Supplementary evidence from the Department for Environment, Food and Rural Affairs (Defra)

We have received the below from the ECCC and have been asked to confirm whether the statement that Paul Thompson made, is correct (regarding Defra's project that he states is underway).

Paul Thompson of the Renewable Energy Association told us in response to Q 50 in the transcript (available committees.parliament.uk/oralevidence/14597/pdf/):

“How much methane is produced from landfill in the first place is, by its nature, an estimate. There have been differences of opinion on that and there is a Defra project under way at the moment, I understand, to try to refine that methodology.”

Within the context of Net Zero emission modelling the quantity of landfill methane generation (from landfills in England) is estimated using a national landfill gas generation model: referred to as ‘MELMod’. This is estimated on a national scale as there is not site-specific estimation within the model. MELmod specifically is a first order decay model, with input data received according to EWC (European Waste Catalogue) codes which are mapped to MELMod categories. Mixed waste codes present (i.e. 19 12 12 and 20 03 01) are mapped to categories using a 2012 study of waste composition carried out by Defra.

Within this model different biodegradability factors are assigned to different categories. In order to gain a calculated emission measurement, methane capture and oxidation data is collected on methane utilized in gas engines, and methane oxidized through flares. This is removed from the generation data.

Additionally, a proportion of the remaining methane generated is assumed to be oxidized by microbes in the soil (10%). This is also removed from methane generated totals, providing an overall methane emission.

Defra has active research projects in the Net Zero space focusing on the waste sector. These include a waste composition project ‘Composition of Residual Municipal Waste and Mixed Waste Codes in England’, and projects focusing on developing direct measurement of Landfill emissions ‘Direct Measurement of Landfill Emissions 1’, ‘Direct Measurement of Landfill Emissions 2’. These will provide updated data on waste composition and biodegradability factors, and initial research which will provisionally enable future site level methane emission estimates.