Trident UV sanitizer

[chem geek]

UV lamps in residential pools at recommend water flow rates output a fluence (amount of UV energy radiating from the lamp over an area) of around 30 mJ/cm2 (some are 40 mJ/cm2). The sun outputs around 300 mJ/sec/cm2/nm (yes that's per second per nanometer of wavelength) in the UV range below 400 nm down to around 340 nm falling off to 150 at 320 nm and then rapidly falling off towards zero (30 at 310, 2 at 300 0.03 at 290) due to ozone absorption of UV in the atmosphere.

Of course, the UV lamps output at lower UV wavelengths that are effective for disinfection, but the sunlight nevertheless has UV in the range that breaks down chlorine and when chlorine breaks down it forms hydroxyl radicals that are very powerful oxidizers. So while the UV in sunlight should not be seen as any form of supplemental disinfection, it most certainly can be seen as a form of supplemental oxidation. It helps in residential pools, but is not enough to make a substantial difference in heavier bather-load pools (i.e. commercial/public).

Since chlorine is the primary disinfectant and in outdoor pools is also a reasonable oxidizer, the only purpose of UV (and ozone, for that matter) would be in inactivating chlorine-resistant pathogens such as Cryptosporidium parvum. However, this pathogen is not found in the environment and would only be introduced into a pool by an infected person (via diarrhea). In indoor pools, a UV system can be helpful even for a residential pool.

[PoolDoc]

Chem Geek, if you'll forgive me, I'll translate and simplify a bit.

Chem Geek is pointing out that UV lamps may emit more UV in lower wavelengths, than the sun does. UV wavelengths are simplified as UV-A, UV-B, and UV-C (see wikipedia, here for more: http://en.wikipedia.org/wiki/Ultraviolet ). Only UV-C (100 - 280nm) is specifically germicidal on its own. The Trident unit mentioned may have either UV-C *or* UV-B. If the lamps are UV-B, they do nothing that sunlight doesn't do much more of. But, even if they are UV-C, the effect is usually functionally insignificant . . . for outdoor pools.

The reason is, sunlight UV (UV-A + UV-B) converts some of the oxidizing chlorine present into extremely powerful hydroxyl radicals, which oxidizes just about everything -- bacteria, viruses, chloramines, and more.

It's true that UV-C units can provide additional protection against giardia and the like, but only if the rather complex operating requirements (below) are met. The simpler solution, followed by most pool owners, is to keep people from pooping in the pool . . . and to evacuate the pool in the case of failure.

---------------------------------------------------------------------



By the way, I have personally seen, many, many times, that solar UV *does* have a very substantial effect on even heavily used outdoor pools: chloramine build up is NEVER a problem on such pools, if adequate chlorine levels are maintained. By contrast, even less heavily loaded indoor pools, often have a problem. Chloramine control on indoor pools seems to me to be the ONLY valid application for UV units.

Controlling the risk from giardia and crypto can be accomplished more easily and effectively by increasing circulation rates (necessary for UV sanitation, too!) and utilizing DE filtration to filter out such large pathogens. Apparently, very substantial improvement can be achieved even with sand filters, by make sure media is correctly sized, keeping rates below 15 gpm/sft and utilizing a 'filter aid' like polyquat. Of course, an even MORE effective step is to exclude fecally incontinent swimmers (infants, older adults with fecal incontinence, all swimmers with diarrhea).

It is true that in specific situations, UV-C systems *can* provide supplemental protection against infection from pathogens, like giardia or cryptosporidium that can be transmitted as oocysts (eggs!), and which are resistant to both chlorine and UV-formed hydroxyl radicals. But -- and this is a VERY big BUT -- providing this protection is very conditional:
=> the circulation has to be continuous and high rate, since the UV units ONLY affect water that is currently passing through the pipes, and have ZERO effect on water in the pool itself.
=> the UV units must radiate in the UV-C range, and must be sufficiently powerful;
=> the glass or quartz tubes in the UV unit must be clean, and the water itself must be clear, since dirt, whether on the glass or in the water, blocks the UV.

Only if all these conditions are met, will the UV unit have a significant effect. But, for residential outdoors pools, and for most other pools, there are simpler and more effective methods of managing the risk.

In certain special cases, such as hydrotherapy pools, working with specific client populations, it may well be worth the effort to provide additional protection, utilizing high circulation rates and DE filtration and UV-C irradiation.