The use of micro-organisms for the remediation of solutions contaminated with actinide elements, other radionuclides, and organic contaminants generated by nuclear fuel cycle activities

L. E. Macaskie, J. R. Lloyd, R. A P Thomas, M. R. Tolley

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Many heavy elements, including actinides, form insoluble precipitates with ligands such as inorganic phosphate (abbreviated Pi). This can be generated biochemically, e.g. using the activity of a phosphatase enzyme of a Citrobacter sp., which forms HPO42- in juxtaposition to nucleation sites on the cell surface; insoluble metal phosphate promotes the formation of large crystals of, for example, HUO2PO4.4H2O, to loads of several times the weight of the biomass. For use the biomass is immobilized within a flow-through column. The metals can be removed efficiently from dilute solution since the continuous production of a high localized concentration of Pi allows the solubility product of the metal phosphate to be exceeded, even in the presence of competing chelating ligands (e.g. citrate). Application of this approach to the removal of uranium, americium, plutonium and neptunium from acid mine drainage waters (U) and laboratory test solutions (Am, Pu, Np) is described. The phosphate 'donor' molecule (phosphatase substrate) is an organophosphate, usually glycerol 2-phosphate. Tributyl phosphate has also been cleaved enzymatically to support the removal of uranium from solution by a new mixed culture. Some metal species such as technetium (VII), TcO4-, do not form insoluble phosphates. Here, the reductase activity of other microorganisms can be harnessed to the bioreduction of Tc(VII) to insoluble species which are precipitated onto the biomass. Special problems can occur in plant decontamination, where soluble metal-ligand complexes may be generated. A mixed microbial culture which grows at the expense of ethylene diamine tetraacetic acid (EDTA) chelated to various metals is described for the first time. This has potential for the release of metals into available, unbound forms for further remediation.In conclusion, there is scope for the use of micro-organisms for the remediation of several types of wastes arising from activities associated with the nuclear fuel cycle. This technology is envisaged as a 'polishing' step, as an adjunct to more conventional physico-chemical treatments, with additional metal transformations, and enhancement of metal availability that would be difficult to achieve by chemical means alone.
    Original languageEnglish
    Pages (from-to)257-271
    Number of pages14
    JournalNuclear Energy
    Volume35
    Issue number4
    Publication statusPublished - 1996

    Keywords

    • Bioremediation
    • Citrobacter sp.
    • Ethylene diamine tetraacetic acid (EDTA)
    • Heavy metal accumulation
    • Nuclear fuel cycle
    • Nuclear waste
    • Remediation
    • Technetium
    • Transuranic elements
    • Tributyl phosphate
    • Uranium

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