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Cotton, Silver and Electricity can Kill Bacteria in Water

stanford university researchers kill bacteria in water with a filter made from silver, cotton, and carbon nanotubesIn honor of Blog Action Day on the topic of water, here is a bit of good news about a new low-cost, energy efficient method for purifying drinking water without the use of chlorine. Scientists at Stanford University have developed a new kind of water filter that uses a combination of silver, cotton, and electricity to kill up to 98 percent of E. coli bacteria in contaminated water. The system was recently described in the American Chemical Society journal.

Killing Bacteria without Chlorine

Exposure to either silver or electricity are known to kill bacteria, so the researchers decided to see what would happen if they combined the two. The new system uses a coating of silver nanowires on cotton, which is then layered with carbon nanotubes. The carbon provide the extra electrical conductivity. Compared to other types of filters, the cotton membrane has fairly large pores, which allow water to flow rapidly through, without the use of energy-intensive pumps. The membrane also resists clogging, which could also help reduce operating costs by reducing down time for cleaning and maintenance.

Chemical Free Water Treatment

Aside from safety concerns and environmental factors, the use of chlorine and other chemicals in whater treatment became extremely problematic for water utilities during the commodities boom that preceded the economic bust of 2008, as prices spiked and shortages cropped up. The search was stepped up for water treatment methods that are not bedeviled by the vagaries of the commodities markets. The silver-cotton filter is just one example. Ultra-violet light is another example, though the reduced use of chemicals is offset by the increased need for energy. Other recent developments include the use of ultrasound for water treatment, a kinetic energy “bomb” that destroys bacteria, and a combination of salt and electricity.

Green Remediation and Water Treatment

Green remediation refers to cleanup methods that rely on natural processes and sustainable sources of energy. It’s most often associated with cleaning up hazardous materials sites, but some of these methods may also apply to drinking water treatment. For example, solar power is being used to run water treatment equipment at a Superfund site, and plants such as vetiver grass are being studied for their ability to absorb contaminants from water.

Image: Silver by tanakawho on

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Written By

Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.


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