Enhanced Cr(VI) removal from groundwater by Fe⁰-H₂O system with bio-amended iron corrosion

A one-pot bio-iron system was established to investigate synergetic abiotic and biotic effects between iron and microorganisms on Cr(VI) removal. More diverse iron corrosion and reactive solids, such as green rusts, lepidocrocite and magnetite were found in the bio-iron system than in the Fe⁰-H₂O system, leading to 4.3 times higher Cr(VI) removal efficiency in the bio-iron system than in the Fe⁰-H₂O system. The cycling experiment also showed that the Cr(VI) removal capacity of Fe⁰ in the bio-iron system was 12.4 times higher than that in the Fe⁰-H₂O system. A 62days of life-span could be achieved in the bio-iron system, while the Fe⁰-H₂O system lost its efficacy after 30days. Enhanced effects of extra Fe²⁺ on Cr(VI) removal was observed, largely contributed to the adsorbed Fe²⁺ on iron surface, which could function as an extra reductant for Cr(VI) and promote the electron transfer on the solid phase. The results also showed that the reduction of Cr(VI) by microorganisms was insignificant, indicating the adsorption/co-precipitation of Cr by iron oxides on iron surface was responsible for the overall Cr(VI) removal. Our study demonstrated that the bio-amended iron corrosion could improve the performance of Fe⁰ for Cr(VI) removal from groundwater.