Microbes and UV Radiation
UVGI Kills Microorganisms and Sterilizes Objects
Ultraviolet germicidal irradiation (UVGI) is one of the most versatile and effective ways of sterilizing an object without causing damage and without generating harmful by-products. Because of its versatility and safety, UVGI has been used to sterilize air, drinking water, aquariums, ponds, laboratory equipment, medical instruments, food and beverages. The beneficial uses of UV light have been known for more than a century. Niels Finsen, a Danish physician and scientist, first used UV radiation to heal tuberculosis lesions and won the Nobel Prize for this work in 1903.
UV radiation generated by our sun comes to the earth in three forms and is classified according to its wavelength: UVA, UVB and UVC. UVA and UVB radiation is responsible for sunburns and photo damage to our skin and can be blocked by clothing or sunscreens. Shortwave UVC radiation is also called ionizing radiation because it has enough energy to quickly destroy important molecular bonds such as those found in deoxyribonucleic acid (DNA), the molecular blue print of all living cells. By creating random breaks in DNA, UV radiation can introduce mutations and in most microorganisms this causes cell death. Fortunately, the earth’s ozone layer absorbs most of the UVC radiation generated by the sun and allows biological processes, in other words life, to exist on Earth. This feature of UVC can be useful, however, to kill potentially harmful microorganisms that are relatively resistant to other forms of sterilization. Ashok Gadgil was the first to use UV radiation to kill microorganisms in water and thereby use UV radiation to sterilize water.
UVGI uses short-wavelength UVC in a contained area to kill microorganisms such as viruses, bacteria and molds some of which can cause human disease and are called pathogens. Some pathogenic microorganisms are resistant to other forms of sterilization such as chemicals and often using heat sterilization is not feasible so UVGI is the only effective means of destroying them. Although UVGI kills microorganisms, it does not remove them, so adding a filtration system to a UVGI sterilization system produces sterile and purified water, free of harmful microorganisms.
Whereas other UV-based germicidal systems pass air or water through or in front of the unit, the miniZapr UVGI product line passes over the target material. As such, the miniZapr UVGI is a “line-of-sight” solution, offering an unobstructed view of the target material. When used according to specifications for speed, distance and number of passes, the miniZapr system is effective at reaching the indicated germicidal kill rates. A repeated, pro-longed treatment program can remove 99.9999% of surface microbes and a significant reduction in microbial burden. Such a high kill rate ensures that the risk of infection for human users is minimal and that the treated facilities are safe for human use.
Target Levels of UVC Energy
Each microorganism has a different level of sensitivity to UVC radiation. Some microorganisms require only a small amount of UVGI to break apart its DNA while others require more. In order to use UVGI to effectively sterilize surfaces, the operator must understand exposure levels required, the intensity of the UVC light source, the distance from the light source to the target surface and the length of time required for optimum exposure.
The miniZapr® is available in two distinct modules: the base unit and the handheld. The base unit is designed to operate 2″ from the target surface and uses eight specifically designed UVC lamps to generate 6,874 µJ/cm² of energy assuming a standard walking speed of 2 mph and three passes. The handheld module requires the operator to control all aspects of exposure such as speed, distance, and the number of passes. Assuming most users will use the handheld unit approximately 2” from the target surface, at a speed of 0.5 feet/s and in two passes, an energy dose of 7,350 µJ/cm² is reached.
In essence, greater exposure time delivers a higher dose of energy. However, the variables contributing to UVGI exposure dosage are as follows:
miniZapr® Base Module – Calculations for Various Operational Speed/Passes for Energy Exposure
|Module/Cart Speed (mph)||2||1||2||1|
|Passes over field||3||3||2||2|
|Peak Exposure @ 2” (µW-s/cm²)||11,125||11,125||11,125||11,125|
|Total CALCULATED Dosage (µJ/cm²)||6,874||13,748||4,583||9,165|
miniZapr® Handheld Module – Calculations for Various Operational Speed/Passes for Energy Exposure
|Module Speed (feet per second – fps)||.5||.5||.5||.5|
|Passes over field||2||3||2||3|
|Peak Exposure @ 2” (µW-s/cm²)||—||—||4,410||4,410|
|Peak Exposure @ 3” (µW-s/cm²)||2,940||2,940||—||—|
|Total CALCULATED Dosage (µJ/cm²)||4,900||7,350||7,350||11,025|
NOTE: The blue highlighted columns represent the recommended basic operation.
The operational requirements of this system are flexible and users can adjust their protocols to meet their needs. Using the basic variables listed above, each user can optimize the UVGI treatment system and design a regular treatment schedule that effectively targets microbes of particular concern. For the optimum results in any setting, however, the user should be aware that a slower, deliberate delivery method delivers significantly higher levels of exposure and more effective germicidal efficacy. Of course, a higher germicidal efficacy provides greater confidence of sterility and safety.
Incident Energies of Germicidal Ultraviolet Radiation at 253.7 Nanometers (UVC) Necessary to Inhibit Colony Formation in Organisms (90%) and for 3-Log (99.9%) Reduction
Energy needed for kill factor Microwatt seconds per square centimeter
|Bacillus magaterium sp. (spores)||2,730||5,200|
|Bacillus magaterium sp. (veg.)||1,300||2,500|
|Bacillus subtilis spores||11,600||22,000|
|Leptospira Canicola-infections Jaundice||3,150||6,000|
|Methicillin-resistant Staphylococcus aureus (MRSA)||2,600||6,600|
|Salmonella paratyphi-enteic fever||3,200||6,100|
|Salmonella typhosa-typhoid fever||2,150||4,100|
|Staphylococcus aureus (Staph)||2,600||6,600|
|Chiarella vulgaris (Algae)||13,000||22,000|
|Bacteriophage (E. coli)||2,600||6,600|
|Common yeast cake||6,000||13,200|
|Aspergillus flavis||Yellowish green||60,000||99,000|
|Aspergillus glaucus||Bluish green||44,000||88,000|
|Mucor racemosus A||White gray||17,000||352,000|
|Mucor racemosus B||White gray||17,000||352,000|