Landfill sites are responsible for producing hundreds of different types of gases which make a significant contribution to global warming. These landfill gases need to be monitored as they can be released into the atmosphere as a result of organic waste decomposition, volatilization and chemical reactions.
Learn about what gases are produced by landfills, how it occurs and what can be done about it in this guide.
What gas is produced by landfills?
Methane and carbon dioxide are the most prominent types of gas produced by landfills. Between 45 – 60% of landfill gas is methane and around 40% - 60% is carbon dioxide. The remaining small percentage is often taken up by some of the following gases:
• Nitrogen: this makes up between 2 – 5% of landfill gases. It’s an odorless, tasteless gas without any color
• Oxygen: 0.1 – 1% of landfill gases. Oxygen is odorless, tasteless and colorless
• Ammonia: 0.1 – 1%. This gas has no color but a very strong odor
• Non-methane organic compounds (NMOC): 0.01 – 0.6%. These are organic compounds that occur naturally or can be formed by synthetic chemical processes
• Sulfides: 0 – 1%. Sulfides are naturally occurring gases that are responsible for creating that rotten-egg type smell that’s often associated with landfills. Even at very low amounts, sulfides can cause unpleasant smells
• Hydrogen: 0 – 0.2%. An odorless and colorless gas
• Carbon monoxide: 0 – 0.2%. Also an odorless and colorless gas
How is gas produced in landfill?
There are three key processes involved in the formation of landfill gas: bacterial decomposition, volatilization and chemical reactions.
Bacterial decomposition
The vast majority of gases in landfill are produced by bacterial decomposition. This occurs when organic waste such as food, garden waste, textiles, wood and paper products are broken down by naturally occurring bacteria in the waste and soil that’s used to cover the landfill. There are four different phases to the bacterial decomposition of organic waste and the composition of the gas changes at each phase.
Volatilization
Landfill gases can be created when wastes such as organic compounds change from a liquid or solid into vapor in a process known as volatilization. Most NMOCs in landfill gases are the result of the volatilization of certain chemicals disposed of in landfill.
Chemical reactions
These can be created by reactions from certain chemicals present in the waste. For example, if chlorine bleach and ammonia come into contact with one another in landfill, a harmful gas can be produced.
What conditions impact landfill gas production?
Each landfill will produce different types of landfill gases at a different rate, this is due to the individual conditions of both the waste and the site. Some factors that may affect a landfill site’s gas production include:
1. Waste composition
The more organic waste present in landfill, the more gases will be produced by bacteria during decomposition. On the other hand, if more chemicals are disposed of, the more likely NMOCs and other gases will be produced through volatilization or chemical reactions.
2. Age of the waste
The age of the waste present in the landfill has a large impact on the number of gases that will be produced. On average, waste that’s been buried less than 10 years ago will produce more landfill gas via bacterial composition, volatilization or chemical reaction than older waste. The majority of gas production occurs between 5 – 7 years after burying.
3. Oxygen present in landfill
Methane gas can only be produced in landfill once oxygen is no longer present, which may mean that waste buried deeper produces more gases.
4. Moisture content
Moisture in landfill can cause an increase in gas production as it encourages bacterial decomposition. Additionally, it can also increase the likelihood of chemical reactions that may produce gases.
5. Temperature
As the temperature in the landfill rises, the activity of bacteria increases, which in turn, causes more gas to be released. Higher temperatures can also increase volatilization and chemical reactions.
What can be done about landfill gases?
The amount and types of gases produced in landfill need to be carefully monitored and managed in order to reduce the environmental impact. Landfill gas sampling should take place regularly throughout the site to check levels and ensure the gas isn’t migrating into soils surrounding landfills. Frequent checks should also be carried out to ensure there are no leaks from gas storage systems or pipework.
Alongside careful monitoring and management, landfill gases can also be captured, converted, and used as a renewable energy source. These gases can then be used to create fuel for electricity generation and there have also been developments in carbon capture technology. Using landfill gas in this way reduces odors, hazards associated with emissions and prevents methane from migrating into the atmosphere.
For more information on landfill gas management, learn about the importance of gas wells in landfill, next.
