Research On The Denitrification Mechanism Of EAM-MFC Biological Cathode And Optimization Of SND Denitrification Performance

Conductive membrane aerated microbial fuel cell(EAM-MFC)coupled with membrane aeration bioreactor(MABR)and microbial fuel cell(MFC)is a novel technology for wastewater nitrogen removal and energy recovery,but it is usually limited by oxygen.In this study,we focus on the cathodic denitrification,analyzed the denitrification performance by controlling different aeration pressures,evaluated the effective electron utilization efficiency,identified different functional genus,explored the biological population in the biofilm,and then revealed the denitrification mechanism in dual electrons acceptors denitrification cathode.Furthermore,the simultaneous nitrification and denitrification(SND)performance of EAM-MFC cathode was explored.In the EAM-MFC denitrification biocathode,electrochemical analysis showed that in the absence of aeration conditions,denitrification and effective electron utilization efficiency were close to 100%.Under aeration conditions,the denitrification efficiency decreased with the dissolved oxygen(DO),showing the best denitrification effect of 80.07%at 0.15mg/L,and the denitrification electrons utilization efficiency reached 76.33%,indicating The lower NO3-N preferentially used the electrons of cathode electrode than oxygen at lower DO conditions.A high-throughput sequencing of 16S rRNA showed with the oxygen increased,the denitrifying bacteria such as TM7 and Psedomonas were replaced by the main oxygen-reducing bacteria of the genus Thauera and Bacteroides.Fluorescence in situ hybridization(FISH)suggested that the functional microbial population had a succession in the distribution of biofilms with the change of DO.The relative position of biofilm and EAM electrode determined the distribution regular of cathodic electrons.Under the lower DO condition,the denitrifying bacteria grew on the surface of the carbon fiber of the EAM electrode,which was the intrinsic reason for achieving the maximum denitrification electron utilization and denitrification effect at 0.15mg/L.In the EAM-MFC cathode SND,electrochemical analysis showed that with the increase of aeration pressure,the removal effect of NH3-N gradually increased,reaching 78.43%at 0.45mg/L.However,the TN removal efficiency showed a trend of increasing first and then decreasing.At 0.30mg/L,the optimal denitrification efficiency of 62.43%was obtained.At this time,the effective electron utilization efficiency reached a maximum of 80.68%.The results of biological microbial analysis showed that under the optimal aeration conditions of 0.30mg/L,the relative abundance of AOB genera,such as Nitrosomonas,Nitrosococcus and Nitrosospira were higher than that of Sphingomonas,Acidovorax and Bacteroides.Compared with single cathode denitrification,the participation of oxygen in the ammonia oxidation was the key reason for changing the cathodic electrons distribution regular.This study provided a theoretical basis for further weakening the electrons competition of oxygen in the dual-electrons acceptors biocathode and revealing the EAM-MFC cathodic SND process.