Spring 2022

Natural Selections

Seunghyeon Jung PhD'21, at the time a biological systems engineering graduate student, left, and Evan Schmid, a biological systems engineering undergraduate student, work on a direct air capture unit in a lab at the Wisconsin Energy Institute at UW–Madison in November 2021. The two are part of a team that is one of the top winners of the XPRIZE Carbon Removal Student Competition. Photos by Michael P. King


Cut greenhouse gas emissions and stave off the harmful effects of climate change. It’s one of the most important challenges we face today. And it’s no small feat. On our current trajectory, many fear the planet faces an imminent “too little, too late” scenario. A new approach is needed.

Fortunately, there’s hope, and it comes in the form of an innovative technology created by a team of UW students and professors. They’ve been working on a way to take carbon dioxide, the most common greenhouse gas, out of the air and seal it away where it can’t contribute to rising global temperatures.

In November 2021, the team was selected as one of the top winners of the XPRIZE Carbon Removal Student Competition. The contest aims to kickstart projects that could mitigate the impacts of climate change by removing carbon dioxide from the air, ground, and oceans. The UW team, which includes members from CALS, received $250,000 — the largest available award in the student competition — to fund their continued work.

“We are really excited about our technology, and it’s cool to be working on something that has the potential of scaling up in a big way and actually have an impact,” says team leader Keerthana Sreenivasan, a graduate student in civil and environmental engineering.

The student challenge is part of the larger $100 million XPRIZE Carbon Removal competition supported by the Musk Foundation, a nonprofit research foundation established by entrepreneur Elon Musk. The multiyear global competition is designed to fund early-stage carbon removal concepts, and Musk encourages teams to “build real systems that can make a measurable impact and scale to a gigaton level.”

Number Crunching

In 2019, global emissions reached the equivalent of 59 gigatons of carbon dioxide, according to the United Nations. A gigaton is 1 billion tons. The Musk Foundation’s multiyear XPRIZE Carbon Removal competition incentivizes participants to submit carbon-removal systems and concepts that can scale to this level.

With the new funding, the UW group can develop its project as the competition advances to subsequent rounds.

“This is just the first step. We have great hopes for the next phase of the XPRIZE Carbon Removal competition,” says Rob Anex, a professor of biological systems engineering in CALS who advises the team with Bu Wang, an assistant professor of civil and environmental engineering.

Detail of the packing materials used in a direct air capture unit being developed by a UW–Madison team. The system aims to remove carbon dioxide from the air to mitigate the impacts of climate change.

The team is developing a two-part system that consists of a direct air capture (DAC) unit that traps carbon dioxide from the air plus a carbonization component that converts the captured CO2 into limestone particles. It’s an idea Anex and Wang have long discussed.

“Bu and I had been working on the basic concept for a while, and then XPRIZE for Carbon Removal came around, which is really about taking an idea and being able to turn it into an engineering system that works and scale that up,” says Anex. “Then we talked to some of our students, and they decided that they should come up with a team.”

Team member Seunghyeon Jung PhD’21, recently a CALS graduate student in biological systems engineering, has been focusing on building the team’s lab-scale DAC unit, which relies on specialized materials and a simple chemical reaction to capture CO2 from the atmosphere.

“We flow a hydroxide solution over the packing material while blowing air over the surface,” says Jung, now a research associate in the UW College of Engineering. “The chemical reaction on the surface captures carbon in the form of carbonate ions.”

From there, the carbonate solution goes into the carbonization component, where it is combined with ash or slag, byproducts of industrial furnaces like those in coal-fired power plants or steel mills. What comes out is a carbonated powder that includes fine limestone and activated silica particles, which can be used in construction in place of cement. A hydroxide byproduct of the limestone-forming step is recycled back into the DAC unit to capture more carbon dioxide.

“In essence, we’re converting carbon dioxide from the air into carbonate minerals that can be upcycled into construction materials, all under ambient conditions,” says Wang, who holds a patent related to the carbonization part of the system.

The team includes six graduate students and two undergraduates from across the UW campus. As it moves forward in the XPRIZE contest, which runs through Earth Day 2025, members will further refine the system, figure out how to scale it up, and develop a plan for its implementation. For those involved, notes Anex, there’s value beyond competing and succeeding in the XPRIZE competition.

“Students learn a lot about building things, running experiments, working in teams, and making presentations. And they gain a lot of experience and maturity,” he says. “Some of these students might make a career out of this. It’s an important problem, and I’d love to see a bunch of them work on solving some of the big environmental problems that face the world.”

For sophomore Evan Schmid, being a part of the project has a dual appeal. He feels good about working toward a solution for one of the world’s most difficult challenges; and while he’s at it, he accumulates practical experience and skills.

“Whenever you’re in a hands-on engineering environment, you get to learn about the process so much — just seeing it play out in front of you,” says Schmid, a biological systems engineering major. “There are things about engineering that you can’t learn from a book or that sometimes you just have to do. You see how things happen in the real world.”

Editor’s note: After press time, it was announced that the UW team was selected in April 2022 as one of the top 60 groups in the global XPRIZE Carbon Removal competition.

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