution, the less expensive S1000FX, combines UV with filtration. Inside a box is a large aluminum cone containing two 30-inch UV lights, two 1-inch prefilters, and a HEPA filter. The combination is designed to provide a compact, high-efficiency purifier and filter unit that can be hung on a wall, or over a drop ceiling. It does not require ducting. An optional volatile organic compound (VOC) sensor triggers the firing of an additional light when tripped, to accomplish high purification quickly.
Cost and maintenance
S1000FX units cost about $3,500 while Bio-Wall systems cost approximately $5,000. Minimal maintenance is required, says Sanuvox. For the duct-installed Bio-Wall, a ballast control box features a countdown timer, LED indicator, and an audible alarm that provides constant monitoring. While lamps require changing every 12,000 to 17,000 hours, the company says that amounts to nearly four years of use.
Ultraviolet caveats
Also known as ultraviolet germicidal irradiation (UVGI), UV light has been used for more than 100 years to kill microorganisms that cause air quality problems. Not until the past 10 years, however—based on the availability of new high-output UV lights—has a concentration of UV energy been available to sufficiently purify a rapidly moving air stream.
Before adding UV systems into cleanroom applications, however, several issues must be considered. At the surface of the UV light itself is a tremendously effective ultraviolet intensity. But just a few inches away from the surface of the lamp, the germicidal wavelength drops off considerably, and more than 80 percent of the UV light is lost. So, factors for achieving a high "kill" of bacteria include the intensity of the UV source, and the length of time the bacteria is exposed to UV light.
Safety factors are few, but include potential eye damage with direct exposure. Another hazard to consider: UV light destroys plastic.—CM