Evaluation of Mountain Beetle-Infested Lodgepole Pine for Cellulosic Ethanol Production by SPORL Pretreatment

The potentials of deteriorated mountain pine beetle (Dendroctonus ponderosa)-killed lodgepole pine (Pinus contorta) trees for cellulosic ethanol production were evaluated using SPORL pretreatment. The trees were harvested from two sites in the U.S. Arapaho–Roosevelt National Forest, Colorado. The infestation age of the trees varied from 0 to about 8 years. A mild (170°C) and a harsh (180°C) SPORL pretreatments were conducted. The chemical charges were sulfuric acid of 2.21% and sodium bisulfite 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 with their corresponding live trees. Total fermentable sugar productions from dead trees (including a tree laying on the ground, its wood chips are shown in the Figure) were 4–14% higher than corresponding live trees were, 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 wood from the corresponding live tree. The results also demonstrated the robustness of SPORL pretreatment for lodgepole pine.