Waste Scope 1 (Direct — biological treatment of waste)

Anaerobic Digestion (Biological Treatment)

Reviewed by Afonso Firmo, Co-Founder & Director · Updated 7 July 2026

Anaerobic digestion carries a factor of 0.028 t CO₂-e per tonne treated under NGA Factors 2025. See worked examples, FAQs and a calculator for reports.

Emission Factor Value

0.028 t CO₂-e/tonne

Try it with your own numbers

Organic waste digested Unit

Estimated emissions

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Emissions from waste treated in a digester you operate are reported under Scope 1. Calculated as tonnes of organic waste digested × 0.028 t CO₂-e per tonne (NGA Factors 2025).

Official Source & Citation

This emission factor is sourced from the Australian National Greenhouse Accounts Factors 2025 , Table 19 — Biological treatment of waste, published by the Department of Climate Change, Energy, the Environment and Water (DCCEEW).

Citation: DCCEEW (2025). Australian National Greenhouse Accounts Factors 2025. Commonwealth of Australia. Available at: https://www.dcceew.gov.au/climate-change/publications/national-greenhouse-accounts-factors-2025

View official publication ↗

Notes

Scope 1 factor for organisations operating anaerobic digestion facilities, from the NGA Factors 2025 biological treatment of waste tables. Emissions are the residual methane and nitrous oxide that escape the process. 1 tonne of organic waste digested = 0.028 t CO₂-e — the lowest factor of any organic waste pathway, below composting (0.046) and far below landfill (2.1 for food waste). The digester operator reports these emissions under Scope 1.

Calculation Example

If your facility digested 800 tonnes of organic waste during the year:

Working	Result
800 t × 0.028 t CO₂-e/t	22.4 t CO₂-e (Scope 1)

Anaerobic digestion deliberately does what a landfill does by accident — decompose organic waste without oxygen — but inside a sealed vessel that captures the methane instead of leaking it. The result is the lowest emission factor of any organic waste pathway: 0.028 t CO₂-e per tonne, reported under Scope 1 by the digester operator.

For water utilities, food manufacturers and councils running digestion facilities, this factor covers the residual process emissions. The captured biogas is a separate story — and a favourable one, since its combustion factor is a fraction of natural gas.

Quick Verdict

Anaerobic digestion has an emission factor of 0.028 t CO₂-e per tonne of organic waste treated under the Australian National Greenhouse Accounts Factors 2025. The emissions are the residual methane and nitrous oxide that escape the sealed process, reported under Scope 1 by the organisation operating the digester. The factor applies to the 2025–26 Australian reporting year. It sits below composting (0.046 t CO₂-e per tonne) and roughly 99% below the 2.1 t CO₂-e per tonne factor for food waste sent to landfill, making digestion the lowest-emission destination for organics. An activity-based emissions calculator can apply the factor directly from feedstock intake records.

How to Calculate Anaerobic Digestion Emissions

Emissions (t CO₂-e) = Organic waste digested (tonnes) × 0.028

Worked Example 1: Food manufacturer

A food manufacturer feeds 800 tonnes of processing waste into its on-site digester during the year.

800 t × 0.028 = 22.4 t CO₂-e (Scope 1)

Worked Example 2: Regional AD facility

A regional anaerobic digestion facility processes 15,000 tonnes of organic feedstock in the reporting year.

15,000 t × 0.028 = 420 t CO₂-e (Scope 1)

Worked Example 3: Small on-site digester

A brewery runs a small digester treating 12 tonnes of spent grain and organics.

12 t × 0.028 = 0.336 t CO₂-e (Scope 1)

Anaerobic Digestion vs Other Waste Pathways

Waste pathway	Factor (t CO₂-e/t)	Scope (who reports)
Food waste to landfill	2.1	Scope 3 (generator)
Garden and green waste to landfill	1.6	Scope 3 (generator)
Sludge to landfill	0.4	Scope 3 (generator)
Composting	0.046	Scope 1 (operator)
Anaerobic digestion	0.028	Scope 1 (operator)

All factors from NGA Factors 2025. Digesting a tonne of food waste instead of landfilling it avoids around 2.07 t of CO₂-equivalent emissions, before counting the fossil fuel displaced by the biogas.

