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Plasmas sterilize water cheaply

Steve Graves


Ionized plasmas like those in neon signs and plasma TVs can sterilize water and make it antimicrobial as well, according to researchers studying the potential to use inexpensive plasma-generating devices to create sterile water in developing countries, disasters areas, and battlefields.

Plasmas are the fourth state of matter after solid, liquid, and gas. They are formed when gases are energized, stripping atoms of their electrons to create a collection of free moving electrons and ions.

Researchers have known plasmas will kill bacteria in water. Now, a new experiment shows that water treated with plasma killed all the E. coli bacteria that were added to it within a few hours of treatment and still killed 99.9 percent of the bacteria added after it sat for a week.

The ionized gas, or plasma, creates various chemical like ozone, nitrogen oxide, and other radicals. When the plasma is put next to water, "the chemicals diffuse to the water, they absorb in the in water, and they have various reactions in the water," David Graves, a professor of chemical and biomolecular engineering at the University of California at Berkeley, explained to me today.

The chemical soup includes well-known antimicrobials such as nitrates and nitrites as well as hydrogen peroxide. Bacteria on our tongues, for example, convert nitrates in leafy green vegetables to nitrites.

However, the concentration of these known antimicrobials dropped over the course of the experiment, yet the water was still able to kill off E. coli that were added to it seven days after the plasma treatment. "So it seems like there is probably chemistry going on that we don't know about yet."

The finding is published this month in the Journal of Physics D: Applied Physics. Graves envisions using inexpensive, spark-plug-like plasma generating devices to sterilize water for medical purposes in natural disaster zones or deep in the wilderness. Whether or not the water is safe to drink, however, is unknown.

"It is possible," Graves said, noting that breast milk, for example, is loaded with nitrates and nitrites. But before he recommends the plasma-treated water for drinking, safety tests need to be conducted.

In earlier experiments, the team also found that plasma can kill dangerous proteins and lipids such as prions — the infectious agents that cause mad cow disease — that standard sterilization processes leave behind, according a news release on the findings.

For more information, check out the release and paper.

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