Construction And Optimization Of Hydrogen Production System By Bacterial Mixed Culture Fermentation

The environmental problems caused by the unrestricted use of fossil fuels are becoming more and more severe.Energy crises and environmental pollution have become inevitable problems that need to be solved urgently all over the world.As the first choice for clean energy,hydrogen is one of the ideal fuels in the future.There is a wide range of sources of industrially-produced hydrogen.Coal-based fuel hydrogen production and hydrogen production from electrolyzed water are the most widely used,but the disadvantages are the huge cost and energy consumption,which limits the development of industrial hydrogen production.As a low-cost,low-energy green energy production technology,biological hydrogen production technology can be combined with organic wastewater treatment and clean energy production,and has gradually attracted attention.To solve the problems of low hydrogen production rate,low substrate utilization rate and poor resistance of strain to acidic environment in the hydrogen preparation reaction,two strains of hydrogen producing bacteria,A1(Bacillus Cereus)and B1(Brevumdimonas naejangsanensis),were used in this study,the main factors affecting the fermentation process were first investigated.Among them,the focus is on the influence of pH,which is greatly critical for the hydrogen production of dark fermentation organisms,because it affects the activity of hydrogenase and metabolic pathways.When the pH value of the fermentation medium is too low,either the metabolic activity of the hydrogen-producing bacterial flora is inhibited,or the metabolic pathway is switched,resulting in the cessation of biological hydrogen production.The results of the study showed that the utilization rate of xylose can be increased from 22%to 75.1%by controlling the appropriate fermentation pH,and the maximum hydrogen production rate of xylose fermentation can reach 1.48 mol H2/mol xylose.Moreover,the addition of 1%phosphate buffer can control the buffer concentration of the fermentation system to about 5.5 without dropping,which is very beneficial for anaerobic fermentation.Research on different substrates found that the hydrogen yield of starch can reach 1.64 mol H2/mol glucose,which is better than xylose and glucose.In addition,the Au-Pd catalyst can significantly reduce the lag period of fermentation and increase the rate of hydrogen production and the amount of hydrogen produced.Biofilm immobilized cells have a very good promotion effect on hydrogen production by fermentation.Studies have confirmed that biofilms can increase the density of microorganisms and increase their environmental response speed,and have the advantages of strong acid and alkali resistance and stable cell metabolism.In this experiment,Strains A1 and B1 were used to cultivate a new layer-by-layer mixed bacteria biofilm structure,which successfully realized the spatial distribution of the mixed flora and improved the synthesis efficiency of the strains.The maximum hydrogen yield can reach 1.78 mol H2/mol glucose.The experiment also found that when the ratio of A1:B1 biofilm was 1:1 and 1:2,the experimental effect was the best.In addition,this multilayer membrane structure has an excellent recycling effect.The average cumulative hydrogen production for five fermentation cycles is 1736 mL/L,which not only saves resources,but also conducive to industrial-scale production.This study also launched a further attempt to construct a multi-cell system,trying to construct a more diverse hydrogen production system.The hydrogenproducing bacteria G(Citrobacter freundii)screened from laboratory sludge has good hydrogen production capacity.When starch is used as a substrate for fermentation,its maximum hydrogen production yield can reach 1.36 mol H2/mol glucose.However,the mixed fermentation effect of strain G and A1 is not ideal.Enterobacter aerogenes is also a kind of bacteria that efficiently produces hydrogen and acid.The mixed culture of the three bacteria was carried out with glucose and starch as substrates.The experiment found that when starch is used as the substrate,the cumulative hydrogen production can reach 1550 ml·L-1.This shows that Enterobacter aerogenes can further combine with the original system to produce hydrogen.Due to the increase in the types of hydrogen-producing bacteria,the fermentation rate is faster,the hydrogen production efficiency is higher,and the hydrogen production curve tends to be linear,which may be dominated by Enterobacter aerogenes.This study combines three different hydrogen-producing strains to conduct mixed-culture hydrogen production research,which provides a new solution for the construction of a multi-cell hydrogen production system.