Biogas, Green Gas, or Biomethane? Explained
What's the difference between green gas, biogas, and biomethane? In our complete guide to biogas, we explain all you need to know about this green gas. Read on to learn how biogas is produced, what green gas is versus biomethane, and where you can buy biogas in the UK.
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Biogas Definition: What is Biogas?
Biogas is a green energy alternative to natural gas (fossil fuel) that is created when organic waste decomposes in an oxygen-deprived environment through a process that is commonly referred to as anaerobic digestion.
The byproduct of the decomposition process is a methane-based gas which we refer to as biogas.
Biogas holds great potential to replace natural gas as a major source of energy due to its naturally occurring nature, its reduced effect on the environment and its easy adaptation to current gas infrastructure.
What is Green Gas?
Green gas is another term used to refer to biogas. In other words, biogas and green gas are the same thing!
Biogas is environmentally friendly and for this reason, it is called “green gas”.
For this article, we use the terms green gas and biogas interchangeably to refer to the same thing.
Did you know?While the name green gas can be confusing, the term “green” refers to biogas’ environmentally friendly qualities and not its actual colour.
How is Biogas Produced?
Green gas is produced when organic waste decomposes in an oxygen-free environment.
As the organic waste biodegrades, bacteria creating the decomposition process release methane gas as a byproduct. The methane is later harnessed as green gas.
This naturally occurring process can be recreated by humans in a biogas plant, allowing for the continued and infinite creation of green gas.
Green gas is considered a renewable and sustainable resource as all living things produce organic waste or bio waste. Bio waste is the key ingredient in creating green gas, and luckily for us, the supply is endless.
There are many different types and methods of producing green gas, however, anaerobic digestion is the most common method. There are also many different types of wastes that biogas plants use. However before we dig into waste types, it’s important to understand what anaerobic digestion exactly means.
Biogas & Anaerobic Digestion
As we explained earlier, green gas is produced through the process of anaerobic digestion, but what is anaerobic digestion?
The term “anaerobic” literally means “without oxygen”. The term “digestion” is used to describe decomposition. Therefore anaerobic digestion means “decomposition without oxygen”.
With anaerobic digestion, organic waste such as human, animal or food waste, is placed in an oxygen-free tank at a biogas plant, called an anaerobic digester, to decompose.
As the bacteria decompose the organic material, they release gases that can be harnessed as green gas or biogas.
However, the decomposed solids also remain in the digester, leaving a second byproduct of nutrient-rich fertiliser, called digestate. This substance can later be treated for safe human use.
Anaerobic digestion is recognised around the world as one of the most efficient ways to recycle food waste, animal waste, and sewage!
Why is Anaerobic Digestion Oxygen-Free? Removing oxygen from the tank makes the decomposition process more efficient and requires less energy.
Types of Waste that Produce Biogas
Biogas can be produced from almost any organic waste. Some of the most common wastes that are used to produce green gas are the following:
- Livestock waste
- Food waste
- Landfill gases
• Livestock Waste vs Food Waste
Livestock waste is one of the most favoured types of organic wastes used to create green gas as it is abundant and widely available. However, food waste offers one of the highest returns of energy-generating potential per tonne of raw waste as it has not yet passed through the digestion tract of animals. This is because enzymes from animals’ digestion tracts lower the energy-generating potential of organic waste.
Did you know?For each tonne of food waste recycled through anaerobic digestion, 0.5 - 1.0 tonnes of CO2 are spared from entering the atmosphere versus traditional landfill methods.
• Landfill Gases
Landfills also release huge amounts of methane as they decompose. Landfill gas is often simply released into the air via vent tubes in the mound. However, landfill gases can be harnessed relatively easily as they are already part of an enclosed system.
Thus, a landfill can essentially act as a large biogas plant. An added benefit to landfills is the mix of bio waste that is found there. Studies reveal that mixing different types of bio waste speeds up the anaerobic process and increases green gas production levels.
It will come as no surprise to you that a major part of human waste is methane gas. For this reason, wastewater treatment facilities also offer a surprising opportunity for green gas development as, much like landfills, wastewater treatment facilities are already part of our current infrastructure. While most wastewater treatment facilities already capture green gas, many do not have the infrastructure in place to correctly use it and sadly decide to simply burn it.
