Filtering radioactive elements from water

"If they used our filter, they wouldn't need to," says Raffaele Mezzenga, Professor of Food & Soft Materials at ETH Zurich. It was four years ago that he and his Senior Scientist Sreenath Bolisetty unveiled their invention of a filter membrane made primarily of denatured whey protein and activated carbon.

In a publication at the time, the researchers demonstrated how efficiently their product removes heavy metals, some radioactive elements such as uranium, and precious metals such as gold or platinum from water.

Filter also suitable for radioactive isotopes

Now, Mezzenga and Bolisetty have used their membrane to purify hospital effluents contaminated with radioactive elements. Over the course of their investigation, the two researchers discovered that their filter is efficient at removing these substances as well. Their study was recently published in the journal Environmental Science: Water Research & Technology.

Laboratory tests show that the membrane is able to remove radionuclides used in the medical field -- technetium-​99m, iodine-​123 and gallium-​68 -- from water with efficiencies of over 99.8% in just one filtration step.

The researchers also tested their filter membrane with a sample of real effluents from a Swiss hospital, which contained radioactive iodine-​131 and lutetium-​177. It removed both elements almost completely from the water.

Storage of radioactive material requires space

Medical professionals use radionuclides to treat cancer, for example, or as a contrast agent in imaging procedures. In most cases, these materials are only slightly radioactive and have a short half-​life of just a few hours or days.

Nevertheless, disposal in the sewerage system is not permitted either for hospital effluents that contain these substances or for human waste from patients treated with them. Hospitals must therefore store the effluents safely and securely in special containers until the radioactivity has dropped to a harmless level. This creates problems with space. But that's not the only issue. It's also necessary to ensure that personnel and the environment are protected from radiation.

Filter membrane effective on a broad scale

Based on the results of their current study, ETH Professor Mezzenga believes the product has what it takes. "The filter membrane eliminates radioactive isotopes on a broad scale," he says. In principle, all radioactive isotopes in the periodic table that lie between the extremes tested, i.e. technetium and uranium, bind to the membrane. These include radioactive caesium, iodine, silver and cobalt, all of which are present in the water leaked from Fukushima. Large quantities of tritium are also present; this is the only element that will likely not bind to the membrane because it is too small.

"If our assumption is correct, the filter membrane could massively reduce the volume of wastewater in Fukushima, meaning that no radioactive water would have to be dumped into the Pacific Ocean," Bolisetty says. He explains that the filters saturated with the highly radioactive elements can be stored as solids, for example in the same place as used fuel rods from nuclear power plants.

It is not particularly difficult to produce the filter membrane. The whey protein used is a waste product of the dairy industry, cheap and available everywhere. The activated carbon component is also readily available. "I'm positive that Japan could start using the filter membrane right now and, in doing so, solve a serious environmental problem," Bolisetty says.