Around 20 miles north of downtown Houston, seated between Interstate 69 and the Sam Houston Tollway, acres of pipeline weave through piles of trash at the Atascocita Landfill. The garbage, which has been rotting for years, creates a gas that rises through the mounds of old banana peels and dinner leftovers. At the top, the gas is collected and cleaned – eventually pumped out to CenterPoint Energy’s main gas lines. 

There are more than 500 landfill-to-energy projects currently operating in the United States across 2,600 total landfills. Texas has 29 working and another 44 under consideration, according to the state  Environmental Project Agency. These include the Atascocita and McCarty in Harris County as of September 2024.

This is because landfills produce some of the highest amounts of methane gas in the world. Methane – colorless, odorless and flammable –  is a potent greenhouse gas that traps heat in the atmosphere, a process which is accelerating global warming. However, methane can also give us energy. 

How is methane connected to trash?

Methane naturally occurs when organic matter, such as plants and animals, decays over time. In a landfill, trash piles on top of trash over and over until the old bread and discarded cheese at the bottom are suffocated of oxygen. Then minuscule bacteria munch on the trash, producing methane gas. 

Because of this, organic municipal solid waste landfills, like Atascocita or McCarty, are the third largest source of methane emissions in the United States. In 2022, these types of landfills released an estimated 100.9 million metric tons of methane into the atmosphere, representing 14.4 percent of total U.S. methane emissions. 

The United States is the second largest emitter of methane in the world, behind China, and Texas is the largest emitter in the country. 

Atascocita, McCarty and the Baytown Landfill make up for 78 percent of the total methane emissions in Harris County, according to a 2024 report.  Houston is in the top 10 cities with the highest urban methane emissions along with Dallas. 

However, methane is also the main ingredient in natural gas, according to Dan Cohan, a professor of civil and environmental engineering at Rice University. Natural gas used to power or heat homes is found in the environment by drilling oil wells or fracking.  The gas that comes straight from already decaying waste products can supplement these natural sources as renewable energy, said Cohan. 

“There’s a lot of benefit to capturing methane and using it as fuel rather than letting it leak straight into the environment,” Cohan said. “However many landfills and trash we have, we should be capturing as much of the resulting methane as possible from them.” 

Landfill companies can collect this methane and move it through a series of pipelines to a renewable energy facility on site. There, the gas is either burned in engines to produce electricity or cleaned for natural gas distribution. 

How does your trash become energy?

From the moment your trash is picked up on the street or collected at your apartment complex, it is decomposing. 

If you live in Houston, your trash is taken to one of the city’s six garbage landfills, where it is dumped and continues to decompose along with everyone else’s trashed pizza boxes, discarded jeans and old ham . Initially, as the decaying trash sits at the top of the pile, it does not produce methane, said Melanie Sattler, the department chair for civil engineering at the University of Texas at Arlington. 

“At the top of the pile, the trash is exposed to oxygen and microorganisms will use the oxygen to decompose the waste,” Sattler said. “But as the trash gets buried under more and more piles of waste, these little microorganisms deplete the oxygen until there is only 1 or 2 percent oxygen left. That is compared to the 21 percent oxygen we have in the atmosphere.” 

Under these conditions—without hardly any oxygen—new microorganisms activate and produce about 50 percent carbon dioxide and 50 percent methane, creating landfill gas. Natural gas, in comparison, is about 90 percent methane. 

This gas combination then rises to the surface of the landfill, bound for the atmosphere. However, at landfill-to-energy projects, gas collection wells are installed at a variety of depths throughout the landfill. These pipes have holes in them so the gas can enter. The interior fans blow the gas up out of the landfill and into a duct system, said Sattler. 

The landfill gas is moved through the ducts to an on-site facility, where it is converted to energy or natural gas. 

At Atascocita, there are 394 gas collectors throughout the landfill, usually at a depth of about 10 feet from the bottom of the trash pile. The landfill gas is sent to a facility, where it is “scrubbed”or cleaned, eventually converting from about 55 percent methane to 90 to 99 percent methane. 

“That gas will go into CenterPoint’s natural gas general pipelines to heat homes, start your stove, our landfill’s natural gas fleet,” said Keith Sharon, gas operations manager for Waste Management in Texas and Oklahoma. “There are a lot of places it can be delivered and used for.” 

For every 1,000 standard cubic feet per minute of landfill gas – meaning the flow rate of gas – processed at Atascocita, the site will produce enough renewable natural gas to power about 10,000 homes in the Houston area. 

What about electricity?

There are some landfills which will convert the landfill gas on site into electricity to be dispersed throughout the general CenterPoint grid. 

At Waste Management landfill Coastal Plains just south of Houston, the process is nearly the same except that the facility combusts the landfill gas to create energy. The byproducts, such as carbon dioxide, nitrogen oxides and sulfur dioxide, are flared into the air, said Sharon. However, about 98 percent of the landfill gas is burned in the process of creating energy, leaving about 2 percent byproducts to be flared out. 

Just recycle, instead 

Despite these benefits, methane conversion is not the solution. Landfills still leak methane gas into the environment every day. Satellite data shows that the Fort Bend Regional Landfill, Blue Ridge Landfill and McCarty Road Landfill in the greater Houston area have some of the highest rates of methane emissions in Texas. 

Fort Bend Regional Landfill emitted 1.5 million metric tons of C02e in the year 2022. This is the same emissions as about 336,777 passenger cars driving for a year, according to the EPA.

 Texas emitted 31 million metric tons of C02e in 2022, or 7 million cars driven in a year. 

CO2e means Carbon Dioxide equivalent. This is a metric used to compare the impact of different greenhouse gases on the climate. In other words, the amount of carbon dioxide emissions that would have the same global warming potential as one metric ton of another greenhouse gas. 

‘’Waste is a major environmental issue in the United States and in Harris County. Houston generates about 4.2 million tons of solid waste a year, with that number expected to increase to 5.4 million tons by 2040. At the same time, some of the biggest landfills have less than 20 years before they reach capacity. 

“It’s not as simple as we get energy from trash so that’s it,” said Cohan. “There’s a lot of energy that goes into growing your food, trucking it to the grocery store, tracking your trash. This is a matter of capturing the methane that is being produced anyway.” 

With the amounts of natural gas we consume daily. cleaner methods of producing energy, such as landfill gas, remain a fraction of the total energy used in the U.S., said Cohan. The real solution: be mindful of what is thrown out and what you can recycle or compost instead. 

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