Microbial mediated iron redox cycling in Fe (hydr)oxides for nitrite removal

•Nitrite was removed effectively associated with microbial Fe(III) reduction.•Redox cycling of nitrite reduction by microbial Fe(III) reduction was achieved.•Biogenic Fe(II) could reduce nitrite ions into gaseous nitrogen species.•Biotic and abiotic denitrification were combined for nitrite removal.

Nitrite, at an environmentally relevant concentration, was significantly reduced with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. The average nitrite removal rates of 1.28 ± 0.08 and 0.65 ± 0.02 (mg L−1) h−1 were achieved with ferrihydrite and magnetite, respectively. The results showed that nitrite removal was able to undergo multiple redox cycles with iron (hydr)oxides mediated by Shewanella oneidensis MR-1. During the bioreduction of the following cycles, biogenic Fe(II) was subsequently chemically oxidized to Fe(III), which is associated with nitrite reduction. There was 11.18 ± 1.26 mg L−1 of NH4+-N generated in the process of redox cycling of ferrihydrite. Additionally, results obtained by using X-ray diffraction showed that ferrihydrite and magnetite remained mainly stable in the system. This study indicated that redox cycling of Fe in iron (hydr)oxides was a potential process associated with NO2−-N removal from solution, and reduced most nitrite abiotically to gaseous nitrogen species.

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