Bioremediation of strontium and technetium contaminated groundwater using glycerol phosphate

摘要

Groundwater at legacy nuclear facilities around the world is contaminated with radionuclides including strontium-90 and technetium-99, which are often present as co-contaminants. Here we investigated whether biostimulation of indigenous microbial communities by glycerol phosphate can co-treat Sr-90 through incorporation into phosphate biominerals, and Tc-99 through microbially-induced reduction of the sediment to form less mobile Tc(IV) phases via reaction with reduced species (e.g. Fe(II)). Results showed that 95% of Sr was removed from solution in sediment microcosms treated with glycerol phosphate, and sequential extraction showed that similar to 18% of the Sr in the resulting solid phase was associated with the pH 5 Na-acetate fraction and 75% was in the ion exchangeable fraction. This removal and partitioning to recalcitrant phases during glycerol phosphate treatment was greater than in the untreated controls, where only 60% of Sr was removed from solution, and of the solid-associated Sr, 95% was present in the exchangeable fraction. Fitting of Sr K-edge EXAFS spectra confirmed these findings, with shell by shell fitting suggesting similar to 30% of sediment-associated Sr was present in a coordination environment consistent with phosphate biominerals following glycerol phosphate treatment, whilst Sr was present only as outer-sphere complexes in the controls. In addition,16S rRNA sequencing of sediments stimulated with glycerol phosphate demonstrated the growth of potential phosphate-solubilising species such as Chryseobacterium and Serratia spp. Finally, glycerol phosphate treatment stimulated bioreduction via addition of electron donor in the form of glycerol to the system, in turn this stimulated the removal of Tc-99 from solution concomitant with microbial Fe(III) reduction to form poorly soluble hydrous Tc (IV)O-2 like phases. In sediments amended with an electron donor, the microbial community also reflected the onset of bioreduction with an increased rela