Treatment Mechanism Of Agricultural Wastewater By Constructed Wetland Microbial Fuel Cell Coupling System

Energy shortage and environmental pollution are two major problems facing the world today,especially in the vast rural areas and small towns in economically backward areas,where the lack of effective treatment of agricultural production wastewater is becoming more and more serious.Therefore,developing simple,practical,economical and efficient treatment methods for agricultural production wastewater has gradually attracted attention.In view of this,the constructed wetland(CW)and microbial fuel cell(MFC)are compatible in structure and function,and the constructed wetland-microbial fuel cell coupling system(CW-MFC)is constructed and applied to the treatment of agricultural production wastewater.CW-MFC coupling system combines the advantages of CW system and MFC system,which can improve the processing capacity and productivity of the system,and has broad development prospects in the field of water treatment.In this study,the treatment characteristics,electricity production performance,substrate enzyme activity and microbial community structure of CW-MFC coupling system were analyzed,and the energy efficiency of the system was comprehensively evaluated on the basis of determining the optimal hydraulic retention time of the system and taking the Atrazine concentration as a variable.Finally,by comparing and analyzing the treatment characteristics,electricity production performance,substrate enzyme activity and microbial community structure of CW-MFC,CW and MFC systems,the synergy between CW system and MFC system was clarified.Through this study,the following conclusions are drawn:1、According to the processing characteristics and power generation performance of CW-MFC coupling system under different HRT conditions,the optimal HRT of the system is determined to be 8 days.2、Under different Atrazine concentrations,the COD removal rate,TN removal rate and catalase activity in CW-MFC coupling system were significantly affected by atrazine,while TP removal rate,Atrazine removal rate,urease activity and alkaline phosphatase activity were relatively stable.In the concentration range of 2～8 mg/L Atrazine,the removal rates of COD,TN,TP and Atrazine in the system reached39.5～54.3%,39.7～53.2%,64.4～68.0%and 78.7～86.9%.The maximum power density is 19.64m W/m~3and the average voltage is 284.4m V when Atrazine concentration is 4 mg/L.The activities of urease,alkaline phosphatase and catalase reached 0.14～0.24mg/(10g.24h),0.25～0.31mg/(g.24h)and 1.06～1.29m L/g,respectively.3、In CW-MFC coupling system,the diversity of microbial community was significantly affected by Atrazine concentration.Proteobacteria is the dominant phylum of the system,and Thick-walled phylum is the dominant electrochemically active phylum of the system.The dominant phylum for degrading Atrazine is Actinomycete,Spirogyra and Micromycota verrucosa.The dominant phylum is Alphaproteobacteria and Actinobacteria,and the dominant genus is Christensenellaceae＿R-7＿group.The primary function of microorganisms in the system is mainly metabolism,while the secondary function is mainly amino acid metabolism,carbohydrate metabolism,cofactor and vitamin metabolism,etc.Atrazine has a certain influence on microbial community function,but it is not significant.4、The coupling of CW and MFC system can promote the treatment performance of COD,TN,TP and Atrazine,and the activities of urease and catalase,while Atrazine inhibition can promote the treatment performance of COD,TN and Atrazine.The micro-electric field for COD,TN and urease was greater than that for plants,but less for TP.The promotion for catalase activity of Atrazine was different according to the concentration of Atrazine.As far as alkaline phosphatase activity is concerned,when the concentration of Atrazine is less than 2mg/L,the coupling of the system can enhance the activity,and the promotion effect of plants is greater than the micro electric field.When the concentration of Atrazine is greater than 4mg/L,only plants can promote its activity,and the activity is not affected by the concentration of Atrazine.The coupling of the system can effectively promote the power generation performance of the system,and its promotion effect is strongest when the concentration of Atrazine is 4 mg/L.5、The coupling of CW and MFC system can significantly improve the diversity of microbial community.Among them,the phylum Acinetobacter,Deltaproteobacteria,Aquabacterium,Geobacter and Subgroup＿6,etc,are affected by plants and micro-electric fields,and their abundance has increased to varying degrees.In addition,microbial functions such as metabolism of terpenoids and polyketones and biosynthesis and metabolism of polysaccharides are affected by plants and micro-electric fields,and their abundance is improved.The coupling of CW and MFC system has a good synergistic effect,which significantly improves the treatment effect of agricultural production wastewater and synchronous power generation performance of CW-MFC coupling system.