Abstract:
Nuclear energy has been proposed as an alternative energy source in the bid to reduce carbon emissions that
results from fossil fuel. Hexavalent uranium [U(VI)] is the most abandoned radioactive waste discharged from
nuclear fuel processing, electricity generation power plants, radioisotope manufacturing plants. Improper
disposal or storage of U(VI) containing waste may poses a threat to aquatic systems and related ecological
systems. Treatment of U(VI) containing effluents from these industrial activities requires the reduction of highly
mobile and radiotoxic U(VI) to tetravalent U(IV) which readily forms the hydroxide precipitate [U(OH)4(s)]
under neutral pH conditions. Processes employing biofilm and fixed-film systems for treatment of wastewater
are considered more robust than planktonic culture systems in the presence of high toxicity, and therefore, are
preferred in the treatment of toxic liquid waste. In this study U(VI) reduction is investigated using a fixed-film
reactor inoculated with U(VI) reducing bacteria isolated from tailing dump soil collected from an abandoned
uranium mine in South Africa. The fixed-film bioreactor was operated as a continuous flow reactor under
oxygen stressed conditions without the addition of external organic carbon source. The results from this study
showed that the fixed-bed bioreactor was able to achieve >90 % U(VI) removal efficiency at U(VI)
concentration of up to 85 mg/L, concentration which is higher than that observed at the study site. This
demonstrates the feasibility of the fixed-bed bioreactor in continuously removing U(VI) in aqueous solutions
without the need of introducing external organic carbon source and without re-seeding the bioreactor. The
bioremediation technology proposed in this study significantly demonstrated the effectiveness of the biofilm
processes in treating process effluent streams and U(VI) contaminated sites as part of the pump-and treat.
Fundamental understanding of uranium-bacteria interactions taking place in a complex biofilm structure under
such conditions would be effective in developing an appropriate radioactive waste treatment system for the
subsurface bioremediation process.
