Evaluation of Mountain Beetle-Infested Lodgepole Pine for Cellulosic Ethanol Production by Sulfite Pretreatment to Overcome Recalcitrance of Lignocellulose

The potentials of deteriorated mountain pine beetle (Dendroctonus ponderosae)-killed lodgepole pine (Pinus contorta) trees for cellulosic ethanol production were evaluated using the sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL) process. The trees were harvested from two sites in the United States Arapaho-Roosevelt National Forest, Colorado. The infestation age of the trees varied from zero to about 8 years. Mild (170 °C) and harsh (180 °C) SPORL pretreatments were conducted. The chemical charges were sulfuric acid of 2.21% and sodium bisulfite of 8% on oven dry wood for the harsh and half of those for the mild pretreatment. The results suggest that beetle-caused mortality enriched glucan content by as much as 3 percentage points (or 7.5%) in wood. The glucan enrichment seems to increase with infestation age. The enriched glucan can be captured after SPORL pretreatment followed by enzymatic hydrolysis. The killed trees are more susceptible to SPORL pretreatment, which enhanced substrate enzymatic digestibility (SED). Enzymatic hydrolysis glucose yields (EHGY) from killed trees were about 5−20% higher than those from their corresponding live trees. Total fermentable sugar productions from dead trees (including a tree laying on the ground) were 4−14% higher than corresponding production from live trees, depending on pretreatment conditions and infestation age. An ethanol yield of 267 L/metric ton of wood or 69% theoretical value was achieved from a tree infested 4 years, 7% higher than the 250 L/metric ton of wood from the corresponding live tree. The results also demonstrated the robustness of SPORL pretreatment for lodgepole pine.