Rags to riches? How trash at landfills can be recycled into energy as flammable gas

When you throw trash in the waste bin and then wheel it out to the curb, a truck usually comes once a week and hauls it away to a landfill. Then what? Maybe you've never thought to ask.

Any organic matter, mostly food waste and yard debris, begins to rot. Microbes and invertebrates move in to aid with decomposition by consuming and metabolizing the decaying organic matter. The process requires time, some moisture and a little oxygen to get started. In turn, it releases hydrogen sulfide, nitrogen, carbon dioxide and methane, among other substances.

Carbon dioxide and methane are greenhouse gases, so-called for their ability to absorb energy from the sun and trap it in the atmosphere. This retention of heat by gases emitted largely from burning fossil fuels is what scientists have concluded is causing climate change. Carbon dioxide is the most common greenhouse gas, but methane is the most powerful.

The U.S. Environmental Protection Agency estimates the warming effect of methane gas at 25 times that of carbon dioxide over a 100-year period. New findings published in the June issue of the scientific journal Nature Communications suggest the damage might be as much as three times greater than that.

In 2020, methane made up about 11% of total greenhouse gas emissions from human activities in the United States. About 17% of that came from landfills.

Highly flammable, methane is also the main ingredient in natural gas, which is widely used to power refrigerators, air conditioners, stoves, heaters, driers and outdoor lighting, to name a few. In 2021, natural gas accounted for 32% of total energy consumption in the United States, according to the U.S. Energy Information Administration.

Now, an Arizona-based landfill company intends to transform the dangerous methane released from landfills into extra fuel and cash while sparing the atmosphere those climate-warming emissions, all from ingredients we throw away every day.

Trash to treasure

Republic Services announced plans in May to partner with Archaea Energy to develop renewable natural gas, or RNG, projects at 39 of its 198 landfills across the country. The venture boasts a budget of $1.1 billion, $800 million from Archaea Energy and $300 million from Republic Services, and aims to convert landfill gas into pipeline-quality RNG that will offset fossil fuel use in a variety of applications.

With experience operating existing RNG and landfill-gas-to-electric projects, Archaea Energy will spearhead engineering and constructing the facilities at Republic Services landfills in 19 states. They expect each location to be operational within four to six months and for the whole suite to be completed by 2027.

While none of the planned sites will be located within Arizona, Republic Services Inc. operates as one of the largest waste disposal and recycling companies in the country, with 14 million customers and 36,000 employees in 47 states, from headquarters in Phoenix. It recently ranked among the highest in stock-market value of any Arizona-based corporation, though it has also fielded more than 4,000 customer complaints in the past three years, some due to trash pickup disruptions related to worker strikes in multiple states.

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Pete Keller, Republic Services' vice president of recycling and sustainability, expects payback on the investment in these new landfill projects to take about two years but said it can depend on state-specific tax incentives and political fluctuations.

“The economics are outstanding," Keller said in an interview with The Arizona Republic. "Part of that is the credits in the marketplace. Those are things that are hard to predict. All indications would suggest the value is going to continue to be there, but there’s no way of knowing."

Some of those projects trade at 10 times their value, Keller said, which makes such investments attractive.

"I think we’ve said publicly that we expect somewhere between $75 to $100 million in incremental annual value."

The concept is not new, but the expansion is notable. According to the U.S. Environmental Protection Agency's Landfill Methane Outreach Program, there were already 541 operational landfill biogas projects in the United States as of March 2022. Arizona hosts two of them, one owned by Waste Management Inc. and the other by Glendale, and has another 17 sites slated as candidate landfills.

“What they’re proposing to do is nothing really radical," said Bruce Rittmann, a professor and the director of the Swette Center for Environmental Biotechnology at Arizona State University as well as an expert in managing microbial communities and capturing renewable energy. "One of the things that was developed around 1990 was the concept that we should recover that methane because it’s a valuable natural gas and a potent greenhouse gas."

What's new is that Republic Services plans to capture it to the tune of "more than 12.5 million MMBtu of RNG annually," the energy equivalent of more than 2 million barrels of oil. (The U.S. uses nearly 20 million barrels of oil each day.) In addition to netting a profit, this aligns with the company's "long-term sustainability goal to beneficially reuse 50% more biogas by 2030."

The captured methane, Keller says, will be purified and injected into the pipeline. Someday they may be able to use it on site to charge batteries that could power an electric trash-pickup vehicle fleet, but that possibility will depend on technological advances in lighter batteries and progress in the federal government's renewable fuel standards and in the market for large electric vehicles making that economical.

In May, Republic Services was ranked 58th on a list of "100 Best Corporate Citizens" in terms of their environmental, social and governance plan. It is also worth noting that a majority of respondents to a recent survey expressed little faith that such plans are taken seriously by corporations and viewed them more as a "marketing exercise."

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Still, the potential is there. Rittmann did some of his own calculations and concluded that Republic Services' estimate for how much methane it would be able to transform into RNG might even be conservative.

