Study On The Effect Of MnFe₂O₄ Nanoparticles On The Process Of Hydrogen And Methane Production From Anaerobic Fermentation

Anaerobic digestion technology is considered a sustainable green energy technology.In this study,conductive nanoparticles-MnFe2O4 NPs were prepared by the co-precipitation method,which were used as additives and added to the anaerobic digestion（AD）reactor to achieve the purpose of enhancing the performance of AD.MnFe2O4 NPs changed the microbial composition of AD sludge,improved interspecific electron transfer,and increased the yield of biogas（H2,CH4）.In the process of AD,the accumulation of VFAs promoted the release of trace elements from MnFe2O4 NPs to promote the growth and metabolism of gas-producing microorganisms.The main conclusions of this research are as follows:（1）The effect of MnFe2O4 NPs on the performance of hydrogen production by mesophilic anaerobic fermentationUsing the easily biodegradable glucose as the fermentation substrate,hydrogen production was carried out at mesophilic（37℃）by adding（20,50,100,200 and 400 mg/L）MnFe2O4 NPs to the anaerobic bioreactor.The results show that 400 mg/L of MnFe2O4 NPs has the most obvious effect on improving the hydrogen production performance of anaerobic fermentation in the process of hydrogen production by medium temperature fermentation.The highest biohydrogen production rate reached 272.7 mL H2/g glucose,which was 40.1%higher than the control group.MnFe2O4 NPs significantly increased the activity of hydrogenase in the anaerobic fermentation,which was 28 times that of the control group.The results of microbial population structure analysis showed that MnFe2O4 NPs can change the microbial population structure and enrich the hydrogen-producing bacteria Clostridium_sensu_stricto₁ and Clostridium_sensu_stricto₇.In this experiment,it was not observed that MnFe2O4 NPs could inhibit the biological hydrogen production by anaerobic digestion at moderate temperature.（2）The effect of MnFe2O4 NPs on the performance of thermophilic d anaerobic fermentation for hydrogen productionUsing glucose as the substrate of anaerobic fermentation,hydrogen production by high temperature（55℃）fermentation was carried out by adding（20,50,100,200 and 400 mg/L）MnFe2O4 NPs to the anaerobic bioreactor.The results show that MnFe2O4 NPs can significantly improve the high-temperature anaerobic fermentation hydrogen production.The addition of 400 mg/L MnFe2O4 NPs in the anaerobic reactor has the most obvious enhancement effect on the high-temperature anaerobic biological hydrogen production,and the highest biohydrogen production rate has been reached 183.4 mL H2/g glucose,an increase of 131.9%compared to the control group.In the thermophilic anaerobic fermentation reactor,400 mg/L MnFe2O4 NPs increased the activity of hydrogenase to 7.2 times that of the control group.Comparing the hydrogenase activity of anaerobic fermentation sludge at mesophilic and thermophilic,it was found that the hydrogenase activity was 5 times that of mesophilic fermentation under thermophilic fermentation conditions.The results of microbial population structure analysis showed that MnFe2O4 NPs changed the microbial population and increased the relative abundance of Clostridium_sensu_stricto₇ and longilinea.It is worth noting that the relative abundance of Clostridium_sensu_stricto₁ in the thermophilic fermentation process is less than 1%.It can be seen that increasing the fermentation temperature will inhibit Clostridium_sensu_stricto₁.（3）The effect of MnFe2O4 NPs on the performance of anaerobic digestion for methane productionUsing sodium propionate and sodium butyrate as fermentation substrates,anaerobic digestion of MnFe₂O₄ NPs（50,100,200,400,and 600 mg/L）was added to the anaerobic bioreactor for methane production experiments.The results show that MnFe2O4 NPs can simultaneously strengthen the DIET metabolic pathways to promote the degradation of propionic acid and butyric acid,and increase the CH4 production in the anaerobic digestion process.The real-time monitoring of CH4 production in the anaerobic fermentation reactors for propionate and butyrate with different concentrations of MnFe2O4 NPs showed that 400 mg/L MnFe2O4 NPs has the most significant effect on improving the performance of anaerobic digestion,making propionate and The CH4 yield of butyrate fermentation increased by 32.4%and 86.8%,respectively.Biological TEM images show that MnFe2O4 NPs can enter the cell to improve the efficiency of microbial electron transfer between species.Microbial population analysis showed that the addition of 400 mg/L MnFe2O4 NPs increased the relative abundance of archaea and bacteria（Methanosaeta,Methanosarcina,Geobacter,etc.）capable of DIET metabolism,and the change in microbial population composition increased propionic acid during anaerobic digestion.And the metabolic efficiency of butyric acid.