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#199084 - 03/28/10 01:18 AM Re: Yet Another Way to Sterilize Water [Re: NobodySpecial]
Susan Offline
Geezer

Registered: 01/21/04
Posts: 5163
Loc: W. WA
It's probably a combination of both, and maybe even the angle of the sun. I've seen advice to put virus-contaminated materials in full sunlight for a day to help reduce the contamination.

But the SODIS site does mention temperature.

"...otherwise the top 6" of every stream and lake would be sterile."

Only if it stayed in the same place long enough. I'm sure the water is always moving, due to current, wind, temperatures within the water source, etc. If molecules were like marbles, their constant movement would limit purity, as new bacteria would constantly be mixing with the cleansed parts.

Sue

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#199092 - 03/28/10 02:25 AM Re: Yet Another Way to Sterilize Water [Re: NobodySpecial]
hikermor Offline
Geezer in Chief
Geezer

Registered: 08/26/06
Posts: 7705
Loc: southern Cal
Originally Posted By: NobodySpecial
I'm inclined to believe it's the temperature rise rather than the UV, otherwise the top 6" of every stream and lake would be sterile.


Perhaps the UV sterilized the shallow rocky potholes from which I used to drink in Arizona. I vividly recall one into which I plunged my face and drank deeply. Finally satiated, I lifted up and noticed some submerged coyote turds about one foot away. I suffered no harmful effects whatever.
_________________________
Geezer in Chief

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#199094 - 03/28/10 02:36 AM Re: Yet Another Way to Sterilize Water [Re: hikermor]
NobodySpecial Offline
Member

Registered: 03/03/09
Posts: 197
Originally Posted By: hikermor
I lifted up and noticed some submerged coyote turds about one foot away. I suffered no harmful effects whatever.

Don't worry they were organic ;-)

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#199101 - 03/28/10 03:51 AM Re: Yet Another Way to Sterilize Water [Re: hikermor]
Byrd_Huntr Offline
Old Hand

Registered: 01/28/10
Posts: 1174
Loc: MN, Land O' Lakes & Rivers ...
Originally Posted By: hikermor
[/quote


Perhaps the UV sterilized the shallow rocky potholes from which I used to drink in Arizona. I vividly recall one into which I plunged my face and drank deeply. Finally satiated, I lifted up and noticed some submerged coyote turds about one foot away. I suffered no harmful effects whatever.



Maybe not, but I just suffered a little psychological damage.
_________________________
The man got the powr but the byrd got the wyng

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#199112 - 03/28/10 02:46 PM Re: Yet Another Way to Sterilize Water [Re: hikermor]
Compugeek Offline
Enthusiast

Registered: 08/09/09
Posts: 392
Loc: San Diego, CA
Originally Posted By: hikermor
Perhaps the UV sterilized the shallow rocky potholes from which I used to drink in Arizona. I vividly recall one into which I plunged my face and drank deeply. Finally satiated, I lifted up and noticed some submerged coyote turds about one foot away. I suffered no harmful effects whatever.


Doesn't necessarily mean you weren't drinking contaminated water. Only that if it was, your system was able to handle it.

And eeeewwwww!!!
_________________________
Okey-dokey. What's plan B?

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#199124 - 03/28/10 05:25 PM heat + Uv = death [Re: NobodySpecial]
EMPnotImplyNuclear Offline
Enthusiast

Registered: 09/10/08
Posts: 382

http://www.sodis.ch/methode/anwendung/ausbildungsmaterial/index_EN
http://www.sodis.ch/methode/anwendung/ausbildungsmaterial/dokumente_material/manual_e.pdf
Quote:
the mortality of the microorganisms increases when they are exposed to both temperature and UV-A light at the same time.



http://www.sodis.ch/methode/forschung/mikrobio/index_EN
Quote:
Water temperature affects disinfection

A warmer water temperature speeds up the process. However, bacteria, viruses, giardia and cryptosporidia are killed by UV-A radiation even when water is cooler.


http://en.wikipedia.org/wiki/Solar_water_disinfection
Quote:
* UV-A interferes directly with the metabolism and destroys cell structures of bacteria.
* UV-A (wavelength 320-400 nm) reacts with oxygen dissolved in the water and produces highly reactive forms of oxygen (oxygen free radicals and hydrogen peroxides), that are believed to also damage pathogens.
* Infrared radiation heats the water. If the water temperatures rises above 50°C, the disinfection process is three times faster.

