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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. |
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