Effect of thermal, acid, alkaline and alkaline-peroxide pretreatments on the biochemical methane potential and kinetics of the anaerobic digestion of wheat straw and sugarcane bagasse

• Highest methane productions were obtained from thermally pretreated whole slurries.
• Furfural and 5-HMF released in acid pretreatment inhibited methane production.
• High phenolic compounds release required a microorganism’s acclimation period.
• Lignin degradation provided the highest hydrolysis rates when inhibition was defeated.
• A novel kinetic model is proposed combining hydrolysis and microorganisms inhibition.

The effect of thermal, acid, alkaline and alkaline-peroxide pretreatments on the methane produced by the anaerobic digestion of wheat straw (WS) and sugarcane bagasse (SCB) was studied, using whole slurry and solid fraction. All the pretreatments released formic and acetic acids and phenolic compounds, while 5-hydroxymetilfurfural (HMF) and furfural were generated only by acid pretreatment. A remarkable inhibition was found in most of the whole slurry experiments, except in thermal pretreatment which improved methane production compared to the raw materials (29% for WS and 11% for SCB). The alkaline pretreatment increased biodegradability (around 30%) and methane production rate of the solid fraction of both pretreated substrates. Methane production results were fitted using first order or modified Gompertz equations, or a novel model combining both equations. The model parameters provided information about substrate availability, controlling step and inhibitory effect of compounds generated by each pretreatment.