UV for killing bacteria in water

[Stevepppp]

Wow! Thanks for all the input!! UV Steripen huh? I'll do a little googling on that. Thanks.

[Boden]

I know of no universal solutions. UV sterilizers are useful, I use one to process all of my water as it comes from my well, but you first need to understand it's limitations. Look at the energy/unit area required to kill various organisms

Some are quite resistant, many organisms aren't listed here also.

A key issue is maintenance. The internal surfaces through which UV energy must pass must be kept clean. The water must be clear too. Some water, due to particulate matter has a very high extinction coefficient.

I doubt the effectiveness of small, under counter, UV sterilizers at anything but the very lowest flow rates.

As to materials, UV is attenuated by many glasses, plastic may be better, but will likely be damaged by UV. Quartz is best.

[Stevepppp]

I'm thinking about strapping a small UV light to my water filter reservoir, about a gallon big. That should do it. Doubt UV light will harm the plastic aside from the heat of the bulb. Thanks.

[C & E]

I'm thinking about strapping a small UV light to my water filter reservoir, about a gallon big. That should do it. Doubt UV light will harm the plastic aside from the heat of the bulb. Thanks.

Blattt! Wrong answer! LOL! Sorry, I thought that it would be a hoot. Anyway, UV light has damaging effects on nearly all plastics. Just think to the things that you've noticed had cracked or faded. I don't believe it will happen tomorrow but it will happen over time. There might be a site around which will assist with an estimate but there are a lot of variables at work. If the resevoir is inexpensive and easy to find you can go for it and see if it fails in the next couple of years.

[C & E]

A less desireable 'presto' is outgassing of the plastic. Haven't you noticed the taste of water left in the car for a couple of days?

[Don Klipstein]

Except that the main germicidal wavelngths of UV (UVC of wavelength around 240-280 nm) are highly blocked by the ozone layer even when the ozone layer is weakened, and these wavelengths also have a high rate of being blocked by plastics that are transparent when thick enough to make bottles from such plastics.

- Don Klipstein ( [e-mail])

[Don Klipstein]

The glass used for making bottles also blocks UVC and even most UVB.

Then again, I have doubt about sterilizing water with a light source that does not exterminate plankton in shallow ponds.

- Don Klipstein ( [e-mail])

[HeyBub]

The blockage may be high, but the resulting radiation is sufficient. At least according to all the studies I've been able to find.

[Stevepppp]

So does mere age accomplish the same thing to all material, a little UV just speeds the damage to some minute degree. Does that mean never buy water sold in clear plastic bottles? No. Sunlight comes through our kitchen for several hours every day for years and nothing plastic has noticeably cracked or deformed. Relax.

Yeah time will do this to everything. The faded part is UV induced but so what?

Bingo.

Nothing will fail in a couple years. Couple decades and it will be mainly due to age.

[Stevepppp]

Yeah and mere heat was the big culprit. Do you know how hot it gets in cars?

[Stevepppp]

What about UV lights? Do they have the desirable germicidal effect? Thanks.

[Stevepppp]

Just buying a UV light and be done with it. I'm lazy.

[Don Klipstein]

I just hope you don't rely on germicidal effects from those "blacklights" whose UV is mainly in the longwave roughly-60% of the UVA range - which does not even cause much suntanning of human skin. (At higher intensities, such longwave UV wavelengths still have ill effects on a couple parts of the human eye and some organic pigments/dyes.)

Killing bacteria with UV depends highly on sufficient exposure to UV wavelengths that are in or very near the UVC range. The main germicidal UV wavelength from "germicidal UV lamps" is 253.7 nm, AKA 254 nm, from low pressure mercury vapor combined with an inert gas, usually argon, sometimes krypton, sometimes neon, sometimes a mixture of argon with either neon or krypton.

- Don Klipstein ( [e-mail])

[Don Klipstein]

That depends on what the UV lights are. There are a few varieties of UV!

Longer wave 65% or so of UVA, 340 to 400 nm or so: This is the "blacklight range", as in the main wavelength range for dim violetish color lamps to cause organic fluorescent substances to glow.

This wavelength range has its "traditional base" being the 365-366 nm cluster of wavelengths of high pressure mercury vapor lamps. Blacklight "fluorescent lamps" (those are actually true fluorescent lamps) of BL and BLB types have a phosphor that absorbs the 254 and 185 nm main wavelengths from glowing low pressure mercury vapor to produce fluorescence in longer-wave UV around 360 nm.

