Synergistic remediation of Cr(VI) contaminated soil by iron-loaded activated carbon in two-chamber microbial fuel cells

The soil remediation by microbial fuel cells (MFCs) is still challenging due to the high mass transfer resistance limiting the overall performance. To improve the remediation of Cr(VI) contaminated soil, iron-loaded activated carbon (AC-Fe) particles were synthesized and spiked into soil to establish an enhanced MFC system. The AC-Fe particles are porous and conductive with a high specific surface area of 1166.5 m2/g. The addition of AC-Fe particles could reduce the overall resistance from 4269.2 omega to 303.1 omega with the optimum dosage of 0.3%. The maximum power generation of MFC was 11.5 mW/m2, and Cr(VI) removal efficiency reached as high as 84.2 +/- 1.2% in 24 h. It was found that AC-Fe particles were able to simultaneously adsorb and reduce Cr(VI) to Cr(III); in the meantime, Fe(II) loaded on the AC-Fe was oxidized to Fe(III). Spiking more AC-Fe particles in the contaminated soil had a negative effect. It was probably because that AC-Fe particles working as the third electrodes would hinder the overall ion electromigration and decrease Cr(VI) reduction at the cathode. The enhanced system which coupled MFC and AC-Fe showed a synergistic removal of Cr(VI), with the maximum improvement of 22.1% compared to the sum of Cr(VI) removals by the individual ones.