A new, promising way to capture carbon dioxide and combat climate change involves combining two natural resources already available all over the world: rivers and rocks.
That’s the focus of a groundbreaking project by researchers at Dalhousie University, and supported by Scotiabank, which involves adding powdered limestone rock to rivers to boost their natural ability to capture carbon dioxide (CO2) and carry it to oceans. The oceans then act as carbon sinks, absorbing the greenhouse gas and storing it away for hundreds of years.
Dalhousie Associate Professor Shannon Sterling with CarbonRun, a Halifax-based company focused on river restoration through deacidification, have launched the first full-scale pilot in the world of this carbon dioxide removal technique in Pictou, Nova Scotia.
“Rivers are like the blood vessels of the landscape,” she said. “While they drain watersheds they receive carbon that's being delivered to the river from forests and different land uses; that carbon is carried by the rivers to the ocean for long-term storage.” Pollution and human impacts interrupt that natural process, she added.
Dalhousie Associate Professor Shannon Sterling
The addition of limestone rock to rivers was originally developed as a way to remediate the effects of acid rain, which forms when pollutants mix with water and air and can damage the natural ecosystem. The limestone increases the alkalinity of the water, helping to neutralize acidity from acid rain — which is still an issue in some parts of Nova Scotia — and restoring the ability of the river to capture carbon dioxide and lock it into bicarbonate. The restoration process is also known as river liming.
Scotiabank’s Climate Action Research Fund recipient in 2023
The Dalhousie project — in partnership with Pictou Landing First Nations, the Government of Nova Scotia, and startup CarbonRun — uses sensors along the river to measure the impact of the added limestone rock and gauge the carbon levels flowing towards the ocean.
“What's cool about rivers is you can see the carbon dioxide removal in real time,” said Sterling, who is also Founder of CarbonRun. “The reactions happen within minutes, and you can observe it directly.”
In 2023, Dalhousie University was one of 10 recipients of Scotiabank’s Climate Action Research Fund, a 10-year, $10-million initiative launched in 2021 that provides grants to organizations conducting research and exploring climate-related initiatives. A call for the submissions for the next cohort of recipients opened up this month.
Scotiabank’s grant to Dalhousie is being used to develop a protocol for monitoring, reporting and verifying the efficacy of the process, called river alkalinity enhancement. That includes the purchase of equipment, sensors, and collecting data over a two-year period to validate the technique.
“Exploring innovative solutions like these could be critical for success in tackling climate change,” said Kim Brand, Vice President, Global Sustainable Business at Scotiabank. “It’s exciting to see such groundbreaking research and top talent coming out of Canada, and hopefully paving the way for made-in-Canada approaches to carbon capture.”
The silo being installed at the West River site.
Grand opening of CarbonRun in 2024.
Grand opening of CarbonRun in 2024.
CarbonRun founders (left to right) Luke Connell, Dr. Shannon Sterling and Dr. Eddie Halfyard.
The silo at the West River site.
A technician collecting data and samples from the river.
River alkalinity enhancement involves adding powdered limestone rock to the river.
Sensors measure carbon levels, pH
CarbonRun’s team first began collecting data as part of the project in West River, Pictou in July 2023. In the spring of 2024, CarbonRun completed the construction of a silo and doser, which dispenses the ground limestone rock into the river. The project held its grand opening in October last year.
Sensors take measurements every five minutes at various points and the scientists can gauge the change in pH levels and carbon concentration at the river mouth.
“Instead of trying to measure all the carbon inputs and outputs in the watershed, with rivers, you can integrate all the changes by measuring the carbon flux at a point at the river entry to the ocean,” Sterling said. “So we can measure the change in the amount of carbon being delivered to the ocean each hour directly thanks to the advances we made with Scotiabank.”
Decades of research in Norway and Sweden show that river alkalinity enhancement has no negative impact on animal and plant life in already affected rivers. However, Sterling’s team is also monitoring data closely to mitigate any potential risks or harm to the ecosystem. That includes ensuring that the amounts of limestone powder added are within certain limits, and fully dissolved, she said.
“We want to be working with rivers impacted by pollution and focusing on those that need restoration and not doing any environmental harm,” Sterling said. “This summer, we'll be doing some work testing different types of rivers to determine carbon capture efficiency, the environmental co-benefits and making sure the project is safe. And then, communities can decide if that's something they want.”
Cost-effective carbon capture
Sterling is optimistic about the potential to implement river alkalinity enhancement as a carbon dioxide removal (CDR) tool on a wider scale in the future.
What’s more, using rivers to capture carbon has the potential to be more cost-effective than some other CDR methods, she said.
Technicians collecting data and samples from the river.
Cost is a major obstacle for other carbon dioxide removal methods when it comes to deploying them at scale. For example, direct air capture is estimated to cost between US$125 to US$335 per tonne of carbon dioxide, according to the International Energy Agency.
Sterling says river alkalinity enhancement costs about US$460 per tonne of CO2 currently, but their goal is to reduce that to US$139 ($200 CAD) per tonne by 2030, and below US$69 ($100 CAD) per tonne in the long term.
“We're learning a lot that's helping to get that cheaper, quite quickly,” she said.
Landmark deal with Frontier
There seems to be market demand as well. In September, CarbonRun signed a river alkalinity enhancement carbon removal deal with Frontier, a U.S.-based advance market commitment fund that aims to accelerate the development of carbon removal technologies by guaranteeing future demand for them.
As part of this landmark agreement — the first carbon removal offtake involving river liming — Frontier’s buyers commit to paying US$25.4 million to remove more than 55,000 tonnes of carbon dioxide between 2025 and 2029 at various sites, starting in Nova Scotia. This deal is part of Frontier’s broader goal to buy an initial US$1-billion of permanent carbon removal between 2022 and 2030. Frontier’s buyers, which include U.S. technology and finance giants, commit to buying the carbon removal credits that can be used to offset the organizations’ other emissions.
Sterling said the work funded by Scotiabank’s grant helped researchers to demonstrate the potential of the technology and lead to the offtake agreement with Frontier, she said.
“This proves and builds confidence that this could work and has potential,” Sterling added.
“If we're going to have hope to mitigate climate change, I do believe that this river system is one of the best ways to achieve that.”
