Increased biogas production from wheat straw by chemical pretreatments

This work investigated the effect of three different chemical pretreatment methods on the biogas production from the anaerobic digestion of wheat straw. The lignocellulosic material was separately pretreated using i) the organic solvent N-methylmorpholine N-oxide (NMMO) at 120 °C for 3 h, ii) the organosolv method, employing ethanol as the organic solvent at 180 °C for 1 h and iii) using an alkaline pretreatment with NaOH at 30 °C for 24 h. All the pretreatments were effective in increasing the biomethane production yield of wheat straw. In particular, the cumulative biomethane production yield of 274 mL CH4/g VS obtained with the untreated feedstock was enhanced by 11% by the NMMO pretreatment and by 15% by both the organosolv and alkaline pretreatment. The three pretreatment methods had a different impact on the chemical composition of the straw. NMMO hardly changed the amount of carbohydrates and lignin present in the original feedstock. Organosolv had a major impact on dissolving the hemicellulose component, whereas the alkaline pretreatment was the most effective in removing the lignin fraction. In addition to the increased biogas yields, the applied pretreatments enhanced the kinetics of biomethane production.