Nitrogen removal enhancement mechanism of Biochar/GO-modified denitrifying biocathode treating low C/N ratio...

In this study, the nitrogen removal enhancement mechanism of the walnut shell biochar/GO-modified electrode in microbial fuel cell denitrifying cathode was discussed through chemical tests and functional potential prediction analysis of the microbial community. The study revealed that the removal efficiency of NO₃^--N achieved 96.40 ± 4.48%, and the total nitrogen (TN) removal efficiency was 70.19 ± 13.29% in BC180, significantly outperforming the control group (CC) and other loading groups. Additionally, its average maximum voltage (124.91 ± 7.38 mV) exceeded other groups. FTIR and SEM analyses demonstrated that abundant redox-active functional groups (phenolic hydroxyl, quinone) on biochar's surface significantly enhanced electron acceptor capacity (EAC) of the cathode (932.39 μmol g^-1) and facilitated the enrichment of microorganisms. Moreover, biochar/GO also improved the electrochemical performance of the modified electrode. High throughput sequencing analysis indicated biochar/GO modification enriched multiple denitrifying bacteria. The relative abundance of typical electroactive bacteria (Thauera, Geobacter) at anode also increased. KEGG pathway analysis indicated that the relative abundance of pathways associated with electron transfer (Biosynthesis of siderophore group nonribosomal peptides, Ubiquinone, flagellar assembly) and key genes involved in the nitrogen metabolism (narG, nirS, and nod) in BC180 were both increased. These research results suggest that biochar/GO can efficiently regulate electrons to the nitrate reduction by regulating the microbial communities and the electron transfer pathways, potentially offering alternative strategies for optimizing denitrification at low-carbon nitrogen ratios.