# How do I estimate methane from my effluent treatment plant?

Canonical: https://senseible.earth/answers/etp-wastewater-methane-emissions

Use the IPCC 2006 method: take the organic load in kg COD a year, multiply by 0.25 kg CH4 per kg COD and by a methane correction factor for how the plant treats it, then subtract methane recovered. A well run aerobic ETP emits almost none; anaerobic tanks or lagoons without gas capture emit a lot.

## The formula

From the 2006 IPCC Guidelines, Volume 5, Chapter 6, for industrial wastewater:

CH4 = (TOW minus S) x EF minus R, where TOW is total organic load in kg COD a year, S is organic load removed as sludge, R is methane recovered, and EF = Bo x MCF.

Bo, the maximum methane producing capacity, is 0.25 kg CH4 per kg COD by default.

## Choosing the methane correction factor

These are IPCC defaults for industrial wastewater. If your ETP has several stages, apply the factor to the COD each stage removes.

- Aerobic treatment, well managed: 0.
- Aerobic treatment, overloaded: 0.3.
- Anaerobic reactor or digester without methane recovery: 0.8.
- Shallow anaerobic lagoon, under 2 m deep: 0.2.
- Deep anaerobic lagoon, over 2 m: 0.8.

## Data you need

- Daily inflow in m3, from a flow meter or pump hours.
- Inlet and outlet COD in kg per m3 or mg per litre, from your lab or pollution control board returns.
- Sludge removed, and any biogas captured and burnt or used.

## Which scope it falls in

Methane from an ETP you own and run is Scope 1. Effluent sent to a common effluent treatment plant (CETP) run by others is Scope 3 Category 5. Wastewater also releases nitrous oxide, which IPCC estimates separately from nitrogen load.

## Worked example: anaerobic tank without gas capture

- Organic load: 50 m3 a day x 3 kg COD per m3 = 150 kg COD a day
- Per year: 150 x 365 = 54,750 kg COD
- Methane: 54,750 x 0.25 x 0.8 = 10,950 kg CH4, about 11 t
- CO2e at GWP 28 (IPCC AR5): 10,950 x 28 = 306,600 kg, about 307 t CO2e
- At GWP 27 (IPCC AR6, non-fossil methane): 10,950 x 27 = 295,650 kg, about 296 t CO2e

No sludge removal or recovery is assumed here. Subtract both if they apply, and use one GWP set for the whole inventory.

## What Senseible does here

Senseible does not calculate wastewater methane; it has no wastewater factor. It reads ETP chemical and power invoices, so the ETP's electricity shows up in Scope 2.

- [Methane and black carbon cuts vs CO2](https://senseible.earth/climate-intelligence/methane-black-carbon-reductions-vs-co2)
- [AR5 or AR6 GWP: which to use](https://senseible.earth/answers/ar5-vs-ar6-gwp-which-to-use)
- [Textile industry](https://senseible.earth/industries/textile)

Sources: [2006 IPCC Guidelines, Volume 5, Chapter 6 (wastewater treatment and discharge)](https://www.ipcc-nggip.iges.or.jp/public/2006gl/), [IPCC AR6 WG1, global warming potentials](https://www.ipcc.ch/report/ar6/wg1/)

Last reviewed 2026-10-15.