"You start with how much organic material is going into the landfill in the United States. Then you can compute on average the amount of methane that is produced. I came up with something like 2% (that will be captured)," Rittmann said. "My conclusion is that the number they’re stating is feasible. It’s in the ballpark. They’re not just blowing smoke here, and actually the potential might be higher."

But like anything that sounds like a climate change silver-bullet solution — other than the central solution recommended internationally by scientists of simply reducing global reliance on fossil fuels — there could be complications.

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An explosive idea?

Landfills are designed to have the top sealed with materials like plastic liners or clay caps, Rittmann said. This prevents water from getting in and gas from getting out.

“As the gas comes up, they’ll capture it. The concept is simple, but the execution is not simple."

That's because landfills are full of all sorts of different materials, some that break down nicely via microbial digestion and some — like construction debris or plastics, glass and other content that should have been placed in the recycling bins — that take up space in these capped landfill cells and make them decompose irregularly.

The ideal inputs are food waste and yard waste, which is why some cities collect compostable material separately. Even some organic material, like cornstalks, are what scientists call lignocellulosic, or a protective part of the plant that has evolved to be less biodegradable and will break down more slowly. All of this causes lumpiness inside the capped landfill cells and variables in how flammable gas can be extracted from them.

This doesn't concern Keller, who says Archaea Energy has shown it can capture emissions from landfill decomposition, even amid the chaff, and purify the approximately 50% that is methane for safe addition to the gas pipeline.

“Once the landfill gas is upgraded, the molecule is identical, it's completely compatible with existing gas distribution," Keller said. "If there’s a risk, it’s execution risk at the individual site. We could get snagged on an interconnect, maybe some unseen things, but the risks aren’t significant. The biggest risk is just time value. We want to get more of these done as soon as possible."

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Another snag in this solution relates to control of methane. The Clean Air Act sets limits for the emission of six hazardous air pollutants: carbon monoxide, ground-level ozone, lead, nitrogen oxides, particulate matter and sulfur dioxide.

“It’s incredibly nuanced, but methane is not currently regulated," Keller said. “The only thing we have to do regarding methane is make sure it doesn’t leave our property in the soil."

Seems simple enough. But the consequences of methane seeping into the ground undetected can be deadly. In addition to not being regulated as an air pollutant, methane processes at landfills are not currently subject to reporting under the EPA's Risk Management Program. And a recent decision by the Supreme Court limiting the EPA's authority to regulate greenhouse gas emissions from power plants suggests there won't be new federal intervention on that any time soon.

A 2020 investigation by the Los Angeles Times and the Center for Public Integrity found that unplugged California oil wells were leaking methane and carcinogenic gases within 600 feet of more than 350,000 people's homes. One family in Kern County was displaced for nine months in 2014 after flames erupting from their wall sockets were traced back to explosive gas leaking from underground pipes.

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Methane generated from the breakdown of organic material at landfills is less likely to build to explosive levels, but incidents such as the 1986 destruction of a home and severe injury of its residents in Loscoe, England, due to colorless, odorless methane seeping into their cellar from a nearby landfill indicate it is possible.

The issue in that case was labeled a "fundamental lack of appreciation of how methane needed to be managed instead of hoping for the best through an 'out-of-sight, out-of-mind' approach."

Since then, facilities have made an effort to flare or capture methane emissions, though one report estimated that there are still nearly a quarter million sites across the U.K. alone that remain subject to "ground gas" leaks from landfills and mines, many of which are poorly documented and seldom reported.

Keller says regulatory and technical improvements since the 1990s, such as the requirement that the base of landfills be sealed to prevent leaks into the soil, leave him confident this is not a situation they will encounter.

“There were examples of methane accumulating in neighbor’s basements and causing unsafe conditions. There might have been a few little explosions. I remember seeing a cartoon about it one time," Keller said. “The sites themselves are lined now. The other way is we have monitors through the site. Absolutely, methane doesn’t migrate from sites that have bottom liners."

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Rittmann, who is not an expert on landfills specifically, says it can be hard to know what is coming off these sites and exactly where it is going.

“There’s a lot of work on actually measuring what is coming out of landfill," he said. "That’s not so easy to do. How do you know if you’re collecting all of it?"

That's one of the reasons he prefers the option of collecting organic waste and sending it to wastewater plants where anaerobic digesters can capture emitted gases in a more controlled environment. That's one focus of his research at ASU and an option he hopes will become more widespread in the future.

For now, though, we have landfills, and separate bins for what goes there versus what goes to recycling facilities. The more people can help keep those streams separated, the better these projects to turn trash into something useful will function, and the lower the risks will be. Modern technology and a focus on climate solutions have created an opportunity for waste to be less wasteful.

"Virtually all the natural gas we use today is fossil," Rittmann said. "Anytime you can replace fossil fuel use, that's a good thing. That's our ultimate goal here."

Joan Meiners is the climate news and storytelling reporter at The Arizona Republic and azcentral. Before becoming a journalist, she completed a doctorate in ecology. Follow Joan on Twitter @beecycles or email her at joan.meiners@arizonarepublic.com.

This article originally appeared on Arizona Republic: How your trash could be turned into a source of renewable natural gas