Impact of various thermo chemical pretreatments on solubilisation and methane production of sunflower stalks

The conversion of sunflower stalks into biomethane by batch mesophilic anaerobic digestion was investigated in this work. Methane potential of sunflower stalks (192 ± 2 mLCH4/g VS) was increased by several thermo-chemical pretreatments: NaOH, H2O2, Ca(OH)2, HCl and FeCl3. The highest production (259 ± 6mLCH4/ g VS) corresponding to a 31.4% increase was reached for the treatment at 55°C with 4% NaOH during 24h. More than 90 % of hemicelluloses were removed by applying acidic pretreatment (10% FeCl3 or 4% HCl) at 170 °C. Oxidative and alkaline pretreatment (4% NaOH, 4% H2O2, 4% Ca(OH)2) at 55°C were found to be more efficient to dissolve lignin than acidic pretreatment with a lignin removal around 22%.A negative linear correlation (R2 = 0.895) was found between the lignin content of raw and pretreated sunflower stalks and the methane potential