Improving simultaneous saccharification and fermentation by pre-saccharification and high solids operation for bioethanol production from Eucalyptus globulus bark

The European Green Deal emerged as a package of policy initiatives for a green transition, aiming to reach climate neutrality by 2050. Accordingly, the pulp and paper industry has been focused on upgrading residues into value-added products within the forest-based circular economy business model. In this context, this study considered the possibility of using bark, a residue available in high volume on factory floors, for cellulosic ethanol production instead of typical burning for energy generation. Bioconversion of lignocellulosic polysaccharides of bark is a challenge and simultaneous saccharification and fermentation (SSF) setup was chosen to boost cellulosic ethanol production. The introduction of a short pre-saccharification (PS) stage (0, 1 and 4 h) in bioethanol production from Eucalyptus globulus bark, previously submitted to a kraft pretreatment, following an integrated configuration, PS-SSF, at the bioreactor scale improved bioethanol concentration. It was observed that the longer pre-saccharification, the higher productivity. Shifting from this batch PS-SSF (4 h) to a fed-batch PSSSF (4 h) configuration allowed to increase the solids loading from 8% to 20% (w/v), raising the final bioethanol concentration from 27.4 to 75.9 g L-1, and improving by itself the overall productivity more than 25%. These results show that in the pulp and paper mills, an integrated biorefinery should be considered to foster the total resources use within the circular economy model.