In lush South Florida, trees and bushes grow all year round. And that means yard waste and dead trees never stop piling up. But leaving them in a landfill is a climate-warming issue.
Two South Florida governments think they have a new solution — light it on fire, but in a planet-friendly way.
Miami-Dade County and Coral Gables, one of the richest cities in the region, are both turning to new technology that leans on ancient farming practices to transform wood waste into a charcoal-like material called biochar.
The material known as “black carbon” has the potential to clean dirty water, nourish soil and even be used in roads.
Plus, it has lower emissions than a simple bonfire, leading to cleaner, healthier air that contributes less to climate change.
“We need to evolve. We need to find solutions that are outside your standard box,” said Coral Gables Mayor Vince Lago, who began looking for green waste alternatives years ago. “The way that we have been disposing of waste and garbage over the last 25 years is outdated, and it’s not environmentally friendly.”
Gables leaders are getting ready to drop millions to create a facility that will use large, futuristic ovens to bake fallen trees and other vegetative waste into biochar, which could be used as fertilizer in golf courses and parks and mixed into concrete and asphalt for sidewalks and parking lots. Lago also believes the machines will help the city combat “illegal dumping” of trees and other green matter waste by landscapers who work all over the county and then use the city as their own personal dumping ground.
Manufacturers say the machines use powerful streams of air to limit the release of smoke, significantly reducing the presence of cancer-causing pollutants. It also produces energy that powers the facility and still gives the Gables some extra charge for its large fleet of electric vehicles, including an electric garbage truck that is currently being tested on the streets.
“We want to look at how we can be better stewards of the environment,” said Coral Gables City Manager Peter Iglesias.
It’s not a cheap project. The city would need to drop about $3.47 million for two biochar-making machines, with a total expected price tag for the project a hefty $7.5 million. The total cost includes an expansion project on the property that would involve cleaning up a nearby contaminated piece of land and the opening of an unrelated training facility for city firefighters.
The City Beautiful, known for its lush tree canopy, expects its waste-to-energy and biochar initiative to save it $1 million annually, and also bring in revenue. Iglesias said the city plans to offer its biochar-making services to other cities, as well as commercial landscapers, with hopes to possibly sell and ship biochar all over the country.
Gables residents won’t necessarily see a decrease in their current garbage fees. Both Lago and Iglesias describe the move as taking control of the city’s future, protecting residents from the possibility of rising garbage and disposal fees as the county’s waste crisis worsens.
After the city’s main waste solution, a trash incinerator, burned down in 2023, Miami-Dade has so much trash that it ships about half by train to out-of-county facilities, increasing both environmental and financial costs, both to the county and the cities that depend on Miami-Dade to dispose of their garbage.
It’s a “Win, Win, Win Win, Win,” Iglesias said, noting that the city is “managing an urban forest” that is home to over 42,000 trees, making it a prime breeding ground for biochar.
Iglesias is hoping to get the Gables biochar facility operating within two years. The county expects to start baking biochar as early as the end of January at the South Dade landfill.
One problem? Both governments are eyeing the same piece of land for trash-related purposes.
A trashy spot
The spot the Gables wants to install the multi-million dollar biochar facility is currently being leased to the county as a waste-transfer site, a holding ground for trash the county collects from all over Miami-Dade before taking it to the landfill.
Miami-Dade County has paid the Gables for the past 30 years to use the property, which is part of the city’s public works facility on Southwest 72nd Avenue. In 2025, the county paid a total of about $520,000 in rent.
But for the Gables, the projected cost-savings of operating its own biochar facility are worth losing the county as a tenant, according to Iglesias.
The city pays the county nearly $1.3 million annually for waste disposal, much of which is trees and other vegetative waste. It projects that operating its own biochar facility will cut the cost by 80%.
Miami-Dade’s lease ends in March, though the Gables is currently in talks with the county to extend the lease — potentially for a higher rental fee — for an additional one to two years to give time for the county to clean up and restore the site, and find an alternate waste transfer location.
