That Cigarette Would Make a Great Water Filter

Clean out the ashtray, add some aluminum oxide, and you've (almost) got yourself a low-cost way to remove arsenic from drinking water.
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(Photo: 42787780@N04/Flickr)

(Photo: 42787780@N04/Flickr)

In further evidence that one person’s trash is another’s treasure—and perhaps life saver—researchers in China and Saudi Arabia have devised a way to use cigarette ash to filter arsenic from water. The technique could prove to be a cost-effective way to deal with contaminated drinking water, especially in the developing world.

Odorless and tasteless, arsenic is more than just the stuff of Agatha Christie novels. It’s also a serious public health threat in some parts of the world, notably Bangladesh, where naturally occurring arsenic compounds are abundant in the soil. Even in wealthy countries such as the United States, a mix of natural and industrial sources poses a threat to public health if it goes undetected and unmanaged. Regardless of the source, long-term exposure through drinking water and from crops irrigated with contaminated water can lead to skin lesions and cancer. Fortunately, richer nations have a number of options for dealing with arsenic, including absorption treatments and methods based on chemical oxidation.

Odorless and tasteless, arsenic is more than just the stuff of Agatha Christie novels. It’s also a serious public health threat in some parts of the world, notably Bangladesh, where naturally occurring arsenic compounds are abundant in the soil.

But in the developing world, finding the money for a state-of-the-art treatment facility isn’t an easy job. Apart from collecting rain water and boiling it, the simplest and most cost-effective way to treat arsenic-laced water is absorption. A standard water filter just passes water through a material that attracts arsenic compounds but lets water molecules flow by.

Here’s where cigarette ash comes in. Tobacco is grown throughout the world, and millions of cigarettes are made and smoked every day—a public-health concern in its own right. But it’s also a good source of water-filtering carbon.

“When people smoke, incomplete combustion emerges as air is sucked through the tobacco within a short time. Thus, a certain amount of activated carbon”—that’s the porous, absorbent stuff in your water filter—“is formed and incorporated into the cigarette soot,” write He Chen and colleagues in Industrial & Engineering Chemistry Research. The team combined that with another material for arsenic removal, aluminum oxide, to create a low-cost, relatively easy-to-make filter.

Neither ash nor aluminum oxide is ideal as a filtering material—ash has to be heat treated to be an efficient water filter, while aluminum oxide tends to clump up or form gels when exposed to water. To get around that, the researchers treated cigarette soot with hydrochloric and nitric acid before mixing the resulting powder with aluminum nitrate, finally producing an aluminum oxide-carbon mix. Finally, the team tested their concoction on a groundwater sample from Mongolia. With about two grams of aluminum oxide to one gram of cigarette-soot carbon, the team removed about 96 percent of the arsenic in the sample, as well as 98 percent of fluoride ions. They also found that they could use the same mix six times without losing filtering capacity. Finally, something good about smoking cigarettes.

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