Enhanced biogas production from sunflower stalks using hydrothermal and organosolv pretreatment

Biomethane production through anaerobic digestion of sunflower stalks was improved by the hydrothermal and isopropanol-based organosolv pretreatments. The pretreatments were conducted at different temperatures (140, 160, 180, and 200 degrees C) for 30 and 60 min with/without addition of 1% sulfuric acid. The pretreatment of stalks with 50% (v/v) aqueous isopropanol containing 1% w/w (based on dry stalks) sulfuric acid at 160 degrees C resulted in the highest lignin removal. Methane production yield of the pre-treated substrate was improved by 45-124% compare to 124 mL CH4/g VS obtained from the digestion of untreated stalks. In the best case, hydrothermal pretreatment at 180 degrees C for 60 min and organosolv pretreatment at 160 degrees C for 30 mm with 1% H2SO4 followed by 45 days anaerobic digestion resulted in 234 and 278 mL CH4/g VS, respectively. Structural analyses of the stalks indicated that lignin removal, crystallinity reduction, and structural modifications by the pretreatments were the main reasons for the improved biogas production. (C) 2015 Elsevier B.V. All rights reserved.