Biological U(VI) Reduction in a Fixed-film Reactor Using Indigenous Culture Under Shock Loading Conditions

Abstract

Uranium (VI) contamination in the environment has become a global problem in aquifers, water supplies and other related ecosystems. Bioremediation has gained importance as a feasible and eco-friendly strategy in remediating uranium contaminated environments. This study investigates biological U(VI) removal in a bench- scale, fixed-film bioreactor using a mixed-culture of bacteria sourced from an abandoned uranium mine in Limpopo, South Africa. Preliminary batch kinetic studies showed that these species have the potential to effectively reduce U(VI) in aqueous solutions by means of more than one mechanism. The bench-scale bioreactor was operated as a continuous flow system under a range of influent U(VI) concentrations (75-100 mg/L) without any added external organic carbon source. Near complete U(VI) removal was achieved in a biofilm reactor operated at influent feed concentrations of 75 mg/L and 85 mg/L. The extent of abiotic U(VI) reduction was also evaluated in this study using cell-free reactor. Results showed insignificant U(VI) removal in a cell-free rector, demonstrating the feasibility of the microbial species used in this study in reducing or immobilizing U(VI) in contaminated wastewater. The proposed bioremediation technology in this study could be applicable to end pipe ex situ bioremediation. The results from this study demostrated the possibility of combining biological processes with non-biological processes for effective treatment and recovery of uranium from U(VI) contaminated wastewater streams.