Disinfecting Water

After natural disasters, especially when flooding has occurred, safe drinking water may not be readily available. Now, researchers have developed a cheap, lightweight material that can disinfect water in as little as five minutes.

When dipped in water contaminated with disease-causing bacteria, the sponge-like gel soaks up the water and kills harmful organisms within seconds. Squeezing the gel then releases drinkable water, and the material returns to its original shape.

The bacteria-killing powers of the new substance, described in the journal Environmental Science & Technology, depends upon very small bits of silver—known as nanoparticles—embedded in the pores of the gel.

Silver nanoparticles are already widely used in consumer products for their antibacterial properties. According to the Environmental Protection Agency (EPA), this includes toothpaste, deodorant, dietary supplements, clothing, and children’s toys.

Silver-Studded Gel Ideal for Disaster Relief

Embedding materials with silver nanoparticles is not a new technique, but the researchers from Singapore and the United States have hit upon a novel support structure—called poly (sodium acrylate)—that is especially suited for purifying water in disaster areas.

“Sodium acrylates are aerogels and absorb water many times more than their weight,” says Anil K. Karumuri, a Ph.D. student in Materials Science and Nanotechnology at Wright State University in Dayton, Ohio.

In addition to being light enough to drop from an airplane—a clear advantage when supplying hard-to-reach disaster zones—tests in the lab showed that a 3.5-inch-long cylinder of this silver-studded gel can soak up and purify half a liter of water with just one squeeze.

The gel, which could be delivered in a pocket-sized case, can also be reused more than 20 times without losing its bacteria-killing powers. Moreover, the researchers estimate that a personal-sized gel could be made for less than 50 cents.

Overcoming Obstacles to Clean Water

During a natural disaster, flooding can dump human sewage and livestock waste into the water supply. These wastes are filled with bacteria like Escherichia coli that can cause diarrhea, abdominal pain, and fever. In more severe cases, bacterial infection can lead to dehydration or kidney failure.

To see if the gels could work on contaminated flood waters, the researchers tested the new material on water laced with two types of potentially harmful bacteria—E. coli and Bacillus subtilis. After 15 seconds, the bacteria levels were reduced to 0.1 percent of the original sample. This dropped to one millionth when the wait time was increased to five minutes.

Another challenge was to keep the silver nanoparticles attached to the gel. In some consumer products, nanoparticles leach out of the material and can be ingested by people, with unknown health effects. A 2013 PLoS ONE study found that tiny bits of silver from these products may also adversely affect the environment.

In the new material, the silver nanoparticles cling more tightly to the gel, keeping them safely out of the drinking water. “Their devices showed very minimal loss—acceptable WHO [World Health Organization] amount of silver content in the treated water—of silver even after prolonged use,” says Karumuri.

While the gel performed well in the lab, it still needs to be tested more widely to make sure it can kill the kinds of pathogens—bacteria, viruses, and parasites—that typically contaminate water sources during natural disasters. The research team is already planning a field test in Myanmar.

Other Ways to Clean Contaminated Water

This new gel is not the only product in development for disinfecting water with silver nanoparticles. Karumuri and colleagues at Wright State University used a similar method to grow silver nanoparticles on a foam-like material of porous carbon structures. “These foams are lighter and comparatively stronger,” says Karumuri. They also allow heat and electricity to be added, which enhances the antibiotic effect of the silver particles.

Their research is presented in a 2013 article in the journal Materials Letters.

It may be some time before either of these silver-powered water treatments are available for use after a disaster. Until they are ready, it's important to play it safe when it comes to drinking water.

In addition to stocking up on bottled water before an emergency, the Centers for Disease Control and Prevention suggests that people use one of these proven methods to disinfect drinking water:

  • Boil the water for at least one minute (three at higher elevations).
  • Add a disinfectant like chlorine bleach, iodine, or chlorine dioxide tablets.
  • Filter the water using a certified water filter.

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