Russian Academy of Sciences, Russia
Alexey Safonov has completed his PhD in Ecology and he is a Senior Researcher, Head of Biotechnology and Radioecology group in Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Science. His interests are: Microbiology of radioactive waste repositories, biogeochemistry and in situ bioremediation, bio-treatment of waste, radioecology, uranium mill tailing, bacterial fungal and algae abilities for metal sorption and reduce, flow-through bio-filters, bio-electrochemistry and biosensors, Tc chemistry, trans-uranium radionuclides and fission products and radio medicine.
Liquid radioactive wastes (LRW) are multi-component systems which contain various macro components like nitrate solution (with the concentration of nitrate ions up to 300 g/L), sulfate ions, extractants, solvents, detergents and well as micro components-uranium series radionuclides, fission products (cesium, strontium, technetium, ruthenium, etc.), tritium and corrosion products.Themain problem in implementation of the core technologies of conditioning and long-term storage of radioactive waste ispresence of huge amount of nitrate ions.The aim of the present work was the utilization of denitrifying bacteria at the stage of waste denitration prior to cementation. Biological denitrification takes place viarespiration process whereby, nitrate ions are reduced to nitrogen through a series of intermediates.The microorganisms separated from extreme habitats: Pseudomonas putida (ecosystems contaminated with radioactive waste, dadwaste repository “Severniy”), Halomonas mono(alkaline lakes of Kulunda steppe with a total salt content of up to 300 g /L and pH 9-11) and Shevanella putrefactions strain from underground water contaminated with nitrate and radionuclides were studies. All strainspossess ability to reduce nitrate anions to molecular nitrogen and metals from high to low valence state.On the base of the data obtained from FSUE “RADON” analytical laboratory the model solutions with the following composition nitratesconcentration 4-100 g/L, sulfates up to 2 g/L, bicarbonate HCO3− up to 10 g/Land pH 9-10were prepared. Laboratory designed biofilters with different types of cultivation (in static and flow-through conditions) were applied. As source of carbon and electron donors for cell respiration saccharose in proportion of 1:1,to nitrate ions was used.The content of nitrate, nitrite in solutions and COD parameterswereanalyzed on supply and outlet points of flow-through biofilter in a 1 per 10 min discrete mode.After cultivation under the static conditions (batch mode) the concentration of nitrate ions decreased by factor 2 to 5. During the cultivation in the flow-through biofilter system the rate and degree of nitrate consumption has significantlyincreased via formation of a surface biofilm on an inert carrier providing higher specific surface.Bacterial cells were able to immobilize radionuclides from the solution U (88-96%), Th (up to 90 %),Sr (50-60 %), Tc, Cs and toxic metals Cr, V, Mo, Lacontributing to complex purification of radioactive waste