Comparative study on hydrolysis and bioethanol production from cardoon and rockrose pretreated by dilute acid hydrolysis

Bioethanol production potential from cardoon (Cynara cardunculus) and rockrose (Cistus ladanifer), pretreated by diluted acid hydrolysis (DAH), was studied and compared by both, separate enzymatic hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes. DAH pretreatment allowed an increase of 5 fold to cardoon and 16 fold to rockrose in cellulose accessibility towards enzymatic hydrolysis. Both plants showed better overall fermentation efficiency and ethanol yield in SSF than in SHF also with shorter processing periods, 24 h against 72 + 24 h, respectively. Results obtained for rockrose are about half the concentration and volumetric productivity of ethanol and 60% of the overall fermentation efficiency of those obtained for cardoon. The recalcitrance of rockrose to enzymatic hydrolysis was explained by higher abundance of lignin and extractives than in cardoon. Comparing the steam explosion (SE) and DAH pretreatments, the former was more advantageous for the recalcitrant rockrose in terms of enzymatic saccharification yield.