Quantification of methane emissions from UK biogas plants

Abstract:

The United Kingdom has an increasing number of operational biogas plants. These plants emit methane, and contribute to national greenhouse gas emissions. Currently the amount of methane emitted by UK biogas production is poorly quantified. There is thus a need to measure emissions from this new source category, and to develop methodologies for CH₄ emission monitoring, quantification and reduction. Mitigating methane emissions is a major scientific and societal challenge in tackling climate change, as CH₄ is a major contributor to global warming.

This study focuses on mobile vehicle-mounted greenhouse gas surveys which were conducted to detect plumes of CH₄ emissions from the biogas plants in southern England. The surveyed biogas plants varied in their size, waste feed input materials and biogas utilization. Total CH₄ emissions from 10 biogas plants were estimated by using Gaussian plume modelling. Methane emission rates varied between 0.1 and 58.7 kg CH₄ hr^-1, and the percentage of losses relative to the calculated production rate ranged between 0.02 and 8.1%. The average emission rate was estimated as 15.9 kg CH₄ hr^-1, and the average loss was 3.7%. Generally, CH₄ emission rates from larger food waste biogas plants were lower than from smaller farm biogas plants. Excluding sewage sludge biogas plants, we estimate that biogas methane emissions may account for between 0.05 and 1.5% (perhaps around 1%) of the total methane emissions from the UK. Thus it is important to reduce CH₄ losses from biogas plants, both to limit their contribution of methane to global warming and to achieve the objective of sustainable renewable energy production.