Environmental trade-offs of biogas utilization pathways: a global life cycle synthesis with policy-relevant insights for Southeast Asia

Biogas plays a key role in sustainable energy transitions, yet its environmental performance varies widely across feedstocks, technology scales, and utilization pathways. This study presents a global systematic review of peer-reviewed life cycle assessment (LCA) studies published between 2015 and 2025, synthesizing evidence from 28 studies to evaluate environmental trade-offs across major biogas utilization pathways. Five pathways are assessed, including direct combustion, combined heat and power (CHP), biomethane upgrading, transport use, and carbon capture and utilization (CCU). The typology-based scoring framework links feedstock, scale, and utilization pathways to environmental performance across global warming potential, eutrophication, acidification, particulate matter formation, and resource use. All results were standardized to 1 MJ useful energy output using a median-based normalization approach. Results show a clear performance gradient: industrial-scale biomethane and CCU pathways outperform conventional uses, while household-scale direct combustion consistently exhibits the highest environmental burdens due to methane leakage, uncontrolled emissions, and incomplete combustion. Southeast Asia, particularly Vietnam and Thailand, is used as a policy-relevant application context to interpret transferability and feasibility constraints. The synthesis indicates that near-term environmental improvements are most consistently achieved through leakage control, improved digestate management, and incremental upgrading, whereas large-scale CCU deployment remains constrained by infrastructure, hydrogen availability, and cost.