One-pot bioethanol production from brewery spent grain using the ethanologenic Escherichia coli MS04

Lignocellulosic biomass residues constitute an alternative for energy generation. In this work, brewery spent grain (BSG) were used as feedstock to produce ethanol using a recombinant Escherichia coli MS04 strain. A sequential process involving pretreatment, saccharification and fermentation steps in one-pot bioreactors, without solids removal, was proposed. Different diluted acid pretreatment times (1 and 1.5 h) using a 15% (w/w) solids load to obtain high monosaccharides yields were evaluated. After the pretreatment and saccharification, the proposed strategy converted the polysaccharides contained in BSG into fermentable pentoses and hexoses, obtaining a syrup composed by monosaccharides (60 g/L), furfural (0.39 g/L), hydroxymethylfurfural (0.07 g/L) and acetic acid (2.56 g/L), which was afterwards fermented for the bioethanol generation. After 30 h, ethanol production resulted in 29.5 ± 0.41 g/L, which means a volumetric productivity of 0.98 g EtOH/Lh based on the consumption of the glucose, xylose and arabinose. These results mean a global yield of 251 L EtOH/ton BSG of this feedstock and were accomplished without the inhibition caused by acetic acid formation (6.87 g/L). Furthermore, the proposed process in this work was developed in a sequential pathway, which comprises an operational advantage to exploit the BSG in the production of second-generation bioethanol.