Radionuclide remediation using a bacterial biosorbent

A Pseudomonas strain, characterized as part of a project to develop a biosorbent for removal of toxic radionuclides from nuclear waste streams, was a potent accumulator of uranium (VI) and thorium (IV), with the metal sequestration process being unaffected by culture age, presence of carbon/energy source and metabolic inhibitor but sensitive to the composition of the growth medium. Further characterization of radionuclide biosorption using lyophilized biomass revealed rapid cation binding of > 90% within 1-10 min of contact and complete removal of U and Th was observed at initial concentrations up to 100 mg l(-1). Initial solution pH strongly affected radionuclide biosorption with an optimum at pH 4.0-5.0. High affinity, efficient and high capacity uranium and thorium binding was indicated, with maximum loading of 541 mg U g(-1) dry mass or 430 mg Th g(-1) dry mass. Good conformity of sorption data with the Langmuir model suggests monolayered U and Th binding. Sorption in presence of several interfering cations and anions indicates a specific U and Th binding by the biomass with significant antagonism offered only by iron (III). Transmission electron microscopy and energy dispersive X-ray fluorescence analysis of metal loaded biomass revealed intracellular U and Th sequestration. More than 90% of biomass-bound radionuclide was recovered using sodium or calcium carbonate. For continuous process application an immobilized biomass system was developed and tested with multiple cycles of sorption-desorption. Overall, the biosorbent appeared suitable for realistic bioremediation. (C) 2004 Elsevier Ltd. All rights reserved.