Photoproduction Of Hydrogen By Rhodobacter Sphaeroides

Hydrogen is widely considered as a potential substitute for fossil fuels because it is a clean, efficient and reproducible energy. Hydrogen production by biological processes is found to be more environmental friendly and less energy intensive compared to thermochemical and electrochemical processes. Photosynthetic bacteria (PSB) have been frequently claimed as one of the most promising candidates for the development of H₂-producing system.Photoproduction of hydrogen by Rhodobacter sphaeroides was studied in this paper. The study included several main parts: (1) the main affecting factors in cell growth and hydrogen production of Rhodobacter sphaeroides;(2) several factors in the activity of nitrogenase, hydrogenase and hydrogen production, furthermore, the relation among the three;(3) continuous hydrogen production in a 1.5L column photobioreactor. The experiment results showed that: (1) Photoheterotrophic growth mode was the preferred growth mode for Rhodobacter sphaeroides. Under this mode, the optimal conditions for cell growth were pH6.5⁸.0, 5000 lx¹0000 lx and 30℃ ³5℃. (2) Malate, succinate, lactate, acetate, pyruvate and glucose were all good carbon source and electron donor for cell growth and hydrogen production of Rhodobacter sphaeroides. The average hydrogen production rate was 15.6 ml H₂/L culture/h²2.2 ml H₂/L culture/h, and the substrate conversion efficiency was 20.4%⁵7.1%. NH₄Cl and glutamate were both good nitrogen source for cell growth of Rhodobacter sphaeroides. Hydrogen production by Rhodobacter sphaeroides was significantly inhibited by NH₄⁺ at a concentration of 2.5mmol/L or above. The concentrations of carbon source and nitrogen source were important limiting factors of hydrogen production. (3) The optimal conditions for hydrogen production were pH7.0⁸.0, 5000 lx¹0000 lx and 30℃³5℃. (4) When NH₄⁺ was used as the sole nitrogen source, concentration above 2.5mmol/L would totally inhibit existing nitrogenase activity in Rhodobacter sphaeroides. As the light intensity increased in the range of 2000 lx⁵000 lx, the nitrogenase activity in Rhodobacter sphaeroidesincreased accordingly. (5) As the nitrogenase activity increased, hydrogen production increased accordingly. Besides, the activity of hydrogenase might be stimulated by the hydrogen production of nitrogenase. (6) Continuous hydrogen production from lactate by Rhodobacter sphaeroides in a 1.5L photobioreactor ran for 40 days. The hydrogen produced was 3.49L. The maximum rate of hydrogen production was 7.7ml/L culture/h. The yield was 6.39L H2/mol C.