Most climate solutions are getting smarter. Solar panels can track the sun. Electric vehicles are equipped with the equivalent of an iPad and may soon be able to drive themselves (according to some people). Startups are inventing stoves with batteries that charge when energy is cheap and heat pumps that learn how you use your home and adjust accordingly.
But when it comes to permanently removing carbon dioxide from the atmosphere, the market is pushing in a different direction. There, it seems, there’s growing excitement for the dumbest, most primitive solutions companies can come up with.
The case in point this week is a $58 million agreement between Frontier, a fund started by tech companies to help grow the carbon removal market, and Vaulted Deep, a startup that collects food waste, poop, and other wet, sludgy, organic material and stashes it away underground. It’s the biggest deal Frontier has made to date, followed closely by a $57 million contract it signed in December with Lithos Carbon, which crushes up rocks and sprinkles the dust on agricultural fields. The rock naturally reacts with carbon dioxide in the air to form bicarbonate, which can essentially lock it away permanently.
There are at least 850 startups around the world trying to figure out the most effective, scalable, low-cost approach to cleaning up the legacy carbon pollution that’s warming the planet. Some of the most promising solutions have involved building big, energy-intensive systems that extract tiny amounts of carbon dioxide from the ambient air. One company I recently wrote about is manufacturing millions of tennis ball-sized sponges that will be stacked in trays, absorb carbon from the air, and then transferred into an oven to bake off the carbon.
Is it possible the answer could be as easy as pulverizing rocks and burying waste?
I ran my observation about the growing enthusiasm for dumb ideas past Hannah Bebbington, a strategy lead at Frontier, and she agreed — “totally,” she said, though she preferred the phrase “low-tech.” Compared to some of the earlier stars of carbon removal, Vaulted Deep and Lithos don’t require as much upfront capital investment or years and years of research and development. “At the end of the day, we are really excited about getting to gigaton scale carbon removal, and it doesn’t have to be the sexiest technology.”
So far, it seems, these lower-tech companies have been able to scale quickly. Vaulted Deep, for instance, launched at the end of August last year and has already delivered more than 2,400 tons of carbon removal. By comparison, the only operating direct air capture facility in the United States is capable of removing 1,000 tons of CO2 per year.
Vaulted Deep’s first project is in Kansas, where it is intercepting “woody waste” like grass clippings and tree trimmings that was destined to be incinerated. Once upon a time, when the plants were alive, they sucked up carbon from the atmosphere. If the clipping had been burned, the carbon would have been released back into the air. By slurrifying the waste and injecting it into a deep well, hundreds of feet underground, Vaulted Deep disrupts the cycle, potentially for millennia.
One advantage of this approach is that the carbon capture work is done for free, courtesy of photosynthesis. (Trees, of course, do this too, but not permanently.) Another is that Vaulted Deep uses mature technology to turn the waste into a slurry that can be injected underground. The company was spun out of Advantek, a waste management business that pioneered slurry injection in the 1980s. Most of the substances we inject into the layers of rock underneath our feet are pure liquid or gas, Julia Reichelstein, the CEO of Vaulted Deep told me. Advantek’s technology enables the company to take solid waste and, with minimal processing and energy, get it injection-ready.
The company’s third advantage is being able to pump its waste into “class five” wells, a designation made by the Environmental Protection Agency. Class five is sort of a catch-all category, encompassing shallow wells used for stormwater drainage and septic systems, to deep wells used for geothermal power. Regulations vary by type and by state, but in general, these are much more common and easier to permit than the “class six” wells used for carbon dioxide sequestration. “There’s, you know, 20, 30 years of permit history now on best practices on how you permit a slurry injection well,” Omar Abou-Sayed, the company’s co-founder, told me. “We comply with or exceed all those regulations. So this isn’t a case of, like, move fast and break things.”
All of this allows Vaulted Deep to charge less for carbon removal than many of its peers — closer to $400 per ton, as opposed to upwards of $600. Bebbington, of Frontier, thinks there’s a promising path to bring costs down a lot further if the company can achieve economies of scale by buying the sludgy organic waste in bulk, or move its injection wells closer to where the material originates.
But any climate solution involving biomass raises a host of questions about where the material came from, and what might have been done with it otherwise. Reichelstein said the company’s internal research found that there was almost a billion tons of bio-sludge produced in the U.S. annually. If it could capture all of it, the company estimated, it could sequester more than 300 million tons of carbon away from the atmosphere each year, after taking into account the emissions involved in collecting, processing, and injecting all that waste.
And yet, “The definition of a ‘waste’ is highly contested,” Freya Chay, program lead at the nonprofit CarbonPlan, which analyzes the integrity of different carbon removal approaches, told me.
For example, some companies are eyeing the use of agricultural waste like corn stalks, which are often left to decompose in fields, but also add nutrients to the soil. If the corn waste is removed and processed and buried underground, will that increase the use of carbon-intensive fertilizer? What if the waste was going into a landfill? There, it would have broken down eventually, but much more slowly than if it had been burned.
These questions get more complicated as projects that utilize waste biomass scale up. Once there’s more of a market for the material, will those counterfactuals that support what Vaulted Deep is doing — like that the waste would have been incinerated — still hold? “It's really hard to govern system-level risks with project-level rules, but that is the situation we are in,” said Chay.
At a second project location, in Los Angeles, Vaulted Deep is collecting sewage from the city’s wastewater treatment facilities that otherwise would have been trucked hundreds of miles out of the city and spread on farmland to decompose, releasing CO2 both during the transport and as it decays. The city has actually been paying Advantek to dispose of some of its sewage since 2008. But now, because of the Frontier deal, the company will drop its fee, allowing the city to divert even more of the waste for slurry injection.
Chay didn’t have any immediate concerns about Vaulted Deep’s biomass sourcing. In fact, she highlighted the co-benefits the company would provide. Oftentimes biomass waste is contaminated with toxic chemicals, and Vaulted Deep is preventing it from getting dumped in communities. “We should celebrate that,” she said.
Editor’s note: This story has been updated to correct the type of waste diverted for the Kansas project.
The 2026 Ioniq 5 Limited. Image courtesy of Hyundai
