Green house gases (GHG) impact of landfills
When organic material such as food scraps and green waste is put in landfill, it is generally compacted down and covered. This removes the oxygen and causes it to break down in an anaerobic process. Eventually this releases methane, a greenhouse gas that is up to 36 times more potent than carbon dioxide. The implications for global warming and climate change are enormous. Methane is also a flammable gas that can become dangerous if allowed to build up in concentration.
Methane gas emission
Landfill gas (LFG) is a natural byproduct of the decomposition of organic material in landfills. One tonne of biodegradable waste produces between 200 and 400 cubic metres of landfill gas which comprises approximately 50-55% methane (CH4) and 40-45% carbon dioxide (CO2).
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), and its emission has significant climate change implications.
According to the US Environmental Protection Agency (EPA), a significant proportion of the emissions shown to have contributed to global warming and climate change can be traced to landfills, and the disposal of food waste.
Landfill gas also includes small amounts of nitrogen, oxygen, ammonia, sulfides, hydrogen, carbon monoxide, and non- methane organic compounds (NMOCs) such as trichloroethylene, benzene, and vinyl chloride.
How is landfill gas produced?
Three processes—bacterial decomposition, volatilization, and chemical reactions—form landfill gas.
- Bacterial decomposition. Most landfill gas is produced by bacterial decomposition, which occurs when organic waste is broken down by bacteria naturally present in the waste and in the soil used to cover the landfill. Organic wastes include food, garden waste, street sweepings, textiles, and wood and paper products. Bacteria decompose organic waste in four phases, and the composition of the gas changes during each phase.
- Volatilization. Landfill gases can be created when certain wastes, particularly organic compounds, change from a liquid or a solid into a vapor. This process is known as volatilization. NMOCs in landfill gas may be the result of volatilization of certain chemicals disposed of in the landfill.
- Chemical reactions. Landfill gas, including NMOCs, can be created by the reactions of certain chemicals present in waste. For example, if chlorine bleach and ammonia come into contact with each other within the landfill, a harmful gas is produced.
Of all the types of landfills, MSW landfills are the most significant source of landfill gas emissions, because approximately 60% of the waste in a typical MSW landfill is organic.
Municipal solid waste (MSW) landfills are the third-largest source of human-related methane emissions in the United States, accounting for approximately 14.1 percent of these emissions in 2017. At the same time, methane emissions from landfills represent a lost opportunity to capture and use a significant energy resource.
The U.S. Environmental Protection Agency (USEPA) reported that greenhouse gas (GHG) emissions from waste landfills amounted to 115.7 Mt of carbon dioxide equivalent (CO2e) in 2015
(Sources: https://www.atsdr.cdc.gov/HAC/landfill/PDFs/Landfill_2001_ch2mod.pdf; https://archive.epa.gov/wastes/conserve/tools/payt/web/html/factfin.html; http://gazasia.com/biogas-source/landfill-sites-2/)