Compared to fossil fuels, including natural gas, biogas, which is made from waste, is a cleaner, greener alternative.
The International Energy Agency estimates that biogas (and biomethane) could meet up to 20 percent of the world’s gas needs during the fossil fuel transition and help us move closer to zero.
But a new study, published in the journal One Earth, says biogas emissions could be higher than we’ve been estimating, and there’s important work to be done to reduce emissions.
Key points:
- Methane emissions escaping from the biogas supply chain were higher, on average, than natural gas
- A few “superemitters” were responsible for most of the methane emitted
- Biogas is still a cleaner fuel than fossil fuels
The researchers analyzed data from European biogas producers.
They found that the rate (not the total volume) of emissions along the biogas supply chain, from production to supply, was comparable and generally higher than that of natural gas, according to lead author Semra Bakkaloglu of Imperial College London.
“The level of emissions was higher than we thought it would be,” Dr. Bakkaloglu said.
“Currently, our results indicate [biogas emissions] they are high, even higher than natural gas, which is clearly a concern. “
It is important to note here that even with high emissions along the supply chain, biogas remains the most environmentally friendly alternative to natural gas.
This is because biogas is created from waste that would otherwise have released emissions as it decomposed naturally.
However, this does not mean that biogas is always climate-neutral.
To create biogas, you start with a raw material, which can be, for example, livestock manure or leftover food.
They break down anaerobically by microorganisms. They mainly create methane and a part of carbon dioxide as by-products, which are captured as gas, but part escapes into the atmosphere.
Biogas can be produced from a series of wastes and what is left in the end, the digestate, has potential as a fertilizer. (arena.gov.au)
Compared to carbon dioxide, which is released during aerobic digestion, methane is a much more potent, but shorter-lived, greenhouse gas, according to Peter Ashman, a professor of chemical engineering at the University of ‘Adelaide, who did not participate in the research.
“What stands out here is important because if you take CO2 from the atmosphere and emit it back into the atmosphere as methane, that methane has a much greater potency as a greenhouse gas than CO2,” he said. Professor Ashman.
Unlike biogas, the International Energy Agency has warned that there can be no new developments in coal, oil or natural gas if the world is to reach zero net by 2050.
Researchers argue that if we use it as a transition fuel, we need to know about biogas emissions so that nations can accurately assess their greenhouse gas footprints.
“If biomethane is to be used to achieve decarbonisation targets in the future, emissions from the biomethane supply chain must be minimized,” Dr Bakkaloglu said.
“We believe that with proper design, detection, measurement and repair techniques, many of the observed emissions can be avoided.”
‘Super broadcasters’ in the spotlight
Once the gas is captured during biogas production, what is left of the raw material at the end is what is known as digestate.
According to the investigation, the largest source of emissions along the biogas supply chain was in the storage stage of the digestate.
The researchers found that methane emissions from the digestate were up to 23% higher than previously reported.
The next highest source of emissions was found during the biogas production stage, mainly from the anaerobic digester.
Professor Ashman said he was not surprised that supply chain emissions could be higher than European biogas producers as they lacked the scale and financial support of most natural gas operators.
“That doesn’t surprise me,” he said.
“Some of these operations are quite agricultural and probably don’t put much effort into capturing these emissions.”
Australia generates some electricity from biogas operations using, for example, pig manure. (ABC Rural: Tyne Logan)
Investigators said there was a favorable coating on their work.
First, they found that there were “super emitters,” a few operations responsible for the vast majority of the methane leak.
In this case, only 5% of biogas producers were responsible for more than 60% of all methane emitted.
Dr. Bakkaloglu said it was a similar case for the fossil fuel gas industry.
“Biomethane and biogas supply chains have emission characteristics similar to those of oil and natural gas, with super emitters present at all stages,” he said.
“In natural gas supply chains, about 50% of emissions are reduced to only 5% of sources.”
When it comes to biogas, this means that targeting these few worst offenders can greatly affect the industry’s global greenhouse gas footprint.
And there are some fairly simple steps to plug leaks in the supply chain.
“We don’t want to discourage the production and use of biomethane,” Dr. Bakkaloglu said.
“Rather, we want to highlight these issues and encourage people to take immediate action to address them.
“Biomethane is an important renewable source, but it has the potential to be even better.”
Want more science from the whole ABC?
Science in your inbox
Get all the latest science stories from all over the ABC.