Valorization of Fruit Processing Wastes for Sustainable Biofuel Production: Composition, Co-Digestion Approaches for Enhanced Biogas Production, and Associated Challenges

Fruit-processing wastes (FPWs) represent abundant, renewable substrates with significant potential for sustainable energy generation through anaerobic digestion. This review consolidates current knowledge on the composition, availability, and bioenergy potential of major FPWs, with a particular emphasis on biogas production. The high carbohydrate, pectin, and moisture contents of FPWs make them suitable for rapid microbial degradation, while co-digestion strategies, especially with nutrient-rich substrates such as cow dung, help optimize C/N ratios, enhance process stability, and improve methane yields. Comparative data from various FPW types demonstrate notable improvements in gas production and quality when synergistic feedstock combinations are applied. The review also examines pretreatment methods for overcoming lignocellulosic recalcitrance, identifies common inhibitory compounds, and discusses the environmental and economic implications of FPW-based biogas systems, including greenhouse gas mitigation and rural energy security. Challenges such as seasonal availability, collection logistics, and process scaling are highlighted alongside potential solutions. By integrating technical, economic, and environmental perspectives, this work underscores the role of FPW valorization in advancing circular bioeconomy goals and outlines research directions for improving efficiency and adoption of decentralized biogas technologies.