New technology uses solar UV to disinfect drinking water

Sep 29, 2011 By Emil Venere
Civil engineering professor Ernest "Chip" R. Blatchley III inspects a parabolic reflector for a prototype water-disinfection system he built as part of an effort to help provide safe drinking water to a large segment of the world's population in developing nations. The system uses ultraviolet radiation from the sun to kill waterborne pathogens. Sunlight is captured by the reflector and focused onto a UV-transparent pipe though which water flows continuously. Credit: Purdue University photo/Andrew Hancock

(PhysOrg.com) -- A team of Purdue University researchers has invented a prototype water-disinfection system that could help the world's 800 million people who lack safe drinking water.

The system uses the sun's to inactivate waterborne pathogens. Sunlight is captured by a parabolic reflector and focused onto a UV-transparent pipe though which flows continuously.

"We've been working on UV disinfection for about 20 years," said Ernest "Chip" R. Blatchley III, a professor of civil engineering. "All of our work up until a couple years ago dealt with UV systems based on an artificial UV source. What we are working on more recently is using ultraviolet radiation from the sun."

Motivating the research is the need to develop practical, inexpensive water-treatment technologies for a large segment of the world's population in developing nations.

"More than 800 million people lack access to what we consider to be 'improved' water," Blatchley said. "The water available for people to drink in many developing countries hasn't been treated to remove contaminants, including . As a result, thousands of children die daily from diarrhea and its consequences, including dehydration. Half of the world's hospital beds are occupied by people who are sickened by the water they drink."

Blatchley built the parabolic reflector in his garage. The team, including an undergraduate student supported by a National Science Foundation program, finished the prototype in the lab, lining it with aluminum foil. The system was then tested on the roof of Purdue's Civil Engineering Building.

"It turns out that the we receive in Indiana at some times of year is intense enough to inactivate some waterborne microorganisms with this type of system," he said. "We demonstrated that we can disinfect water using sunlight. The reactor was very inexpensive to build, less than $100 for the materials."

The natural UV system inactivated E. coli bacteria. However, the system must be able to kill dangerous pathogens such as Vibrio cholerae, which causes cholera, and Salmonella typhi, which causes typhoid, and Cryptosporidium parvum, which causes cryptosporidiosis, a parasitic disease that causes diarrhea.

"In the future we want to prove that our solar-UV system is going work against these other pathogens," said Blatchley, who has worked on the project with doctoral student Eric Gentil Mbonimpa, who is from Rwanda, and Bryan Vadheim, an undergraduate from Montana State University. "We also want to automate it and build sensors for it so that we know how fast the water should be pumped through the system, depending on how sunny it is at any particular time."

The NSF funded Vadheim's work through its Research Experiences for Undergraduates program.

The parabolic reflector is made out of a wood called paulownia.

"That material was selected because the tree grows very rapidly in regions near the equator, where many people lack safe drinking water," Blatchley said. "It is very light, strong and stable, so it's not going to twist or warp or bend or crack in a climate that's alternating between humid and dry."

Natural UV has a longer wavelength than most artificial UV sources, which means it has less energy. Blatchley's hypothesis, however, is that UV from sunlight will inactivate pathogens via the same mechanism as artificial UV: The radiation damages the genetic material of microbes, preventing them from reproducing.

"We are looking at other inexpensive reflecting materials, for example metalized plastic," Blatchley said. "It's similar to the material that's used to make potato chip bags. We've done measurements, and some of these materials are about twice as reflective as ."

Improving water quality in developing countries is one of 14 "grand challenges" established by the National Academy of Engineering and also has been named a "millennium development goal" by the United Nations.

Blatchley also is working on an inexpensive filtration system that uses layers of sand and gravel to clean water. The filters were developed by Aqua Clara International, a Michigan-based non-profit corporation. Purdue and Aqua Clara are teaming up with Moi University in Kenya on that project. Purdue students tested the behavior of the filters in a Global Design Team project in Africa through Purdue's Global Engineering Program.

Water flows slowly through the filter, allowing a bacterial film to establish near the top of the filter to remove organic contaminants while certain pathogens also are removed by attachment to the sand.

However, the water may still require disinfection to kill remaining pathogens, and it might be possible to use the slow-sand filters in combination with a water-disinfection system like the new solar UV approach.

"We want to develop treatment systems that improve water quality for people in developing countries, using Kenya as an example," Blatchley said.

Aqua Clara has developed a business model for the filtration system.

"This provides business opportunities for local entrepreneurs who are trained how to make these filters out of locally available materials," he said. "You can build one of these things for $10, and it's capable of producing something like 40 liters of water a day. It's intended to produce enough water for a family of four."

The use of the filters is becoming more widespread.

"About 1,900 of the sand filters have been installed in villages throughout Kenya," said William Anderson, director of the Global Engineering Program. "More and more, Purdue's faculty and students are extending our land-grant tradition for the benefit of people throughout the world."