At a water temperature of about 30°C (86°F), a threshold solar radiation intensity of at least 500 W/m2 (all spectral light) is required for about 5 hours for SODIS to be efficient. This dose contains energy of 555 Wh/m2 in the range of UV-A and violet light, 350 nm-450 nm, corresponding to about 6 hours of mid-latitude (European) midday summer sunshine.

At water temperatures higher than 45°C (113°F), synergistic effects of UV radiation and temperature further enhance the disinfection efficiency.

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#199137 - 03/28/10 07:57 PM Re: heat + Uv = death [Re: EMPnotImplyNuclear]
scafool Offline
Pooh-Bah

Registered: 12/18/08
Posts: 1534
Loc: Muskoka
Thanks EMP, this is something new to me.
From reading in the SODIS links you supplied it seems they suggest getting the water above 50°C to deal any amoebic dysentery (if present).
50°C = 122°F and while this is lower than pasteurization it is not that much lower. So thanks for the tip about making a WAPI
I assume amoebas would generally be present if there was fecal contamination, or am I wrong about that?
_________________________
May set off to explore without any sense of direction or how to return.

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#199308 - 03/31/10 03:26 AM Re: heat + Uv = death [Re: scafool]
EMPnotImplyNuclear Offline
Enthusiast

Registered: 09/10/08
Posts: 382
Originally Posted By: scafool
Thanks EMP, this is something new to me.
From reading in the SODIS links you supplied it seems they suggest getting the water above 50°C to deal any amoebic dysentery (if present).

It says SODIS will kill ameoba.
Getting the temperature simply speeds up the process, but isnt required for disinfection.

http://www.thewaterschool.org/faq.html
Quote:
7. Is temperature important?
Short Answer

Yes and no. SODIS works much faster at temperatures above 45°C, but in most circumstances the water does not get this hot.
Full Answer

SODIS has been found to work faster above 45°C, and even three times as fast when the water exceeds 50°C (Berney et al). However, it is rare for ambient temperatures to get this high, and because SODIS bottles do not absorb much infrared radiation (which is the form of light that causes an increase in temperature) the water does not usually reach this threshold. For these reasons it is uncommon for this temperature factor to play a role in actual SODIS treatment.

The Water School has done a number of tests in Kisoro, Uganda, which is a mountainous area. In all of these tests the water temperature never approached 50°C, yet 100% kill of E. coli (the standard test organism) was observed. The highest temperature was 43°C and in most cases it was in the low 30's. The important thing is that SODIS is effective at the temperatures we experience in this area. It can be even more effective at higher temperatures, but does not impact our current projects.

Some have recommended SODIS bottles should be painted black on one side to increase the heat absorption from sunlight. Our experience does not support this recommendation. It adds another step and detracts from sustainability. This issue is addressed more fully in Q&A 10.
References

Berney et al., Efficacy of solar disinfection of Escherichia coli, Shigella Flexner, Salmonella Typhimurium and Vibrio cholera. J Appl Microbiol. (2006).

Try this manual, its simpler, although it doesnt include the oxygenation tip (fill 3/4 full, shake 20 seconds, fill full)

http://www.thewaterschool.org/pdf/sodis_training-english.pdf



Originally Posted By: scafool
I assume amoebas would generally be present if there was fecal contamination, or am I wrong about that?

Probably. Its like giardia or cryptosporidium, its present everywhere, but poop doesn't guarantee presence, and eliminating eColi doesnt guarantee giardia/crypto is eliminated. In other words, don't let tests give you false confidence, don't take shortcuts with SODIS.

Quote:
Some organisms such as Enteroviruses, Cryptosporidium,
Giardia and Amoebae however are more resistant than E.coli.
The absence of E.coli therefore does not necessarily indicate
their removal. Spores of sul?te-reducing Clostridia can be
used as an indicator for these organisms [11]. But such
analytical methods cannot be used for routine tests under
?eld conditions as they are time-consuming and expensive.


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