ABSTRACTThe interactions between sulfate reducing anaerobic bacteria and plutonium, with or without bentonite present, were investigated using distribution coefficients {Kd (ml/g)} as an index of the radionuclide behaviour. Plutonium Kds for living bacteria varied within a large range, from 1,804 to 112,952, depending on the pH, while the Kds ranged from 1,180 to 5,931 for dead bacteria. In general, living bacteria had higher plutonium Kds than dead bacteria. Furthermore, the higher Kd values of 39,677 to 106,915 for living bacteria were obtained for a pH range between 6.83 and 8.25, while no visible pH effect was observed for dead bacteria. These Kd values were obtained using tracers for both236Pu and239Pu, which can check the experimental procedures and mass balance.Another comparison was conducted for plutonium Kd values of mixtures of living bacteria with bentonite and sterilized bacteria with bentonite. The range of Kd values for the non-sterilized bacteria with bentonite were 1,194 to 83,648 while Kd values for the sterilized bacteria with bentonite were from 624 to 17,236. Again, the Kd values for the living bacteria with bentonite were higher than those of sterilized bacteria with bentonite. In other words, the presence of living anaerobic bacteria with bentonite increased, by roughly 50 times, the Kd values of239Pu when compared to the mixture of dead bacteria with bentonite. The plutonium Kd values for bentonite alone, both non-sterilized and sterilized, were within a constant range of around 10,000 even though some of the data are not yet available.The bentonite used for this experiment was a product of Japan and the sulfate reducing anaerobic bacteria was previously used for the treatment of a pulp and paper wastewater. The results indicate that the effects of anaerobic bacteria within the engineered barrier system (in this case bentonite) will play a significant role in the behaviour of plutonium in geologic repositories.
Characterization of efficient xylanases from industrial-scale pulp and paper wastewater treatment microbiota
