| In recent years,with the growing world population and the increasing development of the world economy,energy consumption and fuel use inevitably rise with it,which leads to the growing problem of insufficient energy supply in the world,and exploring green alternative renewable energy sources becomes a hot topic.In this thesis,we explored the biomethanation potential of peat as a substrate and built a bioelectrochemical anaerobic digestion(BEAD)system with the goal of improving the efficiency of peat methanation,explored the efficiency of enhanced peat methanation by the bioelectrochemical system under different conditions,and derived the preliminary optimization conditions for peat biomethanation.This thesis is the first application of the BEAD system for enhanced biomethanation of peat,aiming to identify feasible conditions for resource utilization of peat and to contribute to alleviating the energy crisis.In this thesis,the changes of methane yield and content and various microbial communities of peat in the bioelectrochemical anaerobic digestion system under different conditions imposed were investigated.The study and main results are as follows:(1)The mechanism of BEAD-enhanced peat methanation was investigated.Anaerobic digestion(AD)was selected as the control group and bioelectrochemical anaerobic digestion(BEAD)as the experimental group.In conventional anaerobic digestion,methane is mainly produced through intermediates via the indirect interspecies electron transfer(IIET)pathway,and methane production in the bioelectrochemical system is attributed to the direct interspecies electron transfer(DIET)pathway.In bioelectrochemical systems,an electric field is generated between the counter electrodes,which activates the entire electroactive microorganism in the entire reactor system,thus activating the DIET pathway in the reactor solution.Among them:the maximum methane production of the BEAD reactor was 90.4 m L CH4/L.d,which was about two times higher than that of the AD reactor,the alkalinity was stable at 7405 mg/L,which was higher than that of the control reactor at 6015 mg/L,and the COD and VS removal efficiencies were 65.8% and 74.0%,respectively,which were higher than those of the control at 50.1% and 61.3%,and the BEAD reactor was at 0.36 Therefore,the bioelectrochemical system can enrich electroactive microorganisms through electrodes and activate the DIET pathway in the reactor solution by generating an electric field to activate electroactive microorganisms in the reactor solution under a variety of conditions mentioned above,thus greatly enhancing the electron transfer efficiency and thus enhancing the BEAD system’s degradation capacity and improve the methane yield.(2)Enhanced methanation of peat by bioelectrochemical systems under different voltage conditions was investigated.Four reaction groups of 0.5V,1V,2V and 4V were selected for the voltage,and only the electrodes were added as the control group.The results showed that bioelectrochemical anaerobic digestion significantly improved the biodegradation and biomethanation efficiency of peat.The methane production of the BEAD reactor was 264 m L/g peat at a voltage of 4 V,which was significantly higher than that of the control reactor at 16 m L/g peat.the BEAD reactor had a lower solution internal resistance and charge transfer resistance,which improved the electron transfer efficiency of methane production.The abundance of electroactive bacteria Firmicutes and Proteobacteria increased significantly,while the acetic acid methanogenic pathway increased gradually with increasing voltage and the efficiency of peat biomethanation increased significantly.(3)Enhanced methanation of peat by bioelectrochemical systems under different electrode catalyst conditions was investigated.Various parameters of the BEAD system in each reactor were investigated for iron,cobalt,nickel,mixed nickel-cobalt and mixed iron-cobalt-nickel materials as catalysts,among which the best methane production was achieved in the mixed iron-cobalt-nickel group with 237.32 m L and the highest content of 62.09 %,and the stability indexes of the BEAD system such as p H and COD degradation rate were more balanced and stable,and the methane production in CV This indicates that the addition of the appropriate ratio of Fe Co Ni as the electrode catalyst can enhance the direct interspecies electron transfer including on the electrode and in the solution,improve the activity of electroactive bacteria,and make the methanogenic bacteria more active,leading to the further improvement of methane production rate.In general,this thesis explores(1)peat biomethanation potential experiments,(2)oxidation mechanism of peat,(3)effect of different potential conditions on BEAD-enhanced peat methanation,and(4)effect of different catalysts on BEAD-enhanced peat methanation,using peat as substrate,and explores various characterization means,including various water quality indicators,gas yield and content,SEM characterization,electrochemical analysis,microbial community and prediction of metabolic pathways to elucidate the mechanism of BEAD-enhanced peat biomethanation,elaborate the dominant electron transfer pathway of direct intermediate electron transfer in BEAD-enhanced peat,reveal the key roles of various electroactive microorganisms in BEAD-enhanced peat methanation,and validate the experiments by SEM analysis and the abundance of gene metabolic pathways results. |
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