Environmental assessment of anaerobic digestion within net-zero and policy-aligned AFOLU sector futures

Anaerobic digestion (AD) is promoted to decarbonise agriculture while providing renewable energy and improved manure management. This study assesses the technical feasibility and environmental performance of large- and small-scale AD deployment within the agriculture, forestry, and other land use (AFOLU) sector in Ireland to 2050. The national GOBLIN land-balance model was used with detailed feedstock allocation and a life cycle assessment (LCA) model (LCAD 2.0), simulating 160 AFOLU configurations and analysing 14 policy-relevant scenarios in detail. First, only high-ambition AFOLU pathways that substantially reduce beef cattle numbers and reallocate spared grassland to silage and bioenergy crops can reliably supply sufficient feedstock to meet Ireland's 5.7 TWh yr⁻¹ biomethane target; incremental policy pathways offer limited AD expansion and modest emission reductions. Second, large-scale plants deliver the strongest national climate benefits and lowest normalised environmental burdens, whereas widespread deployment of silage-dominated small-scale plants could increase environmental burdens. Third, the net contribution of AD to national climate goals is highly sensitive to how AFOLU transitions, land-sparing strategies, and AD configurations are combined. Overall, optimum AD deployment is contingent on ambitious AFOLU restructuring and carefully targeted technology choices. Land use and AD strategies should be aligned to include targeted incentives for digestion of manure from priority livestock regions, silage or bioenergy crop production in regions spared from livestock and support for high-performing AD configurations. Strategic policy support will be essential to ensure that biomethane expansion contributes to climate neutrality and circular bioeconomy objectives.