Alkaliphilic bacteria retrieved from uranium mining effluent: Characterization, U sequestration and remediation potential

Abstract

Bacteria with the potential to sequester uranium (U) from carbonate-containing alkaline wastewaters were investigated. The two bacteria designated as MPW02 and MPW03 were isolated from uranium mine wastewaters and characterized by molecular methods as belonging to the genera Aeromonas and Bacillus, respectively. Uranium sequestration studies were performed at different carbonate–bicarbonate buffer concentrations and indicated the negative impact on the sequestering property of the two isolates. The observed maximum loading capacity by the two isolates under alkaline conditions was 112 and 36 mg U per gram of dry biomass, respectively. Heat inactivated MPW03 biomass retained the U sequestration capacity as that of living cells, whereas MPW02 dead biomass had a reduced U loading capacity. Kinetic models were applied to the experimental data to determine the mechanism of sequestration and found that two isolates followed a pseudo-second-order kinetic equation. Similarly, the experimental data were also modelled with Langmuir and Freundlich isotherms. The role of amino, hydroxyl and phosphate groups in U sequestration was elucidated by Fourier transform infrared (FTIR) spectroscopy. Further, the study shows that the two isolates adopted distinct mechanisms (chemisorption versus active metabolism dependent process) for U sequestration. Overall, this study signifies the potential application of these two bacteria for treating alkaline wastewaters containing U.