Bacteria-based bioremediation of uranium mining waste waters by using sol-gel ceramics

Sol-gel ceramics with high metal binding capacity were prepared via homogeneous dispersion and embedding of vegetative cells, spores and EDC stabilised surface proteins (S-layers) of Bacillus sphaericus JG-A12. The B. sphaericus JG-A12 strain was recovered from a uranium mining waste pile near the town of Johanngeorgen-stadt, Saxony, Germany (1). The whole cells as well as the purified S-layer protein of this strain possess an ability to bind selectively and very effectively uranium and several other metals such as Cu, Pb, Cd, Al, Pt and Pd (1, 2).
In this work the biosorption of U and Cu by the above mentioned three bacteria-based biological ceramics (biocers) was investigated. In addition, the metal binding capacity of the free SiO2 nanomatrix and of the three individual bacterial components (the vegetative cells, the spores and the S-layers) was studied as well.
Our results demonstrate that the high U and Cu binding capability of the three kinds of biocomponents is influenced by the sol-gel process in a different way. The metal binding properties of the vegetative cells and of the S-layers were not negatively influenced by the sol-gel treatments. The metal binding capacity of the embedded spores was, however, significantly lower than those of the non embedded spores. Very limited amounts of U and no Cu were bound by the silicate matrix alone.
The metal binding capacity of the biocers and also the kinetic of the biosorption were positively influenced by adding water soluble compounds such as sorbitol or by freeze drying instead of air drying. These results are connected to the higher porosity achieved by the mentioned treatments.
Both metals can be completely desorbed and washed from the biocers by using 0.5 M solution of citric acid. Afterwards the biocers can be reused for metal biosorption.
Due to their stability, high metal binding capacity and simple and complete removal of the bound metals described biocers are good candidates for construction of intelligent filters for cleaning of heavy metal contaminated liquid wastes.
The geographic origin of the source of the biocomponents, namely the strain B. sphaericus JG-A12, makes the constructed bioceramics promising for in situ bioremediation of the drain waters of the uranium mining waste piles and mill tailings.

References

1. Selenska-Pobell S., Miteva V., Boudakov I., Panak P., Bernhard G., and Nitsche H. (1999) Selective accumulation of heavy metals by three indigenous Bacillus isolates, B. cereus, B. megaterium and B. sphaericus in drain waters from a uranium waste pile.FEMS Microbiol Ecology 29, 59-67.
2. Raff J (2002) Wechselwirkungen der Hüllproteine von Bakterien aus Uran-abfallhalden mit Schwermetallen PhD Thesis, FZR-Report 358