Sunlight Sterilization of Water

[Turtle]

here's my bright idea for a portable water sterilizer. 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. the gravity flow gets metered by the narrowness of the glass tube. (water reservoir prolly needs a vent. ) whatcha think y'all?

[Moontanman]

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?

[Mercedes Benzene]

Originally Posted by Moontanman

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.

[Turtle]

Originally Posted by Mercedes Benzene

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.

after I get it built? 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. . not sure where i get those agary thingys around here.

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.

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.

and so we go...............

PS as to temp reached at focal point:

Originally Posted by Anonymous Hero

...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)...

[Turtle]

thought it wise to point out that the focused Sun will heat the water very little unless there is some dark surface backing the glass tube.

[Mercedes Benzene]

Originally Posted by Turtle

thought it wise to point out that the focused Sun will heat the water very little unless there is some dark surface backing the glass tube.

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

[Moontanman]

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.

[Turtle]

Originally Posted by Mercedes Benzene

Could you paint it black?

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

Originally Posted by MB

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. 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.

Originally Posted by M-Tan

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. .

[freeztar]

Originally Posted by Moontanman

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?

[lemit]

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