Landfills produce gases as the organic contents present at the site decompose. These gas emissions are generated as a byproduct of bacterial action which occurs naturally, though the process takes place on a much larger scale in landfill environments. The increasing rate at which waste is produced means that waste management companies are shouldering the responsibility of minimising the impact of landfills on the environment.
Landfill gas (LFG) released at landfill sites is considered an environmental pollutant, and when it is allowed to infiltrate the surrounding air and terrestrial ecosystems, it can cause localised effects as well as contributing to an overall global effect. To understand why LFG poses such a risk, it is important to first understand what it is composed of.
Composition of landfill gas (LFG)
Up to 98% of gas emissions from landfills is made up of carbon dioxide and methane. These are two of the most problematic greenhouse gases but for slightly different reasons. Both have a structure which makes it more difficult for solar heat radiation to leave the atmosphere as it normally would. With higher atmospheric concentrations of greenhouse gases comes a warming trend as more incoming heat from the sun is trapped close to the Earth’s surface.
Despite the fact that carbon dioxide isn’t the strongest greenhouse gas and therefore doesn’t trap the most heat per molecule, it is particularly damaging due to the sheer volumes at which it is released into the atmosphere. 33.1 billion metric tons of carbon dioxide is released globally every year, and emissions from waste amount to the equivalent of about 800 million metric tons of carbon dioxide.
Carbon dioxide makes up almost 50% of LFG mixes, and the rest is usually almost 50% methane. Methane is a much more potent greenhouse gas than carbon dioxide, in fact it is 84 times more potent when measured over a 20 year time frame. As such, methane emissions are considered some of the most damaging to the environment and so methane emissions are carefully monitored alongside carbon dioxide and other gas emissions at landfill sites.
Other gases present in landfill gas emissions
So aside from carbon dioxide and methane, what gases do landfills produce? Carbon dioxide and methane make up the largest portion of LFG, but usually between 2% and 10% of LFG is composed of nitrogen, oxygen, ammonia, sulfides hydrogen, and other gases in trace amounts. The gas emissions from landfills are not completely consistent and there will be some variation in the overall composition of landfill gas over time.
Sulfides released by landfills react with hydrogen present in the atmosphere to produce sulfuric acid which lowers the pH of rainwater, making it more acidic and corrosive. This corrosive substance alters plant growth and causes damage to infrastructure over time. Ammonia is another substance that damages the environment and contributes to the acidification of soils and it is dangerous to aquatic life. While nitrogen is a common fertiliser, strong concentrations can cause serious damage to natural ecosystems as it builds up in soil.
The make up of LFG varies depending on the age of the landfill site, the composition of the waste entering the site, the oxygen content, the ambient and atmospheric moisture levels, and the time of year. Hot, humid conditions stimulate bacteria in landfills to break down waste more rapidly, leading to an increase in the rate at which LFG emissions are produced.
Monitoring and managing LFG
Proper monitoring and management of landfill gas emissions is key to minimising the environmental impact of landfills and maintaining operations which meet legal regulations. A large proportion of LFG can be captured and used to create fuel for the generation of electricity and carbon capture technology is rapidly developing, both approaches can go a long way to helping manage and reduce total gas emissions from landfills.
To effectively monitor the emissions produced by waste in a landfill, sampling must take place frequently across the entire site and any associated pipework or gas storage systems to check for leaks into the air. LFG can also leach into the soil surrounding landfills, and from here it can end up travelling away from the site and contributing to the pollution of groundwater.
