Biochemical hydrogen and methane potential of sugarcane syrup using a two-stage anaerobic fermentation process

• Hydrogen recovery by granules and suspended forms were not different.
• Highest hydrogen recovery was achieved by the immobilized C. butyricum TISTR1032.
• Effluent from H2 fermentation by mixed cultures gave a higher methane production.
• Total energy recovery was highest when mixed cultures were the inoculum.
• Two-stage process revealed a better process stability and energy recovery.

The potential of using a two-stage hydrogen and methane fermentation of sugarcane juice was studied. The effects of pure and mixed culture as inocula on hydrogen production were compared. Additionally, the effects of pure culture inocula form, i.e., free cells or immobilized cells of Clostridium butyricum TISTR1032 was compared to different forms of mixed cultures, i.e., granules or suspended cells of heat-treated upflow anaerobic sludge blanket (UASB) granules. The hydrogenogenic effluents from all treatments were used as substrates to evaluate the potential of methane production by non-pretreated UASB granules. Results showed that a pure culture gave a higher hydrogen production potential and a shorter lag time in comparison to mixed cultures. Immobilized cells of C. butyricum TISTR1032 gave a hydrogen production potential that was 1.2 times higher than that of free cells. However, there was no significant difference in hydrogen production potential of granules and suspended cells. Moreover, hydrogenogenic effluent from the first stage fermentation showed a high efficiency in methane production by non-pretreated UASB granules. Although fermentation of mixed cultures resulted in lower hydrogen yield, its hydrogenogenic effluent yielded a higher methane production than that of pure culture. Therefore, overall energy yield when using mixed cultures in hydrogen production stage was higher. The two-stage hydrogen and methane production process removed 94–95% of chemical oxygen demand (COD) resulting in energy recovery in the range of 12–13.4 kJ/gCODadded. Results indicated that the COD removal efficiency and the energy recovery from two-stage hydrogen and methane production was improved 6–7 fold when compared to hydrogen production alone.

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