Study On Technology And Mechanism Of Succinic Acid Production By Carbon Dioxide Biological Method

With the continuous progress of human society,people’s demand for primary energy in production activities is increasing.As a result,the emission of the greenhouse gas carbon dioxide has led to continuous global warming and an increasingly serious energy and climate crisis.One of the effective solutions to this problem is the resource utilization of carbon dioxide.Bio-resourcing is a green and sustainable development pathway,and succinic acid is one of the high value bio-based products,but there are still problems such as low yield and poor selectivity of succinic acid in the biofermentation process.Therefore,in this study,the optimal conditions were mapped and the products were optimized around the technology and mechanism of succinic acid production by carbon dioxide biofermentation,and the main conclusions were obtained as follows.(1)The effects of carbonate species,carbon loading and glucose concentration on the fermentation and synthesis of succinate by Actinobacillus succinogenes were investigated.For the two species of AS 130Z and BS,the yield,conversion rate,production rate of succinic acid produced by fermentation under the condition of magnesium carbonate and the proportion of carbon in the total carbon of the final product are all highest.When the carbon loading is 40 g/L,the production,conversion and yield of succinic acid reach the peak value.At the same time,the by-product lactic acid decreases with the increase of the carbon loading.When the carbon loading is increased to 60 g/L,the output of succinic acid cannot be further increased.When the glucose concentration is 60 g/L,the conversion rate and production rate of succinic acid produced by AS 130Z are the largest.BS can produce less than 20 g/L of succinic acid by fermentation at different concentrations of glucose,but it consumes the most carbon dioxide under the condition of 60 g/L glucose,and it has the potential to synthesize higher yield of succinic acid.Considering the fermentation conditions of AS 130Z and BS,it was determined that 40 g/L magnesium carbonate and 60 g/L glucose were the best fermentation conditions.(2)The effect of different ratios of liquid and gaseous carbon dioxide on the succinic acid production process in the fermentation of AS 130Z and BS was investigated.Under four different liquid and gaseous CO2 ratios,AS 130Z produced higher concentrations of PEPCK,the key enzyme of the synthetic succinate pathway,at a higher ratio of gaseous CO2,with a yield of 20.42 g/L of succinate at 1/9 ratio,while the amount of lactic acid produced The highest amount of lactic acid was produced at 1/9 ratio,indicating that the potential of glucose to produce high valueadded organic acids is higher under these conditions.In contrast,BS produced the highest concentration and conversion of succinic acid at a ratio of 1/9 of liquid to gaseous CO2.The produced by-products lactic acid,formic acid and acetic acid had lower yields under these conditions.Taking into account the cost factors,the two strains of Actinobacillus succiniciproducens were selected to continue optimizing the production of succinic acid at a ratio of 1/9 of liquid to gaseous carbon dioxide with a wider prospect.(3)To investigate the optimization of the effect of succinic acid production by Actinobacillus succinogenes and its influence on microbial metabolic patterns.After CO2 optimization at 0/10 and 1/9 liquid and gaseous CO2 ratios,succinic acid yield and conversion in AS 130Z fermentation increased by 7%-8%,while lactic acid yield was reduced.In contrast,the succinic acid yield and conversion in the fermentation of BS increased by 5%at a ratio of 1/9 liquid to gaseous carbon dioxide,while the yield of lactic acid as a by-product was reduced.In this process,CO2 optimization increased the concentration of PEPCK,a key enzyme-in the synthetic succinate pathway,and to some extent inhibited or reduced the concentration of LDH,a key enzyme in the production of lactic acid as a by-product.Also,CO2 optimization promoted the amount of CO2 fixed during the fermentation of AS 130Z and BS at liquid and gaseous CO2 ratios of 0/10 and 1/9.The optimization of carbon dioxide can further improve the selectivity of succinic acid production by the strains.