Valorization of dairy industry waste streams via anaerobic digestion

The dairy processing industry generates a variety of high-strength waste streams, including brown sludge, dissolved air flotation (DAF) sludge, white sludge, fat-oil-grease (FOG) waste, and dairy effluents, which pose significant environmental and economic challenges if not properly managed. Anaerobic digestion (AD) offers a sustainable and energy-positive solution for treating these organic-rich wastes while recovering biomethane as a renewable energy source. This review presents a comprehensive assessment of the characteristics, treatment challenges, and biomethane potential of different dairy-derived waste streams. Special focus is given to recent advancements in pretreatment technologies, particularly hydrodynamic cavitation (HC), which has shown promise in enhancing sludge disintegration, solubilization, and microbial bioavailability. Compared to traditional physical, chemical, and biological pretreatments, HC offers an energy-efficient, scalable, and environmentally benign approach, especially when integrated into co-digestion strategies involving DAF and brown sludge. The review also highlights techno-economic considerations, demonstrating significant methane yield improvements and net energy gains when optimized HC pretreatment is applied. By synthesizing recent findings and identifying research gaps, this study underscores the transformative potential of HC-assisted AD for the valorization of dairy industry waste streams and provides a foundation for future developments in energy-efficient waste management.