Integrated biorefinery pathways for agricultural waste valorization: a review of conversion technologies and life cycle assessment approaches

Abstract

Wastes from agriculture amount to more than 4 billion tonnes per year globally, posing an environmental challenge and an opportunity for sustainable bioenergy production. A systematic review of biorefinery frameworks for agricultural waste (corn stover, sugarcane bagasse, wheat straw, and rice straw) in the circular bioeconomy is presented. The initial literature search across Google Scholar, ScienceDirect, and Web of Science (2011–2025) yielded 113,221 documents, of which 14 peer-reviewed studies were selected based on strict inclusion criteria and underwent a detailed synthesis. The reviewed studies show that an integrated biorefinery can produce 3–5 value-added products from a single feedstock (bioethanol, biogas, biochar, and platform chemicals). Reported greenhouse gas reduction benefits, however, are very sensitive to methodology choice, such as allocation method (economic: 67–72%; substitution: 85–90%), system boundaries (cradle-to-gate vs. cradle-to-grave), biogenic carbon accounting (dynamic accounting reduces reported reductions by 5–10%) and geographic grid carbon intensity (coal-dependent grids: 55–70%; low-carbon grids: >80%). There is significant variation in Geographic synthesis: Brazil reduces GHGs between 80 and 90% (∼110 g CO₂/kWh grid), while India and China reduce GHGs between 55 and 65% (∼525–670 g CO₂/kWh grid). Major challenges to scaling up include the lack of established LCA methodologies for agro-waste systems, the under-representation of indirect impacts (land-use change, changes in soil organic carbon), data limitations at local scales, and the maximum sustainable removal rates of residues (50–60%). Based on this review, the potential for agricultural waste biorefineries to reduce GHG emissions is high, but the benefits reported are dependent on the methodology and geographically variable. To promote the circular bioeconomy, a universal approach to LCA, regulatory support at the regional level and investment in economic and social aspects are key.