Advances and Challenges in Anaerobic Digestion for Biogas Production: Policy, Technological, and Microbial Perspectives

This review comprehensively examines the advancements and challenges in anaerobic digestion (AD) for biogas production, emphasising technological, microbial, and policy perspectives. It highlights the AD significant potential for valorising diverse organic substrates, including manure, food waste, and microalgae, thereby contributing to renewable energy generation and greenhouse gas mitigation. Key operational factors influencing biogas yield include substrate composition, temperature (preferably mesophilic conditions), pH (6.5–7.5), and the substrate-to-inoculum ratio (SIR), all of which significantly affect microbial activity and process stability. Co-digestion strategies and pretreatments are examined for their roles in enhancing biodegradability and methane yield, respectively. Microbial community dynamics, particularly responses to feedstock heterogeneity and operational parameters, are integral to process optimisation. Advances in metagenomics have provided insights into microbial resilience and adaptation to conditions such as high ammonium levels. This review also discusses various modelling approaches, including kinetic models and machine learning techniques, for predicting and optimising biogas production. Additionally, policy frameworks within regions such as the European Union and Brazil, along with economic incentives and regulatory hurdles, are also considered crucial for scaling up deployment. Challenges such as digestate management and high capital costs persist, underscoring the need for integrated strategies to enhance the sustainability and viability of AD-based biogas projects.