Nitrogen-doped rice husk biochar cathode microbial fuel cell for Cr(Ⅵ) wastewater treatment

A nitrogen-doped rice-husk pyrolysis material(NDK) was prepared to modify the surface of carbon paper,as a cathode catalyst of two-compartment MFC (Microbial Fuel Cell, MFC). The effects of NDK on Cr(Ⅵ) reduction and MFC power-generation performance were investigated, and the diversity of anodic bacteria was also analyzed. The results showed that after nitrogen doping, the surface porosity of the material increased significantly, and the elemental nitrogen content reached 6.75%, which was enhanced by 4.35% compared with the non-nitrogen doped material. The electrochemical performance analysis of the electrodes showed that the electrochemical activity of the carbon paper electrodes was substantially improved after modification with biomass pyrolysis materials. And the electron transfer resistance of the NDK-modified electrode was 238.9 Ω, which was 74.08% lower than that of the unmodified electrode. The two-compartment MFC with NDK-modified carbon paper(NDK-MFC) as the cathode had the best performance. When the initial Cr(Ⅵ) concentration in the device was 200 mg/L,the NDK-MFC was operated for 90 h to achieve Cr(Ⅵ) removal rate of 87.02%, which was 3.38 times higher than that of the MFC of the unmodified electrode. Average output voltage and maximum power density reached 86.21 mV and 1.53 mW/m2 respectively. The excellent performance was maintained at the second cycle of continuous operation. The analysis of bacterial communities and functional genes showed that the anode of the MFC device was enriched with dominant flora related to organic matter degradation and electricity production, while the expression of genes related to microbial reproduction and metabolism was highly active.