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 (53.8 ml H2/gVS) was obtained under thermophilic condition (60 C), 53.5% and 198% higher than the values under mesophilic (37 C) and extremethermophilic (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 67.8 ml 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 7899 mg/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.