There are many UV LEDs with peak wavelength around 395 nm, and fewer with shorter wavelengths but still mostly at least 350 nm. When an LED has nominal peak wavelength 350-375 nm, it tends to dimly visibly glow with a violetsh-white color - due to weak out-of-main-band spectral content combined with the visible-violet-fringe of the main UVA emission band. When a UV or "near-UV" or "nearly-UV" LED has peak wavelength in the

380 to 410 nm range, especially of 395 or 400 or 405 nm common wavelengths, such an LED is typically quite violetish in color and often not especially dim. 400 nm is the "official border" between UVA and "visible light", LEDs with peak wavelength slightly below 400 nm have their main emission bands having some significant spectral content at wavelengths above 400 nm, and "near-UV" of wavelengths only slightly shorter than 400 nm is dimly visible.

The main human health hazards from longer-UVA wavelengths are:

• To the lens of the eye (mainly impacting farm hands and long-haul truck drivers working heavily within roughly 35 degrees latitude from the equator).

• To the retina of the eye, mainly from focused intense images of strong sources of such UV such as staring into a UV LED.

Next shorter wavelength significat subdivision of UV: Tanning UVA. That is roughly 315-340 nm. Keep in mind that "tanning UVA" is not completely harmless to human skin, and can also be harsh on the retina, lens and cornea of the human eye.

Next after that is UVB - 280 to 315 nm. That is a harsher range of UV. UVB content in sunlight reaching Earth's surface is mostly 300-315 nm.

Ill effects to the human eye from shorter wavelengths of UV tend to be more concentrated to more-foreward parts of the human eye. UVB has some prospect to do bad things to the lens of the human eye, but is worst to the cornea. UVB is notably harsh on human skin and blamed for many skin cancers, especially ones of the more-malignant class of "malignant melanomas".

Next down in UV categorization by wavelength is non-vacuum portion of UVC. That is 200-280 nm. "Germicidal UV" is mainly the longwave 50-60% or so of this range, and the shortest UVB wavelengths are indeed are slightly to somewhat germicidal. The 254 / 253.7 nm wavelength from low pressure mercury vapor (combined appropriately with a "noble gas" or a mixture of "noble gases") is the main wavelength for such purpose from lamps made for such purpose.

The main human health hazards from UV wavelengths that short are to the conjunctiva and outer regions of the cornea of the eye, and to the epidermis of the skin. Carcinogenesis to human skin from UVC appears to be a significant problem from significant exposure, and appears to be likely confined to the epidermis - where the more malignant skin cancers of "malignant melanoma" type tend to originate. Just to point out an alarmist thing to watch for - there is such a thing as non-melanin-producing malignant melanoma. That is an uncommon but deadly known "subvariant" skin cancer whose critical early warning sign is otherwise-unexplained growth of a reddish area on the skin, mole-like small or almost that small in size when it is in an earlier stage when having a dermatologist removing it has a good chance of saving your life from removing such a deadly cancer at such a sufficiently early stage.

UV wavelengths in the UVC range also include the 10 to 200 nm range as well as the 200-280 nm range. The sub-200-nm wavelength range is "vacuum ultraviolet" "AKA VUV", absorbed by air and oproducing ozone in the a process. Few transparant solid materials pass significantly even a part of this wavelength range. The main wavelength of low pressure mercury vapor in this range is 184.9 AKA 185 nm.

- Don Klipstein ( [e-mail])

[jack]

And the proof of that is that dogs don't get sick after drinking from puddles! I sure hope nobody follows that advice, cause we aren't dogs.

[Stevepppp]

Skin cancer is over blown. No one ever died from it. Lots of people who've spent most of their lives outdoors live to be over 100. Get out more. Furthermore I ain't gonna be sunbathing by my water tank. So skin exposure isn't even an issue, nor eye problems. I'll black it out from view if it get annoying. =2E. off to get me some UV.

[Stevepppp]

Where did he say bottled puddle water? Your logic escapes me.

[HeyBub]

Right. But an 80-mile long extension cord is out of the question for the little brown babies in remote regions of Kenya.

Maybe a battery-operated one?

[HeyBub]

Right. A Dog's digestive system relies on a different mix of chemicals than a human's. This different mix (I think it's fuming Nitric Acid), kills almost everything. That which is still active, is barfed up and the dog re-eats around the offending material.

[dlzc]

Dear Stevep...:

On Aug 10, 9:34=A0pm, [e-mail] wrote: =2E..

*Lots* of people have died from it. It spreads from the skin to other organs. But a reasonable (non-zero) amount of sun exposure is health and good for you.

David A. Smith