초록
<P><B>Abstract</B></P> <P>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<SUP>−1</SUP> 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<SUP>−1</SUP>L<SUP>−1</SUP>); 1 h in EGSB-10 (19.14 l d<SUP>−1</SUP>L<SUP>−1</SUP>); and 2 h in EGSB-15 (52.40 l d<SUP>−1</SUP>L<SUP>−1</SUP>). 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 H<SUB>2</SUB> mol<SUP>-1</SUP> 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.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A high hydrogen production rate was achieved with a low HRT. </LI> <LI> HLa and EtOH production was favored by decreasing the substrate availability. </LI> <LI> H<SUB>2</SUB> production from HLa was favored by increasing the substrate availability. </LI> <LI> The occurrence of homoacetogenesis was not influenced by the decrease in HRT. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>