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  (Source: Water and Sanitation Health)
Could purify drinking water in the developing world

Cholera, hepatitis, and typhoid are a few examples of diseases found in water in the developing world. Now, Stanford University researchers have discovered a new low-cost, high-speed filter that could be used to purify water in these areas. 

Yi Cui and Sarah Heilshorn, associate professors of materials science and engineering, partnered their teams together to make this discovery. Instead of trapping bacteria like traditional filters, these researchers made a filter that allows the bacteria to pass through with the water, but an electrical field kills the bacteria it passes. 

To make this filter, researchers dipped cotton cloth into a high-tech broth filled with carbon nanotubes and silver nanowires. Silver was used because it has chemical properties that kill bacteria, and has been used as a remedy in the past. Then the electrical field is run through the 2.5-inch thick nano-coated cotton, and as water passes through, bacteria is killed. With the electrical field sending 20 volts of electricity throughout the filter, their research shows that 98 percent of Escherichia coli was killed within seconds. 

"This provides a new water treatment method to kill pathogens," said Cui. "It can easily be used in remote areas where people don't have access to chemical treatments such as chlorine."

This type of filter also allows water to pass through more quickly, since it does not require small pore spaces to trap bacteria like traditional filters. This rids the need for pumps. According to Cui, their filter is 80,000 times faster than traditional trap filters. Also, the new filter avoids biofouling, which is when bacteria forms a film on the filter as it passes through. Biofouling is a problem in traditional traps, with the pores being so small, but the silver in the new filter kills any lingering bacteria. 

What makes the filter ideal for the developing world is that it requires a low amount of electricity and is also low in cost. The electrical current that aids in killing the bacteria is only a few milliamperes strong, and can be provided by a couple 12-volt car batteries or even a small solar panel

Less voltage is required because the nanomaterials are so small in size that they stick to the cotton easily, making a continuous surface on the cotton fibers. This helps electrons move more efficiently, making the filter "very conducting," thus less voltage is needed. 

As far as cost goes, Cui said he wanted to make the filter as inexpensive as possible, so that's why ordinary cotton was used, and the amount of silver used was so small that the cost was "negligible." In fact, Cui mentioned that he bought the cotton right from Walmart. 

With low cost and low electricity already achieved, the only thing left to do is try the filter out on all different types of bacteria and run tests on "successive" filters. 

"With one filter, we can kill 98 percent of the bacteria," said Cui. "For drinking water, you don't want any live bacteria in the water, so we will have to use multiple filter stages."

The study will be published in an upcoming issue of Nano Letters.



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Trade?
By RugMuch on 9/1/2010 11:12:20 AM , Rating: 2
This was done before at UCB they found that you kill the bacteria but eventually it led to heavy metal poisoning. I will take H8 e. coli any day over heavy metal poisoning.




RE: Trade?
By MrBlastman on 9/1/2010 11:34:02 AM , Rating: 5
I suffered heavy metal poisoning back in the 80's... and I'm doing just fine.

You just gotta stand up and shout, all about: "We're not gonna take it! No! We ain't gonna take it! We're not gonna take it... anymore!" ;)


RE: Trade?
By Reclaimer77 on 9/1/2010 12:27:20 PM , Rating: 2
HEHEHEEH come on, who could downrate that? Funny stuff, 80's FTW. If you don't get it kids, don't rate it.


RE: Trade?
By PitViper007 on 9/1/2010 5:03:07 PM , Rating: 2
Now I've got the picture of Dee Snider in full makeup, snarling, with a huge thighbone in his hand stuck in my head. Thanks. : )


RE: Trade?
By nstott on 9/1/2010 11:41:27 AM , Rating: 2
Silver isn't typically considered a heavy metal, even though it literally is one, but too much silver consumption can lead to argyria and become toxic at very high concentrations in the body. However, in this case, the silver nanowires are imbedded in the cloth and are too long to pass through the filter. The length of the nanowires is likely too long for dispersion into water and they are probably not using surfactants in this application to disperse them anyway.

While mild poisoning with e. coli will only make one sick for a day or two, higher doses can lead to acute toxicity and death within hours to days. Heavy metal poisoning is typically more chronic and causes health problems that can be reversed with treatment in some cases. High doses in some forms can possibly lead to death, though. In either case, it depends on the level of poisoning as to which might be worse.


RE: Trade?
By quiksilvr on 9/1/2010 11:59:37 AM , Rating: 2
Whatever happened to the UV water filtering? To me that sounds like the ideal solution. The germs die and you don't get metal poisoning.


