Effect of Bark on Ethanol Production from Steam-Pretreated Spruce

Bark and bark-containing residues have the potential as raw material for ethanol production due to their abundance and low cost. However, the properties and chemical composition of bark may influence the conversion process. Balázs Frankó of Lund University in Sweden assessed the effect of bark on the overall bioconversion in separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF).

Mixtures of different proportions of spruce bark and wood chips were subjected to SO₂-catalyzed steam pretreatment at 210 °C for five minutes. The highest final ethanol concentration was recorded in the samples without bark and decreased significantly with increasing proportions of bark in both processes. Moreover, the ethanol yield also decreased as the fraction of bark also increased.

Results show that it is more difficult to hydrolyze spruce bark than wood chips. Bark had an adverse effect on the whole bioconversion process due to its lower enzymatic hydrolyzability.