Waste to wealth: Circular utilization of dairy waste for sustainability in agri-food industries

The dairy industry is a major contributor to global agri-food systems, producing vast quantities of milk annually while generating substantial volumes of high-strength waste streams, including whey, wastewater, and processing residues. During cheese manufacture, a large proportion of milk is converted into whey, leading to significant quantities of by-products that require effective management. These waste streams are characterized by high organic loads, reflected in elevated chemical oxygen demand (COD) and biological oxygen demand (BOD) values, which pose serious environmental risks if discharged without adequate treatment. This review emphasizes circular economy strategies that transform dairy waste from an environmental liability into a valuable resource. Dairy waste streams are rich in recoverable nutrients, including proteins, lactose, lipids, and essential minerals such as calcium and phosphorus. Whey proteins can be efficiently recovered using membrane separation and advanced bioprocessing technologies, while lactose can be valorized through fermentation into value-added products such as lactic acid, ethanol, and biohydrogen. Anaerobic digestion of dairy wastewater and sludge offers an effective approach for organic load reduction while generating biogas rich in methane, thereby mitigating greenhouse gas emissions and supporting on-site renewable energy production. Integrated dairy biorefinery concepts enable the simultaneous recovery of food-grade ingredients, bio-based chemicals, and bioenergy, significantly enhancing overall resource efficiency compared with conventional single-treatment methods. Life-cycle assessment studies further indicate that circular dairy waste valorization can substantially reduce the carbon footprint of dairy processing and lower waste management costs. Despite ongoing challenges related to scalability, economic feasibility, and variability in waste composition, circular utilization of dairy waste represents a promising pathway toward sustainable dairy processing and a more resilient bioeconomy. • Dairy waste is transformed from an environmental burden into valuable circular resources. • Whey, wastewater, and sludge are rich feedstocks for sustainable valorization. • Microbial and enzymatic bioprocesses enable high-value product recovery. • Integrated dairy biorefineries enhance efficiency and reduce emissions. • Agricultural reuse improves crop yield, soil health, and nutrient cycling.