The Study Of Substrate Metabolism On Hydrogen Production By Photosynthetic Bacteria

This paper is a research supported by the National Natural Science Foundation (No.50676029). mixed photosynthetic bacteria was studied in this paper as research object. The effects of different carbon \ nitrogen sources and hydrogen production Substrate on the growth and hydrogen production of photosynthetic bacteria was studied, Furthermore, the usage of carbon \nitrogen resource and hydrogen production substrate was also discussed in this paper.The result showed that:(1) Photosynthetic bacteria can use fad acid and alchol as carbon source, such as acetic,butyric and pyruvic, TCA cycle (citric acid cycle)intermediate metabolites also can be used by photosynthetic bacteria. Acetic was a good growth carbon and hydrogen producing substrate, and the best added concentration was 80mmol/L and 40mmol/L respectively.When Photo-bacteria utilized acetic as growth carbon, in lagarithmic phase during 48-120h,the top substrate Consumption rate was 1.29mmol/h. When acetic was used as hydrogen produing substrate, 48-96h was hydrogen producing peak phase, the top acetic consumption was 0.64mmol/h.(2) Photosynthetic bacteria was selective in utilizing nitrogen source under growth condition, inorganic nitrogen, especially ammonium-type material is vulnerable to be used by photosynthetic bacteria, organic nitrogen sources was followed, N₂ was the last.When (NH₄)₂SO₄ was used as growth nitrogen source, the best added concentration was 3.5～7 mmol/L, during 24～120h ,in lagarithmic growth phase,the top consumption rate of nitrogen was 0.105mmol/L. The effect of organic and inorganic nitrogen on hydrogen production was not obvious,the organic nitrogen was better than inorganic nitrogen. When (NH₄)₂SO₄ was used as hydrogen producing nitrogen source, the best added concentration was 3.5 mmol/L,the nitrogen source was utilized only at 0～48h, and the top consumption rate was 0.03mmol/L,once the cell entered the peak phase of the hydrogen production, the usage of nitrogen was stoped.(3) Photosynthetic bacteria utilized glucose as substrate to produce hydrogen, when the added concentration of glucose was lower than 0.05%,glucose was used as growth carbon, there was no hydrogen produced; when the added concentration was 0.1～ 0.4%,the cell decomposed glucose to acid, there was only few amount of hydrogen was produced; when the concentration add up to 0.5%,the cell could utilize glucose to produce hydrogen effectivly, the best glucose added concentration of was 3%(4) Cell growth activity was inhibited by glucose for the cell would degenerate glucose into organic acids in the process of utilizing glucose to generate hydrogen. Adding glucose in batch was beneficial to inhibit cell growth decline to a certain extent, but had no promotion on hydrogen production. Exogenous regulation of pH had a significant promotion on cell growth and hydrogen production.(5) In the process of hydrogen production that Photosynthetic bacteria utilized glucose as substrate, 24～96h was the peak phase of the hydrogen production, the main metabolites of glucose was acetic. After 96h the cell came into the end of hydrogen production,and the main metabolites of glucose was butyric.(6)Monod mode1 was used to describe the progress of cell growth in batch tests, the results given by the model are well agreed with the experimental data in growth phase and lagarithmic phase(0～96h).A substrate cousumption model deduced by Monod mode1 was proposed to describe the consumption of glucose in the process of hydrogen production. the simulation given by the model are well agreed with the experimental data in lag and lagarithmic phase(0～72h).however, the model does not apply to describe the substrate consumption date after 72h..