Landfill Gas & Wastewater Treatment Emissions Calculator — Scope 1 CH₄ + N₂O (IPCC First-Order Decay)
Estimate biogenic methane from solid-waste disposal sites and methane plus nitrous oxide from wastewater treatment, using the IPCC 2006 first-order-decay model and mass-balance pathways, with a regulatory AR5 default and an AR6 engineering toggle.
Landfill path — IPCC first-order decay (FOD): methane generation in the reporting year is modelled from the mass of decomposable degradable organic carbon deposited across all prior years, decaying exponentially. The engine runs the full year-by-year recursion per waste stream: decomposable DOC accumulated in year x equals the current deposit’s decomposable carbon plus the previous stock decayed by e−k; the fraction that decomposes in the year is converted to methane by the 16/12 carbon-to-methane mass ratio and the methane correction factor F. Deposited carbon is W × DOC × DOCf × MCF. Because of the built-in six-month delay, waste deposited in the reporting year contributes almost nothing that year and more in the years that follow.
Wastewater path — mass balance: methane equals total organics in the wastewater (TOW, as BOD for domestic or COD for industrial) multiplied by the maximum methane-producing capacity B₀ and the methane correction factor of the treatment or discharge pathway, less any organics removed as sludge and any methane recovered. Domestic effluent nitrous oxide is a separate pathway driven by the nitrogen discharged in effluent.
Methane is biogenic. Landfill and wastewater methane originates from recently-grown biomass, so the engine applies the biogenic methane GWP-100 — 28 at AR5, 27 at AR6 — not the fossil-methane value. Nitrous oxide uses 265 (AR5) / 273 (AR6). The carbon dioxide released by the same decomposition is biogenic and is reported as an excluded memo item, never added to the Scope 1 total. The mode badge on each result reads e.g. FOD · AR5.
Recovery & oxidation: recovered or flared methane is subtracted from generated methane before oxidation and is capped at the quantity generated; the remaining methane is reduced by the cover oxidation fraction (1 − OX). Both recovered and oxidised methane convert to biogenic CO₂ (memo).
Scope boundary: Scope 1 fugitive methane from solid-waste disposal sites the entity owns or controls; methane and nitrous oxide from wastewater the entity treats or discharges. Excluded: emissions from waste sent to third-party sites (a Scope 3 Category 5 line), energy recovery combustion of collected landfill gas (stationary combustion), transport of waste, and the biogenic CO₂ memo.
Scope 1 fugitive process emissions from a solid-waste disposal site or wastewater treatment operation you own or operate.
Enter tonnes disposed by IPCC waste type and year. Each stream decays at its own first-order rate.
Advanced parameters (Tier 2 overrides)
Leave blank to use IPCC defaults. Overrides are flagged in the audit trail and export.
Enter waste deposition above to calculate landfill methane
Results appear instantly. First-order decay emission curve, uncertainty band, audit trail and factor citations available after calculation.
Estimates Scope 1 fugitive methane and nitrous oxide using IPCC 2006 Guidelines Vol 5 (Waste) default (Tier 1) parameters read live from the GreenCalculus MasterBrain. Biogenic carbon dioxide is reported as a memo item and is not included in the Scope 1 total. Results support inventory preparation and screening; site-specific measurement and Tier 2/3 methods may be required for regulatory reporting and third-party verification (e.g. ISO 14064-3).
Landfill gas and wastewater methane are the two Scope 1 lines most waste, water, and food-sector operators either omit or estimate with a single multiplication — and both hide the same trap: the emission you report this year was set in motion by material you handled years ago.
A tonne of food waste buried in 2020 is still generating methane in 2024, and a naive “tonnes this year × a factor” estimate misses it entirely.
A managed landfill holding five years of food and paper waste generates roughly 90 tonnes of methane in the reporting year — about 2,538 tCO₂e at AR5 (2,447 at AR6), using the IPCC first-order-decay model and the biogenic methane GWP. Current-year deposits add almost nothing yet.
