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Sunlight Sterilization of Water


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here's my bright idea for a portable water sterilizer. :P :) i looked around and found nothing like this, and my thinking is that the intense sunlight at the focus needn't necessarily boil the water to kill the germs. :shrug: the gravity flow gets metered by the narrowness of the glass tube. (water reservoir prolly needs a vent. :idea:) :smart: whatcha think y'all? :Alien:

 

 

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In addition to just painting it black, you can get much higher temps with the same amount of sunlight by increasing the pressure inside the glass. Granted, this may very well be beyond what Turtle wa

I think that info should give an idea if whether your UltraViolet Portable Absorption Sterilizing System (UV-PASS :)) should work.   According to the chart you link, bacteria need between 3620 and 220

It would have to heat the water to significantly close to boiling to kill the germs. Have you figured how close to boiling it would have to come to kill the germs?

 

Not necessarily. :)

If the UV exposure was intense enough, it could certainly be enough to destroy microorganisms. However, I think the main issue is going to come down to time. I'm guessing you would need a fairly long exposure, so the flow-rate should be pretty slow.

 

Obviously, combining temperature with UV radiation is a bonus. Have you tried measuring the temperature at the focal point?

 

After you get it built, you should definitely buy some agar plates to see how it works! I'm very interested in seeing the results. :P

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It would have to heat the water to significantly close to boiling to kill the germs. Have you figured how close to boiling it would have to come to kill the germs?
Not necessarily. :smart:

If the UV exposure was intense enough, it could certainly be enough to destroy microorganisms. However, I think the main issue is going to come down to time. I'm guessing you would need a fairly long exposure, so the flow-rate should be pretty slow.

 

Obviously, combining temperature with UV radiation is a bonus. Have you tried measuring the temperature at the focal point?

 

After you get it built, you should definitely buy some agar plates to see how it works! I'm very interested in seeing the results. :)

 

after I get it built? :idea: so anyway, apparently even boiling isn't sufficient to kill some germs. How to Sterilize Water | eHow.com

...Step 1 Realize that boiling water does not sterilize it. There are bacteria that form spores that are resistant to boiling and some strains of bacteria that are themselves resistant to heat above boiling temperatures.

 

but then, i was thinking UV in the equation as you say, so...

Step 4 Utilize the effect of ultraviolet radiation on the most common pathogens. This is of particular use if you are in a circumstance where large amounts of sterile water are needed and you have few resources. Pour off particle matter. Take the clear water and pour it into a clear plastic bottle. Place the plastic bottle on a dark surface. Leave the bottle in sunlight for at least eight hours. The combined effect of ultraviolet radiation from sunlight and heat is effective in producing a primarily safe source of drinking water.

 

the agar plate thing would be the way to go for testing my rig out; we musn't forget to make up a control set of plates from the pre-treated water too, so's we can rule out some instances of contamination after the fact as well as show what was affected. . :idea: not sure where i get those agary thingys around here. :Alien:

 

so my thinking was that by concentrating the Sunlight and slowing the flow i could get a small amount of sterilized water in short order. around here in the Cascades you don't want to drink stream water because of Giardia for example, so testing specifically for that is a must do. geez; i guess testing specifically for everything would be in order. :doh:

 

one final thing, which is whether or not a simple magnifying lens bends UV much or at all? i recall UV telescopes need special long nested mirrors to collect it is why i'm curious on this point. :P

 

and so we go...............:shrug:

 

PS as to temp reached at focal point:

...The theoretical upper limit for the point temperature at the focal length is the same of the source of illumination, about 6000 degrees C for our Sun. No glass lens is 100% efficient and the resulting temperature will be somewhat less, regardless of the lens size. Even a lens the size of the Sun and no atmosphere will not do it. A bigger problem is that the energy deposited is also radiated back off the object, some of that is reflected light (you can't get 100% absorbtion). CR4 - Blog Entry: Magnifying Glasses: Newsletter Challenge (05/16/06)...
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You can drink it if you want but many if not most of the organisms that make water unsafe to drink are not easily killed by UV. a UV sterilization lamp uses many orders of magnitude more intense UV than natural sunlight provides at a much higher more deadly wave length than can get through earths atmosphere. The UV that gets through earths atmosphere isn't especially sterilizing.

