Biomethane (Upgraded Biogas)

Biomethane is what biogas becomes once you strip out the CO₂: near-pure methane, chemically identical to natural gas, ready to inject into the grid or run a fleet. Because its carbon is biogenic, burning it carries almost nothing in your greenhouse gas inventory — the combustion factor is the lowest of any hydrocarbon fuel in the Australian tables.

This entry covers the NGA Factors 2025 biomethane factor, why it sits so far below natural gas, and three worked examples.

Quick Verdict

Biomethane has a combined Scope 1 emission factor of 0.13 kg CO₂-e per gigajoule under the NGA Factors 2025 (Table 5). The CO₂ component is zero because the carbon is biogenic — it is reported separately, not in your CO₂-e total — leaving only trace methane (0.1) and nitrous oxide (0.03). The factor applies to organisations combusting biomethane directly, reported under Scope 1, at an energy content of 0.0393 GJ per cubic metre — identical to pipeline natural gas. Per gigajoule, biomethane emits about 99.7% less than the natural gas it displaces. This is a combustion factor only; upstream production and upgrading emissions are accounted for separately.

How to Calculate Biomethane Emissions

Emissions (kg CO₂-e) = Energy consumed (GJ) × 0.13 kg CO₂-e/GJ

Convert cubic metres at 0.0393 GJ/m³ and megajoules at 1,000 MJ per GJ.

Worked Example 1: Bus depot switching from natural gas

A depot combusts 50,000 GJ of biomethane over the year in place of natural gas.

50,000 GJ × 0.13 = 6,500 kg CO₂-e

6.50 tonnes CO₂-e (Scope 1)

For comparison, the same 50,000 GJ of natural gas would report 50,000 × 51.53 = 2,576,500 kg, or about 2,577 tonnes CO₂-e.

Worked Example 2: Small process-heat load

A food manufacturer burns 8,000 GJ of biomethane in a process boiler.

8,000 GJ × 0.13 = 1,040 kg CO₂-e

1.04 tonnes CO₂-e (Scope 1)

Worked Example 3: Grid injection metered in cubic metres

A biomethane facility injects 1,000,000 m³ into the network, all combusted downstream.

1,000,000 m³ × 0.0393 GJ/m³ = 39,300 GJ

39,300 GJ × 0.13 = 5,109 kg CO₂-e

5.11 tonnes CO₂-e (Scope 1)

How biomethane compares with other gaseous fuels

NGER and AASB S2 Reporting

Direct combustion of biomethane is reported as Scope 1 under the NGER scheme using this factor. Under AASB S2, the combustion figure sits in your Scope 1 inventory with biogenic CO₂ disclosed separately where material. If you claim biomethane supplied via the grid under a certificate scheme, document the basis clearly — assurance providers scrutinise renewable-gas claims closely, and the combustion factor here applies to physical on-site use.