Arsenic (As) groundwater contamination is pervasive at Superfund and other sites, and is a major threat to public health. In situ magnetite precipitation may be an effective method of immobilizing groundwater As; this magnetite strongly retains As and is stable under a wide range of aquifer conditions, including those often associated with groundwater As contamination. Our previous laboratory studies suggest that the formation of nanoparticulate magnetite is stimulated when aqueous Fe(II) and nitrate are added to contaminated aquifer sediments, and that mineral formation is facilitated by microorganisms, but there are several plausible mechanisms by which it could be formed. Here, we perform in situ column experiments using sand and iron-oxide coated sands inoculated with both pure and co-cultures of several microorganisms to see which pathways are most important: (1) dissimilatory nitrate reduction, (2) dissimilatory iron reduction, and (3) nitrate-dependent iron(II) oxidation in the formation of magnetite in sand columns with amended groundwater. Results demonstrate that only nitrate dependent Fe(II) oxidation effectively produces magnetite or green rust, a common magnetite precursor, under the experimental conditions, and that co-cultures of this Fe(II) oxidized with a Fe(III) reducer are effective at stimulating magnetite formation under experimental conditions. We are currently developing reactive transport models using the numerical code PHT3D to quantify each biological process, and to use the resulting information to tune[SC1] field trials testing the proposed remediation method within a contaminated aquifer, and applying these models to optimize the remediation of As and other contaminants at Superfund sites.

Optimization of magnetite based arsenic immobilization strategies: Role of coupled iron oxidation and reduction in magnetite formation

254th National Meeting (2017)

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