Development of an Energy Biorefinery Model for Chestnut ( Castanea sativa Mill.) Shells

Chestnut shells (CS) are an agronomic waste generated from the peeling process of the chestnut fruit, which contain 2.7–5.2% ( w / w ) phenolic compounds and approximately 36% ( w / w ) polysaccharides. In contrast with current shell waste burning practices, this study proposes a CS biorefinery that integrates biomass pretreatment, recovery of bioactive molecules, and bioconversion of the lignocellulosic hydrolyzate, while optimizing materials reuse. The CS delignification and saccharification produced a crude hydrolyzate with 12.9 g/L of glucose and xylose, and 682 mg/L of gallic acid equivalents. The detoxification of the crude CS hydrolyzate with 5% ( w / v ) activated charcoal (AC) and repeated adsorption, desorption and AC reuse enabled 70.3% ( w / w ) of phenolic compounds recovery, whilst simultaneously retaining the soluble sugars in the detoxified hydrolyzate. The phenols radical scavenging activity (RSA) of the first AC eluate reached 51.8 ± 1.6%, which is significantly higher than that of the crude CS hydrolyzate (21.0 ± 1.1%). The fermentation of the detoxified hydrolyzate by C. butyricum produced 10.7 ± 0.2 mM butyrate and 63.9 mL H 2 /g of CS. Based on the obtained results, the CS biorefinery integrating two energy products (H 2 and calorific power from spent CS), two bioproducts (phenolic compounds and butyrate) and one material reuse (AC reuse) constitutes a valuable upgrading approach for this yet unexploited waste biomass.