Research On Conversion Of Carbon Dioxide To Value-added Product Based On Hydrogen Mediated Microbial-inorganic Hybrid System

Hydrogen mediated microbial-inorganic hybrid system have shown unique advantages and great potential for CO2 reduction,which can realize the direct conversion of CO2 to multi-carbon compounds.hydrogen and oxygen,which are generated by water splitting in inorganic system,are in situ utilized by microorganisms to convert CO2 into different compounds.But the current products of this system are still relatively single,most of which are simple alcohols.In addition,there is a mismatch between biological and inorganic system.First,reactive oxygen species(ROS)by-produced in inorganic systems can cause toxic effects on microorganisms.The lower solubility and mass transfer rate constant of hydrogen in water lead to the limited CO2 reduction efficiency in the hydrogen mass transfer process.In view of the above problems,this paper conducts the following research:First,Ralstonia eutropha was used as the chassis cell to construct lycopene engineering bacteria with high yield.Two lycopene synthesis genes(CrtEBIl and CrtEBI2)from different sources and different strengths promoters(Plac,Pphac,PlacRBS,Pj5)were compared.Finally,R.eutropha C5/pBBR-Plac-CrtEBI2 was chosen as stratin for the following experiments.The lycopene yields of constructed lycopene strain under heterotrophic and autotrophic condition could reach 3.29 mg/L and 2.49 mg/L,respectively.By coupling the constructed lycopene strain with an water-splitting system using stainless steel and platinum mesh as cathode and anode,a hydrogen mediated microbial-inorganic hybrid system capable of synthesizing lycopene was successfully constructed.Condition optimization experiments were carried out for the operation method and current value to improve the lycopene yield.In the optimization experiment of current value,the maximum coulombic efficiency of the system was 12.6%at 18 mA,and the maximum yield of lycopene was 1.00 mg/L.Using the actual exhaust gas of coal-fired power plants as the carbon source for lycopene synthesis,the final maximum lycopene yield can reach 1.73 mg/L.After the system was constructed,the research on the problem of poor compatibility between biological and inorganic systems was carried out.Through electron paramagnetic resonance and other experiments,it was proved that the inorganic system would by-produce ROS such as superoxide anion(·O2-);hydrogen peroxide(H2O2),hydroxyl radical(OH·)in the process of water-splitting,which affects the growth of microorganisms.Comparing the survival rate and growth rates of lycopene bacteria and control bacteria in inorganic systems,it is proved that lycopene,as a reducing product,can resist the adverse effects of inorganic catalytic systems.On this basis,two more general methods are designed to improve the antioxidant capacity of biocatalysts,thereby realizing the efficient coupling of biological and inorganic systems.First,R.eutropha overexpressing superoxide dismutase(SOD)and catalase(CAT)were constructed to resist the oxidative stress of inorganic catalytic systems.The overexpressing SOD/CAT strain could withstand the poisoning effect of 35 mM H2O2.The growth rate of overexpressing SOD/CAT strain in the hybrid system was 19.2%higher than the control group.In addition,directed evolution is used to domesticate a group of strains that can adapt to the strong oxidative environment of inorganic systems.During seven consecutive evolutionary cycles,the growth rate and energy efficiency of R.eutropha in the hybrid system were significantly improved.The biomass accumulation rate increased from 4.09 mg/(L·h)to 9.11 mg/(L·h),and the system energy efficiency increased from 5.24%to 10.66%.To solve the problem of low hydrogen mass transfer rate,a strategy of adding nanomaterial was adopted to enhance the gas-liquid mass transfer process.Two nanomaterials were prepared:SiO2 with a particle size of 200 nm and perfluorocarbon(PFC)nanoemulsion.Gas fermentation experiments were carried out in serum bottles to compare the effect of the two materials on the improvement of gas production.After adding different concentrations of nano SiO2,the lycopene yield increased by 20%to 50%.When the volume fraction of PFC emulsion was 4%,it showed the best promotion effect on lycopene production,which can be increased by more than 50%.After adding SiO2 and PFC nanoemulsion,volumetric mass transfer coefficient(kLa)of hydrogen increased from 0.895 h-1 to 1.015 h-1 and 0.972 h-1.In this study,the hydrogen-mediated microbial-inorganic hybrid system was successfully used to realize the conversion of CO2 to high value-added products,which provided ideas for the construction of an electrically driven cell factory using CO2 as a feedstock.