REDUCTION OF HEXAVALENT URANIUM FROM ORGANIC-COMPLEXES BY SULFATE-REDUCING AND IRON-REDUCING BACTERIA

The influence of organic-hexavalent-uranium [U(VI)] complexation on U( VI) reduction by a sulfate-reducing bacterium (Desulfovibrio desulfuri cans) and an iron-reducing bacterium (Shewanella alga) was evaluated. Four aliphatic ligands (acetate, malonate, oxalate, and citrate) and a n aromatic ligand (tiron [4,5-dihydroxy-1,3-benzene disulfonic acid]) were used to study complexed-uranium bioavailability. The trends in ur anium reduction varied with the nature and the amount of U(VI)-organic complex formed and the type of bacteria present. D. desulfuricans rap idly reduced uranium from a monodentate aliphatic (acetate) complex. H owever, reduction from multidentate aliphatic complexes (malonate, oxa late, and citrate) was slower. A decrease in the amount of organic-U(V I) complex in solution significantly increased the rate of reduction, S. alga reduced uranium more rapidly from multidentate aliphatic compl exes than from monodentate aliphatic complexes. The rate of reduction decreased with a decrease in the amount of multidentate complexes pres ent. Uranium from an aromatic (tiron) complex was readily available fo r reduction by D. desulfuricans, while an insignificant level of U(VI) from the tiron complex was reduced by S. alga. These results indicate that selection of bacteria for rapid uranium reduction will depend on the organic composition of waste streams.