Study On Hydrogen Production Efficiency And Mechanism Of Different Metabolic Types Bacteria

Biohydrogen production technology offers a new solution for the energy crisis and the environmental problem. Fermentation technology became the first option of biohydrogen production due to its advantages such as high hydrogen-producing capability, good stability and possibility to transform wastes into resources. The three major types of the fermentation technology for biohydrogen production includes ethanol-type fermentation, butyrate-type fermentation and mixed acid fermentation. The relationship between the growth factors and the microorganisms is very complex and delicate, and the change of each growth factor will impose influences on the biological process of microorganism such as growth, multiplication and metabolism, or even lead to the change of the complete habitat and the succession of ecological system. Therefore, it is very important to probe into the tolerance range and the optimal hydrogen generating condition of hydrogen-generating bacteria. In this study, researches on the major growth factors of Ethanoligenens harbinense YUAN-3, Clostridium butyricum 1.209 and Enterobacter cloacae 1.2022, which represent three typical fermentation processes was introduced. In order to offer a theoretical basis for the further enhancement of hydrogen-generating capability of the fermentation biohydrogen production, the study determined their respective optimal culture conditions, and investigated the hydrogen-generating characteristics of different hydrogen-generating bacteria by continuous flow test.Batch culture experiment was adopted to investigate the influence of Fe²⁺, mC/mN, Na⁺, Mg²⁺, K⁺ and cysteine on the process of growth and hydrogen-generation by E. harbinense YUAN-3, C. butyricum 1.209 and E. cloacae 1.2022. Central composite design and response surface method (RSM) were used to get the optimal cultural condition.For ethanol-type fermentation: the concentration of Fe²⁺ was 0.05-0.1g/L; mC/mN was 15:1-20:1 (glucose and nitrogen source concentration were 20g/L and1-1.33g/L, respectively); the concentration of Na⁺ was 1-1.5g/L; the optimal concentration of Mg²⁺ was 0.1-0.5g/L.For butyrate fermentation: the optimal concentration of Fe²⁺, K⁺, Na⁺ and Mg²⁺ were 0.1⁰.2 g/L, 1.0-2.0 g/L, 2.0-3.0 g/L and 0-0.2 g/L, respectively. For mixed acid fermentation: the concentration of Fe²⁺ was 0.5-1.0g/L; the concentration of K⁺ was 1.0-1.5g/L; the concentration of Na⁺ was 0.5-1.5g/L; the optimal concentration of cysteine was 0-0.7 g/L.Continuous flow test device was adopted so that analyses and comparisons were made on the hydrogen-generating capacity of E. harbinense YUAN-3, C. butyricum 1.209 and E. cloacae 1.2022 under their respective optical culture conditions. The following conclusion was arrived at through analyses and comparisons on biomass of cells, pH value of reaction system, accumulated volume of gases and hydrogen generated, utilization rate of glucose, hydrogen content, hydrogen-generating speed, specific hydrogen-generating speed, and products at the end of liquid phase: C. butyricum 1.209 multiplied rapidly, it lagged in its growth at the initiating stage after being inoculated, and then it grew rapidly and its concentration increased drastically; pH value within 3.6-4.3 was beneficial for the hydrogen-release of ethanol-type fermentative bacteria and butyrate fermentative bacteria; E. harbinense YUAN-3 began to generate gases within the shortest time in the first 80 h of fermentation, and the yield of gases rose within a short time and then it kept stable; however, C. butyricum 1.209 was superior to E. harbinense YUAN-3 and E. cloacae 1.2022 in hydrogen yield per unit volume, utilization rate of glucose and hydrogen content.Based on the analysis by metabolic theory, it may be concluded that E. harbinense YUAN-3 and C. butyricum 1.209 are similar in relation to their hydrogen-generating pathway, both of them belong to Clostridium type hydrogen-generating bacteria, and they differs only in the consumption of NADH product when the hydrogen generation is regulated by the thermodynamic process; under anaerobic condition, E. cloacae 1.2022 ferments glucose through pathway of mixed acid fermentation and generates hydrogen through hydrogenlyase system, and its metabolic pathway is different from that of C. butyricum 1.209 to some extent.