The “clean” energy that needs to clean up its act.
Several billion years ago, on a mass of rock floating around the Sun, little bundles of organic molecules somehow came together and, in a process scientists still don’t fully understand, shuddered into life.
When these first lifeforms were busy coalescing in the primordial soup, the Earth’s atmosphere was mixed very differently, a breathless mass of mostly nitrogen and carbon dioxide (CO2). Some of the earliest microbes that evolved on Earth, therefore, digested organic matter in low or no-oxygen conditions. They produced waste gases including methane and CO2.
Today, these critters, known as methanogens, are still among us, festering in waste heaps and piles of manure, in sewage plants, and at the bottom of stagnant water bodies, happily munching decaying matter and processing it into gases, including a boatload of methane.
That’s a problem, because methane is a greenhouse gas, and it’s around 27 times more potent at heating the planet than CO2. World leaders agreed to slash methane emissions by 30% by 2030 at COP26 last year, though Australia notably refused to commit.
But methanogens can also be harnessed for good – which is where the burgeoning biogas industry comes in. Biogas is a mixed gas composed mainly of methane, CO2 and hydrogen sulphide that can be used as a fuel. Biomethane is similar, but composed largely of methane. Biogas can be converted into biomethane by a process of cleaning and upgrading.
Biogas plants, seen as a potent part of a potential future green energy mix, have specialised facilities, where waste organic matter – animal faeces, sewage water, decaying plant matter – is digested by archaea and bacteria to produce these gases.
When combusted, biogas and biomethane act largely in the same way as natural gas, releasing energy (which can be used for power), CO2, and water. But, crucially, the CO2 released when biogas burns was essentially the same CO2 that had been recently consumed by the creature that produced the organic matter, so it’s already part of the biosphere – meaning there is no net addition of CO2 into the atmosphere.
“Biogas is considered to be a renewable resource because its production-and-use cycle is continuous, and it generates no net carbon dioxide,” explains Semra Bakkaloglu, a researcher at the Sustainable Gas Institute (SGI) at Imperial College London, UK.
“As the organic material grows, it is converted and used. It then regrows in a continually repeating cycle,” Bakkaloglu says.
Trouble in paradise?
So far, so good, but there are pitfalls to this process. This week, Bakkaloglu and co-authors published the results of a new study in the journal One Earth, investigating methane leaks along the European biogas supply chain.
What they found was alarming. Total methane emissions along the European biogas supply chain may account for 18.5 megatonnes of methane emissions per year. That’s twice as much as estimated by the International Energy Agency (IEA), which reported just 9.1 megatonnes in 2021, out of an estimated 185 megatonnes of total methane emissions from the global energy sector in the same year.
That means that while total methane emissions from the biogas supply chain are lower than the emissions produced by oil and natural gas, the amount of methane released relative to total gas production is much higher.
It’s a blow for the burgeoning bioenergy sector. But what’s the solution? And why do we need biogas anyway?
Who produces biogas?
Globally, biogas production has been taken up by facilities like farms, landfills and wastewater treatment plants. Farmers, for example, can construct anaerobic digestion units on site, into which they feed animal manure or food scraps, generating biogas or biomethane which they can either use to power their business, or feed it back into the grid, for compensation.
To get the right bacteria and archaea, producers can buy a culture from other businesses already hooked up to the biogas supply chain.
“When we make yoghurt at home we use the old yoghurt to make the new,” says Richard Blanchard, an expert in bioenergy systems at Loughborough University, UK. “We’ve got the culture of bacteria, we put it into the milk, and then make the new yoghurt, leaving a little bit left for us to make the next batch.”
With the bacterial-archaeal mix needed for anaerobic digesters, it’s much the same.
You take your seed of your existing organic matter from a digester full of bacteria, and then you seed the next digester.
The biggest biogas producers around the world include Germany, Italy, the Czech Republic and France. Australia, on the other hand, is a much smaller producer – in 2017 there were 272 biogas plants in this country, half of which were landfills.
But the Australian biogas industry is slated to grow. In 2021 the first large-scale biogas plant, converting cow manure and other organic waste, was announced for Nowra, NSW, and according to the Australian Renewable Energy Agency (ARENA), Australia’s total estimated biogas potential is 103TWh (terawatt hours), which would place it on par with Germany.
What did biogas ever do for us?
According to Richard Blanchard, biogas and biomethane in particular can be a very useful fuel.
“It’s a flexible fuel because we can use it when we want it,” Blanchard explains.
“With methane, you can store it in pressurised bottles. It’s the same as natural gas in the sense that once you clean it up and get rid of impurities, you can inject it into the gas grid, and you can move it quite easily.
“We can use it to make electricity, we can cook with it, we can use it for heat. So it gives us the same benefits we get with natural gas.”
Another major bonus of biomethane in particular, Blanchard says, is that it has a higher energy density than mixed gas, so you need to use less of it to get the same amount of power.
Some estimates suggest biogas could produce 5% of the UK’s electricity in future.
“Five percent is not to be sniffed at,” Blanchard says . “Nuclear produces 10% of our (UK) energy, so it’s not a small amount.”
Ultimately, he says that provided emissions elsewhere are drastically lowered, biogas could be one of the few sources of CO2 emissions in a future energy mix – keeping total greenhouse gas emissions low.
And there’s another incentive to tighten up the biogas supply chain. Some industrial processes require extraordinarily high heats, which are most easily produced using gas. These include steel and cement making, two of the known problem children in the transition to net-zero.
But Blanchard points out that researchers are exploring how other energy sources, like solar electricity, could produce the heat required.
“So, whether it will have a role depends on what the heat sources could be,” he says. “It’s going to be quite interesting to see how we can do these energy intensive processes.”
Regardless, the biogas sector is gaining pace, with a number of countries offering financial incentives to producers.
“Given the growth in biomethane due to national decarbonisation strategies, urgent efforts are needed for the biomethane supply chain to address not only methane emissions but also the sustainability of biomethane,” says Bakkaloglu.
In Australia, currently in the grip of an acute energy crisis, business and industry leaders have called for a shift away from natural gas for reasons of both energy security and climate commitments. In an open letter, organisations including the Australian Industry Group, the National Farmers Federation, the Property Council and the Clean Energy council recommended a speedier transition to alternatives, including electrification, hydrogen and biogas.
So, what’s the solution?
In their study, the Imperial researchers identified a number of key flaws behind the methane leaks, including intermittent emissions patterns that make them harder to track, insufficient use of processing equipment, and inadequate operations and maintenance.
The authors note that compared with the oil and gas industry, the biogas sector suffers from poorly designed and managed facilities, and fewer resources for monitoring and upkeep.
The good news is that the researchers were able to identify the culprits: 62% of the leaks were concentrated in a small number of facilities and pieces of equipment within the chain, which they call “super-emitters”. That knowledge will enable them to tighten up the chain.
“To prevent biogas methane emissions negating the overall benefits of biogas use, urgent attention is needed including continuous monitoring of biogas supply chains,” says Bakkaloglu.
“We believe that with the proper detection, measurement, and repair techniques, all emissions can be avoided,” she says. “We need better regulations, continuous emission measurements, and close collaboration with biogas plant operators in order to address methane emissions and meet Paris Agreement targets.”
Amalyah Hart has a BA (Hons) in Archaeology and Anthropology from the University of Oxford and an MA in Journalism from the University of Melbourne.