“The transfer site is not something you can just uproot and plant somewhere else the next day. There’s a lot of logistics and a lot of equipment associated with that operation,” said Aneisha Daniel, the Director of Miami-Dade’s Solid Waste Management.
Two companies, same goal
While both Miami-Dade and Coral Gables are pursuing biochar facilities and say they’re open to working together, they’re using two different companies that will deliver two slightly different end products.
The Gables turned to Palm City-based Air Burners, a company whose machines have been used across the world for over 30 years.
Iglesias said the city is still deciding between the many machines Air Burners offers. One possible contender: the “Biocharger,” a machine that prioritizes making energy and quickly disposing of tons of wood waste, according to scientists.
Mike Schmitt, an Air Burners representative, claims that the “Biocharger” burns wood waste 40 times faster than a campfire-style burn and creates three tons of biochar for every 100 tons of wood waste.
It works by a crane dropping wood into the machine’s “fire box”. A generator forces air across the top of the box, making an “air curtain” that blocks oxygen and reduces smoke. There’s a counterclockwise circulation of air inside that box, which forces everything to get re-burned several times. Air Burners claims the process reduces harmful particulates in the air by 90%.
“There’s hardly any emissions that come out of the air curtain burners,” said Deborah Dumroese, a Research Soil Scientist for the USDA, who has worked with biochar for more than 17 years.
The county is going with a startup, Clean Earth Innovations, a Fort Lauderdale biochar startup company, which was awarded $100,000 by the Miami-Dade Innovation Authority to operate a biochar machine at the South Dade landfill. It is already on site, undergoing “fine-tuning.” Once it opens at the end of the month, it will run seven days a week, Daniel said.
Pilot projects with the county can last no longer than one year, and the county hasn’t made any commitments beyond that with Clean Earth Innovations.
Both machines help curb two of the most widespread, deadly air pollutants – fine particulate matter and ozone. Heating everything also kills off PFAS – or “forever chemicals.” But there are some differences. For starters, Miami-Dade’s pilot project is a much smaller operation. The machine will only process 4,000 tons, or less than 1%, of the county’s approximate 500,000 tons of green waste. The county hopes to grow the operation if the tests go well.
“We’re trying to determine if it’s scalable for widespread waste reduction,” said Nick Ciancio, the Resilience Division Director for the Miami-Dade Department of Solid Waste Management. “Every little bit of cutting emissions is good, but I didn’t want to make the impression that this pilot project alone would be a monumental emissions reduction.”
Miami-Dade’s machine doesn’t produce energy like the Biocharger the Gables is eyeing, but it makes more biochar per load. Air Burners said biochar in the Biocharger makes up 3-5% of the end product, while Miami-Dade’s makes around 20%. The type of trees, plants and technology used in the process affects how much carbon the biochar stores.
For the biochar to be created, it needs to be in a low-oxygen environment and cooled with water while it’s in an in-between state of wood and ash. Miami-Dade’s machine has a closed lid and a built-in mister that brings the biochar through a conveyor belt and drops it into a bag.
“It’s more efficient, it’s better for production, and it’s even cleaner … that’s what we’re focused on, doing things that are environmentally pristine,” said Clean Earth Innovations CEO Harold Gubnitsky.
Air Burners’ “Biocharger,” on the other hand, has to be raked out the next morning and dunked in water. By then, the charcoal will be mostly turned into ash, according to Dumroese, a soil scientist for the USDA.
“Ash is full of nutrients, and so you could use it as a fertilizer, but it’s not porous like the charcoal is, and so the soil benefits aren’t as great, and they’re not as long-lasting,” Dumroese said.
Water purifier? Fertilizer? Animal food?
Xianming Shi, a University of Miami professor of civil and architectural engineering, has been in early conversations with Miami-Dade County and the City of Coral Gables about collaborating on ways to use biochar — either in road construction or to help remove pollutants from local waterways.
