Environmental assessment of olive tree pruning valorization via deep eutectic Solvents: Toward a circular and sustainable biorefinery model

This study uses Life Cycle Assessment (ISO 14040) to evaluate the environmental sustainability of olive tree pruning conversion using deep eutectic solvents in a biorefinery following a circular bioeconomy model. A cradle-to-gate approach was adopted to focus the assessment on the fractionation stages and identify specific critical points in the process. Three fractionation scenarios were compared: Scenario 1 (autohydrolysis, acid hydrolysis, and delignification), Scenario 2 (autohydrolysis and delignification), and Scenario 3 (direct delignification). The results obtained with the SimaPro® software identified that the delignification stage with deep eutectic solvents is the main environmental critical point, contributing significantly to the categories of abiotic depletion and photochemical oxidation, representing in some cases up to 90% of the total impact due to energy and reagent consumption. Scenario 3 proved to be the least sustainable as it did not take advantage of the previous hemicellulose fractions, while Scenarios 1 and 2 showed greater efficiency in the use of biomass. The results indicate that solutions must be sought to reduce the environmental burdens associated mainly with the use of deep eutectic solvents in the delignification stage. In this regard, and as supported by the results of a sensitivity analysis, further research should focus on studying the recovery and recyclability of deep eutectic solvents; this action would reduce waste streams, offset the environmental burdens associated with the solvent, and lead to the comprehensive recovery of olive pruning waste within the biorefinery sector, achieving a potential reduction in overall impacts of up to 40%.