For the first time, Halifax-based Planetary Technologies can now cite published results from a field trial of its technology, released in the scientific journal Nature.

The article, titled Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean, includes results from a small-scale trial conducted in Hayle, on Britain’s south coast. Its findings offer a rare window into the research and development work that underpins deeptech startups.

Founded in Ottawa in 2019, Planetary is developing a process to reduce ocean acidification by releasing magnesium hydroxide, which is readily available as a byproduct of the mining industry, into the water. The ocean is the world’s largest carbon sink, absorbing about 26 percent of the atmospheric carbon dioxide humans emit in the form of inorganic carbon. As the water absorbs more carbon, it becomes increasingly acidic, which reduces its capacity to absorb additional CO2 and can be damaging to the marine environment.

The U.K. testing was conducted in 2022 with partners that included the internationally noted Plymouth Marine Laboratories, engineering consultancy Royal HaskoningDHV and Dutch applied research institute Deltares, among others. The collaboration came about after Planetary received a grant in 2021 from the UK Department of Business, Energy, and Industrial Strategy’s Greenhouse Gas Removal competition. Planetary used the money for a feasibility study, which led to the Nature research.

The company and its partners added small amounts of magnesium hydroxide to the wastewater outflow from one of Hayle’s treatment facilities, creating a chemical reaction that reduced the amount of dissolved carbon present in the wastewater and decreased its acidity. Not only did this cause the wastewater to emit less atmospheric carbon from the organic material it contained, but the article’s 10 co-authors expect it will ultimately lead to more carbon being sequestered from the atmosphere.

“In wastewater, a 10 percent increase of average alkalinity led to a 74 percent reduction in aqueous CO2 and pH increase of 0.4 units to 7.78,” say the researchers. “Numerical models have shown that OAE (ocean alkalinity enhancement) can effectively achieve CDR (carbon dioxide removal) and reverse ocean acidification … but their predictions remain untested by field data.

“We show that MH addition leads to a reduction in aqueous CO2 concentration in the final effluent discharged into the coastal ocean.”

In a statement, Planetary added that the effects on the ocean water were limited to the area immediately surrounding the wastewater discharge and barely detectable within about five metres, meaning the surrounding marine environment was not impacted.

“The alkalinization signal was limited to within a few metres of the ocean discharge … and was consistent with rapid dilution of the alkali-treated wastewater,” say the report's authors.

“While this proof of concept field trial did not achieve CDR (atmospheric carbon dioxide removal) due to its small scale, it demonstrated the potential of magnesium hydroxide addition to wastewater as a CDR solution.”

Planetary has built on the U.K. project via a more extensive collaboration with researchers from Dalhousie University, which began in Halifax Harbour last summer and is continuing this year. The partnership came about because Dalhousie scientists had already been independently studying the same possible solution to ocean acidification.

Last year’s trial was relatively small in scope, lasting from the end of August until November. This year’s will last longer, from mid-July until December.