Stimulation of Fe(II) Oxidation, Biogenic Lepidocrocite Formation, and Arsenic Immobilization by Pseudogulbenkiania Sp Strain 2002

An anaerobic nitrate-reducing Fe(II)-oxidizing bacterium, Pseudogulbenkiania sp. strain 2002, was used to investigate As immobilization by biogenic Fe oxyhydroxides under different initial molar ratios of Fe/As in solutions. Results showed that Fe(II) was effectively oxidized, mainly forming lepidocrocite, which immobilized more As(III) than As(V) without changing the redox state of As. When the initial Fe/As ratios were kept constant, higher initial Fe(II) concentrations immobilized more As with higher As-immobilized/Fe-precipitated in biogenic lepidocrocite. EXAFS analysis showed that variations of initial Fe(II) concentrations did not change the As-Fe complexes (bidentate binuclear complexes (C-2)) with a fixed As(III) or As(V) initial concentration of 13.3 mu M. On the other hand, variations in initial As concentrations but fixed Fe(II) initial concentration induced the co-occurrence of bidentate binuclear and bidentate mononuclear complexes (E-2) and bidentate binuclear and monodentate mononuclear complexes (11/ for As(III) and As(V)-treated series, respectively. The coexistence of C-2 and E-2 complexes (or C-2 and V-1 complexes) could contribute to higher As removal in experimental series with higher initial Fe(II) concentrations at the same initial Fe/As ratio. Simultaneous removal of soluble As and nitrate by anaerobic nitrate reducing Fe(II)-oxidizing bacteria provides a feasible approach for in situ remediation of As-nitrate cocontaminated groundwater.