Measuring biogas venting from over-pressurisation of household scale dome biogas digesters: A case study in Kenya and Uganda

Methane emissions from household-scale biogas digesters represent a potentially significant climate concern that has been largely overlooked in rural energy access programmes. This study presents the first assessment of biogas venting patterns, resulting from over-pressure, across 53 household-scale biogas digesters in Kenya and Uganda. We develop and apply a methodology for estimating venting using digital monitoring technology known as ‘Smart Biogas’, which continuously measures pressure and flow data to quantify both the volume and timing of biogas loss.

Our findings reveal a complex picture of household biogas use. By measuring the Biogas Utilisation Factor (BUF) - the ratio of consumed to generated biogas, where a lower BUF indicates higher venting rates - we found that households can achieve excellent performance during optimal periods, with venting rates below 3 % across all digester sizes, which demonstrates the potential for optimised biogas use. However, although most households maintain good biogas utilisation most of the time, periodic episodes of underuse significantly impact overall performance. The mean pressure-driven venting rates ranged from 10.8 % ± 12.7 % for 10 m3 digesters to 20.9 % ± 20.9 % for 6 m3 digesters (overall mean: 15.9 % ± 20.2 %). Temporal patterns also emerge, with increased venting likely during afternoon and nighttime hours, and during agricultural planting seasons when cooking patterns change. Drawing from these insights, we propose strategies to help households maintain the consistent high biogas utilisation they achieve during optimal periods.

The methodology developed in this paper can be applied across other biogas programmes to build a broader understanding of patterns of biogas use and the likelihood of venting. These findings have implications for biogas programme design, carbon credit methodologies, and efforts to maximise both the climate benefits and household value of small-scale biogas systems.