NGER and AASB S2 Reporting

Anaerobic digestion emissions are Scope 1 for the operator, so facilities count them toward NGER thresholds along with any biogas combustion. Under AASB S2 climate disclosures, operators include the factor in Scope 1, while waste generators can present diversion to digestion as a measurable Scope 3 reduction. Keep feedstock intake records as the audit trail and apply the NGA Factors 2025 value consistently across periods.

Composting

0.046 t CO₂-e/tonne

Food Waste (Landfill)

2.1 t CO₂-e/tonne

Sludge Biogas

6.43 kg CO₂-e/GJ

Biomethane

0.13 kg CO₂-e/GJ

Frequently Asked Questions

What is the emission factor for anaerobic digestion in Australia?

Anaerobic digestion has an emission factor of 0.028 t CO₂-e per tonne of organic waste treated under the Australian National Greenhouse Accounts Factors 2025. It is the lowest factor of any organic waste treatment pathway, reflecting that the process captures most of the methane it generates.

Is anaerobic digestion Scope 1 or Scope 3?

The 0.028 t CO₂-e per tonne factor is Scope 1 for the organisation operating the digester. If you send organic waste to a third-party digestion facility, the operator reports those emissions, and your waste avoids the far higher Scope 3 landfill factors.

How does anaerobic digestion compare with composting and landfill?

Anaerobic digestion emits 0.028 t CO₂-e per tonne, composting 0.046, and landfilling food waste 2.1 — so digestion cuts roughly 99% of the landfill emissions. Digestion also produces biogas that can displace fossil fuels, which composting does not.

Why does anaerobic digestion emit so little when landfill emits so much?

Both processes generate methane anaerobically, but a digester is a sealed vessel that captures the gas for use, while a landfill leaks a large share to the atmosphere. The 0.028 t CO₂-e per tonne factor covers only the small residual methane and nitrous oxide that escape the digestion process.

How is the biogas from anaerobic digestion accounted for?

Combusting captured biogas is accounted separately using the gaseous fuel factors — sludge biogas has a combustion factor of just 6.43 kg CO₂-e per GJ because its CO₂ is biogenic. The 0.028 t CO₂-e per tonne digestion factor covers the treatment process itself, not the fuel use.

How do I measure how much waste goes through my digester?

Use weighbridge records or feedstock intake logs showing tonnes of organic material loaded into the digester over the reporting year, then multiply by 0.028 t CO₂-e per tonne. Keep intake records as your audit evidence.

Do anaerobic digestion emissions need to be reported under NGER or AASB S2?

Yes, for operators. Digestion facilities include these Scope 1 emissions in NGER reporting where corporate or facility thresholds are met. Under AASB S2, they sit in the operator's Scope 1 inventory, while waste generators can present diversion to digestion as a Scope 3 reduction initiative.

Where does the 0.028 t CO₂-e per tonne factor come from?

It is published in the Australian National Greenhouse Accounts Factors 2025 by DCCEEW, in the biological treatment of waste tables. The factor expresses the methane and nitrous oxide from anaerobic digestion per tonne of organic waste treated, converted to CO₂-equivalent.

Disclaimer

This page is provided for general information, not professional or compliance advice. The factor shown is reproduced from the official publication cited above, and while we work to keep it current, government factors change — the publication is always the authoritative source.

Before using this value in any formal reporting — including under the National Greenhouse and Energy Reporting Act 2007 — confirm it against the current official publication and the methods specified by the Clean Energy Regulator.
NetNada is independent of the Australian Government, DCCEEW, and the Clean Energy Regulator. Government data is Crown copyright, Commonwealth of Australia.

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