Sources of Ultraviolet Light
Ultraviolet light is a natural component of sunlight. Ultraviolet rays are electromagnetic wavelengths of radiation which are just shorter than those of visible light. The sun's radiation contains many ultraviolet rays.
Higher energy wavelengths of UV rays have the unique ability to destroy harmful microorganisms in water. UV light destroys these microorganisms by disrupting their genetic information (DNA), rendering them harmless.
Of all current methods of water disinfection, UV disinfection is the most efficient, economical and environmentally safe system.
There are four types of UV light within the electromagnetic spectrum which include electromagnetic waves of various frequencies (measured in cycles per second) or wavelengths (measured in metres or nanometres). UV light lies between X-rays and visible light along the spectrum. The regions of energy that have a germicidal effect are known as UV-B and UV-C.
Short-wave UV-C lies between 200 and 280 nanometres (nm). This is where germicidal effects occur. Because short-wave UV is screened out by the earth's atmosphere, naturally occurring UV-C is rarely found at the earth's surface.
Ultraviolet Dosage
Ultraviolet dosage is measured in microwatt seconds per square centimetre (uWs/cm2). The higher the microwatt, the higher the dosage; the longer the exposure time, the higher the dosage; increase the area exposed to the ultraviolet radiation, the higher the kill.
Ultraviolet disinfection of water generally employs low pressure mercury vapour lamps. They generate short wave ultraviolet in the region of 253.7 nanometres, which is lethal to microorganisms including bacteria, protozoa, viruses, moulds, yeasts, nematode eggs and algae.
Approximate dosage rates to kill:
- Bacteria 2,500 - 26,400 uWs/cm2
- Yeast 6,600 - 17,600 uWs/cm2
- Algae 11,000 - 330,000 uWs/cm2
- Viruses 2,500 - 40,000 uWs/cm2
The U.S. Public Health Service published a policy stating the dosage requirement for drinking water should be approximately 16,000 uWs/c2. This statement has formed the basis for a World Wide Standard. Every UVTA™ UV unit emits in excess of 36,000 uWs/cm2,which is more than double the recommended dosage of the U.S. Public Health Service.
For detailed information on critical factors please download the PDF brochure ››
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