Landfill gas

Landfill gas is a combustible gas generated naturally by the anaerobic decomposition of the organic matter contained in waste deposited in landfills.

Its main components are methane (CH₄, around 40-60%) and carbon dioxide (CO₂, around 40-50%), together with traces of compounds such as hydrogen, nitrogen, oxygen and hydrogen sulphide (H₂S). Because methane is a potent greenhouse gas, capturing landfill gas is important for both safety and climate reasons.

How landfill gas forms

The generation of landfill gas occurs in four phases, similar to those of anaerobic digestion:

1. Hydrolysis: breakdown of macromolecules into simpler compounds.
2. Acidogenesis: transformation into volatile fatty acids, alcohols and gases.
3. Acetogenesis: production of acetic acid, hydrogen and CO₂.
4. Methanogenesis: formation of methane and CO₂ by methanogenic archaea.

Risks associated with landfill gas

• Explosions and fires caused by the accumulation of methane in gas pockets.
• Fugitive methane emissions, which contribute to climate change.
• Unpleasant odours from sulphur compounds.
• Health risks for workers and nearby communities.

Energy recovery

Electricity and heat generation

• Combined heat and power engines that produce electricity for self-consumption or sale to the grid.
• Heat used in industrial processes or for heating.

Biomethane production

• Upgrading of the landfill gas (removal of CO₂, H₂S and moisture).
• Injection into the natural gas grid or use as a vehicle fuel (bio-CNG, bio-LNG).

Direct applications

• Use in adapted boilers to produce steam or hot water.

Applicable regulation

• Landfill Directive (1999/31/EC), which requires the collection and treatment of landfill gas.
• Royal Decree 646/2020, on the disposal of waste in landfill in Spain.
• Law 7/2022 on waste and contaminated soil, which prioritises the capture of landfill gas.
• Renewable Energy Directive (Directive (EU) 2018/2001, RED II), which recognises biogas as a renewable energy source.

Benefits of energy recovery

Environmental

• Reduction of methane emissions.
• Substitution of fossil fuels.
• Contribution to climate change mitigation.

Economic

• Revenue from the sale of electricity or biomethane.
• Lower energy costs at waste management facilities.
• Job creation in operation and maintenance.

Social

• Improved social acceptance of landfills.
• Reduction of odours and explosion risks.

Limits and challenges

1. Progressive decline in gas yield as landfills age.
2. High investment costs for upgrading systems.
3. Fugitive leaks that are difficult to control.
4. Need for infrastructure to inject biomethane into the grid.
5. Limited support frameworks compared with other European countries.

Link with the circular economy

Although the landfill sits at the bottom of the waste hierarchy, capturing and using its gas turns the facility into a renewable energy source. In this way, what was previously an environmental liability becomes a resource, helping to close material and energy loops. At Manglai we help companies measure their carbon footprint and prepare their sustainability reporting. Discover how Manglai can help you.