What is the first-order decay model for landfill gas?

It models methane generation as Q_CH4(t) = k × L0 × M × e^(−k×t), where k is the decay rate constant (yr⁻¹), L0 is the methane generation capacity (m³ CH4/Mg), M is the waste mass (Mg), and t is waste age (years). Total LFG is estimated by dividing methane volume by the methane fraction (typically 50%). Generation peaks near placement and declines exponentially over time.

What is a typical k value for municipal solid waste?

For MSW in a humid climate, k is commonly 0.04–0.10 yr⁻¹. Arid climates use lower values (0.02–0.04) because moisture limits decomposition. Wet-cell or bioreactor landfills can reach 0.10–0.30 yr⁻¹. The EPA Landfill Gas Emissions Model (LandGEM) default for conventional MSW is 0.04 yr⁻¹.

What is L0 and how is it determined?

In EPA LandGEM, L0 is the potential methane generation capacity (m³ CH4 per metric ton of waste), typically 100–170 m³ CH4/Mg for MSW and 40–100 m³ CH4/Mg for C&D debris. Total LFG yield is double this amount (200–340 m³/Mg) at 50% methane concentration. It depends on organic content and moisture, determined via laboratory biochemical methane potential (BMP) testing or EPA AP-42 defaults.

Why is methane 50% of landfill gas?

Anaerobic decomposition of organic matter produces roughly equal volumes of methane (CH4) and carbon dioxide (CO2), so LFG is approximately 50% CH4 and 50% CO2 by volume. The exact ratio varies (45–60% CH4) with waste composition, age, and moisture; 50% is the standard engineering default.

How is the energy content of landfill gas calculated?

Methane has a higher heating value of approximately 35.8 MJ/m³ (about 1,000 BTU/scf). Energy output = methane volume (m³/yr) × 35.8 MJ/m³, then converted to MWh by dividing by 3,600 MJ/MWh. Actual electrical output depends on conversion efficiency (typically 25–35% for internal combustion engines).

Does this tool account for gas collection efficiency?

No. The calculator estimates gross LFG generation. A real collection system captures 60–85% of generated gas depending on cover type, infrastructure design, and regulatory requirements. Apply a collection efficiency factor to the output when sizing equipment or projecting recoverable energy.

Landfill Gas Calculator

Enter waste mass, age, and decay constant to estimate annual landfill gas generation, methane volume, and equivalent energy output.

Landfill Parameters

Waste Mass (Mg = metric tons)

1 short ton ≈ 0.907 Mg | 1 Mg = 1 tonne

Waste Type

k — Decay Constant (yr^-1)

L0 — CH4 Capacity (m³/Mg)

Waste Age — Years Since Placement

Use 0 to see peak generation at time of placement.

Default values by waste type

Enter landfill parameters and click Calculate.

LFG Generation at Year —

LFG Generation

—

m³/year

LFG Flow Rate

—

MMscfd

Methane Volume

—

m³ CH4/year

Energy Potential

—

MWh/year

BTU/year

—

Avg MW Output

—

gross

CH4 (scf/year)

—

LFG Generation Over 20 Years

Year	LFG (m³/yr)	CH4 (m³/yr)	Energy (MWh/yr)	% of Peak

Based on Q_CH4(t) = k × L0 × M × e^−kt with 50% CH4 in LFG (EPA LandGEM method). Does not account for gas collection efficiency or cover losses.

Summary

Landfill gas (LFG) forms as buried organic waste decomposes anaerobically. The first-order decay model — used by the EPA and widely adopted in environmental engineering — estimates how gas generation changes over time based on waste mass, a site-specific decay rate constant, and the potential gas yield of the waste. This calculator outputs annual LFG volume, methane fraction, and equivalent energy so engineers and planners can size gas collection systems and evaluate energy recovery projects.

How it works

Enter the mass of waste placed in the landfill and select the waste type to load a default decay constant (k) and methane generation capacity (L0).
Set the current age of the waste (years since placement).
Adjust k and L0 if site-specific data are available.
The calculator applies Q_CH4(t) = k × L0 × M × e^(−k×t) (EPA LandGEM method) to calculate annual methane generation, then derives total LFG assuming 50% methane content.
Energy potential is calculated as methane volume × 35.8 MJ/m³ converted to MWh (and BTU).
The year-by-year table shows how gas generation declines over the first 20 years.

Use cases

Size a gas collection and control system (GCCS) for a new or existing landfill.
Estimate energy recovery potential for a landfill gas-to-energy (LFGTE) project.
Screen sites for EPA Landfill Methane Outreach Program (LMOP) eligibility.
Compare LFG yield from municipal solid waste versus construction and demolition debris.
Support greenhouse gas inventory and carbon credit calculations.
Generate preliminary design data for landfill flaring or power generation equipment.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu