Water Purification

Will Power

Will Power

Joined
Jan 18, 2007
Messages
33,982
The other day on Euro News TV I saw a short programme on water purification that interested me.

Villagers in remote parts of Africa have to trek a long way each day to collect water.This is a woman/girl job it seems and is heavy-going, moreover, the water is anything but healthy. Previously, villagers would have to boil the water which uses precious fuel and pollutes, or they can use chemicals.Both methods make the water taste unpleasant. Now researchers have discovered solar-power as an excellent purifier. Local people decant their water into clear plastic 2 litre bottles and place the bottles on the roof of the house in direct sun, after 4-5 hours the action of the sunlight destroys e-coli and other nasties. This simple method really impressed me and can be used in hotter wilderness/survival situations. They also had some very simple but effective solar cookers/ovens that can get 250c and can cook large quantities. Another eye-opener in hot climes. Anyone else come across any simple solutions lately?
 
Pretty cool idea. Might be useful when you are stationary in an area, like at a cabin or car camping.
 
I did read one report that surfce water from a lake or pond has the least chance of having bugs as the UV kills them. I'll still rely on filters or chemicals, but's nice to know. Someday I want to get one of the UV sterilizers.
 
mm reminds me of solar stills, which are little devices invented for life boats. in case your ship sank and you found yourself stuck in the middle of the ocean with no fresh water, you can use these solar stills to distill the sea water. basically, they are black containers with a U shaped, transparent lid, and something (like a beaker or bottle) to collect the water. on the seas, where the sunlight is usually abundant, the containers heat up and the water evaporates inside them. the vapor is collected by the u shaped lid and would drop into the beaker or bottle beneath it.
 
Lots of coverage over the last couple of years, as well as multi-layer cloth filters to stop larger bacteria (e.g. cholera).

At the very least, it is a good pre-treatment before other methods. Outght to be really good in areas with lots of UV.

I wonder how well colored glass bottles (beer bottles on the shore of very body of water where there are fishermen - or so it seems) would work. Have to experiment.


Discussed here: http://www.bladeforums.com/forums/showthread.php?t=416503&highlight=sodis
 
bah 4 - 5 hours of sunlight here melts plastic, what about the toxins the plastic would give off?
 
xinel said:
bah 4 - 5 hours of sunlight here melts plastic, what about the toxins the plastic would give off?
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That is a VERY good point! Could you use glass, pyrex, or some other material? Plastic, especially the bottles shown on the website, is not good for reuse or heating.
 
I never thought about using it for purification, but I know a guy who built a solar water heater out of black plastic pipe. I think you could easily get it hot enough to kill the wee little beasties.
 
Don't know about toxins from plastic? Water bottles are surely inert. As for melting, well if it works in central Africa it SHOULD be OK in most places. Glass breaks. The plastic system has been used for a few years and water borne diseases amongst the people trying it are greatly reduced. True, they likely have better resistance than outsiders, but I think it's a simple and useful standby which could come in handy in hot places.
 
xinel said:
bah 4 - 5 hours of sunlight here melts plastic, what about the toxins the plastic would give off?
Click to expand...

We just received a warning about our bottled water here in Iraq being left in the direct sunlight. Now, 4-5 hours probably won't be long enough to degrade the plastic bottle, but if you continually used the same bottles, I would be concerned over the long run. Short term, I think you would be okay.

ROCK6
 
Serrinon said:
very interesting. is there anything it wouldnt kill?
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Very large protozoans can be harder to kill with UV alone. There are also many species of bacteria extremophiles, such as D. radiodurans, that has a rapid DNA repair system that renders it almost invulnerable to all but insane levels of radiation.

However, this method can deal with much of the disease-causing microorganisms, such as E. coli and Giardia, which is what matters. The problem is that it's not as consistent as proper purification, because of the condition of the bottle, the weather, the larger particles in the water not settling and block off light, cloudy water etc. If you've got nothing else, though, this method is durn good.

xinel said:
bah 4 - 5 hours of sunlight here melts plastic, what about the toxins the plastic would give off?
Click to expand...

For regular PETE bottles? Trivially insignificant, and it's not like this method is going to be used unless you had no other choice, in which case I doubt you would care.
 
Thomas Linton said:
Lots of coverage over the last couple of years, as well as multi-layer cloth filters to stop larger bacteria (e.g. cholera).

At the very least, it is a good pre-treatment before other methods. Outght to be really good in areas with lots of UV.

I wonder how well colored glass bottles (beer bottles on the shore of very body of water where there are fishermen - or so it seems) would work. Have to experiment.


Discussed here: http://www.bladeforums.com/forums/showthread.php?t=416503&highlight=sodis
Click to expand...

In general, glass is a UV filter. The whole idea of colored beer bottles is to cut the UV damage. And yes, the UV filters sold for photographic use are a good lens protector, but no better UV filter than the lens itself. At one time Hasselblad made a special quartz lens for UV scientific studies because the glass lenses wouldn't work.
 
Aside from solar radiation killing directly, it creates heat inside the closed container (witness all those dead kids and pets left in vehicles in the sun, tinted windows and all). Heat, at sufficient levels, kills everything. The issue is, does it get hot enough. The science linked concludes that it does:
if a water temperature of at least 50°C is reached, an exposure time of 1 hour is sufficient
Click to expand...

Is there contrary science?

Water bottles are made of PETE (AKA "PET"; type 1 for recycling purposes). I can find no evidence of hazard in reusing such containers.

As for literally melting PETE, as in heating to the melting point, I don't know. As noted, the sun is pretty intense in Africa where the research and application took place.

How are the PETE bottles made in the first instance, milled out of solid blocks or melted and cast? :D
 
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