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What is Ultraviolet Sterilization?
Ultraviolet germicidal irradiation (UVGI) is an effective viricide and bactericide. In 1903 Niels Finsen was awarded the Nobel Prize for Medicine for his work in using UV to fight tuberculosis. Today it's a common sight in hospitals, food production facilities and science labs, as well as being used for water purification and disinfecting swimming pools. The technology is also increasingly making its way into domestic households. Waste and drinking water is often treated with UV. Many bottlers of mineral and spring water use UV disinfection. Recent studies have shown that UVC is effective for treating Cryptosporidium oocysts and Giardia cysts.
How does Ultraviolet Sterilization work?
Ultraviolet sterilization utilises UVC at 240 – 260 nanometres (optimum 253.7 nm also known as germicidal UV) to penetrate through the cell membrane and destroy the nucleic acids in these organisms so that their DNA is disrupted. Microorganisms have less protection from UV and cannot survive prolonged exposure to it. A cell that cannot reproduce is considered dead. UV treatment takes place in a stainless steel (grade 304) exposure chamber and leaves no residual in contrast to chlorine disinfection. The exposure chamber houses a quarts sleeve in which the UVC germicidal lamp is seated. Lamp changes should be done at least once a year or after 8 000 hours. No fingerprints should be left on the lamp. UV must always be the last point of treatment. Exposure time between pathogens and the UVC light is of the utmost importance. Always adhere to the flow rate specifications. Water with a high turbidity or suspended solids cannot be irradiated successfully and must be filtered first.
What factors can affect UV?
- Iron and manganese can cause staining of the quarts sleeve and should be less than 0,03 ppm and 0,05 ppm respectively.
- Total Dissolved Solids (TDS) should not exceed 500 ppm.
- Turbidity should not exceed 1 NTU as levels over 1 NTU can shield microorganisms from the UV exposure.
- Suspended solids need to be reduced to a maximum of 5 microns in size. Pre-filtration is a must in all UV applications.
Advantages of Ultraviolet Sterilization
One of the biggest advantages of UV Irradiation is that it adds no chemicals or other substances to water and works faster than chlorine. UV provides an economical, efficient and user-friendly means of producing potable water. The following list shows some of the areas where ultraviolet technology is in use:
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