What This Calculator Covers — Scope, Boundary & the Two Source Categories
Two distinct emission categories share one calculation surface here because both are governed by IPCC 2006 Guidelines Volume 5 and both are Scope 1 for the entity that owns or controls the source. A module switch at the top of the tool selects between them.
Solid Waste Disposal Sites — Landfill Methane
Organic material buried in a landfill decomposes anaerobically and releases methane. The rate depends on how much degradable organic carbon the waste contains, how well the site is managed, the local climate, and how long the waste has been in place. This is not a one-year event: a single year’s deposit keeps generating methane for decades, which is why the IPCC prescribes a first-order-decay model rather than a flat annual factor.
Wastewater Treatment & Discharge — Methane and Nitrous Oxide
Wastewater carries organic load (measured as BOD for domestic flows, COD for industrial) that generates methane under anaerobic treatment or discharge conditions. Domestic wastewater additionally carries nitrogen that produces nitrous oxide once discharged to receiving waters. The calculator handles both gases on the wastewater path; nitrous oxide does not arise on the landfill path.
The Biogenic-CO₂ Memo — Why It Is Excluded from Scope 1
Decomposing waste and treated wastewater both release carbon dioxide alongside methane. That CO₂ is biogenic — the carbon was fixed from the atmosphere by recently-grown biomass — so under GHG Protocol and IPCC convention it is reported as a memo item outside the Scope 1 total, not added to it. The methane and nitrous oxide are counted; the biogenic CO₂ is disclosed separately. Folding biogenic CO₂ into the headline number is a common and material error.
Included vs Excluded Emissions
| Included in this calculator | Excluded — report elsewhere |
|---|---|
| Fugitive CH₄ from owned/controlled solid-waste disposal sites (FOD model) | Waste sent to third-party sites — a Scope 3 Category 5 line, not Scope 1 |
| CH₄ from wastewater treated or discharged by the entity (BOD/COD mass balance) | Energy recovery from collected landfill gas — stationary combustion, reported separately |
| N₂O from domestic effluent nitrogen discharged to receiving waters | Transport of waste and wastewater sludge — mobile combustion |
| Methane recovery and cover-oxidation adjustments (netted against generation) | Biogenic CO₂ from decomposition — a memo item, excluded from the Scope 1 total |
| Industrial and domestic streams handled as distinct activity types with different DOC, B₀, and MCF coefficients | N₂O from the landfill surface — not a quantified pathway under the Tier 1 FOD method |
The Calculation Methodology — First-Order Decay & the Wastewater Mass Balance
The two categories use fundamentally different maths. Landfill uses a time-dependent decay recursion; wastewater uses a static mass balance. Both feed the same biogenic-GWP weighting step at the end.
The IPCC First-Order Decay (FOD) Model
Landfill methane in any given year depends on the entire deposition history, not just the current year’s tonnage. The engine runs the IPCC recursion per waste stream:
Each year, the pool of decomposable carbon in the landfill grows by what you just buried and shrinks by what decayed. Decomposable carbon added this year is the tonnage multiplied by its degradable organic carbon content (DOC), the fraction that actually decomposes (DOCf), and the methane correction factor for the site (MCF). The stock carried over from last year is reduced by the decay factor e−k. Whatever decomposed this year becomes methane via the 16/12 carbon-to-methane mass ratio and the methane fraction F of landfill gas. The built-in six-month delay means the waste you buried this year decomposes starting next year — so current-year deposits contribute close to zero to the current-year number.
That last point is the single most counterintuitive feature of waste accounting and the one verifiers probe hardest. A site that opened this year reports almost no methane this year; a site that closed five years ago still reports methane today. The reporting-year figure is a function of the deposition ledger, not of this year’s gate tonnage.
