- sterilizing the water with light - how clever is that?
- High intensity Ultra Violet rays in the wavelength frequency range of 253.7 nanometres swiftly kill bacteria and other pathogens
- UV radiation is extremely effective in killing micro-organisms such as viruses, bacteria, algae and mould spores without altering or affecting the water balance
- UV is a sterilizer but it is not a primary disinfectant
Exposure time and light-intensity are the 2 factors that determine the disinfectant level. UV dosage is measured in microwatt seconds per square centimeter (MWS/cm2). Occasionally, light intensity and exposure time are expressed in millijoules per square centimeter (mJ/cm2).
Disinfectant level of 6000 to 10,000 MWS/cm2 or a minimum of 60 mJ/cm2are required to destroy pathogenic microorganisms. Wavelength of light is expressed in nanometres.
There are two types of Ultra violet lamps available: -
- Low-pressure/Low-intensity that produce an electromagnetic spectrum between 185 and 254 nanometers.
- Medium-pressure/High-intensity which produce a much wider electromagnetic spectrum of 180 to 400 nanometers.
- UV kills germs most efficiently at wavelengths of 240 - 280 nanometers.
- Wavelengths below 230 nanometers efficiently oxidize Organic compounds by hydroxyl radicals.
- 245 and 340 nanometers is the wavelength range that best destroys the bonds between Chlorine and Nitrogen, and also the wavelength required for the destruction of chloramines.
When you consider that Low-pressure/intensity lights are not very good at ridding a pool of chloramines, it's not surprising that Medium-pressure/High-intensity are much more generally used today, despite their higher cost.
UV light has two main effects on pool water
Firstly, UV destroys approaching 100% of harmful pathogens as they are passed through the sterilizer chamber by the circulation system
- Secondly, UV effectively breaks the links between Hypochorous Acid and ammonia, thereby destroying chloramines
- Chloramines are the root cause of several problems in swimming pools: - strong Chlorine smells, burning eyes and skin irritation
- UV light only kills those micro-organisms that are exposed to it at high intensity, i.e. in the UV chamber, so UV sterilizing is reactive rather than preventative
- Bacteria, algae and viruses that cling to the pool surfaces such as the walls, pipes or filters do not go through the UV chamber and therefore the water must still be sanitized, disinfected and oxidized and the walls and floor of the pool must be brushed regularly. An automatic cleaner is the best solution to regular brushing.
- A floating Chlorine dispenser, used in conjunction with a UV chamber, will not deliver a high enough residual sanitizer level to be effective in killing bacteria in the pipe-work, pump, filter or on pool surfaces as the UV chamber will simply burn off these chemicals as fast as they dissolve
- Any organisms that have not passed through the UV chamber must be destroyed by Superchlorination
- The UV light also rapidly breaks down the Chlorine used for Superchlorination and in 4 to 8 hours the pool water is free of Chlorine
- A UV chamber is perfect for residential pools and will give you the least toxic water you can get - very close to chemical-free water
- This is particularly true if the UV Ionizer is combined with Hydrogen Peroxide as a sanitizer
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Ken Walker - MyPoolGuru©