Stimulation of Fe(II) Oxidation, Biogenic Lepidocrocite Formation, and Arsenic Immobilization by <i>Pseudogulbenkiania</i> Sp. Strain 2002

An anaerobic nitrate-reducing Fe­(II)-oxidizing bacterium, <i>Pseudogulbenkiania</i> 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 (²<i>C</i>)) with a fixed As­(III) or As­(V) initial concentration of 13.3 μM. 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 (²<i>E</i>) and bidentate binuclear and monodentate mononuclear complexes (¹<i>V</i>) for As­(III) and As­(V)-treated series, respectively. The coexistence of ²<i>C</i> and ²<i>E</i> complexes (or ²<i>C</i> and ¹<i>V</i> 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