Ethanol production from 'Eucalyptus' plantation thinnings

Abstract

Conditions for optimal pretreatment of eucalypt ('Eucalyptus dunnii') and spotted gum ('Corymbia citriodora') forestry thinning residues for bio ethanol production were empirically determined using a 33 factorial design. Up to 161 mg/g xylose (93% theoretical) was achieved at moderate combined severity factors (CSF) of 1.0-1.6. At CSF > 2.0, xylose levels declined, owing to degradation. Moreover at high CSF, depolymerisation of cellulose was evident and corresponded to glucose (155 mg/g, ~33% cellulose) recovery in pre hydrolysate. Likewise, efficient scarification with Cellic® CTec 2 cellulase correlated well with increasing process severity. The best condition yielded 74% of the theoretical conversion and was attained at the height of severity (CSF of 2.48). 'Saccharomyces cerevisiae' efficiently fermented crude 'E. dunnii' hydrolysate within 30 h, yielding 18 g/L ethanol, representing a glucose to ethanol conversion rate of 0.475 g/g (92%). Based on our findings, eucalyptus forest thinnings represent a potential feedstock option for the emerging Australian bio fuel industry.