The Mechanisms Of Microbial Response And Efficiency Improvement Of Wastewater Treatment In Microbial Fuel Cell By An Energy Harvesting Approach

Microbial fuel cells（MFCs）are a combination of microorganisms and electrochemical reaction devices,which can treat sewage and achieve energy recovery.How to enhance the power output and pollutant degradation efficiency of the system,and how to analyze the microbiome aggregation and metabolic function regulation mechanism of electroactive biofilm on the surface of MFC electrode is still one of the scientific problems to be solved in the practical application of MFC.Active energy harvesting（AEH）can control energy harvesting and storage of MFCs in real time,which is a new type of microbial electrochemical system control technology.However,the regulatory efficacy of AEH on MFC and the response mechanism of electroactive biofilms on electrode surface under different ecological conditions are still unclear and need further research.Therefore,in order to analyze the regulation mechanism of active energy harvesting on MFCs,this paper carried out the construction of active energy harvesting microbial electrochemical system（AEH-MFCs）.The effects of different AEH methods on the treatment efficiency of domestic sewage and juice wastewater were studied,and the carbon and nitrogen efficiency of MFC coupled electric-flocculation（EC）process for domestic sewage was discussed.Based on functional microbiome techniques,the aggregation and functional response mechanisms of AEH-MFCs and non-AEH-MFCs anodic biofilm communities were analyzed.Firstly,the power output and substrate degradation efficiency of MFCs were compared under different temperature conditions（4℃,10℃,20℃and30℃）.The results showed that the higher temperature got the higher the power output and coulombic efficiency（CE）of MFCs,and the output power of MFC was 894.3m W/m² at 30℃.It is 528.7 m W/m² at low temperature of 4℃.Similarly,the CE dropped from 24%to 16.1%.In order to improve the power output and energy utilization of MFC,the maximum power point（MPP）,the maximum current point（MCP）and open circuit conditions（OCV）of single-chamber air cathode MFC were selected for comparative analysis.The results show that MFC achieves the highest power density of 8.1～9.3 m W/cm² and the highest substrate utilization efficiency of 94.92±0.96%under the MPP condition.On this basis,the regulation of MFC operating efficiency under different MPP energy harvesting modes at 4℃and 10℃were discussed,respectively.Based on dual-chip energy harvesting control,the operating efficiency of MFC at constant MPPT,80%MPPT and MPPT tracking is compared.It is found that the maximum power output of MFC is 714.36±54.36 m W and 1942.18±84.78 m W at 4℃and 10℃,respectively.The improved MPPT control strategy based on adaptive PID control can accurately track the maximum power point of different environmental conditions in real time,so as to ensure the efficient operation of microorganisms.Compared with AEH-MFCs with constant MPP,AEH-MFCs can obtain more energy and higher CE～4.3%.Secondly,the effects of different MPP energy harvesting methods on MFCs treatment of different types of wastewaters were explored.The efficiency of AEH-MFCs in treating juice wastewater with different organic concentrations of1500 mg/L,3000 mg/L,7500 mg/L and 15000 mg/L was investigated.The results show that the power output of MFC-MPP is relatively stable at 239.64-308.67 m W/m² under different organic concentration conditions.The volatile fatty acids（VFAs）produced by AEHs were formic acid,acetic acid and butyric acid.Then,the effect of carbon and nitrogen removal in domestic sewage was compared and analyzed at 4^oC and 10^oC,respectively.It was found that the total carbon removal efficiency of MFC at 10℃and 4℃was 52.51±1.65%and40.46±1.92%,respectively.The removal efficiencies of H₄⁺-N were61.46±2.91%and 47.10±1.42%,respectively.The efficiency of MFCs as EC（M-EC）and AEH-MFCs as EC（T-EC）power supply for low-temperature domestic sewage treatment was compared.It was found that the current output obtained by AEH-MFCs-EC coupling system was significantly higher than 60%of the current obtained by MFCs-EC system.Finally,in order to explore the response mechanism of anodic electroactive biofilms to changes in active energy harvesting,the metabolic function differences of MFCs anodic biofilms at different temperatures were analyzed using genomics.Temperature significantly affected microbial community structure and functional metabolism,and the abundance of genes related to cell wall production and defense mechanism was higher at 4℃.The abundance of genes related to translation and ribosome structure and formation was higher at20℃,while the expression level of genes related to translation and ribosome structure and formation was lower at 30℃.Principal coordinate analysis showed that AEH-MFCs electrode biofilm community structure was significantly difference.Proteobacteria was the dominant phylum in all the reactor microbial communities,and its relative abundance ranged from 31.72 to 63.32%.The relative abundance of electrochemically active bacteria Geobacter in MCP and MPP reactors reached 18.59%and 20.92%,respectively,indicating that AEH-MFC can promote the enrichment of electroactive bacteria in anodic biofilms.In the part of juice wastewater treated by AEHs,community analysis results showed that fermentation bacteria Lactococcus accounted for the highest proportion and its relative abundance was 19.42-37.88%.The relative abundance of Lactococcus does not increase with the increase of OLRs,indicating that AEHs operation mode plays an important role in its enrichment,and fermentable substrates in AEH-MFC system promote the growth of non-electroactive bacteria.The results showed that energy acquisition,temperature and OLRs had significant effects on the aggregation and functional metabolism of electroactive microbial community,and energy acquisition and organic load had synergistic effects on microbial community succession.