Can carbon capture solve desalination’s waste problem?

A startup claims it can store carbon dioxide in the toxic brine produced by desalination plants.

As the world grapples with rising water use and climate-fueled drought, countries from the United States to Israel to Australia are building huge desalination plants to bolster their water supplies. These plants can create water for thousands of households by extracting the salt from ocean water, but they have also drawn harsh criticism from many environmental groups: Desalinating water requires a huge amount of energy, and it also produces a toxic brine that many plants discharge right back into the ocean, damaging marine life. Recent desalination plant proposals have drawn furious opposition in Los Angeles and Corpus Christi, Texas.

But a new startup called Capture6 claims it can solve desalination’s controversial brine problem with another controversial climate technology: carbon capture. The company announced new plans this week to build a carbon-capture facility in South Korea that will work in tandem with a nearby desalination plant, sucking carbon dioxide out of the air and storing it in desalination brine, which it will import from the plant. But that’s not all. Capture6 also claims it can wring new fresh water out of the brine, bolstering the company’s sustainability claims — and its potential profit — even further.

If it works, this facility will deliver a triple benefit. It will decrease the concentration of greenhouse gasses in the atmosphere, create a new source of fresh water, and limit the polluting effects of desalination. But that’s still a very big “if.”

So-called “direct-air capture” facilities use a chemical reaction to pull carbon dioxide out of the air and fuse it with another substance, preventing it from leaking into the atmosphere. The greenhouse gas can then be stored in solid compounds like limestone or in chemical solutions — or, previous studies have shown, in salty brine. Capture6’s innovation is to source that brine from wastewater treatment plants and desalination plants, which have every reason to want to dispose of it in a way that does not open them to charges of pollution.

The newly announced venture in South Korea, known as Project Octopus, takes the process one step further. The facility will be located at the Daesan Industrial Complex, an oil and gas industrial park in a region of the country that has suffered from water shortages due to an ongoing drought. The Korean state water utility, K-water, is building a seawater desalination plant at the industrial park to provide water to the oil and gas plants, which use thousands of gallons of water to cool down their machinery as it operates.

The Capture6 facility will use the brine created by K-water’s desalination plant to capture carbon dioxide, and it will also use the modified brine to extract even more fresh water that the oil and gas plants can then use in lieu of pumping from less sustainable sources. Carbon6 also says that the solvent produced by its direct-air capture operations can then be used for additional point-source carbon capture at the nearby oil and gas plants, providing a double emissions benefit before the company buries all the carbon deep underwater. In other words, Capture6 will use the byproduct of water production to create even more water, and it will use the byproduct of capturing carbon to capture more carbon.

“It’s an interesting example of solvent-based direct-air capture, but what is innovative here is the pairing of direct-air capture with the brine from desalination,” said Daniel Pike, the head of the carbon capture team at the Rocky Mountain Institute, a nonpartisan climate think tank. “Essentially, what’s going on is the company is saying, ‘Hey, where do we get the chemicals for our solvents? We’ll get them from desalination plants.’”

(Capture6 received funding from Third Derivative, a carbon capture accelerator launched by Rocky Mountain Institute, but Pike himself doesn’t have a financial relationship with the company.)

The company, which has received early funding from several venture capital funds as well as the states of California and New York, announced its first facility last year in Southern California. That facility, known as Project Monarch, will store carbon dioxide in wastewater from a water treatment plant in the city of Palmdale, then sell fresh water back to the city’s water system. 

“What we are trying to do is really to decarbonize the water sector,” said Leo Park, the vice president for strategic development at Capture6. “So we’re trying to integrate our facilities into the easiest thing, which is wastewater and desalination plants.”

The company’s initial pilot facility in Korea will operate on a small scale. The test project will capture 1,000 tons of carbon per year. That’s equivalent to the annual emissions of around 220 passenger cars, and about as much as is being captured at a much lauded direct-air capture facility that began operations in Tracy, California, last year. The company’s carbon capture process will yield around 14 million gallons of fresh water, enough to supply around 80 homes. 

But when K-water’s desalination plant gets running at full capacity, Capture6 says it will be able to capture almost 500,000 tons of carbon dioxide each year by 2026. That’s many times more storage than other direct-air capture facilities have achieved so far. The large-scale plant will also produce around 5 billion gallons of fresh water each year, half as much as the Daesan desalination plant itself and enough to supply around 30,000 homes.

Pike says that the company’s growth goal is extremely ambitious, and it’s unclear whether the facility will have a net negative impact on emissions, given that desalination and direct air capture both require a lot of energy. In the case of Project Octopus, that energy will initially come from Korea’s power grid, which relies heavily on fossil fuels.

“Even assuming you have the solvent, you have an intense energy need just to power a direct-air capture process, and a big challenge we have in direct-air capture is how to improve energy efficiency,” he said. “Then, what they’re doing is they’re also running a very energy-intensive process for deriving the solvent, moving a lot of water around. It’s a lot of energy, a lot of water. That big picture is the challenge here.”

If Capture6 can prove that its facilities store more carbon than they emit, the company won’t have any trouble monetizing its technology. The oil and gas companies in Daesan will buy its produced water for their cooling needs, and K-water will rely on the company to minimize the environmental harms of desalination, which generated backlash when the plant was first announced.

“There were a lot of local concerns about brine discharge, because [locals] were worried that it was going to impact the marine ecosystem and fishing activities,” said Park. “Our solution can help minimize brine discharge, so there’s an additional environmental benefit we can generate. This is one of the reasons K-water wanted to work with us.”

Even so, the full-size Capture6 facility will only absorb around half of the brine that the K-water desalination plant produces, meaning the utility will still have to release a lot of toxic liquid into the ocean. Park says he hopes the company can eventually scale up far enough to absorb all the plant’s brine, but they’re not there yet.

Unlike many other direct-air capture companies, Capture6 doesn’t need to sell carbon credits to make money. Park hopes to someday sell credits to private companies seeking to offset their emissions, but for the moment Capture6’s main revenue source is the same as any ordinary desalination plant: water. Park says the company could build future facilities at lithium mines, which also produce brine and need water to operate.

But Ekta Patel, a researcher and doctoral student at Duke University who studies the politics of desalination, said the big question about this business model was how much energy it takes for Capture6 to make the new water. 

“My mind jumps immediately to the issue of energy,” she said. “How much more energy does reclaiming the additional water take, is it from renewable or nonrenewable sources, and what does that do to the cost of the water?” She added that if “addressing challenges related to carbon emissions and water” required a jump in energy usage, the solution was just “shifting around resource problems.”

This story was originally published by Grist with the headline Can carbon capture solve desalination’s waste problem? on Jan 17, 2024.