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Spotted: Rivers naturally deliver carbon from the land to the ocean, helping to keep the planet cool. But today pollution has acidified many rivers, disrupting the natural river-carbon connection. To reverse this effect, startup CarbonRun has developed a technology to trap carbon dioxide and deliver it to the ocean for sequestration.

CarbonRun achieves this by adding powdered limestone to rivers. The alkaline material renders the water less acidic, which in turn increases its ability to absorb more carbon dioxide from the atmosphere. The limestone traps carbon dioxide in the rivers in the form of stable bicarbonate. This is then transported to the ocean, where it can stay locked away for tens of thousands of years.

Sensors placed along the river, and at the river’s mouth, are used to measure the correct amount of limestone to add and whether it’s having the anticipated effect. Continuous monitoring allows the amount of limestone to be fine-tuned to achieve the greatest benefit.

Acidic rivers have, in many places, seen a huge drop in fish, devastating local ecosystems and commercial fisheries. However, another beneficial side effect of CarbonRun’s approach is that the change in pH needed to shift carbon dioxide to stable bicarbonate also renders rivers more hospitable for fish, repairing local riverine ecosystems.

CarbonRun’s first project, in Nova Scotia’s West River, is already underway. The company also recently announced that it expects to raise $25.4 million to support its work and additional projects. This funding was organised through Frontier Climate, which was launched in 2022 by companies including Alphabet, Meta, and Shopify, to fund the development of climate-related technologies and to facilitate carbon-offset sales.

Written By: Lisa Magloff