RESUMEN
Nanoscale zero-valent iron (nZVI) shows excellent reduction of Cr(â ¥), but the passivation on its outer surface can restrict its longevity and performance. To tackle this problem, this work introduced Shewanella oneidensis MR-1, a dissimilatory iron-reducing bacterium, into the chemical reduction system of aged nZVI/biochar (B) and Cr(â ¥). The potential synergistic effect of Cr(â ¥) reduction of aged nZVI/B and MR-1 was systematically investigated under varying conditions. The results indicated that aged nZVI/B and MR-1 exhibited a synergistic effect at a pH of 7, and the removal rate of Cr(â ¥) increased by 51.3%. Further research showed that the synergistic effect could be attenuated with the increase in the initial Cr(â ¥) concentration and enhanced with the increase in the MR-1 concentration. The XPS spectra confirmed that Cr(â ¥) was mainly removed through reduction. The dissimilatory iron-reducing ability of MR-1 played a key role in enhancing the Cr(â ¥) reduction. The reductive dissolution of the oxidation layers not only released reactive sites inside the nZVI, but also reduced Cr(â ¥) by producing ferrous ions. Moreover, B promoted the reduction by dispersing the nZVI and mediating the extracellular electron transfer. This study provides a new insight into solving the passivation problem of the long-term application of nZVI for Cr(â ¥) removal, which is considered a promising solution for synergistically improving the performance of nZVI in environmental remediation.