Basic Information about Landfill Gas
On this page:
- Methane Emissions from Landfills
- Collecting and Treating Landfill Gas
- Landfill Gas Energy Project Types
Landfill gas (LFG) is a natural byproduct of the decomposition of organic material in landfills. LFG is composed of roughly 50 percent methane (the primary component of natural gas), 50 percent carbon dioxide (CO2) and a small amount of non-methane organic compounds. Methane is a potent greenhouse gas 28 to 36 times more effective than CO2 at trapping heat in the atmosphere over a 100-year period, per the latest Intergovernmental Panel on Climate Change (IPCC) assessment report (AR5) Exit.
Methane Emissions from Landfills
Municipal solid waste (MSW) landfills are the third-largest source of human-related methane emissions in the United States, accounting for approximately 15.4 percent of these emissions in 2015. At the same time, methane emissions from landfills represent a lost opportunity to capture and use a significant energy resource.
When MSW is first deposited in a landfill, it undergoes an aerobic (with oxygen) decomposition stage when little methane is generated. Then, typically within less than 1 year, anaerobic conditions are established and methane-producing bacteria begin to decompose the waste and generate methane.
- View a diagram that illustrates the changes in typical LFG composition after waste placement
- Learn more in Chapter 1. Landfill Gas Energy Basics of LMOP's LFG Energy Project Development Handbook
In October 2009, EPA issued a rule (40 CFR Part 98) that requires the reporting of greenhouse gas (GHG) emissions from large sources and suppliers in the United States, and is intended to collect accurate and timely emissions data to inform future policy decisions.
Annually, EPA issues an inventory report to present the U.S. government's estimates of U.S. human-related GHG emissions and sinks for each year since 1990. Emissions from the waste sector as well as other sectors are presented in this inventory.
Collecting and Treating Landfill Gas
Instead of escaping into the air, LFG can be captured, converted, and used as a renewable energy resource. Using LFG helps to reduce odors and other hazards associated with LFG emissions, and prevents methane from migrating into the atmosphere and contributing to local smog and global climate change. In addition, LFG energy projects generate revenue and create jobs in the community and beyond. Learn more about the benefits of using LFG.
Flowchart of a Basic LFG Collection and Processing System
LFG is extracted from landfills using a series of wells and a blower/flare (or vacuum) system. This system directs the collected gas to a central point where it can be processed and treated depending upon the ultimate use for the gas. From this point, the gas can be flared or beneficially used in an LFG energy project. Click on the flowchart to view more details, including photographs of LFG collection and processing systems.
Landfill Gas Energy Project Types
There are many options available for converting LFG into energy. Different types of LFG energy projects are grouped below into three broad categories – Electricity Generation, Direct Use of Medium-Btu Gas, and Upgraded LFG. Descriptions of project technologies are included under each project type. For more information on LFG energy project technology options and the advantages and disadvantages of each, see Chapter 3. Project Technology Options of LMOP’s LFG Energy Project Development Handbook.
About three-fourths of currently operational projects in the United States generate electricity from LFG. Electricity for onsite use or sale to the grid can be generated using a variety of technologies, including reciprocating internal combustion engines, turbines, microturbines, and fuel cells. The reciprocating engine is the most commonly used conversion technology for LFG electricity applications because of its relatively low cost, high efficiency and size ranges that complement the gas output of many landfills. Gas turbines are typically used in larger LFG energy projects while microturbines are generally used for smaller LFG volumes and in niche applications.
Cogeneration, also known as combined heat and power (CHP), projects use LFG to generate both electricity and thermal energy, usually in the form of steam or hot water. Several cogeneration projects have been installed at industrial operations, using engines or turbines. The efficiency gains of capturing the thermal energy in addition to electricity generation can make this project type very attractive.
Direct Use of Medium-Btu Gas
Directly using LFG to offset the use of another fuel (for example, natural gas, coal or fuel oil) occurs in about one-fourth of the currently operational projects. LFG can be used directly in a boiler, dryer, kiln, greenhouse or other thermal application. In these projects, the gas is piped directly to a nearby customer for use in combustion equipment as a replacement or supplementary fuel. Only limited condensate removal and filtration treatment are required, although some modifications of existing combustion equipment might be necessary.
LFG can also be used directly to evaporate leachate. Leachate evaporation using LFG is a good option for landfills where leachate disposal at a publicly owned treatment works plant is unavailable or expensive. LFG is used to evaporate leachate to a more concentrated and more easily discarded effluent volume.
Innovative direct uses of medium-Btu gas include firing pottery and glass-blowing kilns; powering and heating greenhouses; and evaporating waste paint. Current industries using LFG include auto manufacturing, chemical production, food processing, pharmaceuticals, cement and brick manufacturing, wastewater treatment, consumer electronics and products, paper and steel production, and prisons and hospitals.
LFG can be upgraded to a high-Btu gas through treatment processes by increasing its methane content and, conversely, reducing its CO2, nitrogen and oxygen contents. Upgraded LFG (or renewable natural gas [RNG]) can produce the equivalent of pipeline-quality gas (natural gas), compressed natural gas (CNG) or liquefied natural gas (LNG).
Options for use of upgraded LFG include injection into a natural gas pipeline for fueling stationary combustion equipment or creating vehicle fuel. In the case of vehicle fuel, LFG is used to produce the equivalent of CNG or LNG for use in natural gas vehicles. Vehicles can be fueled at or near the landfill (on site) or the upgraded gas can be injected into the pipeline and then compressed or liquefied at an alternate location.