Effect of biogenic iron species and copper ions on the reduction of carbon tetrachloride under iron-reducing conditions

In this study, the cell-mediated and abiotic reduction of carbon tetrachloride (CCl4) by biogenic iron species produced from the reductive dissolution of ferrihydrite in the presence of Geobacter sulfurreducens and copper ions (Cu(II)) were investigated. 9,10-Anthraquinone-2,6-disulfonate (AQDS), serving as a surrogate of natural organic matters and an electron shuttling compound, was added to enhance the efficiency of biological reduction of the solid Fe(III) minerals. G. sulfurreducens drove the reduction of CCl4, primarily through the formation of biogenic surface-bound iron species produced from the reductive dissolution of ferrihydrite, in the presence of 10 μM AQDS. The pseudo-first-order rate constant (kobsCT) for CCl4 transformation in the presence of ferrihydrite was 3.0 times higher than that resulting from the use of G. sulfurreducens alone. Addition of 0.5 mM Cu(II) slightly inhibited both the growth of G. sulfurreducens and the production of biogenic Fe(II). However, the kobsCT values for CCl4 transformation in ferrihydrite suspensions containing G. sulfurreducens and 0.3–0.5 mM Cu(II) were 2.1–4.2 times higher than that observed in the absence of Cu(II). X-Ray powder diffraction analysis indicated that the added Cu(II) reacted with the biogenic Fe(II) ions to produce catalytic cuprous ions (Cu(I)) and secondary iron oxide minerals such as magnetite and goethite, resulting in accelerating the chemical transformation efficiency and rate of CCl4 under iron-reducing conditions.