Fermentative hydrogen production from cassava stillage by mixed anaerobic microflora: Effects of temperature and pH

Fermentative hydrogen production from cassava stillage was conducted to investigate the influences of temperature (37°C, 60°C, 70°C) and initial pH (4–10) in batch experiments. Although the seed sludge was mesophilic anaerobic sludge, maximum hydrogen yield (53.8ml H2/gVS) was obtained under thermophilic condition (60°C), 53.5% and 198% higher than the values under mesophilic (37°C) and extreme-thermophilic (70°C) conditions respectively.

The difference was mainly due to the different VFA and ethanol distributions. Higher hydrogen production corresponded with higher ratios of butyrate/acetate and butyrate/propionate. Similar hydrogen yields of 66.3 and 67.8ml H2/gVS were obtained at initial pH 5 and 6 respectively under thermophilic condition.

The total amount of VFA and ethanol increased from 3536 to 7899mg/l with the increase of initial pH from 4 to 10. Initial pH 6 was considered as the optimal pH due to its 19% higher total VFA and ethanol concentration than that of pH 5. Homoacetogenesis and methonogenesis were very dependent on the initial pH and temperature even when the inoculum was heat-pretreated.

Moreover, a difference between measured and theoretical hydrogen was observed in this study, which could be attributed to homoacetogenesis, methanogenesis and the degradation of protein.