Bacteria-Based Bioceramics for Bioremediation of Uranium Mining Waste Waters

Uranium mining waste piles are an enormous pool for heavy metal resistant bacteria. Many of these bacteria possess different mechanisms to detoxify metals, e.g. bioaccumulation, biotransformation, biomineralization or biosorption. The latter is of special interest for the development of bioremediation processes. We demonstrated that vegetative cells, spores and purified S-layer of Bacillus sphaericus JG-A12 which was recovered from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany, bind selectively U, Cu, Pb, Al and Cd. In this work sol-gel techniques were used to immobilize cells, spores and stabilized S-layer of B. sphaericus JG-A12 in a porous silicate matrix. Processes of sorption and desorption of U and Cu by the produced biological ceramics (biocers) were investigated and compared with the binding properties of the single components. Localization of the bound metals was carried out using scanning electron microscopy and EDX analysis. Formed metal complexes were characterized by extended X-ray absorption fine structure spectroscopy (EXAFS). Our results demonstrate that spores followed by vegetative cells and the S-layer bind large amounts of U and Cu. The silicate matrix binds only small amounts of U and no Cu. The immobilization of the biocomponents in the bioceramics did not have any negative effect on the cells and S-layer but the metal binding capacity of the spores was strongly reduced. Binding capacity and binding kinetics of the biocers were positively influenced by adding water soluble additives as sorbitol or by freeze drying instead of air drying. The bound metals can be completely removed from the biocers by using aqueous citric acid what makes them reusable. EXAFS spectroscopy of the uranium complexes shows that uranium is bound via phosphate and carboxyl groups of the biocomponents as well as by the silicate and hydroxyl groups of the ceramic matrix. Because biocers possess high mechanical stability and metal binding capacity and are in addition reusable they are suitable for construction of intelligent filters for bioremediation.