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 鈥� 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 鈥渂lack carbon鈥� 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.
鈥淲e need to evolve. We need to find solutions that are outside your standard box,鈥� said Coral Gables Mayor Vince Lago, who began looking for green waste alternatives years ago. 鈥淭he way that we have been disposing of waste and garbage over the last 25 years is outdated, and it鈥檚 not environmentally friendly.鈥�
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 鈥渋llegal dumping鈥� 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.
鈥淲e want to look at how we can be better stewards of the environment,鈥� said Coral Gables City Manager Peter Iglesias.
It鈥檚 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鈥檛 necessarily see a decrease in their current garbage fees. Both Lago and Iglesias describe the move as taking control of the city鈥檚 future, protecting residents from the possibility of rising garbage and disposal fees as the county鈥檚 waste crisis worsens.
After the city鈥檚 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鈥檚 a 鈥淲in, Win, Win Win, Win,鈥� Iglesias said, noting that the city is 鈥渕anaging an urban forest鈥� 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鈥檚 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鈥檚 lease ends in March, though the Gables is currently in talks with the county to extend the lease 鈥� potentially for a higher rental fee 鈥� 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.
鈥淭he transfer site is not something you can just uproot and plant somewhere else the next day. There鈥檚 a lot of logistics and a lot of equipment associated with that operation,鈥� said Aneisha Daniel, the Director of Miami-Dade鈥檚 Solid Waste Management.
Two companies, same goal
While both Miami-Dade and Coral Gables are pursuing biochar facilities and say they鈥檙e open to working together, they鈥檙e 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 鈥淏iocharger,鈥� 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 鈥淏iocharger鈥� 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鈥檚 鈥渇ire box鈥�. A generator forces air across the top of the box, making an 鈥渁ir curtain鈥� that blocks oxygen and reduces smoke. There鈥檚 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%.
鈥淭here鈥檚 hardly any emissions that come out of the air curtain burners,鈥� 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 鈥渇ine-tuning.鈥� 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鈥檛 made any commitments beyond that with Clean Earth Innovations.
Both machines help curb two of the most widespread, deadly air pollutants 鈥� fine particulate matter and ozone. Heating everything also kills off PFAS 鈥� or 鈥渇orever chemicals.鈥� But there are some differences. For starters, Miami-Dade鈥檚 pilot project is a much smaller operation. The machine will only process 4,000 tons, or less than 1%, of the county鈥檚 approximate 500,000 tons of green waste. The county hopes to grow the operation if the tests go well.
鈥淲e鈥檙e trying to determine if it鈥檚 scalable for widespread waste reduction,鈥� said Nick Ciancio, the Resilience Division Director for the Miami-Dade Department of Solid Waste Management. 鈥淓very little bit of cutting emissions is good, but I didn鈥檛 want to make the impression that this pilot project alone would be a monumental emissions reduction.鈥�
Miami-Dade鈥檚 machine doesn鈥檛 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鈥檚 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鈥檚 in an in-between state of wood and ash. Miami-Dade鈥檚 machine has a closed lid and a built-in mister that brings the biochar through a conveyor belt and drops it into a bag.
鈥淚t鈥檚 more efficient, it鈥檚 better for production, and it鈥檚 even cleaner 鈥� that鈥檚 what we鈥檙e focused on, doing things that are environmentally pristine,鈥� said Clean Earth Innovations CEO Harold Gubnitsky.
Air Burners鈥� 鈥淏iocharger,鈥� 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.
鈥淎sh is full of nutrients, and so you could use it as a fertilizer, but it鈥檚 not porous like the charcoal is, and so the soil benefits aren鈥檛 as great, and they鈥檙e not as long-lasting,鈥� 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 鈥� 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.
鈥淚t鈥檚 like a sponge capturing both the water-borne pollutants and the airborne,鈥� Shi said.
Biochar鈥檚 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.
鈥淭he potential is there right now. What鈥檚 limiting the development is really that this is so new that the equipment, the market, takes time,鈥� 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.
鈥淩ight after you鈥檙e paving, you can still smell the toxic emissions. Residents get exposed to the toxic fume, even if you don鈥檛 see it. But with biochar, it grabs all the volatile stuff. This is a community benefit,鈥� Shi said.
How biochar changes Gables鈥� hurricane clean-up
Although the Gables says one machine is all it would require to meet the city鈥檚 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鈥檚 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.
鈥淲e鈥檙e a leafy city鈥� and are 鈥渓ooking at every possible way to minimize our footprint on what actually gets put in a landfill,鈥� said South Miami Mayor Javier Fernandez. The mayor said he鈥檚 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 鈥� 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鈥檚 how much debris the Gables usually collects in 2.4 years
鈥淲e don鈥檛 want a science project. We want a facility and this product, these folks have been around for 30 years,鈥� said Iglesias.
鈥淣ot a magic bullet鈥�
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鈥檚 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 鈥� 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.
鈥淭he idea is to make sure everything that鈥檚 burned before it鈥檚 shut down for the day 鈥� But, you know, sometimes you don鈥檛 plan quite right, and it will continue to smolder in the burn box. And, yeah, you get some emissions from that,鈥� Dumroese said.
The machines aren鈥檛 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.
鈥淭hey鈥檙e not a magic bullet, but they are highly effective tools for good,鈥� 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, SA国际传谋 Public Media and the Tampa Bay Times.
