Transformation of carbon tetrachloride by biogenic iron species in the presence of Geobacter sulfurreducens and electron shuttles

Abstract

The transformation of carbon tetrachloride (CT) by biogenic iron species produced from the bioreduction of various Fe(III) oxides in the presence of Geobacter sulfurreducens and electron shuttles were investigated. Cysteine and anthraquinone-2,6-disulfonate (AQDS) at concentrations of 0.5 mM and 10 μM, respectively, were added as the electron shuttles. Addition of electron shuttles enhanced the extent of reduction and rate of ferric oxide reduction. The bioreduction extents of ferric oxides by G. sulfurreducens in the presence of electron shuttles were 22.8–48.3% for ferrihydrite, 6.5–17.2% for hematite, and 3.0–11.3% for goethite. After normalization to the surface areas, a higher rate of CT reduction was observed per unit of adsorbed Fe(II) on crystalline oxides. The produced biogenic Fe(II) from crystalline iron oxides was 2.8–7.6 times lower than that obtained from ferrihydrite, while the surface area-normalized rate constant for iron-mediated CT transformation in the presence of goethite and hematite were, by factors of 2–21, higher than that obtained using ferrihydrite. These results clearly depict that G. sulfurreducens drove the reduction of CT primarily through the formation of biogenic iron species in the presence of electron shuttle under iron-reducing conditions and that it is a surface area dependent process.