Review sustainable energy from livestock waste: a review of biogas production pathways

The growing demand for sustainable energy and the environmental challenges of livestock waste management have intensified interest in biogas as a renewable and circular bioenergy solution. This review critically evaluates biogas production from key livestock wastes such as chicken manure, piggery waste, and cow dung focusing on how feedstock composition, anaerobic digestion pathways, pretreatment methods, and co-digestion strategies influence methane yield and process stability. These substrates differ markedly in biochemical characteristics: chicken manure is nitrogen-rich and prone to ammonia inhibition, piggery waste exhibits high biodegradability and methane potential, and cow dung provides stable digestion but is constrained by lignocellulosic hydrolysis limitations. Comparative analysis of experimental studies reveals wide variability in reported methane yields, driven by differences in operating conditions, reactor design, microbial adaptation, and scale. Persistent gaps between theoretical biomethane potential and experimental performance are discussed, highlighting the roles of ammonia toxicity, hydrolysis-limited kinetics, and scale-dependent losses. Co-digestion and pretreatment consistently enhance methane production by improving nutrient balance and substrate accessibility, yet challenges remain in methodological standardization, process scalability, and long-term operational stability. Key research gaps include limited integration of microbial community analysis, insufficient techno-economic and life-cycle assessments, and minimal validation of digital monitoring systems at full scale. Overall, livestock-based biogas systems represent a viable pathway for renewable energy generation and waste valorization, but their full potential depends on system-level optimization and scalable, economically viable solutions.