Nuovi materiali e composti da sottoprodotti della lavorazione del caffè: un approccio green in una prospettiva di economia circolare

Driven by population growth, the global generation of solid waste is expected to rise in the coming years. Within a circular economy framework, waste can be valorised both as a secondary raw material and as an energy source. Furthermore, the circular economy is regarded as a key instrument for achieving the Sustainable Development Goals outlined in the UN 2030 Agenda, by promoting the sustainable management of water, resources, and energy. In this context, agri-food residues represent promising feedstocks for the recovery of organic compounds, cellulose, and carbon, as well as for the energy production. Here, the valorisation of two coffee byproducts, coffee silverskin and spent coffee grounds, was investigated as potential source of bioactive compounds, cellulose and carbon, with the aim of producing value-added products, in line with circular economy principles, that can be utilized across various sectors. Caffeine and phenolic compounds, including chlorogenic acids, were successfully extracted in water and ethanol from both CS and SCGs, along with triglycerides and diterpenes in organic extracts. Different methodologies were employed for the extraction processes; extraction at room temperature allowed a good recovery of products, but the yields were slightly higher than those obtained from MAE and UAE, which required 30 and 15 min, respectively, compared to 7 days with water and 3 days with the other solvents. Cellulose extraction for paper production and the nanocellulose isolation were also carried out, yielding satisfactory results. The CS-cellulose pulp was valorised mixed with virgin and recycled pulp in the preparation of paper bags in an industrial process. To this end, an LCA study was conducted to assess the environmental impact of the treatments, revealing that the bleaching process, if present, represented the most impactful step. In addition, biochars and activated carbons from CS and SCGs were synthetized and characterized. CS-biochars produced at 700 and 800 °C showed promising performance in reducing E. coli in contaminated water. Preliminary tests with CS-biochar, activated with KOH at 700 °C, exhibited good efficiency in MB adsorption from aqueous solution; results were consistent with the performance of commercial activated carbon. The electrocatalytic activity toward the oxygen reduction reaction (ORR) was investigated to evaluate the combined influence of pyrolysis temperature, N,P co-doping, and NH₄HCO₃ activation. The sample co-doped with N and P, prepared by pyrolysis of SCGs at 900 °C with NH₄HCO₃ activation, exhibited the highest ORR performance, underscoring the synergistic contribution of elevated pyrolysis temperature, efficient dopant incorporation, and the formation of graphitic nitrogen within a hierarchical porous carbon network.