|MadSci Network: Environment & Ecology|
I am sorry that it took so long to get back to you. This question has been passed through five scientists without an answer. I guess, as I am moderator for this group, it is my duty to try and answer it for you as best I can.
Ultraviolet (UV) water treatment systems use light wavelengths near 250 nm to alter the genetic material of microbes in such a manner that they are no longer useful for essential cellular processes. Mold, algae, bacteria, viruses, etc. are all sensitive to this treatment in sufficient doses.
The dose (D) of UV delivered within a UV chamber is the product of the average
intensity (we will use IAVG because "I with a bar over it" is too
hard to code) of UV light multiplied by the retention time (t) of the water
within the chamber:
There has been some research done with ozone treatment that suggests a synergistic relationship between ozone and UV treatments. UV light seems to really get the old ozone fired up (that’s about as scientific as I get with that particular explanation).
I will also caution you that UV light, although effective on microbes, does not do much to reduce chemicals in the water. It can reduce some toxic organic chemicals to less toxic chemicals. If there is a lot of biomass removed in the final filter, the settling mass can and often does reduce suspended solids by simple flocculation—the particles are caught up in a stampede of dead bodies settling out of solution. But that is about it. You really need another system to remove things like dissolved lead. In fact, removing as many particles as possible prior to the UV treatment stage helps to maximize transmittance (T) of UV light in the UV chamber. Transmittance is the percentage of UV light that passes through 1 cm of water. The dirtier the water, the lower the transmittance. Average intensity is directly related to transmittance as the dose is directly related to average intensity.
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