Bioremediation of Radioactive Waste
One technology that holds promise for eventually reducing the toxicity and amount of radioactive waste is bioremediation, using live bacteria. This technology makes use of the ability of live cells or enzymes to clean and reduce the volume of waste.
The organisms that are used metabolize anaerobically, i.e., in non-oxygen conditions, by chemically reacting with metal ions in solution, reducing them to lower oxidation states (lower ionic charge). For some elements, this reduced ion is insoluble, so it precipitates out of solution as a solid. For example, soluble Uranium6+ is reduced to insoluble U4+ which precipitates as solid uraninite, UO2. These precipitates can be recovered easily, then isolated and contained.
A British proposal describes a live cell "bioreactor" to treat liquid uranium waste. Using a specific species of microorganism results in uranium uptake equal to 900 per cent of the live cells' dry mass or 9 grams of uranium per gram of dry cells. Another species, which absorbs 11 grams of uranium per gram of dry cells, has been shown to precipitate relatively pure uranium oxide which is easily recoverable.
Similar organisms may be able to do the same for technetium (Tc) and plutonium (Pu). It has also been suggested that such a micro-organism could be injected underground into uranium-contaminated ground waters to form a barrier to future migration of dissolved uranium.
Many unknowns remain. However, with so few answers to the problem of radioactive waste, such explorations must continue.
From an unpublished report for the Nuclear Guardianship Forum by Rose Kirkham, summarized by Anthony Phillipson.