More than 2% % methane slip can reverse the positive environmental effect of biomethane when compared to petrol. Methane is indeed a 23 times stronger greenhouse gas (GHG) than CO2. A survey in Sweden has monitored the methane slips in biomethane plants. Preliminary results are cited in Arthur Wellinger's presentation.

One of the major issues is to strongly reduce and limit methane slip during the upgrading phase by relevant technologies. Labelling of the resulting biomethane might be the driver. In the framework of the Biogasmax project, Swiss actors on biomethane set up in 2008 a label called "Naturemade star" in order to guarantee the ecological quality of the biomethane injected into the grid. For a producer to be authorised to get this label, the emission of biomethane at the treatment facilities may not exceed 1% of the total biomethane generated by the upgrading plant. The producer has to document all operational interruptions because during stop and restart of the systems the risk of methane slip is increased. To completely avoid gas emissions, the gas produced during interruptions of upgrading or injection must be burned in a flare or a gas burner.

Learn more:
> Biogasmax report "Naturemade biomethane label" - Green certificate for Switzerland as an example for EU wide application on www.biogasmax.eu, section "Downloads".
> Arthur's Wellinger's and Jan-Paul Lindner's presentations: www.biogasmax.eu