Trash-to-Gas Isn’t a Fairytale Climate Solution

Trash-to-Gas Isn’t a Fairytale Climate Solution

It seems like magic: In millions of operations scattered around the globe (some big, some very small), waste is transformed into energy. Landfilled garbage, sewage, and farm effluent are processed into burnable biogas, which can be used as a substitute for natural gas, a fossil fuel. Unlike natural gas, which sits in limited supply deep underground, biogas is considered a renewable source of energy. As long as humans continue to poop and make trash, there can be more biogas.

But, though it’s been hailed as an environmental miracle solution, making and burning biogas still emits greenhouse gases, contributing to climate change. And biogas facilities may be emitting more than their fair share. Researchers in a new study have quantified harmful methane emissions from across the whole biogas supply chain. They found that producing biogas releases more methane than previously estimated. Specifically, their new estimates of biogas methane emissions were twice as high as the 2021 numbers from the International Energy Agency.

Even more startlingly, the researchers found that the biogas supply chain may be emitting methane at a higher rate than oil and natural gas. Meaning that, although the scientists calculated overall global methane emissions from fossil fuel production were about 4.5 times higher than those from biogas, the amount of methane emitted relative to the amount of fuel made was higher for biogas. They further determined that just 5% of facilities were releasing 62% of the estimated methane, according to the paper published Friday in the journal One Earth.

Biogas facilities are multiplying globally, and the U.S. is no exception. President Biden’s stalled “Build Back Better” plan included provisions to further subsidise biogas production as a way to theoretically offset the environmental consequences of big agriculture. But the new research highlights how misguided policies like that could be.

“It is clear that if bio[gas] is to be used to achieve decarbonization goals in the future, bio[gas] supply chain emissions must be minimized. At present, [our] results presented here indicate they are high — higher even than natural gas, which is clearly a worry,” lead study author Semra Bakkaloglu wrote to Earther in an email. Bakkaloglu is an environmental and chemical engineer at Imperial College London in the UK.

To conduct their study, Bakkaloglu and her colleagues combined information from several existing published datasets with newer data on biogas site emissions. They then ran simulations to estimate the total methane emissions across the whole biogas supply chain.

Why is biogas bleeding methane?

Biogas is made through a process called anaerobic digestion. Microbes in an oxygen-starved environment break down wastewater (i.e. poop), food scraps, crops, trash, or animal manure (i.e. also poop). The result of anaerobic digestion is two things: biogas for burning and a byproduct called “digestate.” Digestate can be used as fertiliser, but mostly it’s treated like the waste of the waste, and stored instead of used.

That digestate storage is the biggest source of errant methane emissions in the biogas supply chain, according to the new study. Methane is emitted during normal storage as well as through leaks from poorly maintained equipment. The scientists identified the second biggest culprit as the actual production phase. Other research has found similar results.

Some ways of holding onto digestate are better for methane emissions than others, but the new study points out there’s not much incentivising more responsible management. Plus, biogas is newer and less streamlined than natural gas production, often done at a smaller scale, and poorly monitored and regulated.

“Because oil and natural gas supply chains have been primarily operated by large companies for decades, they have invested more in [methane] leak detection and repair,” the researchers wrote in the study.

One important caveat: lots of the waste used to make biogas would’ve probably emitted methane anyway. Combined, landfills and manure make up 26% of all U.S. methane emissions, according to the EPA. In biogas facilities and trash heaps alike, our waste is constantly leaking greenhouse gas into the atmosphere — largely because of how we choose to store it. At least one past study has even suggested that processing waste into biogas could reduce the overall lifetime methane emissions from some waste. But even if that’s true, it doesn’t mean we should ignore the methane that the biogas industry is producing.

Solving the problem

Any additional methane released into our atmosphere means more warming. And if there’s a way to slow or stop that release, we need to do it to avoid the worst consequences of climate change. Methane traps heat about 25 to 30 times more efficiently than carbon dioxide, and it’s responsible for an estimated 25% of current warming.

But there’s good news here. “We believe that with the proper design, detection, measurement, and repair techniques, all emissions can be avoided. The most important thing is to figure out where the emissions are coming from and how to reduce them,” said Bakkaloglu.

She offered that better storage design, like closed (instead of open) digestate tanks with methane recovery systems, would get rid of a lot of unintended emissions. “Additionally, we need better regulations, continuous emission measurements, and close collaboration with biogas plant operators,” Bakkaloglu added.

Considering that the researchers found such a small proportion of biogas facilities were responsible for such a big chunk of released methane, cutting down on those emissions should be easier than say, slashing car pollution. Those super-emitters are where the scientists are focusing their research next.

“We do not want to discourage the production and use of bio[gas],” said Bakkaloglu. “Rather, we want to highlight those emissions and encourage people to take immediate action to tackle them.”