Explore further: EU leaders seek last-minute climate deal

Related Stories

Duke develops new UV measurement tool

Nov 02, 2005

Researchers at Duke University's Pratt School of Engineering have developed a new way to measure microbes' exposure to ultraviolet light.

UV light stick purifies water

Feb 25, 2010

(PhysOrg.com) -- Today, about one billion people on Earth don't have access to clean drinking water, and that number is expected to increase even more in the coming years. To solve this problem, inventors ...

Recommended for you

Study shows no lead pollution in oilsands region

1 hour ago

New research from a world-renowned soil and water expert at the University of Alberta reveals that there's no atmospheric lead pollution in Alberta's oilsands region—a finding that contradicts current scientific ...

User comments : 10

Adjust slider to filter visible comments by rank

Display comments: newest first

omatumr
1.7 / 5 (6) Sep 29, 2011
Congratulations!

The spectrum of solar radiation - including extreme UV and even "cosmic rays" - has changed over time, as life evolved in response to the evolving Sun [1]

1. Journal of Modern Physics 2, 587-594 (2011)

http://dl.dropbox...5079.pdf

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
http://myprofile....anuelo09
FreeRangeRadical
5 / 5 (4) Sep 29, 2011
I remember seeing an article a couple years ago about kids in school in Africa who were given an empty plastic water bottle such as the ones that bottled water already comes in. Every day, they would fill their bottles at the community water source, then place them on sheets of shiny tin which would reflect the light back into the bottle and, in 6 hours, disinfect the water making it suitable for drinking. Here's a link to the Wikipedia article featuring a photo of this being done.
FreeRangeRadical
5 / 5 (2) Sep 29, 2011
I remember seeing an article a couple years ago about kids in school in Africa who were given an empty plastic water bottle such as the ones that bottled water already comes in. Every day, they would fill their bottles at the community water source, then place them on sheets of shiny tin which would reflect the light back into the bottle and, in 6 hours, disinfect the water making it suitable for drinking. Here's a link to the Wikipedia article featuring a photo of this being done: (OK, it seems that this site won't allow that...ridiculous. Just look for 'solar water disinfection' on Wikipedia.
Nanobanano
5 / 5 (1) Sep 29, 2011
The Green Power Science guy has been doing this for at least a couple years.

Nothing new here.
jimbo92107
1.5 / 5 (4) Sep 29, 2011
Dang, I thought they were talking about a UV-generating meta-material that would coat the exterior of a portable water container. Fill the container, sit it in the sun, and the material would turn sunlight into UV focused into the container's interior, killing the bad bugs inside.

Oh, well.
antonima
1.3 / 5 (6) Sep 29, 2011
Boiling water will kill most bacteria and could be used to prevent much sickness. But, poor people don't feel like doing it. If we aren't able to convince them to boil their water, how are we going to convince them to build a parabolic mirror and then trickle water through it?
eachus
5 / 5 (4) Sep 29, 2011
Boiling water will kill most bacteria and could be used to prevent much sickness. But, poor people don't feel like doing it. If we aren't able to convince them to boil their water, how are we going to convince them to build a parabolic mirror and then trickle water through it?


Sigh. Are you not familiar with the COST of boiling water? I assure you that the poorest people are very familiar, and if they offer you tea--even if you are a soldier there as part of your duties--be very respectful and drink it.

But to boil all drinking water would make it too expensive, not to mention the forests cut down for firewood. Inexpensive solar stills are great, these people are looking to make something even less expensive. (Or the same price for more drinkable water.)
braindead
not rated yet Sep 29, 2011
" But, poor people don't feel like doing it. If we aren't able to convince them to boil their water, how are we going to convince them..." A tad arrogant don't ya think old chap? Come back the British Raj. Eachus hit the problem right on the head with his comment.
What I have noticed is that in many developing country towns and cities (I live in Jakarta) there are thousands of large redundant TV satellite dishes just sitting on roofs as people have switched to cable or the much smaller modern dishes. Lining these mesh dishes with metalised plastic foil could produce both a solar oven and, with a through flow coil of water pipe at the focus, possibly a UV/heat steriliser. The extra cost of the plasticed foil and moving the dish to a suitable location (labour is cheap here) could be a useful source of cheap high grade energy. We need an NGO to get working on this! I am sure many inhabitants would like to get rid of the unsitely junk on their roofs for free. Any ideas?
braindead
not rated yet Sep 29, 2011
x
antonima
not rated yet Oct 01, 2011

Sigh. Are you not familiar with the COST of boiling water? I assure you that the poorest people are very familiar, and if they offer you tea--even if you are a soldier there as part of your duties--be very respectful and drink it.

But to boil all drinking water would make it too expensive, not to mention the forests cut down for firewood. Inexpensive solar stills are great, these people are looking to make something even less expensive. (Or the same price for more drinkable water.)


I didn't think about this. I'm wondering - how expensive is aluminum foil in these places. I suppose the cost of firewood could certainly add up. I'm just very cynical as to how effective such a far-fetched process could be. A square meter of metalized plastic foil can't be too expensive though, and the wood used would probably boil only a gallon or two of water anyways.