The Influence Of Electrode Structure On The Electron Distribution In MFC Cathode Denitrification

The device of microbial fuel cell can convert chemical energy in organic matter into electrical energy under the catalysis of microorganisms.Coupling MFC with a conductive membrane aerated bioreactor,the MFC cathode simultaneous nitrification and denitrification was realized in this coupled system.Previous studies have shown that due to the insufficient structure of the cathode electrode,the electronic competition between O₂ and NOx-N leads to a decrease in the nitrogen removal performance of the system.In order to solve the effect of electrode structure on denitrification,the relative spatial position relationship between the conductive layer of the cathode electrode and the surface of the aeration film was changed,which were 0?m,90?m,and 230?m,respectively.Based on the analysis of the electrochemical performance,carbon removal and nitrogen removal,NOx-N accumulation and TN removal capacity under different influent loading conditions,the effective utilization efficiency of oxygen reduction and denitrification electrons was evaluated,and different groups of organisms were analyzed.Succession of microbial community in the membrane,and the electron distribution mechanism of EAM-MFC cathode denitrification process was analyzed to obtain the optimal electrode structure.The results showed that during the start-up of the reactor,the time gradually increases as the distance between the surface of the aeration membrane and the conductive layer in the electrode structure increases.At a distance of 0?m,the reactor achieved a stable output voltage of 390.0±10.5 m V within 15 days first,and the TN removal effect was 63.18±3.12%.Due to the equilibrium time between the microbial aggregation speed and the bacterial flora competition,when the distance increased to90?m and 230?m,it was completed around 18 days and 22 days,respectively.Under the optimal operating conditions,as the carbon-nitrogen ratio of the feed water decreases,the cathode denitrification capacity of each reactor weakens.When the carbon-nitrogen ratio was 3.75,the optimal TN removal rate of G2 was 78.12%.When the distance increased to 230?m,the microbial community was more abundant,the biochemical performance was the most stable,and the TN removal effect was the smalest.This indicated that the change in the structure of the cathode improved the adaptability of the reactor to a low-carbon environment.When the distance between the surface of the aeration membrane and the conductive layer in the cathode structure was 90?m,the highest utilization rate of denitrification electrons was 66.69%.This showed that the conductive layer was located at the optimal position between the aerobic layer and the anaerobic layer in the biofilm at this time,the oxygen reached equilibrium between the nitrification and the reduction reaction,but also the electrons between oxygen and NOx-N.Based on electrochemical,chemical,and microbial analysis,as the distance increases,the main electron acceptor converted from O₂ to NO₃-N in the reaction.Oxygen consumed by nitrifying organisms may reduce its availability on the surface of the carbon fiber conductive layer,thereby changing the cathode compartment from oxygen-dominated reduction reactions to denitrification dominated.16S rRNA gene high-throughput sequencing analysis of the cathodic biological flora showed that the main species of nitrification and denitrification,Thermomonas and Nitrosomonas,were more abundant in the three groups of reactors.With the change of the structure of the cathode electrode,the dominant species in the biofilm have changed,mainly from the oxygen-reducing bacteria Thauera and Desulfobulbus when the spacing is 0?m,and evolved to 90?m and 230?m,mainly AOB and NOB bacteria such as Commamonas and Simplicispira.