Microsoft Wants Your Poop to Lower Its Emissions

The tech giant is investing in increasingly innovative methods of removing carbon from the atmosphere in an effort to offset the climate impact of its AI data centers

Microsoft's carbon footprint is huge. It thinks storing human waste underground might help solve that problem.

The tech giant's insatiable appetite for power to feed its AI habit is causing a rise in its emissions. To stop its carbon footprint from ballooning, the company is betting on a variety of greenhouse-gas-removal technologies.

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One of these involves buying human and farm waste and piping it thousands of feet underground through a pump that acts like giant syringe.

"We're taking different types of organic waste," said Julia Reichelstein, co-founder and chief executive of Vaulted Deep, the company Microsoft is investing in. "It's sludgy, often contaminated organic waste that today causes problems above ground, and instead we take the waste and put it really deep underground for permanent carbon removal."

Microsoft on Thursday announced a deal to purchase 4.9 million metric tons of durable carbon dioxide removal from Vaulted Deep over 12 years, starting from next year. One ton of carbon sequestered equates to a carbon removal credit.

It is just one of a number of new ways of offsetting carbon that Microsoft is backing, betting that these technologies will help to combat climate change by stopping carbon dioxide and methane from entering the atmosphere.

Other unusual carbon-removal projects to have piqued the interest of Microsoft include regrowing former rainforests in Panama—and inadvertently creating cattle ranchers out of financiers in the process—and collecting the emissions generated during the incineration of swaths of trash from a Norwegian city and burying the gases deep under the North Sea in former oil wells.

How it works

Vaulted Deep collects what it calls "bioslurry"—which could be human waste from a city's sewage system, excess manure from farm fields or sludge left over from paper mills. It then grinds it up before injecting it some 5,000 feet underground.

While most waste comes in the form of solids, liquids or gases—slurries sit in an inbetween state, which makes them harder to treat. Often they are dumped on cheap land or spread over agricultural fields, leading to nutrient runoff and the leaching of harmful chemicals such as PFAS, also known as forever chemicals, into the water system.

Instead, Vaulted Deep collects the slurry from municipal and industrial sites before piping it under natural rock formations. When it comes to manure, deep storage halts decomposition, preventing the release of greenhouse gases like CO2 and methane into the atmosphere. Methane is four times more potent than CO2 when it comes to atmospheric warming.

Vaulted Deep then sells carbon credits based on the amount of carbon it manages to store underground. Currently those credits sell for about $350 a metric ton.

According to experts, Vaulted Deep's appeal is that it gets rid of waste that is unusable and turns it into carbon credits.

"It's the sludgy waste, the stuff we really don't have any other use for, and they want to inject it underground into permanent geological storage," Daniel Sanchez, assistant professor of cooperative extension at the University of California-Berkeley. "It's as simple as one can get," according to Sanchez, who specializes in biomass systems that remove CO2 from the atmosphere.

Sanchez noted that while biosolids like sewage waste and manure can be used as fertilizers, only limited amounts are actually productive when it comes to farming. Excess waste is often dumped, leading to harm for the local environment.

He estimated that the cost of collection at around $150 a ton, though he expected this to lower over time, especially if Vaulted Deep's sites are co-located with waste-management facilities.

The biggest accidental carbon-removal company

Vaulted Deep was started in 2023 by Reichelstein and Omar Abou-Sayed—more by accident than by design.

Going Deep

Companies like Microsoft are betting that storing organic waste thousands of feet below the surface of the ground will help to meet their emissions targets

Source: Vaulted Deep
Illustration by Thomas R. Lechleiter/WSJ

Abou-Sayed's father helped create the technology used to inject the slurry underground. At the time he was looking for ways to bury oil-field waste.

Abou-Sayed then commercialized the technology under the company Advantek, piping excess slurry from a wastewater treatment facility in Los Angeles. Today, the company takes about 20% of the biosolids from the city. Reichelstein said it was during a conversation with Abou-Sayed that she realized they had accidentally built a carbon-removal company.

"I remember looking at him and doing a little bit of math and said, 'I think you run like the largest carbon-removal project in the entire world that I've never heard of,'" she said. The conversation prompted the pair to create Vaulted Deep.

The company is now looking to expand. This week it cut the ribbon on a new facility in Hutchinson, Kan., that takes trucked farm waste from around the region as well as biowaste from the city of Derby. The plant is expected to deliver 50,000 tons of durable carbon removal a year when running at full capacity. Before the deal with Microsoft, Vaulted Deep had a deal to deliver credits to Frontier, a group of largely technology companies, including Stripe.

A good fit

Microsoft is aiming to be carbon negative by 2030, and is seeking by 2050 to remove from the environment more greenhouse gases than the company has emitted since its founding. Between 2020-24, Microsoft emitted a total of 75.5 million tons of CO2 equivalent, according to its sustainability reports.

In an effort to offset some of this it has bought a vast number of carbon removal credits. To date, it has acquired more than 83 million tons of carbon removal, of which 59 million tons have been bought so far this year, according to AlliedOffsets. This doesn't include the deal with Vaulted Deep.

Brian Marrs, Microsoft's senior director of energy and carbon removal, said the tech giant invested in Vaulted Deep partly because of the co-benefits of the design. "Vaulted Deep is a waste-management company that's become a carbon dioxide removal company," he said.

"They're essentially taking biosolids, and much of that today is spread over fields," he said. "It can create nutrient [runoff] and other pollutants for watersheds, and sealing out that biosolid where it can't be a nuisance to the environment and where it will not repatriate carbon into the atmosphere—that approach, that co-benefits approach is very, very interesting to us."

The technology is a safer bet for Microsoft as it is already up and running and is fairly low-cost in terms of design due to largely involving the drilling of a well—an established process, according to Marrs. In comparison, newer technologies are more capital-intensive up front, such as direct air capture.

"You have the old saying in finance that the only free lunch is diversification. We also believe that to be true when you're taking a basket of technologies, particularly first of a kind technologies around CDR, and think that Vaulted Deep fits in that piece of our portfolio as well," he said.

Berkeley's Sanchez said Vaulted Deep would likely see more of its success in North America, as opposed to other regions like Europe where there has been a push to use the same waste for energy purposes. He noted that in places such as Germany, farm waste is used as a biogas and so the company would be in competition for the material.