Removal and biotransformation of U(VI) and Cr(VI) by aerobically grown mixed microbial granules

Abstract

ABSTRACT We assessed the potential of aerobic granular sludge consisting of mixed species of bacteria to remove and immobilize uranium (VI) and chromium (VI). Microbial granules were cultivated in a laboratory sequencing batch reactor (SBR) by feeding with acetate-containing synthetic media. Microbial granules formed in the SBR exhibited excellent settling characteristics and predominantly consisted of rod/cocci shaped bacteria. The microbial granules immobilized 218 ± 2 mg of U(VI) g−1 dry granular biomass. X-ray photoelectron spectroscopy (XPS) showed the association of U(VI) with the microbial granules and transformation of U(VI) to U(IV). Microbial granules reduced Cr(VI) and immobilized to Cr(III) at 0.17 mmoles/d/g under anaerobic conditions. X-ray absorption near edge spectroscopy (XANES) of chromium associated with microbial granules revealed complete conversion of Cr(VI) to Cr(III). Extended X-ray absorption fine structure (EXAFS) analysis of the Cr-laden microbial granules showed similarity to C...