DOC, DOCf, MCF, k, F, OX, R — The Parameter Chain
Seven coefficients drive the landfill result. Six are read live from the MasterBrain waste section; recovery is a user input. The values below are the IPCC 2006 Volume 5 defaults the engine uses and carries as its built-in fallback.
| Parameter | What it is | Default basis |
|---|---|---|
| DOC | Degradable organic carbon per tonne of waste, by stream | Stream-specific — e.g. paper/cardboard highest, inert zero |
| DOCf | Fraction of DOC that actually decomposes | 0.5 |
| MCF | Methane correction factor — how anaerobic the site is | 1.0 managed anaerobic → 0.4 unmanaged shallow |
| k | Decay rate — how fast the stream breaks down, by climate | Stream × climate disaggregated; carries the headline uncertainty range |
| F | Fraction of landfill gas that is methane | 0.5 |
| OX | Oxidation fraction removed by cover soil | 0 uncovered / 0.1 covered-oxidising |
| R | Methane recovered or flared — user input, capped at generation | None by default |
The methane correction factor scales the entire result. A managed anaerobic site (MCF 1.0) generates two-and-a-half times the methane of an unmanaged shallow site (MCF 0.4) from identical waste. Selecting the wrong site-management class is the fastest way to a materially wrong number, and a verifier will expect the classification to match documented site engineering — depth, cover, and gas-management design — not a default guess.
Wastewater CH₄ — the TOW × B₀ × MCF Pathway
The wastewater methane calculation is a mass balance, not a decay model. Total organics in the wastewater — BOD load for domestic flows, COD load for industrial — set the ceiling; the maximum methane-producing capacity B₀ and the treatment pathway’s methane correction factor determine how much of that ceiling is realised.
Methane equals the organic load (kg BOD or kg COD per year) times B₀ — 0.6 kg CH₄ per kg BOD for domestic, 0.25 kg CH₄ per kg COD for industrial — times the methane correction factor of the treatment or discharge pathway. Organics removed as sludge and any methane recovered are subtracted. A well-aerated plant has a low MCF and emits little; an anaerobic reactor or a stagnant discharge lagoon has a high MCF and emits a great deal from the same organic load.
Wastewater N₂O — the Effluent-Nitrogen Pathway
Domestic effluent nitrous oxide is driven by the nitrogen discharged to receiving waters. The engine derives the nitrogen load from population, per-capita protein supply, and correction factors for non-consumed and industrial-and-commercial protein, subtracts any nitrogen removed as sludge, and applies the effluent emission factor of 0.005 kg N₂O-N per kg nitrogen. The result converts to N₂O mass by the 44/28 ratio before the GWP weighting. This pathway is optional and toggled on the domestic wastewater path only.
Recovery & Oxidation Adjustments
On the landfill path, recovered or flared methane is subtracted from generated methane first, capped at the quantity generated — a metered recovery figure that exceeds generation raises a non-blocking warning rather than producing a negative result. The remaining methane is then reduced by the cover oxidation fraction, applied as (1 − OX). Recovered, flared, and oxidised methane all convert to biogenic CO₂ and appear in the memo, never in the Scope 1 total.
Landfill vs Wastewater — Which Pathway Applies to You?
Most operators need only one module. A brief orientation to which, and why the maths differs.
Landfill (SWDS) path
For any entity that owns or controls a solid-waste disposal site — municipal authorities, private landfill operators, and industrial sites with on-site burial. Uses the first-order-decay model, so it needs a deposition history, not just this year’s tonnage. Gas is methane only (plus a biogenic-CO₂ memo). The dominant sensitivity is the site-management class (MCF) and the waste composition (DOC).
Wastewater path
For entities that treat or discharge wastewater — utilities, food and beverage processors, pulp and paper, and any industrial site with its own effluent handling. Uses a single-year mass balance on organic load (BOD or COD). Domestic flows also carry a nitrous-oxide pathway from effluent nitrogen. The dominant sensitivity is the treatment or discharge pathway’s methane correction factor.
An entity that both operates a landfill and treats wastewater runs each module separately and sums the two Scope 1 lines; the calculator does not merge them, because the deposition-history model and the annual mass balance are not comparable structures.
