Efficient nitrate removal via microorganism-iron oxide co-evolution on biocathode surface.

Sediment microbial fuel cell (SMFC) is a device for biological denitrification, in which electrons produced by sediment microorganisms can be transferred to the upper layer of the water column lacking electron donors. However, the low efficiency of denitrifying bacteria in acquiring electrons and enriching at the cathode greatly hinders the application of SMFC for nitrogen removal. In this study, we report a novel method of constructing a high-performance biocathode by modifying electrodes with zero-valent iron to enhance the enrichment and electron transfer of electroactive bacteria. The surface chemical and biological analysis of the biocathode revealed that the ZVI gradually oxidized to form magnetite and goethite, and finally stabilized into better crystallized lepidocrocite. On the other hand, the microbial community of the biocathode gradually evolved into a community dominated by denitrifying bacteria, specifically Clostridium. The co-evolved "Clostridium-lepidocrocite" composite endows the sediment microbial fuel cell with a 99% nitrate removal capacity. These results indicate that the cathode constructed by using ZVI modified electrode achieves efficient nitrate reduction by denitrifying bacteria. Furthermore, the construction method of biocathode may also have the potential application in water remediation and the geochemical cycling of elements.