Waste Scope 1 (Direct — wastewater treatment)

Wastewater Treatment (Domestic)

Q: What is the emission factor for wastewater treatment in Australia?

It depends on the treatment method. Under the NGA Factors 2025, anaerobic digesters, reactors and deep lagoons (>2 m) carry 0.3276 t CO₂-e per person served per year, shallow anaerobic lagoons (<2 m) 0.0819, unmanaged aerobic treatment 0.1229, and well-managed aerobic treatment is effectively zero.

Q: Is wastewater treatment Scope 1 or Scope 3?

The process emissions are Scope 1 for the organisation operating the treatment plant — typically a water utility or council. Businesses connected to the sewer network do not apply these factors directly; any wastewater-related emissions in their inventory would sit in Scope 3 via their utility.

Q: Why do anaerobic treatment methods emit so much more than aerobic ones?

Anaerobic conditions produce methane, a far more potent greenhouse gas than CO₂. Deep lagoons and digesters without full gas capture release that methane, giving 0.3276 t CO₂-e per person per year, while well-managed aerobic plants keep the wastewater oxygenated and generate negligible methane.

Q: What activity data do I need to apply the factor?

The population served by each treatment method over the reporting year — person-years. Multiply persons served by the method-specific factor: for example, a deep-lagoon plant serving 8,000 people emits 8,000 × 0.3276 = 2,620.8 t CO₂-e. Utilities usually hold population-served figures by plant.

Q: What if a plant captures the biogas from its digesters?

Captured sludge biogas that is combusted is accounted separately under the gaseous fuel factors — sludge biogas has a combustion factor of just 6.43 kg CO₂-e per GJ because its CO₂ is biogenic. Gas capture and flaring or use substantially reduces the methane that the treatment factors represent, so facility-specific NGER methods often apply.

Q: How does lagoon depth change the factor?

Depth determines how anaerobic the lagoon is. Lagoons deeper than 2 metres are treated as fully anaerobic at 0.3276 t CO₂-e per person per year, while shallow lagoons under 2 metres, where more oxygen reaches the water, carry a quarter of that at 0.0819 t CO₂-e per person per year.

Q: Do wastewater treatment emissions count under NGER or AASB S2?

Yes. Water utilities report wastewater methane as Scope 1 under NGER, and large utilities routinely exceed reporting thresholds. Under AASB S2, treatment emissions form part of the operator's Scope 1 inventory and are often the dominant line for water sector entities.

Q: Where do these wastewater factors come from?

They are published in the Australian National Greenhouse Accounts Factors 2025 by DCCEEW, in the wastewater treatment tables. The factors express methane from domestic wastewater treatment per person served per year, converted to CO₂-equivalent, for each treatment method.

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

Anaerobic wastewater treatment carries a factor of 0.3276 t CO₂-e per person served per year under NGA Factors 2025. Worked examples, FAQs and calculator.

Emission Factor Value

0.3276 t CO₂-e/person/year (anaerobic treatment)

Try it with your own numbers

Population served (person-years) Unit

Estimated emissions

—

Select the treatment method to apply the matching NGA Factors 2025 factor: anaerobic digester/reactor or deep lagoon 0.3276, shallow anaerobic lagoon 0.0819, unmanaged aerobic 0.1229 t CO₂-e per person per year. Well-managed aerobic treatment is effectively zero. Result = persons served × method factor.

Official Source & Citation

This emission factor is sourced from the Australian National Greenhouse Accounts Factors 2025 , Table 17 — Wastewater treatment, 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 operators of domestic wastewater treatment, from the NGA Factors 2025 wastewater tables. Emissions are methane from the treatment process, scaled by population served and treatment method. Anaerobic digesters, reactors and deep lagoons (>2 m) = 0.3276 t CO₂-e per person per year; shallow anaerobic lagoons (<2 m) = 0.0819; unmanaged aerobic treatment = 0.1229; well-managed aerobic treatment ≈ 0. The treatment operator (typically a water utility or council) reports under Scope 1.

Calculation Example

If your utility treats wastewater for 50,000 people using anaerobic digesters:

Working	Result
50,000 persons × 0.3276 t CO₂-e/person/yr	16,380 t CO₂-e (Scope 1)

Wastewater treatment is one of the few emission sources measured not in litres or tonnes but in people. Under the NGA Factors 2025, a treatment plant’s methane emissions scale with the population it serves — and the factor swings from effectively zero for a well-managed aerobic plant to 0.3276 t CO₂-e per person per year for anaerobic digesters and deep lagoons, all reported under Scope 1 by the operator.

For water utilities and councils, that method-dependence is the whole story: two plants serving identical populations can differ by thousands of tonnes of CO₂-e purely on how the treatment train is configured.

Quick Verdict

Domestic wastewater treated in anaerobic digesters, reactors or deep lagoons (>2 m) carries an emission factor of 0.3276 t CO₂-e per person served per year under the Australian National Greenhouse Accounts Factors 2025. Shallow anaerobic lagoons (<2 m) carry 0.0819, unmanaged aerobic treatment 0.1229, and well-managed aerobic treatment is effectively zero. The emissions are methane from the treatment process, reported under Scope 1 by the plant operator — typically a water utility or council — for the 2025–26 Australian reporting year. Activity data is simply person-years served by each method. An NGER reporting tool can apply the method-specific factors across a utility’s plant portfolio.

