2004 Volume 27 Issue 7 Pages 473-479
The influence of substrate concentration and pH on hydrogen fermentation of a mixed substrate by a mixed microflora was investigated using a batch experiment. The batch reactor with a working volume of 1.0 liter was operated at 35°C at a constant pH for each experimental run. Dog food was used as the substrate. The seed microflora was a mixed culture having Clostridium pasteurianum and Sporolactobacillus racemicus M116. It was obtained by acclimatizing a thermophiledigested sludge using glucose as the substrate. The experiments were conducted by changing the pH from 4.0 to 7.5 at various substrate concentrations of TS2%, TS5%, and TS10% to evaluate substrate decomposition, gas production and metabolic production under each condition. Hydrogen fermentation was greatly affected by pH at each TS concentration and the optimal pHs for obtaining maximum hydrogen yield were identified to be 4.5-5.5 for TS2%, 5.5 for TS5% and 6.5 for TS10%. The maximum hydrogen productions at TS2%, TS5% and TS10% ranged from 93.9 to 108 ml·g-1 VS, and no significant influence caused by the substrate TS concentration was noted. These results indicate that hydrogen fermentation can be effectively operated under a high-substrate condition as well as at TS10% by maintaining an optimum pH. The H2 yield at the optimal pH was as high as 1.80 mol H2·mol-1 glucose. Lactic acid was the main product at a low pH, while a complex fermentation pattern was obtained at a pH close to 7.0. Both these fermentation patterns resulted in a decrease in H2 production.