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Could you paint it black?

 

possibly, although uneven heating then might break the glass. something dark & heat absorbing in contact fo' shizzle. :Alien:

I have a lens that's started fires with dry leaves before. What type of lens were you planning on using?

 

just a little folding pocket lens that i carry. :shrug: at ~ 2", i use it to light my cigs when circumstances allow. :) the trick there is to hold the cig in your hand and put the focus on the tobacco, not the paper, as the white paper simply reflects most of the light. :smart:

 

You can drink it if you want but many if not most of the organisms that make water unsafe to drink are not easily killed by UV. a UV sterilization lamp uses many orders of magnitude more intense UV than natural sunlight provides at a much higher more deadly wave length than can get through earths atmosphere. The UV that gets through earths atmosphere isn't especially sterilizing.

 

acknowledged. looking more like i'd need to add a heat absorber, a condensing coil, and go for distilled water, since boiling & UV not enough. . :P :idea:

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You can drink it if you want but many if not most of the organisms that make water unsafe to drink are not easily killed by UV. a UV sterilization lamp uses many orders of magnitude more intense UV than natural sunlight provides at a much higher more deadly wave length than can get through earths atmosphere. The UV that gets through earths atmosphere isn't especially sterilizing.

 

I'm unable to find studies related to UV effectiveness, can you please provide some sources?

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This is fascinating.

 

I've had giardia. I went for two months before I got it diagnosed. It isn't fun and I wouldn't recommend it, but I've had worse.

 

Where I grew up, we had water from a deep well about a half mile from a coal vein. It stuck to your ribs and probably provided more than the daily requirements of a lot of mineral supplements.

 

Speaking of where I grew up, if you aren't trying to make a hip-pocket purifier, how about a still like some folks back there had? Wouldn't that do the job?

 

That isn't a leading question. I don't know much about purifying. I wish I had when I was drinking that oily stuff.

 

--lemit

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I'm unable to find studies related to UV effectiveness, can you please provide some sources?

 

i found some stuff. :shrug:

 

Ultraviolet - Wikipedia, the free encyclopedia

The Sun emits ultraviolet radiation in the UVA, UVB, and UVC bands, but because of absorption in the atmosphere's ozone layer, 98.7% of the ultraviolet radiation that reaches the Earth's surface is UVA. (Some of the UVB and UVC radiation is responsible for the generation of the ozone layer.)

 

Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths while Silica or quartz glass, depending on quality, can be transparent even to vacuum UV wavelengths. Ordinary window glass passes about 90% of the light above 350 nm, but blocks over 90% of the light below 300 nm.[4][5][6] ...

 

Ultraviolet Water Sterilization | BuyUV.com

Ultraviolet radiation is a type of light, unlike visible light, that cannot be seen. Its wavelengths, expressed in Angstrom units (one Angstrom unit wavelength equals one hundred-millionth of a centimeter), are shorter than the wavelengths of visible light and carry more energy. Because of this high concentration of energy, UV radiation has the unique ability to kill microorganisms with which it comes in contact.

 

HOW DOES ULTRAVIOLET RADIATION WORK?

 

Ultraviolet radiation sterilizes water. Sterilization implies that life such as bacteria, viruses, yeasts, molds, and algae are destroyed. For UV radiation to work, a 2537 Angstrom unit (254 nanometers) wavelength must come in contact with the microorganism to inactivate it. When ultraviolet rays reach the microorganism, they strike the heart of the organism destroying the DNA (deoxyribonucleic acid) and preventing it from reproducing. Table I give the amount of UV necessary to kill various microorganisms.

