Danish national effort to minimise methane emission from biogas plants - lessons learned

Methane emission from biogas plants may reduce or even eliminate the greenhouse gas mitigating effect of this renewable energy source. In 2019, a national effort was initiated to monitor methane emission from Danish biogas production, and to work towards mitigation. The sum of measured methane emission from 69 biogas plants was found to be equal to 2.5% of sum of gas production. However, high variation between plant types and within plant types was observed, where the lowest methane loss was 0.3% and the highest 40.6%. Significant sources of methane emission included pressure relief valves on digesters and biomass storage w/o gas collection. Measurement of methane emission before and after mitigating actions at biogas plants showed that the emissions were significantly reduced afterwards. Conceptual design solutions to reduce methane loss were developed for some of the participating plants. In some of these, the added revenue due to increase in energy production could finance the investment and running costs.