High-solids ethanol production from waste paper through consolidated bioprocessing using advanced Saccharomyces cerevisiae strains.

High-solids simultaneous saccharification and co-fermentation (SScF) of paper wastes were compared in lab-scale fed-batch (vertical) and batch (horizontal) bioreactor cultures. Fermentation of untreated label backing (LB), multilayer paper-based packaging (ML) and potato paper sacks (PS) paper wastes were optimised for solid loading to minimise the exogenous enzyme dosage with advanced consolidated bioprocessing (CBP) yeast strains, to achieve maximum technical performances in terms of ethanol concentration, yield and enzyme efficiency. Using cellulase-producing CBP yeast (Cellusec® 2.0, 3.3 or 4.0) improved the enzyme efficiency by 1.5-fold at a final solid loading of 20% (w/w dry) compared to a higher solid loading of 30% (w/w) in fed-batch SScF. At 20% (w/w) solid loading and 2 FPU/g ds, enzyme efficiencies of 0.109, 0.078 and 0.067 g ethanol/FPU were recorded with corresponding ethanol titres of 59.3, 45.2 and 38.2 g/L and ethanol yields of 58.5, 43.9 and 57.1% of the theoretical maximum for LB, PS and ML, respectively. Whereas batch SScF at 30% (w/w) solid loading and 2 FPU/g ds achieved higher ethanol titres of 65.6, 50.7 and 54.3 g/L, the corresponding ethanol yields and enzyme efficiencies were markedly lower at 36.7, 28.0 and 52.1% of the theoretical maximum and 0.069, 0.050 and 0.062 g ethanol/FPU for LB, PS and ML, respectively. Fed-batch SScF in a vertical bioreactor at 20% (w/w) final solid loading was, therefore, the preferred configuration due to more favourable enzyme efficiencies, ethanol yields and enzyme cost.