Landfill gas use is the collection and treatment of methane or other gaseous substances from the decomposition of the waste in a landfill to create power, heat and energy.
In addition to fossil fuels and farming, municipal solid waste (MSW) landfill gas was third in the world as the contributor to methane emissions as a greenhouse gas.
At the COP26 Climate Change conference held in Glasgow in November 2021, a group of nations including the US, the UK, and the EU pledged to capture the landfill gas from all current landfills. Methane is a potent greenhouse gas that traps heat in the atmosphere. It was previously thought to be 28 to 36 times more effective than CO2 over a 100-year period until very recently. However, the ratio has now been raised to ver 80 times more damaging than CO2.
Methane and carbon dioxide are the main constituents and the emission of methane is prevented at its most simple by flaring the collected landfill gas.
The landfill gas industry which provides the equipment and the labour force to install landfill gas extraction systems is expected to grow rapidly in the next few years as a result of rising demand for their products and services.
The aim globally is to halve or better the current rate of greenhouse gas emissions from the world's municipal solid waste landfills.
Basic information about landfill gas
Landfill gas (LFG) is a mixture of various gases produced by microorganisms within a landfill as they break down organic waste, such as food waste and paper trash. Landfill gas is made up of between 40% to 60% methane, with the rest being largely carbon dioxide.
The remaining 1% is made up of trace levels of other volatile organic compounds (VOCs) (non-methane organic compounds). A wide range of substances, mostly simple hydrocarbons, make up these trace gases.
In the US the Agency for Toxic Substances and Disease Registry of the U.S. Environmental Protection Agency, Department of U.S. Energy Information Administration provides guidance on exposure limits for these substances.
LFG is a renewable energy resource that can be harvested, processed, and utilised.
Methane emissions from landfills
In the United States, the Clean Air Act mandates the installation and operation of a landfill gas collection and control system for municipal solid waste landfills of a specific size. Some landfills minimise landfill gas emissions by catching and burning the gas, which is known as flaring.
CO2 is produced when methane in landfill gas is burned, however, CO2 is not as potent a greenhouse gas as methane. Many landfills collect and process landfill gas to remove carbon dioxide (CO2), water vapour, and hydrogen sulphide (H2S – spelt hydrogen sulfide in the US).
To assess the health impacts of landfill gas exposure, studies have been done in communities near landfill waste and waste lagoons. These trials lasted many months and revealed health issues that correlated with increasing hydrogen sulphide levels and landfill smells.
Eye, throat, and lung discomfort, nausea, headache, nasal obstruction, sleeping difficulties, weight loss, chest pain, and asthma exacerbation were among the health issues noted. Despite the presence of other substances in the air, many of these effects remain consistent with the known effects of H2S exposure.
When LFG is collected and either flared, combusted to power a generator, or upgraded to make a more valuable fuel known as biomethane the gases such as H2S and other odour forming compounds in the LFG are either removed or destroyed in the flame. The gas produced contains toxic substances such as NOx emissions are also reduced by landfill gas use.
LFG collection systems
Landfill gas collection is often achieved by installing wells in the trash pile that are positioned vertically and/or horizontally. Vertical wells should be separated approximately 50–200 feet apart in the centre, according to design heuristics, while horizontal wells should be spaced about 50–200 feet apart in the centre, according to commonly adopted design wisdom. Horizontal wells are not recommended due to clogging.
To avoid gas migration issues, landfills should always install gas collection systems.
Landfill Gas Energy Production
The Landfill Methane Outreach Program (LMOP) of the United States government provides basic information regarding landfill methane use in the United States. According to its most recent report, there are 548 operating LFG energy projects in the United States as of September 2021, and 483 landfills that are strong prospects for future projects.
Landfill gas production generally starts when the methane-producing bacteria begin to multiply between 3 months and 5 years after any part of a landfill is filled with waste. The maximum output from any part of the landfill will vary between 5 and 15 years generally.
