Lessons learned from the treatment of organosolv pulp with ligninolytic enzymes and chemical delignification agents

Although organosolv pretreatment allows extensive delignification of beech wood, the residual lignin present in the pulp may hinder the subsequent hydrolysis of the cellulose into fermentable sugars. With the purpose of increasing sugar production from cellulose hydrolysis, enzymatic and chemical oxidation stages were applied to the pulp previously to a stage of enzymatic hydrolysis with cellulases. Neither lignin content was reduced, nor sugar yield was improved after the versatile peroxidase treatment. On the other hand, laccase oxidation caused an increase in total lignin and kappa number and did not influence digestibility. Similarly, the chemical oxidation with H₂O₂ had also a negligible impact on the sugar yield. Only a significant removal of the lignin content in fibers was attained after ethanol wash, also confirmed by FT-IR analysis, which allowed increasing cellulose digestibility by 8.4%, and reducing the phenol content of the hydrolysate by 45.5%. Although the improvement of cellulose digestibility was lower than expected, this work provides valuable lessons for practical use on the opportunities of organosolv pulp.