 

a list of some 'germs' and the UV dose needed to kill them: >> Germicidal Disinfection Information

 

This is fascinating.

 

I've had giardia. I went for two months before I got it diagnosed. It isn't fun and I wouldn't recommend it, but I've had worse.

 

Where I grew up, we had water from a deep well about a half mile from a coal vein. It stuck to your ribs and probably provided more than the daily requirements of a lot of mineral supplements.

 

Speaking of where I grew up, if you aren't trying to make a hip-pocket purifier, how about a still like some folks back there had? Wouldn't that do the job?

 

That isn't a leading question. I don't know much about purifying. I wish I had when I was drinking that oily stuff.

 

--lemit

 

a still is ideal. :lol: for my hip-pocket needs, well, rucksack, i'm currently using a fiber/charcoal filter unit, and i carry a little bottle of bleach too. as it is, it would be a rare thing for me these days to take an adventure without taking all the water i need. :help: :cap:

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Could you paint it black?

 

In addition to just painting it black, you can get much higher temps with the same amount of sunlight by increasing the pressure inside the glass. Granted, this may very well be beyond what Turtle was thinking, or might require higher tech resources than he'd planned to use, but by pressurizing the tube itself you can get a LOT more bang for each solar buck.

 

I'm thinking of something similar to the evacuated tubes they use in many new solar hot water heater applications.

 

Beyond Oil Solar: Solar Evacuated Tubes

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In addition to just painting it black, you can get much higher temps with the same amount of sunlight by increasing the pressure inside the glass. Granted, this may very well be beyond what Turtle was thinking, or might require higher tech resources than he'd planned to use, but by pressurizing the tube itself you can get a LOT more bang for each solar buck.

 

I'm thinking of something similar to the evacuated tubes they use in many new solar hot water heater applications.

 

Beyond Oil Solar: Solar Evacuated Tubes

 

kewl units! :)

what i was really going for with my original idea was the UV doing the work, but I suspect that a magnifying glass won't bend UV to the focus, and second, the lens may absorb 90% or more of the UV that does strike it. :) oh well. :) :)

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i found some stuff. :)

 

a list of some 'germs' and the UV dose needed to kill them: >> Germicidal Disinfection Information

 

I think that info should give an idea if whether your UltraViolet Portable Absorption Sterilizing System (UV-PASS :)) should work.

 

According to the chart you link, bacteria need between 3620 and 22000 microwatts per centimeter squared of UV to be sterilized. The only convincing source I could find on the amount of UV the earth's surface receives is this page. It gives between approx. 400 and 1800 µW/cm2 for UV-A.

 

Needing 22,000 µW/cm2 and having (on the low end) 500 µW/cm2, you would need the surface of the magnifying glass to be (22000 / 500) 44 times larger than the surface of the target. That's not that bad really. If the target is one square centimeter then that's only a magnifying glass with a radius of (sqrt(44/pi)) 3.74 centimeters which is a diameter of about 3 inches.

 

That sounds very doable. The only thing I would worry about is how much UV the magnifying glass and the glass tube absorb. If it is something like 50 percent each then you'd have to make the area of the magnifying glass 4 times larger.

 

In thinking about whether the above numbers could be correct I'm reminded that my UV light keeping my pond clear of algae is 9 watts and I figure the surface area it illuminates is about 315 cm2 which comes out to 38,100 µW/cm2 which isn't much higher than the 22,000 that the magnifying glass with a diameter of 3 inches would achieve. And my UV light is very good at killing algae and water moves through the light very quickly.

 

I would wonder about parasites though. According to your chart protozoa require quite a bit more UV to kill. Are water-borne parasites protozoa? I wonder if that's the kind of thing the chart is referring to between 26,400 and 318,000 µW/cm2. It would be discouraging if the intensity needed to be that high, but this is encouraging:

 

The United States Department of Health has determined that a UV system should provide a minimum of 16,000 Microwatts per Centimeter Square.

