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The full utilization of agricultural waste and its recycle into a new chain of value are of primary importance for the development of a sustainable and profitable agricultural industry. Chestnut shell waste (CSW) is an interesting case of study, whose valorization has been though partially investigated to date. This work aims at exploring the complete utilization of CSW, in terms of obtaining both value-added compounds and enriched cellulose and lignin fractions. The results were obtained via the unreported combined use of two classes of nonconventional organic solvents, namely natural deep eutectic solvents and bio-based ionic liquids (bio-ILs). At first, combinations of choline chloride (ChCl)-based DESs with an acid, a polyol, or a sugar as hydrogen bond donors were employed for the extraction of polyphenols from the CSW. The best performing system was found to be ChCl:oxalic acid dihydrate (ChCl:Oax2H 2 O). The extraction efficiencies of the DESs tested correlate well with the measured Kamlet−Taft α parameters. After polyphenol removal, the residual solid material was treated with a bio-IL [cholinium glycinate (ChGly)] for further separation of lignin and cellulose. The products obtained by the fractionation process were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis, which confirmed the separation of the residue into a lignin-rich material and a cellulose-rich material. The results obtained were further corroborated by a three parallel reaction model combined with the distributed activation energy model, which allowed for predicting the composition of the pristine CSW and of the ChCl:Oax2H 2 Otreated CSW as well as the two fractions obtained after ChGly treatment. The recyclability of the best performing DES and the recovery of the bio-IL have also been proven, which make the whole process viable and amenable for large-scale applications.

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The traditional use of organic solvents in various branches of industry is being rethought as these compounds very often display high volatility, toxicity and lipophilicity (related to the ability to interact with biological membranes). More recently, developments in the field of Green Chemistry are focusing on the design of more sustainable and cost-effective solvent alternatives like Ionic Liquids (ILs), bio-based solvents and natural deep eutectic solvents (NADESs). The present study aimed at performing an ecotoxicological screening of 15 NADESs using an extensive set of marine and freshwater bioassays, based on different endpoints as the following: immobilization of the crustacean Daphnia magna, growth inhibition of Raphidocelis subcapitata and of Phaeodactylum tricornutum, larval development alterations on the serpulid Ficopomatus enigmaticus and bioluminescence inhibition of Aliivibrio fischeri. What emerged was a general absence of toxicity of all samples. However, both algal assays showed a certain degree of biostimulation, up to over 100% growth increase in respect to controls with 8 out of 15 compounds tested with Raphidocelis subcapitata. Despite NADESs-induced negligible toxicity effects to invertebrates, encouraging their labelling as “sustainable” solvents, the liability of their intentional or accidental release into aquatic systems may represent a serious risk in terms of ecosystem functioning impairments.

Key features of the deep eutectic solvent-microwave assisted simultaneous extraction of polyphenols and delignification pretreatment of chestnut shell waste are presented.

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