Cotton Cloth Coated in Nanotubes Electrifies Bacteria to Purify Water


Image via Stanford University

Fresh, clean, drinkable water is an increasingly rare thing on this planet, especially in places that are suffering through catastrophes like floods or must deal with high levels of pollution without the resources to set up water treatment facilities. But a project from Stanford University researchers could see cheap, simple filtration devices distributed through developing nations. How simple? Well, it's just a piece of cotton cloth coated in nanotubes that filter out nearly all bacteria at a rate faster than other filtration methods. A press release from Stanford University states that cotton cloth can simply be dipped in a "high-tech broth full of silver nanowires and carbon nanotubes" which allow water to flow through the cloth as quickly as it normally would because rather than trapping the bacteria, it is killing it.

Most filtration systems keep bacteria and particles from passing through to the other side, so that only about 0.1% of bacteria remains in the water that people drink. However, the new technology from Stanford kills the bacteria with an electrical field that runs through the cotton. This way, only about 2% of the bacteria is still living when it reaches the other side of the cotton cloth.

"In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick," according to the release. It can also filter about 80,000 times faster than filters that trap bacteria.

The up side is that this new technology could be a fast, effective way of dispatching diseases like cholera, typhoid, and hepatitis and without filters that have to be replaced every X gallons. The down side is that you need to be hooked up to a power source, which can be problematic in poor, remote areas.

Luckily, it only takes a small amount (about a fifth of what a filtration pump needs) that could be supplied with a "small solar panel or a couple 12-volt car batteries." The team also suggests that the electricity could be generated from a stationary bike or a hand-cranked device. This adds to the number of parts (and thus expense as well as possible points of failure) needed to run the system.

And there's also the issue of safety. After all, we learn early on that electricity and water are a dangerous combination. How to keep people -- especially children playing around the water pump -- safe from being shocked will have to be taken into consideration in the design process.

The role of using simple cloth as a way to keep disease out of water is actually quite old. In India, using sari cloth to filter water has been shown to help reduce the spread of cholera by as much as 48% village-wide. And that's without nanotechnology.

Next on the to-do list for the research time is trying out the filter on a wider range of bacteria types and adding layers of filters so that rather than 98% of bacteria killed off, the system reaches a 100% rate.

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Tags: Concepts & Prototypes | Drinking Water