Deep eutectic solvent pre-treatment of residual biomass streams – Effects on anaerobic degradability

The suitability of residual biomass from biorefineries as biogas substrate, including the effect of DES pre-treatment on biogas potential and biomass composition was evaluated. Three different biomasses, i.e., cork dust, olive tree pruning, and common reed, were treated with a deep eutectic solvent (DES; i.e., choline chloride and formic acid, 1:2 M ratio, 1:10 (g mL −1 ) solid to solvent ratio) under various conditions. While being ineffective under less severe conditions, significantly increased biogas potentials were observed for all biomasses at 130 °C and 40 and/or 60 min of pre-treatment. Cork dust had the highest relative increase in biogas potential of 125 % (130 °C, 60 min). With an increase of 90 mL N g VS −1 (+21 %), olive tree pruning showed the highest absolute increase. Common reed demonstrated a notable increase of 12 %. Concurrently, kinetic modelling revealed shifts in degradation kinetics, such as altered lag phases and higher maximum biogas rates, hereby the Cone Model provided the best fit for the data. The change could be attributed to delignification and retention of the fermentable glucan fraction in the solid biomass. Despite considerable differences among the biomasses, the results underscore the efficacy of DES pre-treatment in enhancing the anaerobic degradability of residual biomass. • DES treatment altered biomass composition and structure. • Pre-treatment retained cellulose, while dissolving hemicellulose and lignin. • DES treatment led to higher biogas yields and change in degradation kinetics. • Biogas yield increase: 125 % (Cork dust), 21 % (Olive tree) and 12 % (Common reed). • Kinetic investigations show increased biogas production rates & altered lag phases.