| Microbial fuel cell（MFC）is widely concerned because it can remove pollutants and recover electric energy at the same time.In the field of wastewater treatment,nitrogen removal is an important part.Double chamber MFC can consume COD and generate power at the anode,and at the same time carry out cathodic biological nitrogen removal,which provides a new idea for wastewater nitrogen removal.Because the technology restricts the capacity of MFC,and the nitrogen removal rate in MFC is also low.In this study,a technology combining magnetic field and MFC was proposed to solve the problem of MFC power generation performance and nitrogen removal,in order to provide theoretical support for improving the power generation performance and nitrogen removal capacity of double chamber MFC.The main conclusions are as follows:（1）Four groups of double chamber MFCs were applied with 20 mT magnetic field respectively in the way of no magnetic field,anode magnetic field,cathode magnetic field and two poles magnetic field.The power generation performance and nitrogen removal ability of MFCs started under different magnetic field application methods were compared.The results show that:compared with the control group MFC-0,the start-up speed of MFC-A is faster,the average peak voltage increases from 400m V to442 m V,and the maximum power density increases from 123.01 m W/m2 to 145.92m W/m2,and the removal rate of COD and TN increased from 87.46%to 92.24%and54.75%to 57.75%respectively.The average peak voltage and maximum power density of MFC-C were 414 m V and 132.09 m V respectively under the condition of magnetic field applied on the cathode,and the removal rate of COD was 88.20%,and the TN removal rate increased from 54.75%to 59.52%.Under the combined action of the two magnetic fields,MFC-AC achieved the best power generation performance and nitrogen removal capacity,with the average peak voltage,maximum power density,anode COD removal rate and TN removal rate of 456m V,165.89 m W/m2,92.61%and 60.22%respectively.The effect of magnetic field on MFC is unsustainable but reversible.When the magnetic field is removed,the power generation performance and pollutant removal rate of MFC will decrease correspondingly.With the application of magnetic field again,the power generation performance and pollutant removal rate of MFC will be restored.（2）The effects of magnetic fields of 0 mT,20 mT,40 mT,80 mT and 140 mT on the power generation and nitrogen removal performance of double chamber MFC were investigated.Based on the characteristics of microorganisms,the mechanism of different magnetic fields on MFC was further analyzed.The results show that:under the condition of low magnetic field（≤80mT）,the operating characteristics of MFC-140increase with the increase of magnetic field strength,and with the further increase of magnetic field strength to 140mT,the operating characteristics of MFC-140 decrease slightly compared with that of MFC-80 under 80mT.The average peak voltage and maximum power density of MFC-80 are 529 m V and 249.64 m W/m2,respectively;the removal rates of COD in anode,COD in cathode,NH4+-N and TN are 94.17%,92.14%,95.38%and 63.32%,respectively.Proteobacteria,Xanthobacteria and SM1A02 were the most abundant genera of anode and cathode microbial communities in all groups.After the magnetic field was applied,the community abundance of dominant bacteria increased in varying degrees.The higher magnetic field intensity promoted the biomass growth of MFC,and enhanced the activities of anode dehydrogenase and cathode denitrifying enzyme.（3）When magnetic field was applied to double chamber MFC anode to enhance MFC power production,the biological activity of cathode microbial community was enhanced under the effect of enhanced current,and the amount of electrons transferred from anode to cathode was increased,and the amount of available electrons received by denitrifying bacteria increased,which indirectly enhanced the denitrification ability of MFC cathode.Magnetic field was applied to the cathode of double chamber MFC to enhance the denitrification ability of MFC.At the same time,the electron utilization rate of the cathode bacteria increased,which accelerated the electron transfer process,resulting in the accelerated degradation of COD by the anode electricity producing bacteria,which indirectly enhanced the electricity producing ability of double chamber MFC.（4）The electrophilic denitrifying microbial bacteria can use the electrons transferred from the anode to the cathode and nitrate as the electron acceptor to achieve denitrification.Two groups of denitrifying MFC were constructed,one group as control（CK group）and the other group applied 80 mT magnetic field（M group）.The effects of acclimation process of denitrifying bacteria and gradual change of external resistance on electricity production and denitrification ability of denitrifying MFC were investigated,and the differences of electricity production and denitrification ability of MFC with or without magnetic field were compared.The results show that:when the cathode carbon nitrogen ratio is reduced to 0,the power generation performance of MFC in both groups is the best,and the power generation performance of group M is better than that of group CK;the NO3-N removal rate of MFC in both groups is significantly reduced,and the NO3-N removal rate of group M is higher than that of group CK;the maximum accumulation concentration of NO2-N increases,and the maximum accumulation concentration of NO2-N in group M is lower than that of group CK.With the decrease of external resistance,the NO3-N removal rate of MFC in both groups increased first and then decreased.The maximum NO3-N removal rate of group M was 59.76%when the external resistance was 100Ω,and the maximum NO3-N removal rate of group CK was 31.20%when the external resistance was 200Ω. |
