Bioeconomy and environmental issues envisage industrial by-products such as Brewer’s
spent grain (BSG) as renewable resources for their recycling and reuse within a biorefinery concept.
This study aimed to investigate the production of bioethanol from subcritical water (subW) pretreated
BSG, following the conversion of the BSG biopolymers cellulose and hemicelluloses. The subW
pretreatment was performed in a batch reactor at 174 ◦C, during 60 min and 5% (w/v) of dry BSG
charge. The behavior of BSG biopolymers under subW pretreatment was monitored by evaluating
the chemical composition of the liquid and solid streams and the chemical and structural changes
caused in the solid residues by scanning electron microscope (SEM), CHNS elemental analysis
and water retention value (WRV). The production of bioethanol from subW-pretreated BSG was
assessed by separate hydrolysis and fermentation (SHF) and also by simultaneous saccharification
and fermentation (SSF) by using the enzymatic cocktail Celluclast 1.5 L (40 FPU/gsolids) and the yeast
Ethanol Red®. The higher bioethanol productivity (1.073 g·L
−1
·h
−1
) and concentration (32.18 g/L)
were achieved by SSF with higher solids’ loading (25%) and following a fed-batch strategy. These
results suggest that subcritical water pretreatment is a promising technology for the valorization of
BSG as a feedstock for second-generation bioethanol production.
