Below, we discuss and compare biogas and biomethane.
We explain what each one is, but also identify the main differences between them.
We also outline how compressed natural gas (CNG), and also liquefied natural gas (LNG), both relate to biogas.
Biogas vs Biomethane: Main Differences & Comparison
Biogas is more of a broad term, and refers to one of several products that are derived from biomass
Specifically, ‘biogas’ describes gases that come from the anaerobic decomposition of biomass, and also the conversion of biomass.
On an industrial scale, raw biogas can intentionally be produced from the anaerobic digestion of organic material and organic waste
It can also be captured from landfills, from animal manure management operations, waste water and sewage treatment plants, and other places where gas capture systems and digesters are installed and operating
Raw biogas can also be refined into biomethane, which has had carbon dioxide and other elements removed from it so it can meet natural gas industry standards.
So, raw biogas and biomethane are both considered types or forms of biogas.
But, biomethane specifically comes from the refinement of raw biogas.
Biomethane can also be converted into either CNG, and LNG.
Types Of Biogas
The main types of biogas might be:
– Raw biogas (also called untreated biogas)
– Biomethane, or renewable natural gas, that has been refined from raw biogas
– Converted biogases
Raw Biogas
What Is Raw Biogas?
Raw biogas is the gas produced from the anaerobic decomposition or conversion of biomass (organic waste and organic materials)
Raw biogas is typically made of methane and carbon dioxide, and trace amounts of other gases.
However, what it’s made from precisely depends on the biomass it comes from, and the production methods used
Where Raw Biogas Comes From
It can come from several sources:
– On an industrial level, raw biogas can come from anaerobic digesters at biogas plants
– Some livestock manure management systems (livestock manure holding ponds), farms, and also waste water and sewage treatment plants also have digesters on-site to capture raw biogas
– Raw biogas can also be captured at landfills
– Raw biogas also occurs naturally in nature
How Is Raw Biogas Made?
– At biogas plants, a range of different organic waste materials can be put in contained anaerobic biogas digesters to make raw biogas
Digestate, which is a nutrient rich solid or liquid material, is also produced from the digestion process.
Digestate can be used as a soil amendment.
This might be considered a form of recycling the nutrients in the organic matter
– Raw biogas can also be generated at landfills when organic waste breaks down in anaerobic conditions to produce methane
– Farms, waste water and sewage treatment facilities, and other places that have biodigesters tanks installed can also make and capture biogas
nationalgrid.com notes that (paraphrased) the UK has dedicated biogas plants, and countries like the US have anaerobic digesters on farms and at water resource recovery facilities, as well as stand alone systems and land fill gas capture projects
Where Biogas Production Mostly Comes From
iea.org indicates that (paraphrased) most biogas production currently comes from the use of crops and animal manure as feedstock
What Is Raw Biogas Used For?
Raw biogas is first captured where it’s generated i.e. in digesters, at landfills, etc.
After generation and capture, raw biogas can be used with little or no processing or refinement.
It can be burnt for heat, or it can also be turned into electricity using a range of methods.
So, it has multiple potential uses
Biomethane (Renewable Natural Gas – RNG)
What Is Biomethane?
Biomethane is also referred to as renewable natural gas, or RNG.
It involves the processing or refinement of raw biogas, so that it can meet natural gas industry standards.
How Is Biomethane Made?
To make biomethane, elements like carbon dioxide, water vapor, and other trace gases are usually removed from raw biogas in a refinement process
This leaves biomethane as a near pure source of methane (similar to traditional natural gas methane)
Upgrading biogas, and thermal gasification of solid biomass followed by methanation are two of the main methods used to make biomethane.
iea.org explains these two methods in more detail
What Is Biomethane Used For?
Some of the different uses might include:
– Being used as a replacement gas for natural gas (i.e. traditional methane)
– Being used in existing natural gas infrastructure, such as pipelines.
– Replacing a certain percentage of natural gas used in pipelines and other infrastructure
– Being used for the same purposes as natural gas, such as heating and cooking.
What About Compressed Natural Gas (CNG) & Liquefied Natural Gas (LNG)?
Biomethane can be converted into either CNG (when it’s compressed) or LNG, and used as a vehicle fuel.
What About Landfill Gas?
Landfill gas is produced when organic waste breaks down in landfills under anaerobic conditions.
Landfills with landfill methane capture systems can capture and use the methane as an energy source.
This form of biogas is usually different to the biogas that comes from controlled biogas digesters, as the nutrients usually can’t be recycled, and obviously the conditions of digestion can’t be controlled as closely or contained.
Sources
1. https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy
2. https://www.nationalgrid.com/stories/energy-explained/what-is-biogas
3. https://en.wikipedia.org/wiki/Biogas#Benefits_of_manure_derived_biogas
4. https://www.eia.gov/energyexplained/biomass/landfill-gas-and-biogas.php
5. https://www.iea.org/reports/outlook-for-biogas-and-biomethane-prospects-for-organic-growth/an-introduction-to-biogas-and-biomethane
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