Consolidated bioprocessing of beech wood to of ethanol in a multispecies biofilm membrane reactor enhanced by fungal in situ lignin modification

Beech and other hardwood residues are attractive lignocellulosic feedstocks for biorefineries due to their year- round availability and their high energy density. However, they typically show a higher lignin content and are more recalcitrant to enzymatic sugar release than typical herbaceous residues. Consequently, harsh pretreatment conditions are required, leading to an increased consumption of energy and to the formation of enzyme and fermentation inhibitors.

In order to enable efficient saccharification of wood at overall milder pretreatment conditions, we investigate the combination of steam pretreatment and an in situ biological treatment with lignin degrading fungal strains during consolidated bioprocessing of beech wood to ethanol based on a consortium of microorganisms. To select a suitable fungal strain, a screening of seven white rot fungi was performed by growing them in submerged and biofilm cultures on mildly steam pretreated beech wood followed by enzymatic hydrolysis of the residual solids. The treatment with Irpex lacteus for 14 days in a biofilm reactor decreased the lignin content of beech wood and almost doubled the glucose yields in enzymatic hydrolysis compared to the control receiving only steam pretreatment. Furthermore we investigate how the steam pretreatment conditions are related to the extent of lignin degradation and digestibility improvement by fungal treatment.

For maximal process integration we will incorporate Irpex lacteus in a defined consortium of T. reesei, S. cerevisiae and S. stipitis growing in a biofilm membrane reactor that enables concomitant delignification, enzymatic hydrolysis of carbohydrates and ethanol fermentation of the released sugars in one reactor.