Anaerobic Digestion of Lignocellulosic Materials Using Ethanol-Organosolv Pretreatment

Biomethane potential from the anaerobic digestion of rice straw, hazelnut skin, and cocoa bean shell was investigated after applying an organosolv pretreatment. Pretreatment of the three lignocellulosic materials was performed at 150°C and 180°C for 60 min using 50% (v/v) ethanol as organic solvent. Afterward, untreated and pretreated feedstocks were used in batch biomethane production tests under mesophilic conditions (37 ± 1°C). The highest efficiency was obtained pretreating the rice straw at 180°C, which resulted in a 42% higher biomethane production yield from the 235 mL CH4/g volatile solid obtained with the untreated straw. A lower increase was achieved for hazelnut skin, whereas a partial inhibition of the biomethane production was observed for cocoa bean shell, compared with untreated materials. Compositional analyses showed that, after organosolv pretreatment, a reduction of the lignin and hemicellulose content was achieved in the three lignocellulosic residues, together with a relative increase of cellulose content.