Integrated biorefinery approaches for the sustainable valorization of agricultural residues into biofuels, bioplastics, and bioactive compounds

More than 5.5 billion tons of agricultural waste are generated every year globally, presenting major environmental issues and offering enormous potential as renewable bioresources. This review discusses an integrated assessment of various biorefinery-based strategies for the sustainable valorization of agricultural waste into biofuels, bioplastics and bioactive compounds. The discussion covers thermochemical, biochemical and hybrid biotechnological pathways, including fermentation, Solid- State Fermentation, pyrolysis and hydrothermal liquefaction with special emphasis on system-level optimization for resource efficiency. Microbial and enzymatic valorization by Bacillus licheniformis and Aspergillus niger showed 1321 ± 13 U/mL protease and 9.6 ± 0.76 IU/gds cellulase, respectively, thereby justifying the feasibility of enzyme-driven conversions. Thermochemical processes resulted in a yield of up to 20.6 wt% bio-oil with a heating value of 17.23 MJ/Nm³, whereas the products obtained through integrated fermentation processes are 0.703 g/g ethanol from sugar beet pomace and 18.9 ± 0.3 g/L ethanol from spent coffee grounds. Next-generation nanobiocatalytic and hybrid thermo-biochemical systems enhanced conversion efficiency by 25–30 %, enabling the realization of scalable circular biorefineries. Techno-economic assessments and life cycle analyses indicate that greenhouse gas emissions can be reduced by up to 90 percent compared to conventional fossil-based alternatives. Review highlights the urgent need for the development of integrated multi-product biorefinery systems to facilitate the transition from agricultural waste to high-value bioproducts, aligning with the principles of a circular bioeconomy.