Effects Of Operating Microbial Fuel Cells On Methane Emissions,Electricity Generation And Microorganisms In Constructed Wetlands

Constructed wetland(CW)is one of the important sources of greenhouse gases in nature.As one of the main components of greenhouse gases,the greenhouse effect of CH₄is 20 to 30 times that of CO₂.Therefore,controlling CH₄ emissions from CW is of great significance to mitigate the greenhouse effect.This study explored the electrochemical method for regulating CH₄ emissions from CW.The use of microbial fuel cells(MFC)coupled with CW to conduct CH₄ emissions-related research.Constructed wetland microbial fuel cell(CW-MFC)test device was constructed.Under different operating modes(sequence batch mode and continuous flow mode),the operation of MFC and the rhizosphere position of plants to the coupling system CH₄ emission flux,Effects of electricity generation performance,water quality characteristics,and microbial morphology and structural characteristics.The main conclusions are as follows:In terms of CH₄ emissions,running MFC in CW can effectively suppress CW's CH₄emissions.When the external resistance was fixed,the CH₄ flux emissions of the plant rhizosphere located in the cathode system were lower.The smaller the external resistance,the better the effect on suppressing CH₄ flux emissions in CW.When the external resistance was 50?and the circuit was open,the CH₄ emission flux of the power generation group was the smallest(the rhizosphere was at the anode:0.91 mg·m²·h^-1,and the rhizosphere was at the cathode:0.60 mg·m²·h^-1)and maximum(the rhizosphere was at the anode:2.06 mg·m²·h^-1,the rhizosphere was at the cathode:2.15 mg·m²·h^-1).The longer the hydraulic retention times(HRT),the more significant the effect of CW-MFC on suppressing CH₄ emissions.When the HRT was 24 h,the CH₄ emission fluxes of the control group and the power generation group(the rhizosphere were at the anode and cathode)were 95.57,33.01,and 29.20 mg·m²·h^-1,respectively.When the HRT was 96 h,the reactor methane.The minimum emission fluxes were 2.20,1.39,and 1.23 mg·m²·h^-1.In terms of power generation performance,plant rhizosphere location had a significant impact on electricity generation performance.Under the same external resistance(except for 1 K?and 50?),the plant rhizosphere had higher power density,coulomb efficiency(CE)and current density when it was located at the anode.When the external resistance was 50?,the CEs of the rhizosphere located at the anode and the cathode reached 11.84%and 11.99%,respectively.When the external resistance was 1 K?,the maximum output power density was 73.32 m W·m^-3 and 59.43 m W·m^-3,respectively.Under the same HRT,the rhizosphere of the plant was located at the anode and had a higher output voltage.With the extension of HRT,both the maximum power and CE increased.In terms of water treatment efficiency,the effect of running MFC on DO and ORP was significant,and the effect of plant rhizosphere position on p H and DO was not significant.The change and distribution trend of ORP was about the same as that of DO.Running MFC significantly improved the COD removal rate,and the COD removal rate of the power generation group reached more than 95%.Three-dimensional fluorescence analysis showed that a large amount of soluble microbial by-products and aromatic proteins were produced in the reactor effluent,and the electricity generation function enhanced the removal of such substances.Both MFC operation and rhizosphere location had significant differences in the product types and concentrations of effluent during the degradation process.The longer the HRT,the better the COD removal effect.In terms of microbial characteristics,scanning electron microscopy(SEM)results showed that the bacterial density in the control group was lower than in the electricity generation system.Rod-shaped bacteria dominated the anode of the electricity-generating reactor.The cathode was mainly composed of coccus.Running MFC and plant rhizosphere position as well as external resistance and HRT caused significant differences in bacterial and archaeal community structure.In terms of bacterial community structure,when exploring the external resistance,Gammaproteobacteria and Nitrospira were the dominant bacteria in the cathode of the electricity-producing group and the control group,respectively.Betaproteobacteri,Gammaproteobacteria and Deltaproteobacteria were the dominant bacteria in the anode of the reactor.When exploring HRT,the mainly dominant bacteria in the anode and cathode of the reactor were:Betaproteobacteria,Alphaproteobacteria,Gammaproteobacteria,Planctomycetacia,Acidimicrobiia and Anaerolineae.Archaea community structure:When exploring external resistance,Methanosarcinales,Methanobacteriales and Desulfurococcales were the dominant bacteria in the reactor at the anodic order level;when exploring HRT,Methanobacteriales,Methanosarcinales,Halobacteriales and Methanomicrobiales were the dominant bacteria in the reactor.