The Parameters That Drive the Result
Ranking the inputs by how much they move the landfill result helps direct data-collection effort to where it matters. The chart below is approximate, for a typical managed site; the exact ordering shifts with waste composition and climate.
Approximate influence of each input on the reporting-year landfill result for a typical managed site. Site class and waste composition set the level; the decay rate governs both level and the shape of the emission over time; recovery reduces the net figure where gas capture is installed.
Site Management & MCF — The Single Highest-Leverage Choice
Covered in the methodology callout above: MCF scales the whole result and must trace to documented site engineering. A managed anaerobic site takes MCF 1.0; a managed semi-aerobic site 0.5; unmanaged deep and shallow sites 0.8 and 0.4; an uncategorised site 0.6.
Waste Composition & DOC
Degradable organic carbon varies more than tenfold across waste streams — paper, cardboard, and wood carry the most; food and garden waste a moderate amount; inert construction and demolition material almost none. A site accepting mostly inert rubble generates far less methane per tonne than one taking food and paper, even at identical MCF. Where a composition profile is used instead of a stream-by-stream ledger, the accuracy of that profile drives the accuracy of the result.
The k Decay Rate & the Time-Lag Problem
The decay rate k determines both how much methane a given deposit produces this year and how that production spreads across future years. Fast-decaying streams like food waste release their methane over a few years; slow streams like wood release it over decades. Because k is climate-disaggregated, the same waste in a warm, wet climate decays faster — and emits sooner — than in a cold, dry one. The k rows carry the widest uncertainty in the model, which is what sets the headline confidence band on the result.
Worked Example — Managed Landfill, Five-Year Deposition Ledger
This is the scenario the calculator loads by default, in regulatory AR5 mode. The inputs and results are fixed so the figures reconcile against the live engine on the date of review.
A managed anaerobic site (MCF 1.0) in a boreal/temperate-wet climate, uncovered (OX 0), with no gas recovery, reporting for 2024. The deposition ledger runs five years, dominated by food waste with paper and garden fractions in the early years. The engine runs the FOD recursion across all five years and reports the methane generated in 2024 only.
| Deposition year | Streams deposited |
|---|---|
| 2020 | Food 2,500 t · Paper/cardboard 2,000 t |
| 2021 | Food 2,600 t · Garden/park 1,500 t |
| 2022 | Food 2,700 t |
| 2023 | Food 2,800 t |
| 2024 | Food 2,900 t |
| Result (2024 reporting year) | AR5 (regulatory default) | AR6 (engineering toggle) |
|---|---|---|
| Methane generated in 2024 | ≈ 90.6 t CH₄ | ≈ 90.6 t CH₄ |
| Biogenic methane GWP-100 | 28 | 27 |
| Scope 1 total | ≈ 2,538 tCO₂e | ≈ 2,447 tCO₂e |
| Biogenic CO₂ | memo — excluded from the Scope 1 total | |
Note what the 2024 deposit of 2,900 t of food waste contributes to the 2024 figure: almost nothing. Under the six-month delay it begins decomposing in 2025. The 90.6 tonnes of methane come overwhelmingly from the 2020–2023 deposits, with the older, larger food fractions and the 2020 paper contributing the bulk. Switching to AR6 changes only the GWP weight — the methane mass is identical — so the total falls by the ratio 27/28, about 3.3%.
Second Example — Domestic Wastewater, Anaerobic Reactor
For an entity on the wastewater path, the equivalent default reconciliation: a domestic system serving 250,000 people at a per-capita BOD of 60 g/person/day, discharging entirely through an anaerobic reactor (MCF 0.8), with a per-capita protein supply of 40 kg/person/yr and no sludge removal, in AR5 mode.
| Wastewater line | Value (AR5) |
|---|---|
| Total organics in wastewater (TOW) | 5,475,000 kg BOD/yr |
| Methane | ≈ 2,628 t CH₄ → ≈ 73,584 tCO₂e |
| Effluent nitrous oxide | ≈ 17.3 t N₂O → ≈ 4,581 tCO₂e |
| Scope 1 total | ≈ 78,165 tCO₂e |
The contrast is instructive: the same anaerobic pathway that makes a reactor efficient at treating organic load also makes it a large methane source when the gas is not captured. Adding methane recovery to this scenario is the single largest abatement lever on the wastewater side.
