Bacterial Culture And Simulation Of Hydrogen Production From Fermentation Of Hydrogen

To investigate the culture of hydrogen-producing bacteria and the effects of organic acids and pH value on fermentative hydrogen production from biomass, under anaerobic conditions, at temperature of 25℃ and by using continuous and semi-continuous fermentative devices designed by ourselves, some experiments concerned were carried out with anaerobic digestive sludge as inoculums of hydrogen-producing bacteria.(1) At batch fermentation, eleven organic acids (citric, malic, lactic, formic, pyruvic, oxalic, fumaric, succinic, butyric, propionatic and acetic acid) were used to study their effects on hydrogen production. It was shown that hydrogen gas was produced when using citric, malic, lactic, formic, pyruvic, oxalic and fumaric acid and the hydrogen yields is 171.3, 117.4, 93.5, 79.6, 75.6, 24.6 and 23.7ml/g, respectively. However, no hydrogen was generated when using succinic, butyric, propionatic and acetic acid. At continuous fermentation, except for formic acid, hydrogen could not continuously produced when using the other acids.(2) It was found that formic acid can be used to culture hydrogen-producing bacteria and control pH value of the system. Even at continuous fermentation the hydrogen yield can reach 273ml/g, the rate of energy conversion could be 63.80%.(3) During hydrogen production from sucrose, formic acid was used to culture hydrogen -producing bacteria and control pH value of the system. It was found that the rate of gas production was 28.52 L/Ld, with the fastest rate of 30.68 L/Ld. Under suitable condition (with 5~15g/L sucrose), the hydrogen content, the yield of hydrogenproduction, the rate of energy conversion would be 43.4%, 174ml/g, 8.29%, respectively. It was also found that when organic acid and sucrose were used, pH and accumulation of volatile fatty acids(VFA) played key roles in hydrogen production. The most suitable range of pH is 4.5~5.5. When pH is under 4.3, no hydrogen was produced at the beginning. If pH is above 5.5, a lot of methane was generated, companied by the phenomenon of absorbent hydrogen. The accumulation of VFA was mainly caused by acetic, propionatic and butyric acid. The latter two acids play an important role in inhibiting hydrogen production, that is why hydrogen uncontinuously and unsteadily. Although acetic acid does not have a prominent inhibition on hydrogen production, its considerable accumulation can significantly decrease the rate of energy conversion.Compared with the highest value of 11.28 L/Ld in China and 5.33 L/Ld in Japan, the rate of hydrogen production when using sucrose in our system was 18.04% and 150% higher, respectively. The gas yield of 341.2ml/g in our system is equivalent to the highest value of 340ml/g in China.