AP Syllabus focus:
‘Landfill mitigation includes burning waste for energy and restoring habitat on former landfills. Captured gases from landfill decomposition can be combusted to generate electricity and reduce landfill volume.’
Landfills can be managed to reduce pollution and, in some cases, turn waste into usable energy. Mitigation focuses on controlling emissions and safely reusing closed landfill sites while protecting nearby communities and ecosystems.
What “mitigation” means for landfills
Landfill mitigation aims to reduce the environmental impacts of existing or closed landfills, especially air emissions and long-term land degradation.
Key mitigation goals include:
Reducing greenhouse gas emissions (especially methane)
Controlling nuisance impacts (odours, pests, fire risk)
Stabilising the site for safe, long-term land use
Improving post-closure land value through habitat restoration
Energy recovery from waste and landfills
The syllabus emphasises two energy-recovery ideas: burning waste for energy and combusting captured landfill gases.
Burning waste for energy (waste-to-energy)
Some communities reduce the amount of waste requiring long-term disposal by combusting municipal solid waste under controlled conditions to produce heat/steam that can generate electricity.
Diagram of a mass-burn waste-to-energy plant, showing how municipal solid waste is burned to produce heat that makes steam in a boiler. The steam then drives a turbine-generator to produce electricity, while air-pollution control equipment treats flue gases and ash is collected for disposal or further handling. Source
In mitigation terms, the main purpose is volume reduction of incoming waste and offsetting some fossil-fuel energy demand.
Important tradeoffs to recognise:
Benefits depend on strong pollution controls and careful ash handling.
It is a mitigation strategy when it reduces the burden on landfills and recovers useful energy from materials that would otherwise be discarded.
Capturing landfill gas (LFG) for energy
As buried organic waste decomposes under low-oxygen conditions, it produces landfill gas, which can be collected and used as a fuel.
Landfill gas (LFG): A mixture of gases produced by anaerobic decomposition in landfills, primarily methane and carbon dioxide, that can be captured for combustion.
Capturing and using LFG supports mitigation because it:
Prevents methane from escaping to the atmosphere
Produces usable energy (electricity and/or heat)
Improves site safety by reducing subsurface gas buildup
How LFG energy recovery works (high-level process)
Typical components and steps include:
Cutaway diagram of a landfill gas (LFG) collection system, highlighting vertical extraction wells connected by lateral and header piping. The schematic emphasizes how gas is pulled through the piping network to centralized control equipment for treatment and either flaring or energy recovery, which reduces methane emissions while producing usable fuel. Source
Installing gas collection wells and a pipe network within the landfill
Applying suction to pull gas toward a central collection point
Removing moisture/impurities as needed for equipment protection
Combusting the gas in an engine, turbine, or boiler to generate electricity and/or heat
Monitoring gas flows over time as landfill decomposition slows
Using captured gas aligns directly with the specification: captured gases from landfill decomposition can be combusted to generate electricity and this approach can also help manage the landfill’s overall footprint and operational risks.
Habitat restoration on former landfills
After a landfill closes, mitigation can include restoring habitat on former landfills so the land supports ecological functions and safer human use.
Habitat restoration (landfill context): The process of re-establishing vegetation and ecological conditions on a closed landfill to create stable, functional habitat while maintaining the integrity of the capped waste.
A restored landfill site typically focuses on:
Establishing plant communities that limit erosion and improve soil stability
Creating wildlife habitat (often grassland or shrub habitat) suited to shallow soils
Managing stormwater to protect nearby surface waters
Maintaining long-term access for monitoring and repairs
Because buried waste can settle over time, restoration planning usually prioritises land uses compatible with continued monitoring and site maintenance, while still providing ecological and community benefits.
FAQ
Yes. With additional cleaning and separation, LFG can be upgraded to renewable natural gas (RNG).
Typical upgrades include removing moisture, carbon dioxide, and trace contaminants before compression and distribution.
Gas production depends on waste composition (amount of organic material), moisture, temperature, and how the landfill was operated.
Production generally peaks years after disposal and then declines gradually over decades.
As waste decomposes and compacts, the ground surface can sink unevenly.
Restoration designs often use flexible grading plans and vegetation suited to shallow, changing soils to maintain cover without damaging site infrastructure.
They track gas flow rates, methane concentrations at the surface, and the performance of energy equipment.
They also inspect vegetation cover and erosion patterns to confirm the restored habitat remains stable.
Landfill mining is excavating buried waste to recover materials, reduce long-term liabilities, or create space.
It may be considered where land is scarce, disposal costs are high, or recovery of metals and combustibles is economically viable.
Practice Questions
State one way landfills can recover energy and one environmental benefit of doing so. (2 marks)
Identifies an energy recovery method (e.g., combust captured landfill gas to generate electricity / burn waste for energy) (1)
States a valid environmental benefit (e.g., reduces methane emissions / reduces landfill volume / offsets fossil-fuel energy use) (1)
Describe how capturing landfill gas can be used as a mitigation strategy and explain how closed landfills can be managed to restore habitat. (6 marks)
Explains that anaerobic decomposition produces landfill gas containing methane (1)
Describes collection using wells/pipes and extraction to a central system (1)
States that captured gas is combusted to generate electricity and/or heat (1)
Links capture/combustion to reduced methane release and improved environmental performance (1)
Describes habitat restoration actions on closed landfills (e.g., establish vegetation to reduce erosion, create habitat) (1)
Mentions the need for ongoing monitoring/maintenance to ensure site stability during restoration (1)
