Valorisation of Spent Coffee Grounds in integrated biorefineries: a comprehensive review of biofuels and value-added products potential

The coffee-making process generates substantial quantities of organic residues. Spent Coffee Grounds (SCG) represents a major waste stream produced after beverage preparation. Its rich composition in lipids, lignocellulosic fractions, proteins, phenolics and other bioactive compounds makes it a promising feedstock for integrated biorefineries. This review critically evaluates SCG valorisation routes for biofuels and value-added products, with particular attention to oil extraction, biodiesel production, defatted SCG (DSCG) utilisation and biorefinery development. Literature indicates that SCG generally contains approximately 10–20wt.% oil, with a biodiesel conversion efficiency of ∼95%. Nevertheless, biodiesel scalability remains constrained by high acidity, moisture removal, solvent recovery and feedstock logistics. Anaerobic digestion is promising, as DSCG can generate higher methane yields than SCG, with reported values of 336±7 mLCH4/gVS and 310±2 mLCH4/gVS, respectively. Pellet, biochar and activated carbon pathways appear more scalable because they require fewer high-purity separation steps, whereas bioethanol, nutraceutical, bioactive compound and bioplastic routes require more intensive pretreatment, extraction, purification and product validation. Technology Readiness Level, techno-economic feasibility, environmental benefit and scalability indicate that integrated biorefineries are more realistic than single-product valorisation. Coupling Techno-Economic Analysis with Life Cycle Assessment is essential for identifying SCG valorisation pathways that are technically feasible, environmentally beneficial and commercially viable.