Steve:
Here's some info from aquarium hobbiest who also use Ozone and injects it into and mixes it with the water and...
UV sterilizers in direct contact with water...(UV sterilizers in aquariums use special bulbs in quartz tubes that are in direct contact with water.)
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... ozone can also be generated by intense ultraviolet light. The ozone generators sold by Ultralife fall into that category. These devices use a special light bulb producing short wavelength UV light (often 185 nm). During UV exposure at this wavelength, O2 molecules in air passing near the bulb absorb the light and are broken apart:
O2 --> 2O
As with electric discharge units, these oxygen atoms can then combine with O2 to form ozone:
O + O2 --> O3 (ozone)
The manufacturers of these types of units claim that their advantages are that the air need not be dried, and that fewer nitrogen-containing byproducts are formed (e.g., nitric acid). Additionally, their bulb is said to last for two to three years before needing replacement. Competitors have claimed that these types of ozone generators lose about 20% of their rated output after a few hours of operation, and that the electrical power consumption is much higher for a UV based system than for corona discharge. The maximum concentration of ozone that can be obtained in a given air volume is lower (01 - .1% by weight O3 in air for UV systems compared to 0.5 to 1.7% O3 in air for dried air using corona discharge). Note that the UV type ozone generators' output often is not adjustable.
Also noteworthy is that these units are distinctly different from UV sterlizers. Ultraviolet sterilizers use a longer wavelength of UV light (about 254 nm, typically) and kill organisms by UV's direct interaction with the tank's water as it passes by. Molecules such as DNA in the organisms absorb the 254 nm UV and the molecules break apart, killing them. Ultraviolet light at 254 nm does not produce significant ozone.
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Interestingly, information above tells us a difference of 254 nm not cause much change to oxygen (in water) where 185 nm (in air) does.
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Ultraviolet radiation, referred to as UV or UVC radiation for sterilization purposes is a form of ionizing and non-ionizing radiation. UVA and UVB that are can reach the Earth’s surface are primarily non-ionizing and do not have enough energy to ionize atoms. However, the longer wave UVA and UVB can cause molecules to vibrate and rotate resulting in heating up.
The shorter wave UVC (used in UV Sterilization) light will ionize many atoms and molecules as compared to the even shorter wave Gamma Rays which will ionize most atoms.
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