Bioremediation of Cr (VI) contaminated groundwater by Geobacter sulfurreducens: Environmental factors and electron transfer flow studies

In this study, the removal of Cr (VI) was examined in the presence of bio-produced Fe (II) from hematite, sulfate and dissolved organic matter by Geobacter sulfurreducens. The adaptation results of G. sulfurreducens showed that cells growth was stimulated up to 576 μM of Cr (VI) concentration. The first-order rate and electron transfer rate in each step during Cr (VI) reduction by G. sulfurreducens in the presence of hematite was clearly modeled and calculated. For Cr (VI) reduction rate, both separately dissolved and adsorbed bio-produced Fe (II) were faster than G. sulfurreducens although bio-produced Fe (II) contributed only 20% to total Cr (VI) removal in a combined system containing Cr (VI), hematite and G. sulfurreducens. The electron transfer rate from G. sulfurreducens to hematite (R2) to produce Fe (II) was a limited step and electron transfer rate from acetate to Cr (VI) (1.8 μeq L-1 h-1) by G. sulfurreducens was much higher than that to hematite (0.272 μeq L-1 h-1, producing Fe (II)). Cr (VI) reduction was enhanced in the presence of SO42- due to sulfate boost cells growth. AQDS enhanced Cr (VI) reduction by serving as an electron shuttle thus accelerating the electron transfer rate.