Hydrogen production from sugarcane juice in expanded granular sludge bed reactors under mesophilic conditions: The role of homoacetogenesis and lactic acid production

Abstract

The influence of hydraulic retention time (HRT) (24 to 1 h) on hydrogen production during sugarcane juice fermentation was evaluated in three expanded granular sludge bed (EGSB) reactors under mesophilic conditions (30 ± 1 °C). The sugarcane juice concentrations were 5, 10 and 15 g L−1 in EGSB-5, EGSB-10 and EGSB-15, respectively. Maximum hydrogen production rates were observed under low HRTs, namely, 1 h in EGSB-5 (6.96 l d−1L−1); 1 h in EGSB-10 (19.14 l d−1L−1); and 2 h in EGSB-15 (52.40 l d−1L−1). The main metabolites detected in EGSB-5 and EGSB-10 were acetic (35.0–59.0 %), butyric (10.0–44.0 %) and propionic (8.0–23.0 %) acids. Lactic acid and ethanol were the main metabolites detected in EGSB-15, together comprising more than 53.0% of all metabolite products at HRTs of 24 to 8 h. The maximum hydrogen yields were 0.21, 0.54 and 0.73 mol H2 mol-1 hexose for EGSB-5, EGSB-10 and EGSB-15, respectively. These values can be attributed to homoacetogenesis, with maximum acetic acid values of 59.0%, 50.0% and 25.0% for EGSB-5, EGSB-10 and EGSB-15, respectively.