RE: Trade?
By nstott on 9/1/2010 12:21:11 PM , Rating: 2
The throughput is much lower. It works well for personal and home use but not so well to clean up water for a larger community. It would be possible to couple smaller parallel tubes with UV irradiators together to increase the throughput, but the number of UV lights required would drive up the cost significantly.

Oh, and enough with the heavy metal poisoning, already! You're more likely to get heavy metal poisoning from your user name! :P


RE: Trade?
By nafhan on 9/1/2010 2:18:27 PM , Rating: 2
It sounds like this process may have an advantage in longevity, simplicity, and electricity usage compared to UV, but it's not commercially available, so it's impossible to say.


RE: Trade?
By Smartless on 9/1/2010 3:13:37 PM , Rating: 2
Hmm I wonder if through-put is going to be that big a factor. Most small-type UV can do about 15 gpm which is enough for small community though you're right the electrical cost and UV lights are pretty expensive. What I'm wondering is how durable is this filter. It's made out of cotton to keep the price down but they would still need to filter out objects that could damage it like sediment. Also, will cheap material handle the water pressure or are they thinking open channel pipes.

As for heavy metal poisoning.. I'm with MrBlastman. "I guess every rose has its thorn...."


RE: Trade?
By JediJeb on 9/2/2010 1:49:22 PM , Rating: 2
Were it a different metal maybe heavy metal poisoning would be a problem, but with silver you really don't have anything to worry about. Silver can be taken in quite high doses, even to the point it turns your skin gray before it becomes truly toxic. If enough silver was dissolving off the filter to reach that point then the filters wouldn't last long enough to be any good at all.


RE: Trade?
By Smartless on 9/1/2010 3:13:43 PM , Rating: 2
Hmm I wonder if through-put is going to be that big a factor. Most small-type UV can do about 15 gpm which is enough for small community though you're right the electrical cost and UV lights are pretty expensive. What I'm wondering is how durable is this filter. It's made out of cotton to keep the price down but they would still need to filter out objects that could damage it like sediment. Also, will cheap material handle the water pressure or are they thinking open channel pipes.

As for heavy metal poisoning.. I'm with MrBlastman. "I guess every rose has its thorn...."


RE: Trade?
By Smartless on 9/1/2010 3:17:54 PM , Rating: 2
Damn is my spam filter double clicking or something? Can I have a delete button please.


RE: Trade?
By RivuxGamma on 9/1/2010 6:06:40 PM , Rating: 2
Nothing happened to it. UV doesn't filter a thing. It just kills some bacteria.


UV Sterilizer
By Integral9 on 9/1/2010 4:13:51 PM , Rating: 3
would be a better solution I think. The bulbs are slightly expensive at about $30, depending on unit size, but cheaper than silver I imagine and no heavy metal poisoning.




RE: UV Sterilizer
By Souka on 9/1/2010 6:37:37 PM , Rating: 2
UV takes a lot of power for a given volume of water....and time.

You can't even filter a small trickle of water with a 30w UV lamp as the exposure time is too short.

The discussed filter here is much faster and arguably cheaper.


RE: UV Sterilizer
By Integral9 on 9/22/2010 9:21:37 AM , Rating: 2
A trickle? I've seen 36W UV sterlizes rated for up to 1200 Gallons per hour.


Silver Poisoning
By rwpritchett on 9/1/2010 3:10:08 PM , Rating: 2
I wonder if there are any chances of developing Argyria?

Makes you look like a Smurf.

<a href="http://www.google.com/images?rlz=1C1_____enUS346US...">Argyria?</a>




RE: Silver Poisoning
By JediJeb on 9/2/2010 2:03:19 PM , Rating: 2
To get a dose large enough for that to happen you would be dissolving the silver completely off the filter very quickly.

quote:
The reference dose, published by the United States Environmental Protection Agency in 1991, which recommends the estimated daily exposure which is unlikely to incur a appreciable risk of deleterious effects during a lifetime, is 5 µg/kg/d; meaning 5 microgram of silver per kilo of weight per person each day – about 1 liter of 10 ppm colloidal silver per month for a 66 kg person.


Maybe if you drank from this every day for 40 years you might begin to see some evidence you were being exposed, but metallic silver is not very soluble in water, otherwise your sterling silver utensils and serving bowls would dissolve away quickly. This filter should be as safe as a silver teapot or silver fork and spoon. If the water was highly acidic then you may begin to see some of the silver dissolve into solution, but here in the lab we need at least a 1% Nitric Acid solution to be able to dissolve silver or most metals quickly.


I Hope That...
By mmatis on 9/1/2010 12:02:14 PM , Rating: 1
they get this working and widely available as quickly as possible. It will be very useful even in developed countries after the EMP attack.




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