Hexavalent chromium removal by a new composite system of dissimilatory iron reduction bacteria Aeromonas hydrophila and nanoscale zero-valent iron

Core-shell Fe@Fe2O3 nanowire is one special nanoscale zero-valent iron (NZVI) with an iron core and an outside shell of iron oxide containing the surface bound ferrous ions, which has been used to remove various pollutants including Cr(VI). However, it can be easily oxidized to accumulate iron oxides on the shell, resulting in the loss of reactive activity during its long-term application. Therefore, the dissolution of iron oxides by reduction is required to maintain NZVI reactivity. In this study, we combine NZVI and a dissimilatory iron reduction bacteria (DIRB), Aeromonas hydrophila HS01, to establish a composite system for a sustainable anoxic reduction of Cr(VI). HS01 can stably coexist with NZVI, reduce the oxidized Fe on NZVI and generate more dissolved Fe(II) under anoxic conditions. This presence of HS01 can maintain the core-shell structured morphology and relatively more Fe-0 and Fe(II) on NZVI surface, and enhance the reactivity in Cr(VI) removal. Our results indicated that a suitable DIRB can be used to prolong the reactivity of NZVI, and their combination is an efficient method for anoxic Cr(VI) removal.