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Beware of Water with Arsenic
March 27, 2014   
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Arsenic is one of the strongest poisons found in nature. It is present in rocks in the earth’s crust, but it can also get into drinking water, and may then pose a serious threat to humans. A Polish researcher is building a pilot installation for cleaning water of this dangerous element in Z這ty Stok, southwestern Poland.

According to international norms, the concentration of arsenic in water should not exceed 10 micrograms per liter. However, in some areas in the world, including in Europe, the arsenic content is as high as several thousand micrograms. Poland is no exception, as exemplified by the southwestern town of Z這ty Stok. The local brook and mine waters are heavily contaminated with arsenic. What’s more, potable water in Z這ty Stok contains up to 3,000 micrograms of this poison per liter.

ㄆkasz Drewniak, Ph.D., from the University of Warsaw, has set out to tackle this problem. He has developed a method for purifying water to get rid of the arsenic. To design and build the pilot water treatment installation in Z這ty Stok, he received more than zl.1 million in financial support from the National Center for Research and Development’s Lider (Leader) program. The project will be carried out over three years.

Why does the water in this small town contain so much arsenic? Arsenic naturally occurs in more than 200 minerals and is not dangerous in such a form. It begins to poison people if it gets into the water or air. Then it can be fatal; it damages the DNA and deactivates all proteins in the body.

Arsenic can get into the water as a result of microbial activity. However, more often this occurs as a result of human activity, for example during the extraction of copper and gold, as a result of chemical processes in the steel industry or the mining sector. Then arsenic is leached from the minerals and gets into the water, or—in the form of particulate matter and gaseous compounds—into the air. This is the case in Z這ty Stok.

Around the world there are already technologies for cleaning the environment of arsenic, but they are not effective enough. Most require this element to be pre-oxidized with the use of chemical oxidizing agents—chlorine, chlorine dioxide, hypochlorite, mineral and organic chloramines or ozone, says Drewniak. But these oxidizing agents can cause side effects even more devastating than the untreated water itself.

In his method for removing arsenic from water, Drewniak plans to use microorganisms that specifically oxidize arsenic, while not affecting other compounds in the environment.

“Unfortunately, very often technologies using microorganisms do not work in practice, because the bacteria cannot survive in the environment,” says Drewniak. “We intend to use a strain that—even if the bacterium itself is unable to survive—will pass its genetic material to other organisms, which will thus acquire the ability to oxidize arsenic. This technology does not require large expenditure and is environmentally friendly. We have filed for a patent for the bacteria strain we want to use.”

The water treatment installation will consist of a system of reactors with varying capacity. The arsenic-oxidizing bacteria will be locked inside one of them. The contaminated water will flow through this reactor first. Then, after the arsenic is oxidized by the bacteria, the water will pass through filters to a sump. Then the bacteria will be returned to the reactor, and the water will be fed into another reactor with a sorbent that will capture the oxidized arsenic.

“We aim to achieve flows of up to 5 cubic meters per hour,” says Drewniak. In addition to the pilot installation in Z這ty Stok, he plans to develop technology to neutralize water contaminated with arsenic in Bulgaria and perhaps also in France.

Olga Majewska
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