Assessment of organosolv, hydrothermal, and combined organosolv and hydrothermal with enzymatic pretreatment to increase the production of biogas from Napier grass and Napier silage

The effects of organosolv, hydrothermal, combined organosolv, and hydrothermal processes followed by enzyme pretreatment on Napier grass and silage were evaluated for their efficacy in enhancing methane production. The pretreatment of Napier grass and silage by organosolv followed by enzymatic hydrolysis significantly improved methane yields by 1.9–2.0 times compared with untreated Napier grass and silage. In addition, organosolv-treated Napier grass followed by enzymatic hydrolysis yielded 7.8% more methane (410 mL/g-volatile solidadded (VSadded)) than organosolv-treated silage followed by enzymatic hydrolysis (378 mL/g-VSadded). Organosolv pretreatment enhanced lignin removal, while hydrothermal pretreatment effectively hydrolyzed hemicellulose. Delignification and reduction of crystallinity during organosolv improve the degradability of Napier grass and silage, resulting in their significantly higher energy recovery of 14.8 and 13.6 kJ/g-VSadded, respectively, which were higher than the energy recovery attained from the hydrothermal process.