Sustainable Energy Production From Waste: A Review of Hybrid Approaches Combining Anaerobic Digestion and Gasification

This paper provides a comprehensive review of hybrid waste-to-energy (WTE) systems that integrate anaerobic digestion (AD) and biomass gasification, emphasizing their synergistic benefits in sustainable energy production and waste management. By combining biochemical and thermochemical processes, these hybrid systems maximize energy recovery, optimize resource utilization, and significantly mitigate environmental impacts. The study highlights the principles and operational dynamics of standalone AD and gasification technologies, showcasing how their integration addresses limitations such as incomplete biomass conversion and excessive digestate production. Hybrid systems demonstrate superior performance in converting diverse biomass feedstocks, including municipal solid waste (MSW), agricultural residues, and food waste, into renewable energy and valuable by-products. Advancements in reactor designs, pretreatment techniques, and system configurations are discussed, with a focus on enhancing energy efficiency and reducing greenhouse gas (GHG) emissions. Pretreatment methods such as AD pretreatment and advanced sorting mechanisms are explored to address feedstock variability and improve process stability. Key synergies, such as utilizing waste heat from gasification to dry AD residues, further boost overall system efficiency. The paper identifies critical operational parameters such as feedstock composition and reactor conditions that influence system performance and explores emerging solutions. Economic and environmental benefits, such as improved energy yields and cost efficiency, demonstrate the potential of hybrid AD–gasification systems. Despite the advantages, challenges persist, particularly in scaling hybrid systems and managing feedstock variability. Infrastructural limitations and the complexity of balancing AD and gasification processes remain significant barriers to widespread adoption. By reviewing existing research and case studies, this paper underscores the critical role of hybrid systems in achieving global renewable energy goals and sustainable waste management practices. Ultimately, hybrid AD–gasification systems offer a promising pathway for transitioning to cleaner energy systems, maximizing waste valorization, and supporting the global shift toward a circular economy.