Solar UV water treatment

[Willshikabob]

Hi all. So for the UN Sustainable Development Goals, I was thinking of using UV rays to clean water. From my understanding, solar UV rays are powerful enough to mutate and kill the bacteria in water and sterilize it. I'm wondering if this is true, and if so, would the death of the bacteria, if enclosed, contaminate the water? Thank ya very kindly. If you're interested in what else I'm doing, I can allow you to comment on my document.

[CharonY]

UV is already in use to treat drinking water (you can buy home units, for example). However, bacterial components, including toxins remain (though with sufficient power at least some of them may also be destroyed by photolysis).

[StringJunky]

27 minutes ago, CharonY said:

UV is already in use to treat drinking water (you can buy home units, for example). However, bacterial components, including toxins remain (though with sufficient power at least some of them may also be destroyed by photolysis).

I think I read of micro-porous filter that will remove much of the toxins

[CharonY]

There are a variety of options to further purify water, including reverse osmosis and a bewildering range of filter materials and resins. Not entirely sure what the ultimate goal of OP is, though.

[Willshikabob]

Okay, I'll give some context. So, the UN Dev Goal I'm doing is clean water. I'm trying to create a solution that people living under the poverty line can create. It's cheap, effective, and reliable. There's some compromise, but it's the best they can make. They need to use what they have. I've thought of UV, but I'm open to suggestion. It just needs to fit those requirements. I've looked at UV filters, and they're hecka expensive in Canada, so I'm trying to stay away from those.

[StringJunky]

Probably the cheapest way is to pump the water upwards into a layered filter system with the coarsest grade at the bottom and clean sand at the top. The greatest expense is the manual pump and pipe. What you've got here is a filtration system under pressure but it is able 'give' because the particulates can move upwards to relieve excess pressure as the filter fills up with filtered matter, which acts a finer filter further still. You could put a charcoal layer in for toxin removal - this can be made on-site. If it was big enough and left long enough bacteria would colonize the substrate and break down the organic matter and nitrates. This latter step, if you use the bacteria rather than regularly rebuild the filter substrate,  would probably require the final water to be chlorinated which might be outside your hypothetical budget. Perhaps @CharonY might comment on that last part regarding the safety with using bacteria without post-chlorination for drinking purposes. I'm thinking perhaps the people that would use this system may be more tolerant to such bacterial species that inhabit such a system. I'm thinking in terms of least-harm compared to what is probably already available - untreated  river water or pond water.

With regard to your original idea, you need UVC rays for a germicidal effect in reasonable time and these are pretty much completely filtered out by the upper atmosphere. You need specific light bulbs that emit this range. UVB and UVA are not energetic enough to cause damage quickly enough and cells have evolved to repair such damage. Here's a NASA article about it:

https://earthobservatory.nasa.gov/Features/UVB/

Edited May 8, 2018 by StringJunky

[John Cuthber]

Are you aware of this?

https://en.wikipedia.org/wiki/Solar_water_disinfection

[Willshikabob]

4 hours ago, John Cuthber said:

Are you aware of this?

https://en.wikipedia.org/wiki/Solar_water_disinfection

No, I was not. Thank you! I just need something to get the chemicals and heavy metals out. I had an idea of a gravity filter, with some sediment and sand, as well as a cloth dripper. Could this combo work?