Why the Biogenic Methane GWP Shapes the Result
Methane dominates the landfill result and the wastewater methane line, and the specific GWP the engine applies is a deliberate accuracy choice worth understanding. Landfill and wastewater methane is biogenic — the carbon came from recently-grown plant matter — so the engine uses the biogenic methane GWP-100, not the fossil value.
The distinction is not cosmetic. Fossil methane carries an AR6 GWP-100 of 29.8 because oxidising it adds new CO₂ to the carbon cycle; biogenic methane is 27 because the carbon was already part of the short-term cycle. Many calculators hardcode the older AR4 value of 25, or apply the fossil figure indiscriminately. Applying 29.8 instead of 27 to the worked example’s 90.6 tonnes of methane would overstate the landfill line by roughly a tenth. Using the biogenic value is the defensible choice and one a verifier can trace to the source.
Nitrous oxide, on the wastewater path, carries a far larger weight — 273 at AR6, 265 at AR5 — so even the small nitrogen-driven N₂O mass becomes a material CO₂e line. In the wastewater worked example, 17.3 tonnes of N₂O contribute nearly 4,600 tCO₂e.
Uncertainty Disclosure — FOD’s Time Lag & the k-Range Confidence Band
The first-order-decay model carries two distinct kinds of uncertainty. The first is structural: because the reporting-year figure depends on a multi-year deposition history, any gaps or estimates in that history propagate into the result — a site with incomplete records before a certain year cannot produce a fully reconciled current-year number. The second is parametric: the decay rate k carries the widest uncertainty range of any coefficient in the model, and the MasterBrain k rows carry explicit low and high bounds that the engine surfaces as the headline confidence band. Where landfill methane is a material inventory line, moving from the Tier 1 defaults to site-measured gas-generation data narrows the band substantially.
Audit Checklist — What Gets Flagged in Waste-Sector Verification
Verification under ISO 14064-3 traces each material source from activity data to reported tonnes. Waste and wastewater draw scrutiny because the models are unfamiliar to general practitioners and the errors are systematic rather than random.
- Current-year tonnage treated as current-year emission. Applying a flat factor to this year’s gate tonnage instead of running the decay model over the deposition history. The FOD model attributes almost none of this year’s deposit to this year’s emission — a flat-factor estimate is both wrong and untraceable.
- Biogenic CO₂ folded into the Scope 1 total. The CO₂ from decomposition is a memo item, excluded. Adding it to the methane figure inflates the reported number and misclassifies a biogenic flow as a Scope 1 emission.
- Fossil or legacy methane GWP applied to biogenic methane. Landfill and wastewater methane is biogenic — GWP 27 (AR6) / 28 (AR5). Using the fossil 29.8, or the obsolete AR4 value of 25, misstates the line.
- Site-management class (MCF) not matched to site engineering. Defaulting to managed-anaerobic (MCF 1.0) for a site that is semi-aerobic or unmanaged overstates methane by up to 2.5×. The classification must trace to documented depth, cover, and gas-management design.
- Recovered gas double-counted or uncapped. Methane sent to energy recovery is a stationary-combustion line elsewhere; it must not also remain in the fugitive landfill figure. Metered recovery exceeding generation is a data error, not a negative emission.
- Third-party waste reported as Scope 1. Waste sent off-site to a landfill the entity does not control is a Scope 3 Category 5 emission, not Scope 1. Only owned or controlled sites belong here.
- Wastewater organic load entered on the wrong basis. Domestic flows use BOD; industrial flows use COD. Mixing the two bases, or applying the domestic B₀ to a COD load, produces a systematically wrong methane figure.
