The increasing generation of dairy and fruit-processing residues has created both an environmental challenge and an opportunity for sustainable resource recovery. Among these residues, milk whey and fruit-processing wastes are particularly attractive because of their high content of biodegradable organic matter, carbohydrates, nutrients, and other potentially recoverable compounds. This review critically examines an integrated biorefinery approach for converting these heterogeneous food-processing residues into biofuels, renewable energy, stabilized organic materials, and biofertilizers within a circular bioeconomy framework. The valorization potential of whey through anaerobic digestion and lactose-based fermentation for biogas and bioethanol production is discussed, with emphasis on substrate characteristics, microbial conversion, process stability, and major operational constraints. Fruit-processing residues are evaluated as feedstocks for biological conversion, aerobic stabilization, nutrient recovery, and production of organic fertilizer or soil amendments. Particular attention is given to cascading resource recovery, in which different fractions and residual streams are directed toward the most appropriate conversion pathway rather than relying on a single-product process. The review further considers feedstock collection, digital traceability, process integration, residual-stream management, product safety, and the challenges associated with scale-up. Environmental sustainability, techno-economic feasibility, carbon and energy balances, and life-cycle assessment are identified as essential criteria for evaluating the practical potential of integrated whey–fruit biorefineries. Overall, the integration of dairy and fruit-processing residues provides a promising pathway for shifting food-processing waste management from disposal toward resource recovery, renewable energy generation, nutrient recycling, and circular bioeconomy development, although pilot-scale validation and system-level sustainability assessment remain necessary.
