Environmental Adaptability Of Microbial Fuel Cell Coupled Aerobic Granular Sludge System Under Different Matrix Carbon Sources

With the continuous development of industrialization,the problem of air,land and water pollution has become increasingly prominent.The discharge of nitrogen and organic pollutants into water will not only cause serious damage to the ecology,but also cause irreversible damage to human health.Traditional wastewater treatment processes not only consume high energy,but also release large amounts of greenhouse gases during operation.Microbial fuel cells（MFC）can collect electrons produced during microbial metabolic processes,thereby converting chemical energy in organic pollutants into electricity.At the same time,aerobic granular sludge（AGS）has a rich biological structure and can achieve efficient nitrogen removal in the sewage treatment process.In this study,aerobic granular sludge（AGS）was coupled to the microbial fuel cell（MFC）cathode and two sets of microbial fuel cell-aerobic granular sludge（MFC-AGS）systems of the same specification were constructed,with sodium acetate（a）and glucose（b）as organic carbon sources,respectively.The changes of power generation efficiency,pollutant removal rate and microbial biomass in the anode chamber of MFC-AGS（a）and MFC-AGS（b）systems were explored under different operating temperatures and influent pH environments,and biodiversity and metabolic pathways were analyzed by high-throughput sequencing technology.Subsequently,the artificially configured anode liquid was switched to comprehensive domestic wastewater to test the versatility and specificity of substrate utilization by anode microorganisms raised on different types of substrates.The main experimental results are as follows:（1）By varying the operating temperature,the performance of both MFC-AGS systems fluctuates to varying degrees.Among them,MFC-AGS（a）had the best performance of carbon and nitrogen removal synergy power production in the environment of 30～32°C,with a COD removal rate of 93.54%and a removal rate of NH₄⁺-N of 85.06%.The peak voltage reached during the operating cycle is 785 m V,and the maximum output power density is 332.82 m W/m²;The coulomb efficiency is30.6%.At the same time,the anode microbial community enriched the most electrogenic bacteria under this condition.At the phylum level,the total relative abundance of Firmicutes,Proteobacteria,and Bacteroidota with electrochemical activity was 74.2%;At the class level,the relative abundances of Clostridia,Bacilli,Alphaproteobacteria,Gammaproteobacteria,Anaerolineae and Bacteroidia as representatives of electrochemical strains were 30.7%,23.6%,18.6%,0.9%,2.3%and 0.6%,respectively.The MFC-AGS（b）needs to achieve the best carbon removal and power production performance in an environment of 33～35°C,the COD removal rate at this time is 89.84%,the peak voltage reached during the operating cycle is 771m V,and the maximum output power density is 327.68 m W/m²;Coulomb efficiency was 21.8%;However,the removal rate of NH₄⁺-N under this condition is slightly lower than the removal rate of NH₄⁺-N at 30～32°C.In addition,the total relative abundance of Firmicutes,Proteobacteria,and Bacteroides enriched in the anode microbial community was 74.0%.The relative abundances of Clostridium,Bacillus,α-Proteobacteria,γ-Proteobacteria,Anaerolineae and Bacteroidia were 25.2%,19.8%,6.9%,1.2%,3.7%and 20.8%,respectively.As the main function of microbial metabolic pathway,metabolism mainly includes carbohydrate metabolism and amino acid metabolism,and its relative abundance was also highest under the optimum temperature conditions of the two groups of MFC-AGS systems,which are B1（17.8%）and C2（17.7%）,respectively.（2）The operating temperature of MFC-AGS（a）and MFC-AGS（b）was controlled at 30～32°C and 33～35°C,respectively,and then the influent pH was adjusted to 5,7,9 and 11 by HCl and Na OH,respectively.The results show that both MFC-AGS systems achieve the best performance output under the condition of pH=9in the influent water.Among them,the COD removal rate of MFC-AGS（a）was95.73%,and the removal rate of NH₄⁺-N was 89.24%.The peak voltage reached during the operating cycle is 814 m V and the power density is 381.81 m W/m²;The coulomb efficiency is 34.0%.The COD removal rate of MFC-AGS（b）under this condition was 94.13%;The removal rate of NH₄⁺-N was 85.46%;The peak voltage reached during the operating cycle is 792 m V and the power density is 345.04m W/m²;The coulomb efficiency is 24.4%.Under these conditions,the total relative abundances of Firmicutes,Proteobacteria and Bacteroidota in the two groups of MFC-AGS anode microorganisms also reached the highest values,80.1%and 76.0%,respectively.At the class level,the relative abundance of Clostridia,which can decompose carbohydrates and is closely related to the peak voltage of the MFC system,changed significantly in each group,and the specific distribution was E1（25.6%）,B1（30.7%）,F1（55.8%）,and G1（11.3%）.E2（14.1%）、C2（25.2%）、F2（33.8%）、G2（37.2%）。The relative abundance of Carbohydrate metabolism and amino acid metabolism in the second level of the metabolic pathway in each group of samples can always maintain a certain homeostatic range,which may be that microorganisms can secrete inhibitory amino acid metabolism during carbohydrate metabolism metabolism)functional substance.（3）Based on the above two experiments,the performance of the two groups of MFC-AGS systems has undergone great changes after ensuring that the MFC-AGS（a）and MFC-AGS（b）systems switch the artificially equipped anode liquid to comprehensive domestic sewage in their respective optimal environments.Overall,the MFC-AGS（a）system is more severely affected.Due to the NO₃^--N content in the new anode liquid and the possible presence of residual dissolved oxygen,the NH₄⁺-N content of the anode effluent is reduced.In addition,the COD removal rate of MFC-AGS（a）was 73.59%,and the removal rate of NH₄⁺-N was 73.41%.The peak voltage reached during the operating cycle is 216 m V,the power density is 59.85m W/m²,and the coulomb efficiency is 8.7%;The COD removal rate of MFC-AGS（b）under this condition was 80.10%;The removal rate of NH₄⁺-N was 83.51%;The peak voltage reached during the operating cycle is 332 m V and the power density is 68.64m W/m²;The coulomb efficiency was 16.7%.The presence of more complex complexities in glucose-fed anode microbial communities demonstrates versatility and specificity for substrate utilization,and is more adaptable to the complex composition of integrated domestic sewage.