What a tiny sun-powered water purifier could mean for developing countries

Scientists have developed a quicker, cheaper way to purify water – with a solar-powered device half the size of a postage stamp. 

Beawiharta/Reuters
Villagers cross the polluted Ciujung river at Astana Agung village in Serang, Indonesia's Banten province August 14, 2012. According to a villager in Astana Agung, the villagers must walk to another location to get clean water, bathe and wash their clothes as the Ciujung river is polluted from waste being dumped by factories located along the river.

Clean water may soon be more accessible in developing countries, thanks to a new water purification device powered by sunlight. 

The tiny device, developed by researchers at the SLAC National Accelerator Laboratory and Stanford University, is able to disinfect water quicker and far more cheaply than existing methods, according to a report published Monday in the journal Nature Nanotechnology. 

Using the sun to disinfect water is already common in developing countries. But the process of using UV rays to kill bacteria is relatively lengthy: it takes six hours for the process to begin, and can take up to 48 hours to complete. In contrast, the new device is able to kill 99.999 percent of bacteria in 25 milliliters of water in just 20 minutes, leaving only pure water in its wake. 

"Our device looks like a little rectangle of black glass. We just dropped it into the water and put everything under the sun, and the sun did all the work," explained Chong Liu, lead author of the report, in an SLAC news release. 

While the device is relatively simple to use, creating it was a slightly more complex process. The device, which is roughly half the size of a postage stamp, is lined with thin, closely spaced films, or "nanoflakes," of molybdenum disulfide.

Typically, molybdenum disulfide is used as an industrial lubricant. However, when it's made into layers just several atoms thick, it becomes a photocatalyst. When light reaches it, many of the electrons shift away from their usual locations, leaving "holes" behind and paving the way for chemical reactions to take place. 

To get the device to absorb as much visible sunlight as possible, the researchers had to make the molybdenum disulfide walls exactly the right thickness. They then topped each wall with a thin layer of copper: this allowed them to use that sunlight to trigger reactions that produce "reactive oxygen species," such as hydrogen peroxide, to kill bacteria in the water. 

Beyond being useful for hikers and other outdoor adventurers, researchers say the cheaply and easily manufactured device also has potential for widespread use in developing countries lacking clean water. 

Access to better drinking water has improved significantly in the past several decades, as 2.6 billion people have gained access to clean water since 1990. However, that still leaves 783 million people around the world without clean water, most of them in developing countries. 

The device has currently only been tested on three strains of bacteria, but the researchers expect that it will work on other strains and microbes as well. The team plans to conduct additional tests in rivers in developing countries in the near future, as it has so far only been tested in a laboratory setting on less than an ounce of water mixed with bacteria.

Though the device doesn't have the capability to remove chemical pollutants from water, as a filter might, researchers expect that its ability to eliminate bacteria in a quick and cost effective way could greatly improve the quality of life for many people around the world. 

"It's very exciting to see that by just designing a material you can achieve a good performance. It really works," said Ms. Liu. "Our intention is to solve environmental pollution problems so people can live better."

The device likely will not be available for commercial sale for another three to five years, SLAC spokesman Andrew Gordon told The Mercury News. 

You've read  of  free articles. Subscribe to continue.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.