Optimized combination of zero-valent iron and oxygen-releasing biochar as cathodes of microbial fuel cells to enhance copper migration in sediment.

[Display omitted] • nZVI was used in sediment microbial fuel cell (SMFC) to improve Cu2+ removal. • Cu precipitation was found on the surface of nZVI-based O 2 -releasing bead (ORB). • nZVI-based ORBs were added to the SMFC cathode to improve power generation. • The obvious change of Fe-O group improves participation of nZVI in the reaction. Membrane-less single-medium sediment microbial fuel cells (single-SMFC) can remove Cu2+ from sediment through electromigration. However, the high mass transfer resistance of the sediment and amount of oxygen at the cathode of the SMFC limit its Cu2+ removal ability. Therefore, this study used an oxygen-releasing bead (ORB) for slow oxygen release to increase oxygen at the SMFC cathode and improve the mass transfer property of the sediment. Resultantly, the copper removal efficiency of SMFC increased significantly. Response surface methodology was used to optimize the nano zero-valent iron (nZVI)-modified biochar as the catalyst to enhance the ability of the modified ORB (ORB m) to remove Cu2+ and slow release of O 2. The maximum Cu2+ removal (95 %) and the slowest O 2 release rate (0.41 mg O 2 /d·g ORB m) were obtained when the CaO 2 content and ratio of nZVI-modified biochar to unmodified biochar were 0.99 g and 4.95, respectively. When the optimized ORB m was placed at the single-SMFC cathode, the voltage output and copper removal increased by 4.6 and 2.1 times, respectively, compared with the system without ORB m. This shows that the ORB m can improve the migration of Cu2+ in the sediment, providing a promising remediation method for Cu-contaminated sediments. [ABSTRACT FROM AUTHOR]