8 ms·

Student’s six-foot water and solar-powered lens purifies polluted water

68 points by Walkman 12y ago

hcrisp 12y ago
Another alternative is water filters. This is used in Brazil by Neymar-backed Waves For Water (90k filters) and Project AmaZon (10k filters). The latter filter design uses cheap sedimentary layers inside a framed structure. Pour the turbid water on top, and clear water comes out the bottom.
lotsofmangos 12y ago
I'd be interested to know how it goes with different types of plastic as well. I'd expect ETFE to perform a lot better (and last longer) than PTFE, for instance.
sitkack 12y ago
beautiful. use a coil as the water conduit and make it a continuous process with total heat supplied to the volume part of an inexpensive? feedback loop. How fast does the water evaporate ? Can oil or gas be floated on top to stop it? Could one just put water in metal cans painted black? Had no idea it only took temps of 130F to kill the pathogens that harm.
- fernly 12y ago
  There seems to be two bits of water involved, as you probably realize. One bit, several gallons, is sitting in a saggy plastic sheet, whose bulge forms a lens. You ask a good question, could one float a skin of oil on that to keep it from evaporating? The bit that gets purified is in a separate container held (manually?) at the focal point of the water lens, and gets hot. But as the sun moves so does the focal point, so a very patient person has to be shoving the heating container along every few minutes. This doesn't seem very practical to me.
slug 12y ago
Looks nice, but can 150 ºFahrenheit (65ºCelcius) "kill 99.9% of bacteria and pathogens" ? From https://en.wikipedia.org/wiki/Sterilization_%28microbiology%29 https://en.wikipedia.org/wiki/Sterilization_%28microbiology%... it would seem that's not the case. Wonder if the article considers the effects of sun ultra-violet radiation to help in that process.
- mpyne 12y ago
  Even if it could kill 99.9% of bugs now, just wait until we get the inevitable HRSA superbugs after 20 years of this. Though this does sound neat, and it's still much better to have than nothing at all.
  - azakai 12y ago
    It's not clear to me that bacteria and other pathogens could evolve around heat sterilization. I'm sure they can adapt in some ways to some amount of temperature change, but at some point (maybe hotter than this device can achieve) surely no organism can survive. It's like the old saying, it's easy to destroy HIV - the hard part is doing it inside a human body. In the case of sterilizing water, we don't have that problem, the water will remain usable.
    - Retric 12y ago
      A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122 °C (113 and 252 °F) http://en.wikipedia.org/wiki/Thermophile http://en.wikipedia.org/wiki/Thermophile So, 150 °F is not really all that hot as some organisms thrive at 250°F or well above boiling. However, I suspect organisms that thrive at 150+°F are unlikely to also thrive in the human body. A more important issue is the effort to sterilize water by hand is unlikely to be made with any real consistency.
      - eru 12y ago
        > A more important issue is the effort to sterilize water by hand is unlikely to be made with any real consistency. That's what safety margins are for.
  - patio11 12y ago
    This sort of thinking is often invoked to justify why the world can't get better for e.g. poor Africans, while ignoring the fact that the rest of the world has been doing it in a more effective fashion (e.g. boiling water with a fire) for literally millennia with no ill effects.
thorum 12y ago
Is this better than boiling water over a fire?
- ams6110 12y ago
  That was my thought. A small fire can heat a litre of water to boiling in a lot less than an hour. And you don't need to actually boil water to sterilize it, 160-180 degress F is adequate.
  - deleted 12y ago
    [deleted]
- dublinben 12y ago
  Indoor cooking fires are a significant source of pollution in developing countries. A solar-powered solution would be a significant improvement.
  - ams6110 12y ago
    Wood or other biomass-fueled fires are CO2-neutral, but do cause particulate pollution. There have been a number of efforts to develop clean-burning wood stoves for developing countries to combat that problem.
    - ghshephard 12y ago
      "Wood or other biomass-fueled fires are CO2-neutral" Okay, I'll bite. How does burning wood not result in a net increase in CO2? Are you assuming that for every cord of wood burnt, that someone is simultaneously planing and growing a cord's worth of tree (which, of course, pulls carbon out of the air?) That's a pretty big assumption.
      - nathannecro 12y ago
        In fact, I took his statement the other way: At one point, there was some n amount of CO2 in the air. A tree was planted. Through a few biological cycles, CO2 is exchanged and stored as various sugars within the wood. Burning the wood releases the CO2 back into the air. This is a net zero process.
cardamomo 12y ago
This strikes me as a particularly creative and refreshingly simple device for sanitizing drinking water, but given the frequency with which we see articles with headlines like "So-and-so invents such-and-such device to clean water," the problem of access to drinking water would long since be solved. That is, unless it's not really a technical problem. Articles such as this don't often delve into broader issues of public health, education, or even poverty, but with an issue as complex as water access, perhaps we out to discuss it in a more complex context.
- barry-cotter 12y ago
