Microbial reduction and fixation of pentavalent vanadium enhanced by natural Fe(II) mineral-biomass

Abstract:

[Objective] The environmental hazard of heavy metal vanadium is increasingly concerned. Microorganisms can achieve reductive immobilization of highly toxic pentavalent vanadium (V(V)), while electron donor is the key to this bioprocess. Although both natural Fe(II)-bearing minerals and natural biomass have been reported to independently support microbial V(V) reduction, the characteristics of microbial V(V) reduction under mixotrophic condition based on these two materials have not been revealed yet. [Methods] In this study, natural Fe(II) minerals and biomass were preferentially selected and compounded in combination to investigate the reduction mechanism of V(V) in a mixotrophic biological system. [Results] The results showed that the highest V(V) removal efficiencies of 54.2%±3.4% and 67.1%±3.1% were achieved for pyrrhotite and woodchips, respectively. The highest V(V) removal efficiency of 82.7%±3.1% was achieved when the preferred combination of pyrrhotite and woodchips was compounded at a ratio of 1:3. V(V) was reduced to insoluble V(IV) precipitate, while Fe(II) and S(-II) were oxidized to Fe(III) and SO₄^2-, respectively. In the mixotrophic system, chemolithoautotrophic bacterial genera such as Desulfurivibrio and Thiobacillus might be involved in the oxidation of pyrrhotite coupled to V(V) reduction and the synthesis of organic intermediate metabolites using inorganic carbon sources. Together with the decomposing products of woodchips by cellulose degrading bacteria such as Acholeplasma, these organics were utilized by chemoorganoheterotrophic V(V) reducers such as Bacteroidetes_vadinHA17 to reduce V(V). [Conclusion] This study provides a promising remediation method for groundwater V(V) contamination.