- Missing method, tier, and factor-vintage citation. Stating a methane figure without naming the IPCC 2006 basis, the FOD tier, the MCF class, and the MasterBrain version leaves the number unverifiable. The engine’s export carries all four.
Sector & Stream Guidance — MSW, Industrial Waste, Sludge, Effluent
The practical work on the landfill path is classifying each waste stream to the right degradable-organic-carbon category; on the wastewater path it is measuring or estimating the organic load correctly. The table below orients the main streams. The DOC and organic-load values are IPCC 2006 defaults read live by the engine — confirm against site-specific assay where the line is material.
| Stream | Category | Notes |
|---|---|---|
| Paper & cardboard | Landfill — high DOC | Among the highest methane yields per tonne; slow-to-moderate decay. |
| Wood & straw | Landfill — high DOC | High carbon content but slow decay — emissions spread over decades. |
| Food waste | Landfill — moderate DOC | Fast decay; emits most of its methane within a few years of burial. |
| Garden & park waste | Landfill — moderate DOC | Moderate decay; seasonal in composition. |
| Construction & demolition | Landfill — very low DOC | Largely inert; minimal methane per tonne. |
| Sewage sludge (to landfill) | Landfill — low DOC | Distinct DOC from raw waste; classify as sludge, not MSW. |
| Domestic wastewater | Wastewater — BOD basis | B₀ 0.6 kg CH₄/kg BOD; carries the effluent N₂O pathway. |
| Industrial wastewater | Wastewater — COD basis | B₀ 0.25 kg CH₄/kg COD; sector-specific COD load; no effluent N₂O pathway. |
The most frequent stream-level error is treating a mixed municipal load as a single average when the calculator supports a per-stream ledger. Where the composition is known, entering each stream separately with its own DOC and decay rate produces a materially more accurate and more defensible result than a bulk average.
Geographic & Regulatory Context — IPCC, UK, EU, Singapore
Global Baseline — IPCC 2006 Guidelines Volume 5
The 2006 IPCC Guidelines, Volume 5 (Waste), are the methodological basis for both paths in this calculator. The first-order-decay model, the DOC and MCF defaults, and the wastewater mass-balance parameters all derive from that source. The parameters here are the 2006 defaults — the calculator does not apply a later refinement to the waste chapter, so a page citing this tool should name the 2006 basis specifically rather than a more recent revision.
Corporate Reporting — GHG Protocol Scope 1
Under the GHG Protocol Corporate Standard, fugitive landfill methane and wastewater emissions from owned or controlled sources are Scope 1. The operational-control boundary determines what counts: a site the entity operates is in; waste consigned to a third-party facility is out, moving instead to Scope 3 Category 5. Corporate and science-based reporting uses the AR6 GWP basis — the engineering toggle here — while national-inventory work stays on AR5.
UK and EU — National Inventory and Landfill Regulation
UK national-inventory accounting reports waste-sector methane on the same IPCC 2006 FOD basis, at the AR5 GWP convention that DEFRA’s factor set carries throughout. UK and EU landfill regulation — the diversion of biodegradable municipal waste from landfill and the requirement to capture and treat landfill gas at permitted sites — shapes the deposition histories and recovery rates that feed the model, though the specific directives are not linked here. Operators reporting under these regimes should default to AR5 and document their recovery metering.
Singapore and Other Jurisdictions
Singapore incinerates the bulk of its municipal solid waste rather than landfilling it, so the landfill path is narrow there — relevant mainly to the residual ash landfill and to entities reporting overseas operations. Wastewater methane and effluent nitrous oxide remain relevant to water and food-sector operators. Under the Singapore Carbon Tax Act, verify whether waste-sector emissions fall within a taxable facility’s boundary before finalising a submission. The IPCC 2006 basis at AR6 is the defensible default where a jurisdiction does not mandate a specific factor set.