  >That is, unless it's not really a technical problem. It isn't. This has the same problem as all the other solar sterilisers, it says "I'm poor." People are empirically not willing to use these things. You'd probably be better off with a public education campaign to normalise their use, something objectively ridiculous like having middle class families that actually have decent running water doing it, visibily and publicly.
fallinghawks 12y ago
Throw in some watertight sealing plastic bags and they could have sous vide as well. ;)
pflanze 12y ago
A simpler approach that forgoes the lens, relies on the combination of UV and heat, and is promoted under the name "SODIS" and already in use in some places: https://en.wikipedia.org/wiki/Solar_water_disinfection https://en.wikipedia.org/wiki/Solar_water_disinfection
ChuckMcM 12y ago
I like the simplicity. We used to do the solar still thing where you put a pan of tainted water in a hole with a plastic sheet over it and a rock in the middle and the collection can under the rock. The heat evaporates the water from the pan, which condenses on the sheet and then runs down and drips off into the collection can. Not very fast of course. Of course often times the trick is getting the water in the first place.
ahi 12y ago
Water with a lot of pathogens is likely to have high turbidity as well so your lens is going to be a bit opaque.
arjn 12y ago
I've seen this approach tried before - it has problems : "Due to the sun’s movement throughout the day, Henry needs to repeatedly shift the container to match the focal point. "
- mbubb 12y ago
  I wondered about this as well. Also an issue with NOT moving it to stay fucused on the water... a lens like that could start a grass / wood fire
- astrodust 12y ago
  Unless the project participants are willing to depend on this thing for fresh drinking water as part of their testing, the project itself is insultingly academic.
dmcg 12y ago
That focal point must move in a predictable way, I wonder if a shaped vessel could be under it for long enough.
short_circut 12y ago
I am not entirely sure what is new here. I knowpeople that have been doing this for years. The Channel GREENPOWERSCIENCE has done many videos on exactly this.
lifeisstillgood 12y ago
Clean drinking water is not a technical issue - as pointed out downthread, a cloth filter and boiling it on a fire will work and has done so for thousands of years. Poverty and deprivation is tied up with a huge range if issues, from water table effects to climate change to local politics and public health and education and ... Well, if the infrastructure existed to build a million of these frames and organise water to be brought to them and then handed out to those without clean water, then any number of other technologies could easily substitute. So not saying that supplying ten thousand of these to villages whose water tables just moved five miles won't be a fantastic use of our dollars, it's just that seems a small effect. There is a good ted talk on tackling poverty amount at Maori I can't find it though. It walks through a lot of these issues.
robomartin 12y ago
I built a rig with my son using a 65 inch Fresnel lens we harvested from an old rear projection TV. It could easily produce 2,000 degrees F under ideal conditions. Focal length was about three fee. A 2x4 passed through the focal point would catch on fire pretty much instantly (as quickly as one could count to one). We successfully fried an egg (more like instantly scorched an egg) by bouncing the beam pre-focal point off a high quality front surface mirror (also harvested from the TV) and focused it onto the bottom of a cast iron skillet. Anyhow, the realization was that this thing was incredibly inconvenient and also dangerous to use. We built it into an articulated wooden frame with the explicit idea of being able to track the sun. Power output peaked and dropped off very quickly and was near useless during low-horizon times. You had to be super aware of where the focal point was at all times or risk a very serious accident. This is an obvious point but you don't fully comprehend how serious a point this is until you start setting wood on fire instantly. Even putting the thing away for the day we had to be sure to rotate it 90 degrees so that the sun hit the edge of the lens. Even then, we threw a black cloth over it just to make sure. This thing could set your house on fire in a fraction of a second. We ended up destroying it after playing with it for a month or so. Just too dangerous to be around and pretty much useless for anything practical. After a while you get tired of demonstrating how quickly you can set a piece of wood on fire. A long intro to say the following. Neat trick by this student and a fantastic learning experience I am sure. Kudo's should be given. Kids learn tons of stuff doing off the wall scientific experiments like this one. In practical terms though, well, it isn't practical at all. But, who cares, this is about learning and on that point it is absolutely brilliant. I remember seeing an article many years ago about using a folded-up t-shirt as a first-pass filter and then simple clear two liter plastic bottles left under the sun for 24 hours to make water safe to drink. People would fill these bottles with t-shirt-filtered water and either place them on a table outside or on the roof for a day. They'd rotate sets of plastic bottles for a continuous supply of safe drinking water. I couldn't think of anything simpler, cheaper or more effective. Here's on version of that: http://www.sodis.ch/methode/anwendung/index_EN http://www.sodis.ch/methode/anwendung/index_EN

