Spent coffee grounds: Insights and future prospects for bioenergy and circular economy applications

Coffee is the second most consumed beverage in the world and the second most traded commodity, behind only petroleum. Spent coffee grounds (SCG), a solid residue generated after coffee preparation, are produced on a large scale but are still underutilized. Its valorization can bring environmental, economic, and social benefits, boosting the circular bioeconomy. This bibliometric review analyzed 403 articles published in the Web of Science over more than 10 years, highlighting the revaluation of SCG and its integration into biorefineries as a sustainable strategy. With the advancement of biorefineries, studies indicate the possibility of almost complete recovery of SCG, although research in this area is still limited. Several studies report its application in producing biocomposites, bioplastics, biofuels, adsorbents, and food additives, reducing the environmental footprint and promoting sustainable alternatives to petroleum-derived materials. The valorization of SCG reduces costs, minimizes waste, and boosts the bioeconomy, but most studies are still in the laboratory phase and need to be scaled up for industry. The SCG biorefinery has the potential to produce high-value bioactive compounds and bioenergy on a large scale, increasing its economic viability. In conclusion, future research should focus on producing biochar, biogas, bioactive extraction via the SCG biorefinery, and improving geopolymer materials for green construction.