Regional Biogas Potential from Agricultural and Livestock Residues: A Sustainable Renewable Energy Strategy for Madagascar

Madagascar faces major energy challenges while producing large quantities of agricultural and livestock residues that currently are poorly managed or openly burned. This study assesses the potential of recoverable agricultural residues for biogas production for domestic energy generation in agricultural areas of Madagascar through decentralized farm-level anaerobic digestion (AD) and identifies regions with the highest biogas production potential. Organic substrate production data for 24 regions were combined with residue-to-product ratio (RPR), total solids (TS) and volatile solids (VS) contents, and livestock manure characteristics. The results estimated 2389 Mm3·y−1 of theoretical biogas potential and 129,319 TJ·y−1 of available energy throughout Madagascar. Sofia region showed the highest biogas potential, followed by the Atsimo-Andrefana and Atsinanana regions. The study also evaluates the sustainability of decentralized AD at a farm-scale level by treating cattle manure in a 2.5 m3 digester, estimating that it is possible to save around 5.65 kg wood·day −1 inhabitant−1 through biogas combustion, with significant ancillary benefits in terms of improved energy security and reduced deforestation. A 10% TS slurry concentration and a 30-day hydraulic retention time (HRT) are considered for preliminary reactor sizing. While providing important advantages such as clean renewable energy generation, reduced deforestation, and efficient waste management, critical aspects for diffused decentralized AD deployment are connected to costs and reactor maintenance, which require skilled personnel, as well as the need for knowledge sharing with local stakeholders (farmers and inhabitants) to highlight the advantages of biogas generation at a farm-scale level. Dedicated financial incentives, in addition, might be provided by the government to boost diffused decentralized AD implementation in Madagascar. These preliminary findings demonstrate the significant theoretical potential of agricultural and livestock residues for renewable energy production in Madagascar through decentralized AD, while highlighting the need to carefully address feedstock collection, logistics, water availability, infrastructure, and institutional constraints for practical AD development.