How to Calculate Wastewater Treatment Emissions

Emissions (t CO₂-e) = Population served (persons) × method factor (t CO₂-e/person/yr)

Worked Example 1: Utility with anaerobic digesters

A water utility treats wastewater for 50,000 people using anaerobic digesters (factor 0.3276).

50,000 × 0.3276 = 16,380 t CO₂-e (Scope 1)

Worked Example 2: Shallow lagoon town

A council runs a shallow anaerobic lagoon (<2 m) serving 8,000 people (factor 0.0819).

8,000 × 0.0819 = 655.2 t CO₂-e (Scope 1)

Worked Example 3: Unmanaged aerobic plant

A regional plant provides unmanaged aerobic treatment for 12,000 people (factor 0.1229).

12,000 × 0.1229 = 1,474.8 t CO₂-e (Scope 1)

Wastewater Treatment Methods Compared

Treatment method	Factor (t CO₂-e/person/yr)
Anaerobic digester or reactor	0.3276
Anaerobic lagoon — deep (>2 m)	0.3276
Unmanaged aerobic treatment	0.1229
Anaerobic lagoon — shallow (<2 m)	0.0819
Managed aerobic treatment	0 (negligible)

All factors from NGA Factors 2025, expressed in CO₂-equivalent. Capturing digester biogas changes the picture further: combusting sludge biogas carries just 6.43 kg CO₂-e per GJ because its CO₂ is biogenic.

NGER and AASB S2 Reporting

Wastewater methane is Scope 1 for the treatment operator and is a core NGER category for water utilities, which commonly exceed reporting thresholds. Under AASB S2 climate disclosures, treatment emissions are often the dominant Scope 1 line for water sector entities, so method choices and gas capture belong in transition planning. Keep population-served data by plant and method as the audit trail and apply the NGA Factors 2025 values consistently across periods.

Sludge (Landfill)

0.4 t CO₂-e/tonne

Sludge Biogas

6.43 kg CO₂-e/GJ

Composting

0.046 t CO₂-e/tonne

Anaerobic Digestion

0.028 t CO₂-e/tonne

Frequently Asked Questions

What is the emission factor for wastewater treatment in Australia?

It depends on the treatment method. Under the NGA Factors 2025, anaerobic digesters, reactors and deep lagoons (>2 m) carry 0.3276 t CO₂-e per person served per year, shallow anaerobic lagoons (<2 m) 0.0819, unmanaged aerobic treatment 0.1229, and well-managed aerobic treatment is effectively zero.

Is wastewater treatment Scope 1 or Scope 3?

The process emissions are Scope 1 for the organisation operating the treatment plant — typically a water utility or council. Businesses connected to the sewer network do not apply these factors directly; any wastewater-related emissions in their inventory would sit in Scope 3 via their utility.

Why do anaerobic treatment methods emit so much more than aerobic ones?

Anaerobic conditions produce methane, a far more potent greenhouse gas than CO₂. Deep lagoons and digesters without full gas capture release that methane, giving 0.3276 t CO₂-e per person per year, while well-managed aerobic plants keep the wastewater oxygenated and generate negligible methane.

What activity data do I need to apply the factor?

The population served by each treatment method over the reporting year — person-years. Multiply persons served by the method-specific factor: for example, a deep-lagoon plant serving 8,000 people emits 8,000 × 0.3276 = 2,620.8 t CO₂-e. Utilities usually hold population-served figures by plant.

What if a plant captures the biogas from its digesters?

Captured sludge biogas that is combusted is accounted separately under the gaseous fuel factors — sludge biogas has a combustion factor of just 6.43 kg CO₂-e per GJ because its CO₂ is biogenic. Gas capture and flaring or use substantially reduces the methane that the treatment factors represent, so facility-specific NGER methods often apply.

How does lagoon depth change the factor?

Depth determines how anaerobic the lagoon is. Lagoons deeper than 2 metres are treated as fully anaerobic at 0.3276 t CO₂-e per person per year, while shallow lagoons under 2 metres, where more oxygen reaches the water, carry a quarter of that at 0.0819 t CO₂-e per person per year.

Do wastewater treatment emissions count under NGER or AASB S2?

Yes. Water utilities report wastewater methane as Scope 1 under NGER, and large utilities routinely exceed reporting thresholds. Under AASB S2, treatment emissions form part of the operator's Scope 1 inventory and are often the dominant line for water sector entities.

Where do these wastewater factors come from?

They are published in the Australian National Greenhouse Accounts Factors 2025 by DCCEEW, in the wastewater treatment tables. The factors express methane from domestic wastewater treatment per person served per year, converted to CO₂-equivalent, for each treatment method.

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.

Back to all emission factors

NetNada applies these factors for you

Our platform reads your invoices and receipts, matches each line to the right government emission factor, and builds your Scope 1–3 inventory automatically.

Book a Demo or start a free trial

Compliance

Data Source

Australian National Greenhouse Accounts Factors 2025

Published by: Department of Climate Change, Energy, the Environment and Water (DCCEEW)

Official source ↗