If the temperature or moisture content rises, the gas output will rise as well. Barometric pressure has also been shown to affect LFG output. When the atmospheric pressure drops after a period of high pressure an effect rather like the fizzing which occurs on opening a bottle of lemonade takes place and often results in a higher gas flow for a period of a few days.
A landfill can emit gases for more than 50 years, even though production of these gases typically peaks in five to seven years.
Collecting and treating landfill gas
Methane and CO2 are well-known greenhouse gases that contribute significantly to global warming when anaerobic bacteria decompose organic waste to produce biogas.
There are advantages to collecting and treating landfill gas by flaring, its use in a generator engine, or upgrading it to become a natural gas replacement beyond climate change mitigation. Using LFG reduces smells and other risks connected with LFG emissions, as well as methane migration into the atmosphere, which contributes to local pollution and global climate change.
To collect the gas (LFG) involves drilling perforated pipes into the waste and then applying suction to pull the landfill gas out. Leachate may be present in the landfill, and this must be drained in a manner that prevents it from getting into the gas wells.
Renewables vs Natural gas
Landfill gas is classed as a renewable gas because the majority is produced from recently grown organic matter. In contrast, natural gas is extracted from the ground from deposits that were laid down over geological time amounting to millions of years. There is no way in which those geological deposits can be renewed in a significantly shorter period. For this reason natural gas is non-renewable.
Landfill gas, which is also biogas, is also created by the decomposition of organic waste in anaerobic digestion facilities. Renewable energy sources such as landfills and the commercial development of the anaerobic digestion process are a big opportunity to provide a transitional renewable energy source to aid global decarbonisation.
Direct Use of Medium-Btu Gas
Microorganisms acting on organic wastes, such as a landfill, produce a medium Btu gas comprising methane and carbon dioxide. Firing pottery and glass-blowing kilns, generating and heating greenhouses, and evaporating waste paint are all examples of innovative direct applications of medium-Btu gas from landfills.
The burning of natural gas in conjunction with:
- oil extraction, or
- when done on landfill sites,
- is known as gas flaring.
The practise dates back over 160 years, and it occurs in the oil industry owing to a variety of factors, including market and economic limits, a lack of sufficient regulation, and political wilfulness.
The first landfills to start to produce LFG were discovered to be “gassing” in the late 1970s. As noted already, due to concerns about the rate of climate change, and the ability of a reduced methane gas emission rate to reduce global warming the world's governments will now be legislating to require the collection and flaring or use of all landfill gas.
Financing Landfill Gas Projects in Developing Countries Landfill gas management can help mitigate greenhouse gas emissions and contribute to the overall safe operation of a landfill, simultaneously generating revenue.
Installing a reciprocating landfill gas engine is technically the easiest and lowest capital cost option as long as there is a user for the power nearby or a suitable electrical power line nearby through which to export the electricity.
Microturbines are primarily employed for lower LFG volumes and specialist applications, while gas turbines are frequently used in bigger LFG energy projects.
In the United States, over 70% of currently active LFG energy plants generate electricity. To produce energy for onsite consumption and/or sale to the grid, a number of technologies can be utilised, including reciprocating internal combustion engines, turbines, microturbines, and fuel cells. Because of its low cost, high efficiency, and size ranges that complement the gas production output of various landfills, the reciprocating engine is the most often utilised conversion technology for LFG electrical applications.
Landfill gas treatment
Since 2017 and rising awareness of the benefits of using methane as a heavy goods vehicle fuel to replace the high current cost and polluting effects of diesel landfill gas treatment has moved on to the purification of the raw LFG to a natural gas replacement known as renewable natural gas (rNG) or compressed biomethane. The other landfill gases are removed from the biogas to make pure methane gas and the separated carbon dioxide can also have a value when sold.
LFG when upgraded to renewable natural gas (RNG), a high-Btu gas, through treatment processes by increasing its methane content and, at the same time reducing its CO2, nitrogen and oxygen contents. RNG can be utilised as pipeline-quality gas, compressed natural gas (CNG), or liquefied natural gas in place of fossil natural gas (LNG).
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