An alternative for value aggregation to the sugarcane chain: Biohydrogen and volatile fatty acids production from sugarcane molasses in mesophilic expanded granular sludge bed reactors

Abstract

The main objective of this study was to investigate the influence of hydraulic retention time (HRT) (24–1 h) on continuous biohydrogen production from sugarcane molasses in three expanded granular sludge bed (EGSB) reactors under mesophilic conditions (30 ± 1 °C). The sugarcane molasses concentrations were 5 g L−1 (EGSB-5), 10 g L−1 (EGSB-10) and 15 g L−1 (EGSB-15). In EGSB-5, hydrogen was not detected. The main volatile fatty acids produced were acetic (30.0–50.0%), butyric (13.0–30.0%) and propionic (13.0–45.0%) acids. In this reactor, the formation of acetic acid through the homoacetogenesis reaction (23–51%) explains the absence of hydrogen. The maximum hydrogen production rates were observed at an HRT of 1 h in EGSB-10 (4.56 L day−1 L−1) and EGSB-15 (13.92 L day−1 L−1). The main metabolites detected in EGSB-10 and EGSB-15 were butyric (8.0–51.0%), lactic (6.0–50.0%) and propionic (4.0–57.0%) acids. The metabolic pathways responsible for hydrogen production in both reactors were similar and were associated with increased production of butyric acid and lactic acid, thus explaining the low hydrogen yields (maximum of 0.25 mol H2 mol−1 hexose).