Influence of bark inclusion on fuel ethanol production from steam pretreated spruce

Bark, which is mainly used as a cheap energy source, has the potential to be a source of polyphenolic compounds and also a potential feedstock for bioconversion to ethanol. However, the presence of bark also constitutes many challenges for the wood-to-ethanol process. Therefore, the aim of the present work was to assess the feasibility of utilizing bark or bark together with spruce wood chips for fermentative conversion of biomass into ethanol. Bark mixed with spruce at different ratios were subjected to SO₂-catalyzed steam pretreatment. The compositions of the raw materials and pretreated materials were analyzed and component yields were compared to evaluate how bark content affects the efficiency of steam pretreatment. Enzymatic hydrolysis experiments were run in order to evaluate the impact of bark inclusion on hydrolysability of pretreated materials. Separate hydrolysis and fermentation was performed to assess the fermentability of the pre-hydrolyzed materials. Simultaneous saccharification and fermentation experiments were performed to compare the two process configurations in terms of overall ethanol yield. In order to increase hydrolysability of spruce bark, optimization of the SO₂-catalyzed steam explosion was performed.