How much methane leakage must a biogas digester deduct under CCTS tool BM-T-008?
BM-T-008 deducts a fixed share of the methane a digester produces: 2.8% for steel, lined concrete or fibreglass digesters with a gas holder, 5% for UASB and floating gas holders without a water seal, and 10% for unlined masonry, fixed dome digesters, covered lagoons or an unknown type.
What the tool counts
- Project emissions: electricity and fossil fuel used to run the digester, methane lost through maintenance, roof and wall leaks and safety valves, and methane from flaring.
- Leakage: methane from digestate stored in a lagoon deeper than one metre or dumped, and methane and nitrous oxide from composting the digestate.
- Not counted: nitrous oxide from leaks, transport of feed and digestate, gas pipelines and land application.
Methane produced
Either measure methane flow with BM-T-005, logged hourly or more often, or measure biogas volume and apply defaults: methane = biogas m3 x 0.6 x 0.00067 t per m3. The global warming potential the tool applies to methane is 29.8, from IPCC AR6.
Digestate storage defaults
- Liquid digestate, remaining methane capacity as a share of methane produced: 0.10 for covered lagoons, 0.15 for UASB, filter bed and fluidised bed digesters, 0.20 for conventional digesters, 0.05 for two-stage digesters.
- Or measure: stored volume x COD x 0.25 t methane per t COD x a methane conversion factor of 0.8 for storage 2 m or deeper, 0.2 for 1 to 2 m, and 0 below 1 m.
- Solid digestate sent to a dump: 0.15 for two-phase digesters, 0.35 for all others.
Electricity defaults when not metered
- 0 for gravity-fed covered lagoons and conventional digesters.
- 0.01 MWh per t of methane for UASB, filter bed and fluidised bed reactors.
- 1.02 MWh per t for stirred tank digesters treating wastewater.
- 1.54 MWh per t for solid waste digesters with pre-processing such as pulverising.
Worked example: digester type changes the deduction
- Biogas collected: 1,000,000 m3 a year (illustrative)
- Methane: 1,000,000 x 0.6 x 0.00067 = 402 t
- Fixed dome digester, 10% leak: 40.2 t x 29.8 = 1,198 t CO2e deducted
- Steel digester with gas holder, 2.8% leak: 11.3 t x 29.8 = 335 t CO2e deducted
- Difference: about 863 t CO2e of credits a year
What Senseible does here
Senseible gives carbon credit eligibility signals from your records; it does not register projects or issue credits. It keeps dated, fingerprinted fuel and electricity invoices that a project's monitoring records can draw on.
Sources: BEE, BM-T-008 Project and leakage emissions from anaerobic digesters (CCTS Offset Mechanism, version 1.0, 27 March 2025): data and parameter tables 1 to 10, BEE, Methodologies and Tools under the CCTS Offset Mechanism
Last reviewed 2026-10-25.