Methane Gas (CH4) is the most common by-product of Landfills. The sanitary or municipal waste landfills have become the most common waste disposal in USA and other countries.There are certain rules and regulations for the allowable methane gas emissions from the landfill sites. Sometimes, it is important to capture the gas at the site and destroy to meet the regulatory standard. Landfill gas (LFG) can also be used as a source of energy (alternate energy source).
Anaerobic microbes decompose the waste products and thereby produce “Landfill Gas”. The landfill gas is composed of 50% methane and 45% of carbon-di-oxide. Landfill contributes about 7% of the total methane emission worldwide. Methane is also the most abundant organic chemical in atmosphere.Regulation of the emission of methane from the Landfills helps reduction of odor due to methane gas and also reduces the global warming potential.
The rate of gas production from a landfill is controlled by various factors such as –
- Composition of garbage
- Moisture content
- Partial pressure of methane gas
Organic Components –>Amino Acids –> Intermediate and Simple fatty acids –> mostly acetic acid
In presence of air: Fatty Acids (CH3COOH)–>CO2+H2O
Fatty Acids (CH3COOH)–> CH4+CO2
Cellulose (paper/wood fiber): C6H10O5 –>2CH4 + CO2
Mechanism of Garbage Decomposition:
There are five distinct phases of garbage decomposition. The first 3 phases are short and transitional into more stable phase 4 which actually determines the commercial landfill gas production. Phase 5 is when the gas production is nearing zero along with no or minimal biological activities. Drilling and field tests are required to gather information about a specific landfill site and predict life of the methane gas generation.
- Beneficial and profitable is enough methane gas can be generated and used as a source of energy.
- Helps reduction of methane emission to the atmosphere, thereby reduce global warming.
- EPA regulations under the Clean Air Act require landfill owners to collect or combust landfill gas.
- LFGTE (Landfill Gas To Energy) projects offer alternate source of energy, create associated jobs.
- The Landfill Methane Outreach Program (LMOP) was created as a part of President Clinton’s Climate Change Action Plan which has more than 200 Allies and Partners who have voluntarily working with EPA to develop cost effective LFGTE projects.
LGEM is a mathematical model developed by EPA and used for estimating the amount of landfill gas emission. The model is based on a simple first order decay equation. The estimated production of methane is calculated from
1. L0 (methane generation potential)- accounts for the volume of methane produced per unit weight of refuse. (cubic meter/Mg)
2. K – Gas generation constant (1/yr)
3. R – Average refuse acceptance rate (Mg/yr)
4. t –Age of landfill at closure (yr)
The model uses a default 170 cubic meter/Mg for L0 and 0.05 /yr for k.
The LGEM software can be downloaded for FREE from EPA website at
LGEM is simple to use and can be used to calculate the time of closure, amount of methane gas generation potential etc.
Article by: Ankan Basu