BIOSORPTION OF URANIUM BY PSEUDOMONAS-AERUGINOSA STRAIN CSU - CHARACTERIZATION AND COMPARISON STUDIES

Pseudomonas aeruginosa strain CSU, a nongenetically engineered bacteri al strain known to bind dissolved hexavalent uranium (as UO22+ and/or its cationic hydroxo complexes), was characterized with respect to its sorptive activity (equilibrium and dynamics). Living, heat-killed, pe rmeabilized, and unreconstituted lyophilized cells were all capable of binding uranium. The uranium biosorption equilibrium could be describ ed by the Langmuir isotherm. The rate of uranium adsorption increased following permeabilization of the outer and/or cytoplasmic membrane by organic solvents such as acetone. P. aeruginosa CSU biomass was signi ficantly more sorptive toward uranium than certain novel, patented bio sorbents derived from algal or fungal biomass sources. P. aeruginosa C SU biomass was also competitive with commercial cation-exchange resins , particularly in the presence of dissolved transition metals. Uranium binding by P. aeruginosa CSU was clearly pH dependent. Uranium loadin g capacity increased with increasing pH under acidic conditions, presu mably as a function of uranium speciation and due to the H+ competitio n at some binding sites. Nevertheless, preliminary evidence suggests t hat this microorganism is also capable of binding anionic hexavalent u ranium complexes. Ferric iron was a strong inhibitor of uranium bindin g to P. aeruginosa CSU biomass, and the presence of uranium also decre ased the Fe3+ loading when the biomass was not saturated with Fe3+, su ggesting that Fe3+ and uranium may share the same binding sites on bio mass. Although the equilibrium loading capacity of uranium was greater than that of Fe3+, this biomass showed preference of binding Fe3+ ove r uranium. Thus, a two-stage process in which iron and uranium are rem oved in consecutive steps was proposed for efficient use of the biomas s as a biosorbent in uranium removal from mine wastewater, especially acidic leachates. (C) 1996 John Wiley & Sons, Inc.