Efficient nitrogen removal in microbial fuel cell – constructed wetland with corncobs addition for secondary effluent treatment

Abstract

Treatment of secondary effluent from municipal wastewater treatment plants (WWTPs) is urgently needed owing to the fact that excess nitrogen in secondary effluent can cause eutrophication. To promote nitrogen removal and bioelectricity generation performance of microbial fuel cell - constructed wetland (MFC-CW) when treating secondary effluent from WWTPs, the corncobs as external biomass carbon sources were added on the surface of wetlands. Besides, the MFC system was constructed to explore the effect of wetland plants (water hyacinth). In order to investigate the optimal dosage of corncobs, the performance of MFC-CW with different dosages (0, 30 and 70 g/m2) of corncobs were compared. Results revealed that 70 g/m2 of corncobs addition significantly enhanced denitrification performance and bioelectricity generation, with the highest nitrate removal of 99.3% and 100%, and maximum power density of 0.87 mW/m2 and 1.92 mW/m2 in MFC and MFC-CW, respectively. High-throughput sequencing analysis indicated that microorganisms related to organics degradation were detected in both anode and cathode areas. The functional genera such as Nitrospira, unclassified_Comamonadaceae, and Bacillus were higher in MFC-CW, which contributed to higher nitrogen removal and bioelectricity generation. Functional genes and enzymes revealed that nitrification, denitrification and anammox might participate in the nitrogen metabolism together. This research provides a promising way to utilize biomass carbon sources in MFC-CW to treat secondary effluent for simultaneous nitrogen removal and energy recovery.