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In this paper, the effect of Ni2+ concentration ranging from 0 to 50mg/L on fermentative hydrogen production by mixed cultures was investigated in batch test. The results showed that at 35°C and initial pH 7.0, Ni2+ was able to enhance the hydrogen production rate with increasing Ni2+ concentration from 0 to 0.2mg/L, and enhance the hydrogen production potential and hydrogen yield with increasing Ni2+ concentration from 0 to 0.1mg/L. The maximum hydrogen production potential of 288.6mL and the maximum hydrogen yield of 296.1mL/g glucose were obtained at the Ni2+ concentration of 0.1mg/L. In all tests, the major soluble metabolites produced by mixed cultures were ethanol, acetic acid and butyric acid, without propionic acid. Ni2+ had little effect on the substrate degradation efficiency with increasing concentration from 0 to 50mg/L. Ni2+ was able to enhance the biomass production yield with increasing Ni2+ concentration from 0 to 0.1mg/L. The maximum biomass production yield of 232.5mg/g glucose was obtained at the Ni2+ concentration of 0.1mg/L. In all tests, the final pH after fermentative hydrogen production was lower than the initial pH. [Copyright &y& Elsevier]

The effect of ammonia concentration ranging from 0 to 10g N/L on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate at 35°C and initial pH 7.0. The experimental results showed that during the fermentative hydrogen production, the substrate degradation efficiency increased with increasing ammonia concentration from 0 to 0.01g N/L. The hydrogen production potential, hydrogen yield and average hydrogen production rate increased with increasing ammonia concentration from 0 to 0.1g N/L. The maximum hydrogen production potential of 291.4mL, maximum hydrogen yield of 298.8mL/g glucose and maximum average hydrogen production rate of 8.5mL/h were all obtained at the ammonia concentration of 0.1g N/L. [Copyright &y& Elsevier]