68 points by Walkman 12y ago

Another alternative is water filters. This is used in Brazil by Neymar-backed Waves For Water (90k filters) and Project AmaZon (10k filters). The latter filter design uses cheap sedimentary layers inside a framed structure. Pour the turbid water on top, and clear water comes out the bottom.

lotsofmangos 12y ago

I'd be interested to know how it goes with different types of plastic as well. I'd expect ETFE to perform a lot better (and last longer) than PTFE, for instance.

sitkack 12y ago

beautiful. use a coil as the water conduit and make it a continuous process with total heat supplied to the volume part of an inexpensive? feedback loop. How fast does the water evaporate ? Can oil or gas be floated on top to stop it? Could one just put water in metal cans painted black? Had no idea it only took temps of 130F to kill the pathogens that harm.

fernly 12y ago
There seems to be two bits of water involved, as you probably realize. One bit, several gallons, is sitting in a saggy plastic sheet, whose bulge forms a lens. You ask a good question, could one float a skin of oil on that to keep it from evaporating? The bit that gets purified is in a separate container held (manually?) at the focal point of the water lens, and gets hot. But as the sun moves so does the focal point, so a very patient person has to be shoving the heating container along every few minutes. This doesn't seem very practical to me.

slug 12y ago

Looks nice, but can 150 ºFahrenheit (65ºCelcius) "kill 99.9% of bacteria and pathogens" ? From https://en.wikipedia.org/wiki/Sterilization_%28microbiology%29 https://en.wikipedia.org/wiki/Sterilization_%28microbiology%... it would seem that's not the case. Wonder if the article considers the effects of sun ultra-violet radiation to help in that process.

mpyne 12y ago
Even if it could kill 99.9% of bugs now, just wait until we get the inevitable HRSA superbugs after 20 years of this. Though this does sound neat, and it's still much better to have than nothing at all.
- azakai 12y ago
  It's not clear to me that bacteria and other pathogens could evolve around heat sterilization. I'm sure they can adapt in some ways to some amount of temperature change, but at some point (maybe hotter than this device can achieve) surely no organism can survive. It's like the old saying, it's easy to destroy HIV - the hard part is doing it inside a human body. In the case of sterilizing water, we don't have that problem, the water will remain usable.
  - Retric 12y ago
    A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122 °C (113 and 252 °F) http://en.wikipedia.org/wiki/Thermophile http://en.wikipedia.org/wiki/Thermophile So, 150 °F is not really all that hot as some organisms thrive at 250°F or well above boiling. However, I suspect organisms that thrive at 150+°F are unlikely to also thrive in the human body. A more important issue is the effort to sterilize water by hand is unlikely to be made with any real consistency.
    - eru 12y ago
      > A more important issue is the effort to sterilize water by hand is unlikely to be made with any real consistency. That's what safety margins are for.
- patio11 12y ago
  This sort of thinking is often invoked to justify why the world can't get better for e.g. poor Africans, while ignoring the fact that the rest of the world has been doing it in a more effective fashion (e.g. boiling water with a fire) for literally millennia with no ill effects.

thorum 12y ago

Is this better than boiling water over a fire?

ams6110 12y ago
That was my thought. A small fire can heat a litre of water to boiling in a lot less than an hour. And you don't need to actually boil water to sterilize it, 160-180 degress F is adequate.
- deleted 12y ago
  [deleted]
dublinben 12y ago
Indoor cooking fires are a significant source of pollution in developing countries. A solar-powered solution would be a significant improvement.
- ams6110 12y ago
  Wood or other biomass-fueled fires are CO2-neutral, but do cause particulate pollution. There have been a number of efforts to develop clean-burning wood stoves for developing countries to combat that problem.
  - ghshephard 12y ago
    "Wood or other biomass-fueled fires are CO2-neutral" Okay, I'll bite. How does burning wood not result in a net increase in CO2? Are you assuming that for every cord of wood burnt, that someone is simultaneously planing and growing a cord's worth of tree (which, of course, pulls carbon out of the air?) That's a pretty big assumption.
    - nathannecro 12y ago
      In fact, I took his statement the other way: At one point, there was some n amount of CO2 in the air. A tree was planted. Through a few biological cycles, CO2 is exchanged and stored as various sugars within the wood. Burning the wood releases the CO2 back into the air. This is a net zero process.

cardamomo 12y ago

This strikes me as a particularly creative and refreshingly simple device for sanitizing drinking water, but given the frequency with which we see articles with headlines like "So-and-so invents such-and-such device to clean water," the problem of access to drinking water would long since be solved. That is, unless it's not really a technical problem. Articles such as this don't often delve into broader issues of public health, education, or even poverty, but with an issue as complex as water access, perhaps we out to discuss it in a more complex context.

