(582cq) The Effect of Bark Inclusion On Bioethanol Production in a Spruce-to-Ethanol Process

In order to face up to climate change, one of our greatest environmental challenge, greenhouse gas emissions have to be reduced. One way to fulfill this intention is to replace fossil fuels in the transport factor, with biofuels, such as bioethanol. The production of fuel ethanol from softwood is well documented; and spruce is considered a promising abundant biomass source for bioethanol production in Sweden. Low-cost forest residues will contain large amounts of bark but the inclusion of bark in the feedstock have not be investigated to a large extent.  The composition of spruce bark is very complex. The bark could have an adverse effect on the wood-to-ethanol process in many ways.  For instance, the high lignin content of spruce bark can render the material more recalcitrant to hydrolysis, it could also contain several compounds such as extractives and phenolics that could be inhibitory to the yeast. Therefore, the inclusion of spruce bark in the production process was investigated.

The influence of bark has been studied by increasing the amount of bark from 0% to 100% (based on dry weight). The mixed materials were impregnated with SO₂ (2.5% w/w moisture) prior steam pretreatment at 190^oC for 5 min. Pretreated materials have been evaluated by analysis of solid and liquid phases. Enzymatic hydrolysis, fermentation of the liquid phase (fermentability) and simultaneous saccharification and fermentation (SSF) were performed to determine the sugar and ethanol yield. Enzymatic hydrolysis have been performed at 5% water-insoluble solid (WIS), while SSF have been performed at 10% WIS content in order to avoid the impact of high WIS content. It has been planned to continue the study with performing SSF at high WIS content in batch, fed-batch mode and also with pre-hydrolysis in order to become aware of the best possible process configuration that can be applied to achieve high ethanol concentration in the broth and also high ethanol yield, thus to reduce production cost of the process. In mixtures, where bark inclusion had a negative effect, compared to just spruce chips, methods, such as running low pressure steam through the material before pretreatment, treatment with boiling water before or after pretreatment and leaching with hot dilute acid, can also be the target of future research to eliminate the negative effects of bark on the process.