Valorization of Agroindustrial Waste from Chestnut Production

In recent years, the consumption of fruits of European chestnut has considerably enhanced due to theirpositive health effects. However, the chestnut peeling process generates solid residues (inner and outershells), which account for about 10-15% of the whole chestnut weight. In the present study, an integrationbetween a chemical and a thermochemical process is proposed as a valorization route for the chestnutresidues: the extraction of polyphenols, a class of strong natural antioxidants, and the slow pyrolysis forbiochar production. The chestnut residues after the polyphenols extraction are used as pyrolysis feedstock,and the produced biochars are applied as adsorbing materials to simplify the recovery of the extractedpolyphenols.The aim of this study is to evaluate how the physical and chemical characteristics of biochar from chestnutresidues influence the adsorption of polyphenols. The biochar production was carried out in a slow pyrolysisreactor using two feedstocks (as received and post-extraction chestnut residues) and three pyrolysistemperatures (500 °C, 600 °C and 700 °C), thus resulting in six different biochars. Each biochar was used asan adsorbent material for the polyphenols in the aqueous extracting solution obtained from chestnut residues.Specific classes of polyphenols were considered, such as non-tannin polyphenols, hydrolysable tannins andcondensed tannins. The adsorption efficiency of biochar increases in the char produced at 700 °C for both theconsidered feedstocks. The analysis of the specific polyphenols groups shows that, despite having an overalladsorption capacity much lower than activated carbon, biochars have a great selectivity for the adsorption ofnon-tannin polyphenols.