Enhanced Microbial Extracellular Electron Transfer Process Of Electrochemical Active Bacteria And Mechanism Analysis

The microbial extracellular electron transfer(EET)process is an important biological process in the nature,which also plays an key role in the environmental area.The EET process exists in both the anaerobic wastewater treatment system and water/soil restoration system and deeply influences the microbial activity in the wastewater treatment and environment restoration process.The EET rate is one of the most important factors that determine their effect on the microbial activity;and the fast EET rate could greatly promote the corresponding microbial electrochemical activity,which would increase their pollutants removal rates and environment restoration ability.In this study,the EET process is identified as the study subject,with the specific steps of direct EET process being analyzed;it could be very meaningful in both practice and theory to investigate the enhancement method and corresponding mechanism.About the electron transfer process from cell to the electrode,the EET rate was analyzed by the three-electrode system as the detection platform;the results showed that the prepared carbon quantum dots could increase the electroactivity of cytochrome c on the cell membrane,which enhanced the electron transfer ability of cell,the peak current increased to 39.48?A,which was 5.13 times of the control one.Otherwise,the carbon quantum dots addition can also facilitate the flavin secretion,wich the riboflavin concentration increased to 1.09 mg/L,4.19 times of the control one,which promoted the indirect EET process.Otherwise,this study utilized the double-chamber microbial fuel cell(MFC)as the research platform and explored to regulate the electron transfer process and metabolic way of electroactive bacteria by adding fumarate;the indirect EET process of Shewanella was restrained to transform the metabolic way to the pattern with fumarate as the electron acceptor,which could quicken the metabolic rate of Shewanella and increase the biomass concentration of Shewanella;when the lactate concentration was 18 mM and 9 mM fumarate was added into the anode chamber,the maximum voltage increased from 123 mV to 339 mV,the anode surface biomass increased from 74.61?g/cm~2 to131.72?g/cm~2,the OD600 increased from 0.15 to 0.25,the ratio of anode biomass to the total biomass increased from 9.29%to 13.22%.However,the riboflavin concentration was only 0.10 mg/L with the fumarate addition,much lower than that of the control one(0.25 mg/L),which could inhibit the indirect EET process.About the interspecies direct electron transfer process,the biochar derived from surplus sludge was utilized as the exogenous mediator and the Geobacter coculture system with the interspecies electron transfer ability was utilized as the detection platform;the results showed that the prepared biochar could promote the interspecies electron transfer process;the facilitation effect increased with biochar dosage,when the Biochar-700 addition increased to 2 g/L,the ethanol consumption rate and succinate production rate increased to 0.23 mM/d and 2.37 mM/d,which were 2.09 and 2.59times of the control one,respectively.The results of the facilitation effect of the biochar of different showed no positive relationship with the bichar conductivity but with the oxygen element content(R~2=0.90),indicating that the oxygen-containing surface functional group played an important role in promoting interspecies electron transfer process.Otherwise,the research also found that the morphology and surface charge can also influence the facilitation effect on the interspecie electron transfer process.Otherwise,the MWCNT(Multiwalled carbon nanotube)was also added into the system of Geobacter cocultures;the results showed that the facilitation effect of MWCNT on direct electron transfer increased with the MWCNT dosage increasing from 0 to 1.5 g/L and decreased with higher MWCNT concentration.MWCNT enchanced the direct electron transfer by the conductivity property.Based on above results,the“adsoption-filtration”process was applied to prepare the MWCNT inserted hybrid biofilm,whose EET performance was determined by the single-chambern MFC;the results showed that this hybrid biofilm can enhance the EET ability of the anode biofilm,with the maximum current increased from 0.51 mA(the control)to 0.73 mA,with the maximum power density and coulombic efficiency increasing to 1.13 W/m~2 and 44.9%;the start-up period was shortened by 53.8%to 13days.The specific mechanism analysis showed that the MWCNT insertion can reduce the resistance of the electron transfer through the biofilm,with the charge transfer resistance being reduced by 47.96%to 2.17?,indicating that the inserted MWCNT reducded the trans-biofilm resistance.The microbial community analysis showed that the inserted optimized the community structure and increased the microbial diversity.