Late next year, across the street from a Beam Suntory whiskey distillery in Kentucky, anaerobic digesters will turn spent grains from the distilling process into biogas.

Anaerobic digesters are essentially industrial-size “stomachs,” explains Heath Jones, managing director of Hitachi Zosen Inova North America, which is providing the technology to turn that waste into what’s called renewable natural gas. “We’re taking that stillage, or that byproduct, and we’re releasing the energy that’s still in that material through a natural process with enzymes and microorganisms,” he says.

That stillage will release methane, which the facility will then capture and “clean” (as in, process to a certain purity standard) and pipe back to the distillery across the street. That renewable natural gas should then, according to Beam Suntory, which makes Jim Beam, provide 65% of the distillery’s power, while cutting its emissions in half.

Projects for renewable natural gas, also called biogas or biomethane, have been on the rise lately, spurred in part by investments from the Inflation Reduction Act. That climate bill gives qualified biogas projects that begin construction before December 2024 a maximum tax credit of 50% of eligible project costs.

But interest in renewable natural gas was increasing even before the bill’s passage. According to the World Resources Institute, the number of such production facilities in the country grew from about 40 before 2014, to nearly 160 in 2020. Though it has the potential to reduce emissions and be an alternative to fossil fuels, climate experts caution that renewable natural gas only makes sense in certain situations with specific sources of waste.

WHAT IS RENEWABLE NATURAL GAS?

Renewable natural gas describes the methane captured from organic waste, and can come from a few different sources. There’s the spent grains from whiskey distilleries and breweries; there’s also food waste, landfills, animal manure (like from dairy cows), wastewater, and more.

“When any organic material breaks down in the absence of oxygen, it makes methane,” says Dan Lashof, the U.S. director of World Resources Institute, a global research nonprofit. Landfills are the third-largest source of human-related methane emissions in the U.S., according to the EPA, following oil and gas systems and livestock manure. In an open landfill, that methane is released into the atmosphere, adding to our greenhouse gas emissions. And methane is particularly harmful: It has 80 times the warming power of carbon dioxide (though it doesn’t last as long in the atmosphere).

Renewable natural gas is a way to capture that methane and reuse it for fuel. With an anaerobic digester, “you’re actually in a closed process where you can capture that methane and ultimately decide how you want to use it,” Jones says. It could go to power a facility, be put into a pipeline, or be used to generate electricity.

CAN RENEWABLE NATURAL GAS REPLACE FOSSIL FUEL-DERIVED NATURAL GAS?

Capturing methane is helpful for the climate, but how and where renewable natural gas is used could still pose environmental problems. Lashof believes that our primary climate strategies should focus on electrifying everything. “But there are hard-to-electrify activities,” he notes, like heavy industry, including manufacturing and cement and steel production, where you need high temperatures. Electrifying those operations could be costlier, and renewable natural gas could fit into the current systems, rather than requiring an entire retrofit. (Getting the greatest benefit out of electrifying everything, of course, also means that electricity has to come from clean energy.)

Renewable natural gas also seems to make sense for dairies, as a way to capture that methane from manure, but that can get complicated. While it’s definitely better to capture that methane than to let it go into the atmosphere, Lashof notes that turning this methane into renewable natural gas is a controversial solution. Some policies to reduce emissions incentivize farmers for the capture of methane by paying them for how much they capture, but that could eventually lead to unsustainable practices, where farms are then creating more methane than usual, so they can get paid more. “[It could] actually cause farmers to treat their waste in a way that generates more methane than it otherwise would, because it becomes very valuable to capture it,” he says.

Methane capture on dairy farms is also associated with groundwater pollution, another reason some environmental justice groups have called for California to eliminate its credit to farmers for captured methane in part for these reasons.

To Jones, the alcohol industry—not only distilleries but wineries and breweries—are ripe for using renewable natural gas. “If you think about corn going through the distilling process and it was utilized in its first phase of life to generate an alcohol, you still have remnants of a corn mash product and there’s still a lot of energy potential. I think that it only makes sense to truly try to maximize the utilization of that product,” he says. With the Beam Suntory facility, that stillage will get yet another use: After releasing methane in the digesters, it becomes a fertilizer that will go to local farmers.

Distilleries also make a convenient closed loop; the byproduct is created right there, gets turned into renewable natural gas onsite (or just across the street), and goes right back into the facility as fuel. But even in those positive use cases, any gas that goes through a combustion process, whether a biogas or a fossil fuel, will still produce greenhouse gas emissions, Lashof says. Plus, at the Beam Suntory facility, fossil fuel gas is still needed: The company says 35% of its energy will come from fossil-based natural gas. It’s not clear if this will eventually be replaced by renewable natural gas. Whenever renewable natural gas is used, though, it locks in that gas infrastructure (shutting the door on electrification, which requires an entirely different infrastructure).

NOT A PLUG-AND-PLAY CLIMATE SOLUTION

By using renewable natural gas, Beam Suntory’s overall emissions will be reduced. But, more broadly, the emissions reduction benefits of replacing natural gas with RNG don’t always outweigh other risks. “The idea of taking renewable natural gas and just putting it into the existing natural gas distribution system is not a good strategy,” Lashof says, “because that does tend to perpetuate our dependence on mostly fossil gas, and it will stay mostly fossil gases because there’s not enough sources of renewable natural gas to replace all the fossil gases that we are currently using.”

Renewable natural gas can’t be a plug-and-play climate solution for all the places we use fossil gas. If RNG is put into our current natural gas pipe system, like for home heating, that could come with other environmental hazards. “We know that that network is somewhat leaky,” Lashof says. One study found that U.S. natural gas pipelines experience the equivalent of one leak every 40 hours; according to the Environmental Defense Fund, U.S. natural gas pipelines are leaking between 1.2 million and 2.6 million tons of methane per year. If renewable natural gas methane leaks, it’s the same problem as fossil fuel methane leaking.

It’s also not clear what percent of gas that goes through a pipeline would be biogas versus fossil based. The question then becomes, “is this just a fig leaf for the fossil gas business?” Lashof says.

In this situation, electrifying home heating systems are the preferred climate solution. Lashof cautions against using renewable natural gas in vehicles, since they can easily be electrified as well. But in certain industries that aren’t easily electrified, or specific situations that solve waste management problems, renewable natural gas can help curb emissions.

“We do see a role for renewable natural gas,” Lashof says. “But I would say it is a limited role. It’s more of a niche than a comprehensive, core emission reduction strategy.”