Data Sources, Factor Versioning & the AR5→AR6 Question
Coefficient Provenance
The landfill parameters (DOC by stream, DOCf, MCF by site class, k by stream and climate, F, OX) and the wastewater parameters (B₀ for BOD and COD, per-region BOD, per-sector COD, the treatment-pathway MCF values, and the effluent N₂O factors) are IPCC 2006 Guidelines Volume 5 defaults, read live by the calculation engine from the MasterBrain waste section. The biogenic methane and nitrous-oxide GWP values are read from the MasterBrain GWP section. Each coefficient lookup carries a built-in fallback equal to the IPCC default, used only if a row is missing or the data layer is unavailable at load.
The tool computes from built-in IPCC 2006 defaults, shows an amber “data layer offline — built-in IPCC defaults used” banner, and notes how many factors fell back. The reproducibility stamp still records the MasterBrain version the calculation ran against, so a result produced during a data-layer outage is still traceable. The built-in defaults are numerically identical to the live values, so a fallback result matches a live result.
The AR5 → AR6 Question
This calculator defaults to AR5, unlike most corporate tools, because waste-sector reporting is dominated by national-inventory work that stays on the AR5 convention. The AR6 toggle is provided for corporate and science-based reporting that requires the current basis. The two differ only in the GWP weights — biogenic methane 28→27, nitrous oxide 265→273 — not in the underlying methane or nitrogen mass. Do not mix the two bases within a single inventory total, and restate a prior-year time series onto one basis rather than splicing AR5 history to an AR6 current year. The mode badge on every result records which basis produced the number.
Version History
The calculator’s factor data is sourced from the live MasterBrain waste and GWP sections. IPCC waste-sector defaults update only when the IPCC revises Volume 5; the current 2006 basis remains in effect. The data-version stamp in the calculator footer reflects the live MasterBrain version, and the audit trail on each calculation records the source of each coefficient and the basis applied.
What’s Next? Completing Your Scope 1 Inventory
You have completed landfill gas and wastewater — the two waste-sector Scope 1 lines. Most operators pair these with fuel combustion and, where relevant, fugitive process emissions to close out Scope 1.
| Step | Scope 1 line | Covers |
|---|---|---|
| ✓ Completed | Landfill Gas & Wastewater | FOD methane + effluent N₂O |
| → Next | Stationary Combustion | On-site fuel burning |
| → Then | Fugitive Methane | Oil & gas and process leaks |
The complete first-order-decay derivation, the wastewater mass-balance detail, the full DOC and MCF default tables, and the biogenic-CO₂ memo treatment are set out in the methodology page. Read it before preparing a verified Scope 1 waste-sector submission.
Frequently Asked Questions
For the entity that owns or controls the landfill, fugitive methane is a Scope 1 emission. For an entity that sends waste to a third-party site it does not control, the same emission appears in Scope 3 Category 5 (waste generated in operations). The operational-control boundary decides which applies.
The IPCC first-order-decay model has a built-in six-month delay: waste deposited in a year first begins decomposing the following year. So the reporting-year methane comes almost entirely from waste buried in prior years, and a site’s current-year gate tonnage is a poor proxy for its current-year emission. This is why the calculator needs a deposition history, not a single tonnage figure.
Landfill and wastewater methane is biogenic — the carbon came from recently-grown biomass — so the calculator applies the biogenic methane GWP-100 of 27 at AR6 (28 at AR5). The fossil-methane value of 29.8 applies to methane from fossil sources and is not appropriate here; the older AR4 value of 25 is obsolete. Using the biogenic value is the traceable, defensible choice.
Decomposition releases biogenic CO₂ alongside methane. Because that carbon was fixed from the atmosphere by recently-grown biomass, it is reported as a memo item outside the Scope 1 total, not added to it. The calculator surfaces it separately. Adding biogenic CO₂ to the methane figure is a common error that inflates the reported number.
The calculator defaults to AR5 because waste-sector reporting is dominated by national-inventory work, which stays on the AR5 convention. Switch to the AR6 toggle for corporate, voluntary, and science-based reporting, which uses AR6. Do not mix the two within a single inventory year, and restate a time series onto one basis rather than splicing AR5 history to an AR6 current year.
