The use of thermochemical pretreatments to improve the anaerobic biodegradability and biochemical methane potential of the sugarcane bagasse

• Enhancing anaerobic biodegradability of sugarcane bagasse using pretreatments.
• Delignification for improving biochemical methane potential of sugarcane bagasse.
• Production of renewable energy via anaerobic digestion of sugarcane bagasse.
• Sugarcane bagasse pretreatment optimisation by using response surface methodology.

Lignocellulosic material can be used as biomass for power generation via biogas if it is pretreated to improve the anaerobic hydrolysis step, by either solubilising the hemicellulose (total reducing groups, TRG) or removing lignin (Lig), with consequent exposition of the cellulose fibre to anaerobic degradation. We evaluated the effects of acid, alkaline, and hydrothermal pretreatments on sugarcane bagasse to increase its anaerobic biodegradability and biochemical methane potential (BMP). The highest sugar production (31.14 g TRG/g substrate) was achieved with the acid pretreatment in 6.4 min at 138 °C, with a HCl concentration of 0.63 M, and the highest lignin removal (23.24 g Lig/g substrate) was found with the alkaline pretreatment after 47 min at 184 °C and a NaOH concentration of 0.8 M. However, the best values of BMP (197.5 L CH4/kg substrate) and anaerobic biodegradability (27.4%) were achieved by the hydrothermal pretreatment after 10 min at 200 °C, which was sufficient to generate power of 6.8 MJ/kg substrate. The results showed that the methane derived from the anaerobic digestion of these hydrolysates produced less energy than the direct burning of the dry bagasse. Thus, the recovered lignin, with its high added-value, may be used to improve environmental sustainability and profitability of the process. In this case, the alkaline pretreatment extracted 80.2% of the lignin present in the bagasse, and the hydrolysate could generate 313.4 L CH4/kg substrate.