As you have already heard, green gas is largely methane-based. In fact, the typical biogas composition is around 65% Methane and 35% CO2. However, some other gases do appear in trace amounts.
- Biogas composition:
- Methane (CH4)
- Carbon dioxide (CO2)
- Hydrogen acid (H2S)
- Water vapour (H2O)
What is the difference between Biogas & Biomethane?
Green gas or biogas are the blanket terms used to describe any gas made from organic waste. As we’ve just seen, the majority of green gas is methane.
However, green gas is not pure enough to be used in all instances due to the high amounts of CO2 it contains.
Therefore, biogas is often purified through a process called “upgrading” to create a purer form of biogas called biomethane.
In other words, biomethane is the purer form of green gas which means it has reached the same level of purity as natural gas from fossil fuels. For this reason, sometimes biomethane is referred to as “renewable natural gas” or RNG.
What is Biogas Used for?
We are happy to report that there are many uses of biogas and green gas!
Raw biogas, or the green gas that is produced before being refined to create biomethane, can be burned in a boiler and used to heat buildings. Likewise, green gas is often reutilised at the biogas plant to power the operations and the biogas digester. Green gas can also be converted into electricity through a combustion engine, turbine or fuel cell and sent back to the electricity grid.
If green gas is refined or upgraded to biomethane, It can also be used as an exact replacement for natural gas or liquid propane gas (LPG) and sent to homes to be used for cooking and heating. In some places, it can also be compressed and used as fuel to power automobiles, such as hybrid cars.
Uses of Biogas Summarised:
- Burned in boilers to heat buildings
- Burned to Create Electricity & Heating
- Upgraded for use on the natural gas grid
- Upgraded to power motor vehicles
Advantages of Biogas
Green gas also offers several advantages over natural gas.
For one, green gas is less harmful to the environment as it helps deal with the problem of properly disposing of, and recycling, organic waste. Green gas is also a renewable and sustainable resource that will always be around as long as living organisms exist, meaning it is a good tool for fighting climate change. While green gas still emits CO2 into the atmosphere, it emits considerably less than natural gas making it more ecological.
Green gas can also easily be substituted for fossil fuels, versus other forms of renewable energy, as it can be used on existing infrastructure, such as the natural gas grid.
Biogas Advantages Summarised:
- Resolves the organic waste problem
- Renewable & sustainable
- Emits less CO2 than natural gas
- Adapts to current infrastructure
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Biogas in the UK
The UK is home to many green gas plants or anaerobic digestion plants. While most of these plants are privately owned on farms and the like, their number is growing thanks to renewed interest in sustainably developing the UK to resist climate change.
The exact number of green gas plants in the UK is contested. However, as of 2019, there were 398 biogas plants in the UK.
274 of these biogas plants are agricultural anaerobic digestion plants, and a further 124 are considered other waste plants.
All of these plants however are using anaerobic digestion to create green gas and digestate. While nearly 400 plants sounds like a lot, there is ample room for future biogas plants to be added to the market.
Biogas UK Statistics
Despite the UK being home to nearly 400 green gas plants, as of 2020, Britain had reached only ⅕ of its biomethane generating potential.
Currently, only 15% of household food waste in the UK is collected and recycled through anaerobic digestion, and estimates show that over 10,000,000 tonnes of food per year are not recycled when you include industrial food waste numbers.
To combat this, future biogas plants need to be added. In fact, an additional 4,500 biogas generator plants would be needed for Britain to reach its maximum biomethane generating potential by 2030. However, if the UK could take full advantage of biomethane using existing technology, in the future biogas plants could produce enough green gas to provide heat to six million households.
Where Can I Buy Biogas in the UK?
There are only a few green energy providers for green gas in the UK.
Residential Biogas UK providers include:
The percentages above reflect the percentage of green gas included in their gas tariffs.
As you will note, Green Energy UK is the only provider that offers 100% green gas for its customers.
However, as the world moves to limit its carbon emissions, more suppliers are looking to invest in green gas as an alternative to fossil fuels. Therefore we anticipate the number of suppliers offering green gas tariffs to rise in the coming years.
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