barry-cotter 12y ago
>That is, unless it's not really a technical problem. It isn't. This has the same problem as all the other solar sterilisers, it says "I'm poor." People are empirically not willing to use these things. You'd probably be better off with a public education campaign to normalise their use, something objectively ridiculous like having middle class families that actually have decent running water doing it, visibily and publicly.

fallinghawks 12y ago

Throw in some watertight sealing plastic bags and they could have sous vide as well. ;)

pflanze 12y ago

A simpler approach that forgoes the lens, relies on the combination of UV and heat, and is promoted under the name "SODIS" and already in use in some places: https://en.wikipedia.org/wiki/Solar_water_disinfection https://en.wikipedia.org/wiki/Solar_water_disinfection

ChuckMcM 12y ago

I like the simplicity. We used to do the solar still thing where you put a pan of tainted water in a hole with a plastic sheet over it and a rock in the middle and the collection can under the rock. The heat evaporates the water from the pan, which condenses on the sheet and then runs down and drips off into the collection can. Not very fast of course. Of course often times the trick is getting the water in the first place.

ahi 12y ago

Water with a lot of pathogens is likely to have high turbidity as well so your lens is going to be a bit opaque.

arjn 12y ago

I've seen this approach tried before - it has problems : "Due to the sun’s movement throughout the day, Henry needs to repeatedly shift the container to match the focal point. "

mbubb 12y ago
I wondered about this as well. Also an issue with NOT moving it to stay fucused on the water... a lens like that could start a grass / wood fire
astrodust 12y ago
Unless the project participants are willing to depend on this thing for fresh drinking water as part of their testing, the project itself is insultingly academic.

dmcg 12y ago

That focal point must move in a predictable way, I wonder if a shaped vessel could be under it for long enough.

short_circut 12y ago

I am not entirely sure what is new here. I knowpeople that have been doing this for years. The Channel GREENPOWERSCIENCE has done many videos on exactly this.

lifeisstillgood 12y ago

Clean drinking water is not a technical issue - as pointed out downthread, a cloth filter and boiling it on a fire will work and has done so for thousands of years. Poverty and deprivation is tied up with a huge range if issues, from water table effects to climate change to local politics and public health and education and ... Well, if the infrastructure existed to build a million of these frames and organise water to be brought to them and then handed out to those without clean water, then any number of other technologies could easily substitute. So not saying that supplying ten thousand of these to villages whose water tables just moved five miles won't be a fantastic use of our dollars, it's just that seems a small effect. There is a good ted talk on tackling poverty amount at Maori I can't find it though. It walks through a lot of these issues.

robomartin 12y ago

I built a rig with my son using a 65 inch Fresnel lens we harvested from an old rear projection TV. It could easily produce 2,000 degrees F under ideal conditions. Focal length was about three fee. A 2x4 passed through the focal point would catch on fire pretty much instantly (as quickly as one could count to one). We successfully fried an egg (more like instantly scorched an egg) by bouncing the beam pre-focal point off a high quality front surface mirror (also harvested from the TV) and focused it onto the bottom of a cast iron skillet. Anyhow, the realization was that this thing was incredibly inconvenient and also dangerous to use. We built it into an articulated wooden frame with the explicit idea of being able to track the sun. Power output peaked and dropped off very quickly and was near useless during low-horizon times. You had to be super aware of where the focal point was at all times or risk a very serious accident. This is an obvious point but you don't fully comprehend how serious a point this is until you start setting wood on fire instantly. Even putting the thing away for the day we had to be sure to rotate it 90 degrees so that the sun hit the edge of the lens. Even then, we threw a black cloth over it just to make sure. This thing could set your house on fire in a fraction of a second. We ended up destroying it after playing with it for a month or so. Just too dangerous to be around and pretty much useless for anything practical. After a while you get tired of demonstrating how quickly you can set a piece of wood on fire. A long intro to say the following. Neat trick by this student and a fantastic learning experience I am sure. Kudo's should be given. Kids learn tons of stuff doing off the wall scientific experiments like this one. In practical terms though, well, it isn't practical at all. But, who cares, this is about learning and on that point it is absolutely brilliant. I remember seeing an article many years ago about using a folded-up t-shirt as a first-pass filter and then simple clear two liter plastic bottles left under the sun for 24 hours to make water safe to drink. People would fill these bottles with t-shirt-filtered water and either place them on a table outside or on the roof for a day. They'd rotate sets of plastic bottles for a continuous supply of safe drinking water. I couldn't think of anything simpler, cheaper or more effective. Here's on version of that: http://www.sodis.ch/methode/anwendung/index_EN http://www.sodis.ch/methode/anwendung/index_EN