| In recent years,the consumption of fossil fuel-based energy has posed a serious challenge to sustainable development as energy sources have become increasingly scarce and demand for energy has increased.Hydrogen（H2）and methane（CH4）have great potential as an alternative energy source as no harmful substances are produced during combustion.In this study,carbon nanotubes（CNTs）and hydroxyapatite（HA）were used as raw materials for H2 production and CH4 production.The anaerobic sludge was used as the source of H2 producing bacteria,and glucose,propionic acid（HPr）and butyric acid（HBu）were used as substrates for dark fermentation to produce H2 and CH4.（1）To investigate the effect of CNTs on H2production from glucose anaerobic fermentation,CNTs with different concentrations were added to the anaerobic reactor in this study to explore the efficiency of H2 production from dark fermentation.In the dark fermentation H2 production system,the 48h H2 production of the reactors with CNTs addition was higher than that of the control group.When 200 mg/L CNTs were added,the cumulative hydrogen production（CHP）was 1366.33±63.02 m L,and the mean H2yield was 273.27±12.61 m L/g glucose,which was 44.18%higher than that of the control group.The result showed that the addition of CNTs could effectively improve H2production.When 200 mg/L CNTs were added,the concentrations of ethanol（Et OH）,acetic acid（HAc）,HPr and HBu at the end of fermentation were 353.98±16.30,1543.35±43.61,224.09±6.55 and 3445.64±55.85 mg/L,respectively,which were higher than those of the blank control group.It indicated that the conditions with HA could promote the degradation of glucose to produce various soluble substances.Microbial community analysis showed that CNTs significantly increased the abundance of Firmicutes from44.20%（0 mg/L CNTs）to 52.83%（200 mg/L CNTs）,which played an important role in bio H2 production.the abundance of Clostridium＿sensu＿stricto＿1 increased from 21.13%（0 mg/L CNTs）to 23.22%（200 mg/L CNTs）and became the dominant bacterium for fermentative H2 production.This also revealed that appropriate concentrations of CNTs could significantly increase the yield of bio H2.（2）To investigate the effect of HA on H2 production from anaerobic fermentation of glucose,different concentrations of HA were added to the anaerobic reactor in this study to explore the performance of H2 production from dark fermentation.In the dark fermentation H2 production experiment with the addition of HA,the highest bio H2 yield obtained with the addition of 400 mg/L HA was 182.33±2.41 m L/glucose,which was55.80%higher compared to the blank control.The existence of HA promoted the degradation of organic matter and increased the concentration of SMPs,which contributed to the H2 production in HBu-type fermentation.Microbiological analysis showed that the abundance of Clostridium＿sensu＿stricto＿1 increased from 15.33%（0mg/L HA）to 45.17%（400 mg/L HA）as the dominant bacterium in the 400 mg/L HA reactor.The also revealed that appropriate concentrations of HA could significantly increase the yield of bio H2.（3）In order to investigate the effect of HA on CH4 production from HPr fermentation,different concentrations of HA were added to the anaerobic reactor in this study to explore the performance of CH4 production from anaerobic fermentation.The experimental results showed that the CH4 yield of 100 mg/L HA reaction group was 283.40±4.73m L/m L HPr,which was 42.41%higher than that in the control group（100.00±8.19m L/m L HPr）.With the addition of 100 mg/L HA,the concentration of SMPs at the end of the fermentation was 10342.73 mg/L,which was 2.21%higher than that of the control.The addition of HA increased microbial diversity.Euryarchaeota and Methanobacterium became the dominant methanogenic bacteria.The abundance of Firmicutes increased from 19.40%（0 mg/L HA）to 22.26%（100 mg/L HA）.The abundance of Bacteroidetes increased from 19.40%to 28.08%.The abundance of Bacteroidetes＿Vadin HA17increased from 14.77%（0 mg/L HA）to 25.56%（100 mg/L HA）.（4）In order to investigate the effect of HA on CH4 yield by HBu fermentation,different concentrations of HA were added to the anaerobic reactor in this study to explore the performance of CH4 yield by anaerobic fermentation.The CH4 yield of the reaction group was 631.60±30.84 m L/m L HBu with the addition of 600 mg/L HA,which was65.77%higher than that of the control group（381.00±29.31 m L/m L HBu）.The microbial community analysis indicated that the addition of HA promoted methanogenic microbial diversity in HBu-type fermentation.The abundance of Firmicutes increased from 26.61%（D1,0 mg/L HA）to 33.48%（D6,600 mg/L HA）.Euryarchaeota accounted for 99.10%of the total archaea sequence and became the dominant methanogenic bacteriahe in optimal experimental group D6 with the addtion of 600 mg/L HA. |
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