Promoting Mechanism Of Ferrihydrite Nanomaterials On Hydrogen Fermentation By Clostridium Sp. BZ-1

Biological hydrogen production is a mild and environmentally friendly way of hydrogen production,which has broad application prospects in the current carbon peak and carbon neutral background.In view of the current technical problems of low conversion rate of microbial fermentation hydrogen production substrate and high cost of fermentation hydrogen production,a Clostridium hydrogen producing BZ-1 was isolated from paddy soil in Guangdong Province in this study,and its culture system was optimized.By adding iron-containing nano material,ferrihydrite to the culture system and constructing a simultaneous nitrogen fixation and hydrogen production system,the hydrogen production and substrate conversion rate of the strain BZ-1 were improved,and the related mechanism was studied,which provided practical information for the practical application of microbial hydrogen production.The application provides a theoretical basis.The main research conclusions are as follows:（1）In this research,a hydrogen-producing microorganism was isolated from a paddy field in Guangdong,and it was identified as Clostridium sp.BZ-1.The optimum temperature for hydrogen production was 37 ℃and pH 7.Under suitable culture conditions,the total amount of hydrogen produced by fermentation was 38.46 ± 2.54 mol/L,and the conversion rate of hydrogen production substrate was 1.20 mol H₂/mol Glucose.Under the optimum hydrogen production conditions,the average hydrogen production rate can reach 5.33±0.27 mmol/（L·h）.Adding 2-（N-morpholino）ethanesulfonic acid（MES）buffer reagent to the culture system can increase the ability of strain BZ-1 to consume glucose from 32.17 ± 3.22 mmol/L to 48.52 ± 3.16 mmol/L,but No increase in hydrogen production per substrate（2）The addition of nano-ferrihydrite can improve the hydrogen production capacity of strain BZ-1.Among them,2 mmol/L is the optimum addition amount.Under these conditions,the hydrogen production of strain BZ-1 increased by 83.72%;the conversion rate of the fermentation hydrogen production substrate increased from 1.20 mol H₂/mol Glucose to 1.74 mol H₂/mol Glucose.Ferrihydrite had a certain buffering effect on the pH of the medium in the early stage of strain BZ-1 culture.Under the condition of adding 2mmol/L ferrihydrite,the total amount of glucose fermented by strain BZ-1 increased from34.83±1.82 mol/L to 47.78±0.02 mol/L;the accumulated amount of acetic acid and butyric acid increased from 7.89±0.17 mmol/L,16.69±0.48 mmol/L increased to12.48±0.52 mmol/L,26.69±0.51 mmol/L;lactate production decreased from 5.74±0.58mol/L to 0.31±0.01 mmol/L;hydrogenase activity of strain BZ-1 Significantly increased.70.51% of ferrihydrite was reduced during fermentation.To sum up,the possible mechanism of nanoferrihydrite-enhanced strain BZ-1 is as follows:a)Enhance the buffering capacity of the medium;b)Enhance hydrogen-producing pathways and inhibit non-hydrogen-producing pathways;c)Improve hydrogenase activity;d)Provide electron acceptors to maintain intracellular electron balance.（3）Strain BZ-1 can synergistically fix nitrogen and produce hydrogen under the condition that nitrogen is the only nitrogen source.Under the conditions of synergistic nitrogen fixation and hydrogen production,the substrate conversion rate of the fermentation hydrogen production of strain BZ-1 increased from 1.20 mol H₂/mol glucose to 1.50 mol H₂/mol glucose.Under the condition of simultaneous nitrogen fixation and hydrogen production,the acetogenic pathway was significantly enhanced,from 5.49 mol/L±0.17 to8.80±0.08.The reduction of BZ-1 biomass under this condition may also be one of the reasons for the enhanced hydrogen production capacity of strain BZ-1.Nanoferrihydrite can inhibit the lactate pathway by enhancing the butyrate and acetate production pathways,and further improve the hydrogen production capacity of the strain BZ-1 under the condition of simultaneous nitrogen fixation and hydrogen production.The hydrogen production rate per substrate reaches 1.86 mol H₂/mol glucose.