Fermentative hydrogen production at high temperature has been tested. We had been looking for new bacteria that produce H_2 at a high production rate at high temperature and we could get a new mesophilic bacterium. The experimental temperatures and pHs were set at 41,44, 47, 50°C and 5.5, 6.0, 6.5, 7.0, respectively. The H_2 production rate was the fastest at 47°C and pH6.0, respectively. The rate was approximately 150mmol L-culture~(-1) h~(-1). The yield of hydrogen increased along with the increase of temperature and the decrease of pH. The yield was the best at 50°C and pH5.5 respectively. These reasons were that this bacterium grew faster at high temperature and shifted the metabolic pathway from lactate production to acetate and ethanol production along with the increase of temperature. Butyrate and lactate production decreased along with the increase of temperature and pH, while formate concentration increased along with the increase of pH.
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