Storm runoff carries a lot of nitrogen, phosphate and heavy metals. According to Shi, biochar can trap those contaminants and purify the water. Then, there is a possibility to reuse the biochar as fertilizer.
“It’s like a sponge capturing both the water-borne pollutants and the airborne,” Shi said.
Biochar’s benefits were first discovered more than 2,000 years ago, but research into its modern uses has accelerated over the last decade. There are even small studies looking at adding it to cow feed to see whether it can reduce methane emissions.
“The potential is there right now. What’s limiting the development is really that this is so new that the equipment, the market, takes time,” Shi said.
While its effectiveness as a soil amendment and water purifier is well established, its use in concrete is still relatively new. Shi said he found a way to replace 30% of a cement mix with biochar and up to 20% in asphalt pavement.
“Right after you’re paving, you can still smell the toxic emissions. Residents get exposed to the toxic fume, even if you don’t see it. But with biochar, it grabs all the volatile stuff. This is a community benefit,” Shi said.
How biochar changes Gables’ hurricane clean-up
Although the Gables says one machine is all it would require to meet the city’s green waste needs, it wants to buy two Air Burner machines, both to help with extra debris after hurricanes and as a potential side business handling green waste from other cities.
It expects to recoup the $7.5 million remediation and setup costs in three to five years. It plans to seek partnerships with FPL and other entities, as well as apply for federal and state grants, to help offset the project’s costs.
The Gables has already begun discussions with neighboring cities, including the City of Miami, South Miami and Pinecrest about turning their own green waste into biochar.
“We’re a leafy city” and are “looking at every possible way to minimize our footprint on what actually gets put in a landfill,” said South Miami Mayor Javier Fernandez. The mayor said he’s concerned about the future increases in trash fees and looking for possible sustainable solutions. He said the city wants to work with Miami-Dade and is trying to negotiate a better interlocal agreement with the county that makes financial sense for the city.
Iglesias also sees a biochar set up as a faster, more efficient solution for a big problem for the Gables — clearing up downed trees after a hurricane.
When Hurricane Irma struck, for example, the city collected 360,000 cubic yards, or about 62,000 tons of yard waste following the storm. That’s how much debris the Gables usually collects in 2.4 years
“We don’t want a science project. We want a facility and this product, these folks have been around for 30 years,” said Iglesias.
“Not a magic bullet”
Because the Gables is eyeing placing their machines on a piece of land near a neighborhood, it matters how much smoke this process creates. By all accounts, the answer is not much.
During a recent tour of Air Burner’s warehouse, the Herald was taken to a nearby landscaping company that uses one of the biochar-making machines. However, no workers were present and the machines were not operating. There was a Firebox with visible smoke coming out the top – the nearby area smelled like a campfire.
Dumroese, the USDA soil researcher, said there will be some smoke at the beginning and towards the end of the day when the system is trying to get everything cooled down.
“The idea is to make sure everything that’s burned before it’s shut down for the day … But, you know, sometimes you don’t plan quite right, and it will continue to smolder in the burn box. And, yeah, you get some emissions from that,” Dumroese said.
The machines aren’t perfect, said John Webster of the US Biochar Initiative, a nonprofit group that promotes biochar. Once, a barbed wire got into their machine, and they had to burn it and then reach in with a hook to fish it out. The county, too, is already grappling with how to ensure the loads are clean of contaminants like paint and plastic.
“They’re not a magic bullet, but they are highly effective tools for good,” Webster said.
Correction: An earlier version of this story incorrectly stated that Miami-Dade sends half its trash out of state. It sends it out of the county.
Ashley Miznazi is a climate change reporter for the Miami Herald funded by the Lynn and Louis Wolfson II Family Foundation and MSC Cruises in partnership with Journalism Funding Partners.
This story was originally published by the Miami Herald and shared in partnership with the Florida Climate Reporting Network, a multi-newsroom initiative founded by the Miami Herald, the Sun-Sentinel, The Palm Beach Post, the Orlando Sentinel, WLRN Public Media and the Tampa Bay Times.
