Microbial fuel cell-upflow biofilter coupling system for deep denitrification and power recovery: Efficiencies, bacterial succession and interactions

The excess organic carbon is often added to meet denitrification requirements during municipal wastewater treatment, resulting in the carbon waste and increased risk of secondary pollution. In this study, microbial fuel cell (MFC) was coupled with an up-flow denitrification biofilter (BF), and the long-term performances of denitrification and power output were investigated under the different carbon source concentration. With sodium acetate (NaAc) of 600 mg/L and 300 mg/L, the favorable denitrification efficiencies were obtained (98.60%) and the stable current output was maintained (0.44 mÃ0.48 mA). By supplying NaAc of 150 mg/L, the high denitrification efficiency remained in a high range (89.31%) and the current output maintained at 0.12 mA, while, the denitrification efficiency dropped to 71.34% without coupling MFC. Electron balance analysis indicated that both nitrate removal and electron recovery efficiencies were higher in MFC-BF than that in BF, verifying the improved denitrification and carbon utilization performance. Coupling MFC significantly altered the bacterial community structure and composition, and while, the diversified abundance and distribution of bacterial genera were observed at the different locations. Compared with BF, the more exoelectrogenic genera (Desulfobacterium, Trichococcus) and genera holding both denitrifying and electrogenic functions (Dechloromonas, Geobacter) were found dominated in MFC-BF. Instead, the dominating genera in BF were Dechloromonas, Desulfomicrobium, Acidovorax and etc. By coupling MFC, the more complex and diversified network and the closer interaction relationships between the dominant potential functional genera were found. The study provides a feasible approach to effectively improve the denitrification efficiency and organic carbon recovery for deep denitrification process.