The methane correction factor captures how anaerobic a landfill is — how much of the decomposing carbon actually becomes methane rather than being oxidised aerobically. It ranges from 1.0 for a managed anaerobic site to 0.4 for an unmanaged shallow one, so the same waste can produce 2.5× more methane depending on the classification. It is the single highest-leverage input and must match documented site engineering.
No. Waste sent to a site the entity does not own or control is a Scope 3 Category 5 emission, not a Scope 1 line. This calculator’s landfill path is for sites under the entity’s operational control. Use a Scope 3 waste calculator for consigned waste.
Domestic wastewater methane is calculated on biochemical oxygen demand (BOD), with a maximum methane-producing capacity of 0.6 kg CH₄ per kg BOD. Industrial wastewater uses chemical oxygen demand (COD), at 0.25 kg CH₄ per kg COD, with sector-specific COD loads. The two bases are not interchangeable — applying the domestic factor to a COD load produces a systematically wrong figure.
Yes, on the domestic path. Nitrogen discharged in effluent produces nitrous oxide, calculated from population, per-capita protein supply, and correction factors, at an effluent emission factor of 0.005 kg N₂O-N per kg nitrogen. It is an optional pathway toggled on the domestic wastewater module. The landfill path does not produce a quantified N₂O line under the Tier 1 method.
Recovered or flared methane is subtracted from the generated methane before the oxidation step, capped at the quantity generated. It is the largest abatement lever on both paths. Note that methane sent to energy recovery becomes a stationary-combustion line elsewhere in the inventory — it leaves the fugitive figure but does not vanish from the total.
Methodology Notes and Limitations
Tier 1 defaults. The coefficients are IPCC 2006 Guidelines Volume 5 Tier 1 defaults. Where landfill or wastewater methane is a material inventory line, site-measured gas-generation or load data (Tier 2) produces a more accurate and defensible result.
Deposition history drives the landfill result. The first-order-decay model requires a multi-year deposition ledger. The steady-state input mode, which back-fills a flat history, is an accessibility fallback for operators without records and is labelled as an approximation in the tool — its result is less defensible than a real ledger.
Biogenic CO₂ is a memo, not a Scope 1 emission. The CO₂ from decomposition and from oxidised or flared methane is biogenic and excluded from the Scope 1 total by convention. It is disclosed separately.
Operational-control boundary. Only owned or controlled sites belong on the landfill path; consigned waste is a Scope 3 Category 5 line. Confirm the boundary before reporting.
No site-specific verification. This calculator is a calculation aid, not a measurement system. Regulatory submissions requiring site-specific accuracy need independent verification against field measurement data.
Sources: IPCC 2006 Guidelines for National Greenhouse Gas Inventories, Volume 5 (Waste) — Chapter 3 (Solid Waste Disposal, first-order decay) and Chapter 6 (Wastewater Treatment and Discharge) · GHG Protocol Corporate Accounting and Reporting Standard (Scope 1 boundary) · IPCC Sixth Assessment Report (AR6), Working Group I (2021) for the biogenic methane GWP-100 of 27 and the N₂O GWP-100 of 273 · IPCC Fifth Assessment Report (AR5, 2013) for the biogenic methane GWP-100 of 28 and the N₂O GWP-100 of 265 · DEFRA / DESNZ UK national-inventory convention (AR5 basis) · coefficient values read live via the MasterBrain waste and GWP sections.
Methodology standard: IPCC 2006 Guidelines Vol 5 first-order-decay and mass-balance methods · Aligned with the Landfill Gas & Wastewater methodology · Last reviewed: May 2026.
Results produced by this calculator are estimates. They do not constitute professional advice and should be reviewed by a qualified GHG accounting practitioner before use in regulatory submissions, investor disclosures, or science-based target filings. GreenCalculus accepts no liability for decisions made on the basis of calculator outputs alone.