Environmental Performance of Biogas Systems in South West Nigeria: A Lifecycle Assessment

Biogas systems deploying anaerobic digestion of agricultural and household organic waste have been promoted in South West Nigeria as a clean energy and waste management solution, yet their net environmental performance relative to conventional fuel alternatives has not been quantified through rigorous lifecycle assessment at the local scale. This study conducts a lifecycle assessment of household and community-scale biogas systems in Ogun, Oyo, and Ekiti States, South West Nigeria, quantifying greenhouse gas balances, non-methane air pollutant emissions, water use, and land use impacts across the full biogas system lifecycle. Primary data on feedstock composition, system operations, gas utilisation patterns, and digestate management were collected from 28 operational biogas installations through field measurement campaigns and operator interviews. Background lifecycle inventory data were sourced from the ecoinvent database and customised for Nigerian grid electricity and transport conditions. The functional unit was defined as provision of cooking energy equivalent to one megajoule of useful heat. Results demonstrate that biogas systems achieve lifecycle greenhouse gas savings of 78 to 92 percent compared to kerosene cooking alternatives and 65 to 80 percent compared to liquefied petroleum gas, depending on feedstock type and digestate utilisation practices. Methane leakage from poorly sealed systems is identified as the key determinant of net climate performance, with leakage rates above 5 percent significantly eroding climate benefits. The study recommends mandatory leak testing protocols for biogas installer certification programmes. Keywords: lifecycle assessment, biogas, environmental performance, South West Nigeria, greenhouse gas balance.