| Volatile Organic Compounds(VOCs)are one of the important precursors of air pollutants.Toluene is widely used in petrochemical,painting and dyeing,chemical and pharmaceutical industries,and is a representative pollutant due to its high potential for ozone and secondary organic aerosol generation.In recent years,biological methods have been widely used in the treatment of VOCs at home and abroad.Among them,the accumulation of electrons generated by the biodegradation of toluene in cells is a key factor affecting the removal efficiency.Microbial Fuel Cell(MFC)can increase the rate of bioelectron conduction out of cells,thereby enhancing the microbial uptake and degradation of toluene.As the carrier of microorganisms,the anode of MFC plays the role of receiving and transmitting biological electrons,which is a key component.Carbon nanotubes(CNTs)are able to penetrate the cell membrane structure and promote electron transfer,which is an ideal choice for MFC anode materials,but CNTs are difficult to form three-dimensional structures.In order to use CNTs electrodes to enhance the conduction process of bioelectrons from microorganisms to electrodes,super-aligned carbon nanotubes(SACNT)were fabricated into SACNT sponge electrodes by a simple freeze-drying method to provide an efficient direct electron transfer channel for the electrons generated by the degradation of VOCs.At the same time,through the introduction of electron transfer intermediates,the indirect electron transfer process between microorganisms and electrodes was improved,thereby realizing the efficient enhancement of electron transfer in the process of MFC degradation of toluene,and the mechanism of SACNT-enhanced electron transfer was studied from different angles.The specific research results are as follows:An MFC was constructed with the SACNT sponge structure bioelectrode as the anode,which could generate electricity while removing toluene waste gas.At the maximum toluene injection concentration(10.34 g/m3),the peak current density of SACNT-MFC was 0.80 A/m2,which was about 1.94 times that of C-MFC(0.41 A/m2).The peak power density of SACNT-MFC was 0.384 W/m2,which was about 3.39 times that of C-MFC(0.113 W/m2).When the toluene exhaust gas was continuously injected,the removal efficiency and output voltage of SACNT-MFC were higher than those of C-MFC at different concentrations.The maximum coulombic efficiency of SACNTMFC could reach 3.51%,which was 1.6 times that of C-MFC.In addition,SACNT had micron-scale macropores with a BET specific surface area of 92.62 m2/g,which was suitable for microbial growth and reproduction.The biomass loaded on the SACNT bioelectrode was more than three times that of the carbon paper bioelectrode,and the biofilm formed hydroxyl groups to enhance the hydrophilicity and the uptake of toluene in the liquid phase.The results of the voltammetry curve showed that SACNT could enrich the electron transfer mode and strengthen the electron transfer process.The method and mechanism of enhancing indirect electron transfer in MFC system were studied,and the electron transfer kinetics were simulated.Adding the endogenous electron transfer intermediate pyocyanin to the anode chamber basically did not affect the removal efficiency of MFC to toluene,and could significantly enhance the output voltage of SACNT-MFC,which was a better way to strengthen the indirect electron transfer of SACNT-MFC.After adding 1 mg/L pyocyanin,the apparent internal resistance of SACNT-MFC decreased by 46.7%when 4000 mg/m3 toluene was injected.The Monod model fitting results showed that the maximum current density(IAmax)of C-MFC was 0.865 A/m2,the half-saturation constant(Ks)was 1252 mg/m3,and the maximum current density(IAmax)of SACNT-MFC was 0.954 A/m2,the halfsaturation constant(Ks)was 514.33 mg/m3.The lower Ks of SACNT-MFC indicated that the microorganisms in the system had a higher affinity for toluene,and the toluene molecules were more likely to enter the biological cells.Through high-throughput sequencing,biostatistical analysis and gene function annotation were used to study the mechanism of the enhanced MFC performance of SANCT sponge-structured bioelectrodes from the microbial level.The construction of the MFC,the injection method and concentration of toluene all affect the distribution of bacteria.After 35 days of continuous toluene exhaust gas injection,the distribution of bacterial species in SACNT-MFC was more uniform,and the proportion of electrochemically active bacteria was higher.Compared with carbon paper bioelectrodes,SACNT bioelectrodes could increase the diversity of species,improved the stability of the MFC system,and were more conducive to the long-term efficient and stable operation of the system.The results of gene function annotation showed that:after the film hanging of SACNT-MFC,the outer membrane receptor protein content was higher than that of C-MFC and the original flora and the content of methylases involved in ubiquinone/menaquinone biosynthesis was much higher than C-MFC after 35 days of continuous operation.This provided biological evidence that SACNT bioelectrodes enhanced direct and indirect electron transfer between organisms and electrodes... |
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