Study On CO/CO₂ Continuous Gas Acclimation Of Mixed Bacteria And Its Fermentation Performance For Ethanol Production

In the utilization of biomass energy,lignocellulose cannot be used well because of its difficult degradation.The pyrolysis gas with CO,CO₂ and H₂ as the main part can be converted into carbon containing organic matter（such as acetic acid,ethanol,butanol,etc.）by pyrolysis and gasification.In the selection of strains using biomass pyrolysis gas as substrate,it can be divided into pure bacteria fermentation and mixed fermentation.However,for complex pyrolytic gas components,pure bacteria fermentation is often unable to adapt to the complex pyrolytic gas because of its single strain and low tolerance.However,mixed fermentation can adapt to the pyrolysis gas better based on the diversity of its own flora,and is more suitable for actual production.Therefore,it is necessary to domesticate the mixed bacteria group to get the mixed bacteria group which can adapt to the biomass thermolysis fermentation.Besides the selection of strains,the fermentation conditions will have a significant impact on the fermentation of pyrolytic gas.For example,the initial inoculation amount,pH value of fermentation liquid,the composition of thermolysis gas,etc.,among which,in terms of metabolism and alcohol production,the pH value of fermentation liquid will significantly affect the metabolic path of the bacteria group,and the pH value of the suitable bacteria group growth is often not consistent with the pH value of the suitable alcohol production.Therefore,the pH value of the suitable bacteria group growth is not consistent with the pH value of the suitable alcohol production.Therefore,the pH value of the fermentation liquid is not consistent with the pH value of It is necessary to use pH two-step method to control the growth and metabolism of ethanol to increase ethanol production.In addition,in wood ljungdahl pathway,hydrogen is generated by hydrogenase,but the low solubility of hydrogen leads to low electron production.Therefore,it is necessary to improve the electronic supply for the thermolysis gas fermentation system.Cd S nanoparticles can be formed on the surface of bacteria by self-sensitization of bacteria,which can stimulate CDs to produce electrons under light,and provide them to biomass thermolysis gas fermentation system,to solve the electronic limitation.In this study,the bacteria in rabbit feces were enriched and domesticated by continuous supply of simulated biomass pyrolysis gas.After the effective mixture was obtained,the effects of inoculation amount,pH value,thermolysis gas composition on the alcohol production performance of the rabbit were studied.In order to further improve the ethanol production,on the one hand,two-step pH was used to control the growth and alcohol production of bacteria in the thermal desorption environment,on the other hand,the self-sensitization of bacteria was used to enhance the electronic production rate of bacteria to enhance the alcohol production capacity.The main conclusions of this paper are as follows:（1）The effective strains were obtained from rabbit manure by continuous gas domestication.The results showed that the structure of the domesticated bacteria group changed significantly after 16S r RNA analysis.Blautia,which can produce ethanol by CO/CO₂,has become the dominant bacteria,and its relative abundance is increased by5.4 times,reaching 41.1%,while the relative abundance of Bacterides,which can only be used for growth and metabolism by organic carbon,has decreased significantly,from 40.5%to 4.2%.In terms of fermentation products and carbon fixation capacity,the fermentation ability of the bacteria group was improved after continuous supply of thermolysis gas domestication,and the highest ethanol concentration of 1.41 g L^-1 was obtained,and the highest carbon fixation rate reached 14.07%.（2）The effects of initial inoculation concentration,constant pH value and concentration of pyrolytic gas on the growth of bacteria,TOC in fermentation liquid,metabolites and bacterial group structure were studied.The results show that the lower concentration of inoculation amount will limit the maximum bacterial density of bacteria and reduce its fermentation performance;on the contrary,the higher concentration of inoculation amount is conducive to the enhancement of the maximum density of bacteria,and the maximum absorbance at OD₆₀₀ reaches 1.51,and it can shorten the fermentation time of acetic acid and prolong the ethanol fermentation time.In addition,when the pH of the fermentation liquid is 7,the growth rate of the bacteria group is the fastest,the highest density of the bacteria group reaches 1.39 at OD₆₀₀,while when the pH of the fermentation liquid is 6,the ethanol production concentration is the highest,reaching 5.15g L^-1.In terms of the influence of pyrolytic gas composition,CO became the preferred substrate of mixed bacteria.Under 56%CO,the highest density of bacteria group reached1.34 in OD₆₀₀,the highest ethanol yield reached 5.44 g L^-1,and the relative abundance of Clostridium reached 98.13%.（3）Based on the rule of pH of fermentation liquid affecting the growth and metabolism of bacteria,the growth and alcohol production of the same type of acetic acid producing bacteria were regulated by two-step pH control.It was found that after the growth of the bacteria group to the stable stage,the pH control not only increased the concentration of ethanol,reached 5.85 g L^-1,but the maximum density of the bacteria was not affected,but the pH control of the bacteria would increase in the exponential growth period,although the ethanol production would increase,the bacteria would increase Colonization is limited.In addition,the electronic restriction problem in fermentation process was solved by the self-sensitization of bacteria,and the hybrid system of acetic acid producing bacteria/Cd S was successfully constructed.The surface of bacteria was attached with Cd S nanoparticles formed by Cd and S elements.Under the light condition,more electrons were excited,which provided more reduction equivalent for biomass thermolysis fermentation,to enhance the fermentation performance.Although self-sensitization can inhibit the growth of bacteria,the density of bacteria is 12.32%lower than that of non-photosensitized cells,but the highest alcohol production concentration is5.14 gL^-1,which is 37.43%.