 

 

~modest

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I think that info should give an idea if whether your UltraViolet Portable Absorption Sterilizing System (UV-PASS ;)) should work.

 

According to the chart you link, bacteria need between 3620 and 22000 microwatts per centimeter squared of UV to be sterilized. The only convincing source I could find on the amount of UV the earth's surface receives is this page. It gives between approx. 400 and 1800 µW/cm2 for UV-A.

 

Needing 22,000 µW/cm2 and having (on the low end) 500 µW/cm2, you would need the surface of the magnifying glass to be (22000 / 500) 44 times larger than the surface of the target. That's not that bad really. If the target is one square centimeter then that's only a magnifying glass with a radius of (sqrt(44/pi)) 3.74 centimeters which is a diameter of about 3 inches.

 

That sounds very doable. The only thing I would worry about is how much UV the magnifying glass and the glass tube absorb. If it is something like 50 percent each then you'd have to make the area of the magnifying glass 4 times larger.

 

roger all that, and nice acronym. ;) your source below says

pure-fused Quartz which has a transmission rate of approximately 98 percent.

 

my hand lens is plastic and i couldn't find much on its transmissibility of UV, but i found a lot on how damaging UV is to plastic. :evil: so, if we have ourselves a pure-fused quartz lens & tube, i still have questions/doubts whether the lens will bend the UV to the focus or if it will simply pass straight through?? :) :eek:

 

 

I would wonder about parasites though. According to your chart protozoa require quite a bit more UV to kill. Are water-borne parasites protozoa? I wonder if that's the kind of thing the chart is referring to between 26,400 and 318,000 µW/cm2. It would be discouraging if the intensity needed to be that high, but this is encouraging:

 

not sure on the protazoa/parasite business. will have a look. :hyper:

 

The United States Department of Health has determined that a UV system should provide a minimum of 16,000 Microwatts per Centimeter Square.

 

 

~modest

 

since they don't mention parasites/protazoa there as far as their UV sterilization systems, and they do have a pretreating filter in front of the UV treatment in those systems, maybe they filter out the parasites/protazoa? ;) more sleuthing. :eek2:

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Dudes, and possibly dudettes, you seem to think that all UV is created equally. There is UV and then there is UV UVC and even shorter wave lengths is what is used to sterilize water. UVA and UVB rain down on the earth all the time, a great many microbes have adapted to them and are very resistant to them. The UV in sun light is not particularly germicidal. it can be on some organisms but to rely on it to sterilize water I am going to drink..... well you drink it not me..... Even if you are using germicidal UV light from a dedicated UV sterilizer it can be very tricky to get 100% sterilization even in several passes. i helped designed a UV sterilizer for the DuPont company when i worked there, It was a very difficult to achieve 100% , even tiny globs of organic material can protect microbes from the UV. If you must use sunlight use it to boil the water do not rely on UV in sunlight to sterilize anything.

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Dudes, and possibly dudettes, you seem to think that all UV is created equally. There is UV and then there is UV UVC and even shorter wave lengths is what is used to sterilize water. UVA and UVB rain down on the earth all the time, a great many microbes have adapted to them and are very resistant to them. The UV in sun light is not particularly germicidal. it can be on some organisms but to rely on it to sterilize water I am going to drink..... well you drink it not me..... Even if you are using germicidal UV light from a dedicated UV sterilizer it can be very tricky to get 100% sterilization even in several passes. i helped designed a UV sterilizer for the DuPont company when i worked there, It was a very difficult to achieve 100% , even tiny globs of organic material can protect microbes from the UV. If you must use sunlight use it to boil the water do not rely on UV in sunlight to sterilize anything.

 

please read the links we have provided regarding UV & Sunlight; they cover your objections & misunderstandings. :)

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