Effect of hydrothermal pretreatment of sunflower oil cake on biomethane potential focusing on fibre composition

The aim of this study was to elucidate the effect of hydrothermal pretreatment at 25, 100, 150 and 200 °C on fibre composition and the biomethane potential of sunflower oil cake (SuOC). An increase in pretreatment temperature from 25 to 200 °C caused a decrease in hemicellulose content in the solid pretreated fraction from 13 to 6% while the lignin content increased by 16%. Soluble compounds also increased with temperature. Digestion of solid fractions from pretreatments at 25, 100, 150 and 200 °C in batch assays at 35 ± 1 °C resulted in methane yields of 114 ± 9, 105 ± 7, 82 ± 7 and 53 ± 8 mL CH4 g−1CODadded, respectively. The corresponding methane yields for the liquid fractions were 276 ± 6, 310 ± 4, 220 ± 15 and 247 ± 10 mL CH4 g−1CODadded, respectively. Therefore the overall methane yield was highest for SuOC pretreated at 100 °C; however, this value was only 6.5% higher than that achieved after pretreatment at 25 °C.