Cascaded biorefineries for agro-industrial biomass residues: Sustainable waste-to-value engineering

Abstract

Agro-industrial processing generates large, compositionally diverse residue streams that remain underutilised despite their potential to support circular production of chemicals, fuels and functional materials. This review develops a comparative engineering framework for ten major residue classes comprising spent coffee grounds, brewery spent grain, olive mill waste, cocoa by products, citrus processing waste, sugarcane bagasse, tea waste, date pits, palm kernel shells and rice husk. These residues are produced in substantial quantities and are concentrated at processing sites, which lowers collection burdens compared with field dispersed biomass. Together, they represent an estimated 183–213 million tonnes of dry matter per year. The analysis integrates feedstock composition, moisture content, pretreatment requirements, biochemical and thermochemical conversion pathways, advanced-materials routes, techno-economic evidence and life-cycle performance within a value-ranked cascade architecture. The evidence shows that single-product pathways underperform when high-value lipids, phenolics, proteins or soluble carbohydrates are not recovered before conversion of the residual solids. Biodiesel-only routes, for example, capture only approximately 10–20% of the revenue attainable through sequential cascades that recover specialty extracts, fermentation products, biogas and carbon materials. Quantitative thresholds for anaerobic-digestion inhibition, membrane fouling and environmental performance are consolidated, indicating that upstream removal of long-chain fatty acids, polyphenols, d-limonene and caffeine is required before effective biological conversion. The review also identifies an underexplored opportunity to co-process low-moisture date pits with high-moisture spent coffee grounds or brewery spent grain, reducing drying-energy penalties and strengthening circular-bioeconomy options in arid regions. Commercial deployment appears most credible in co-located, regionally adapted plants that align residue supply, shared utilities, regulatory requirements and product markets. The resulting framework distinguishes evidence-supported cascade configurations from unresolved scale-up gaps and identifies feedstock–process combinations that warrant pilot validation before industrial adoption.