Turning a seaweed crisis into an energy opportunity

In 2019, Legena Henry, SM ’10, and the students in her renewable energy course at the University of the West Indies in Barbados wondered how to help their island stop using fossil fuel by 2030. Their first thought was to emulate Brazil—home to the world’s largest fleet of cars that run on sugar-based ethanol. But the small volume of sugarcane crops in Barbados made that impractical. Even the island’s plentiful distilleries, which once primarily used sugarcane to make rum, now depend on imported molasses.

COURTESY OF LEGENA HENRY

What happened next was pure serendipity. One of Henry’s undergraduates, Brittney McKenzie, commuted to the lab every day past resort beaches covered in brown mounds of invasive sargassum seaweed. “Why don’t we look at sargassum?” she asked Henry. 

After mixing wastewater from the rum distillery with sargassum, they ran some experiments in the lab. “And the thing is, it worked!” says Henry, who has a master’s in mechanical engineering from MIT and a PhD from the University of the West Indies (where she is a lecturer). Microbes in the mix fed on sugar in the wastewater and digested the seaweed—and what Henry thought might turn out to be a “nice paper” has since become what she calls a “game changer.” 

Sargassum, which has been distributed by ocean currents to become the world’s largest macroalgal bloom, fills over 800 dump trucks on a bad day in Barbados. But thanks to this research, instead of being taken to a landfill, the seaweed can now be converted into renewable natural gas to fuel cars. (In addition to the distillery wastewater, manure from local Blackbelly sheep is often in the mix.) 

“All the islands in this region of the Caribbean have a sargassum problem and a rum wastewater problem—and ultimately a climate-change problem,” Henry told Nature. “This solution is a win-win-win.”

Henry is now the CEO of Rum & Sargassum, a startup she cofounded in 2021. In recent test drives—one in Barbados and another in Grenada  as part of the Second European Union–Caribbean Global Conference on Sargassum—the biofuel operated a portable generator, which in turn charged an electric vehicle.

The project requires collaboration among people with a wide spectrum of expertise, and Henry credits MIT with showing her that the best solutions come from a multidisciplinary approach. It also requires getting support for what some may see as a “small nation” solution, Henry explains. But she is very hopeful.

“Sargassum has now become part of the conversation that will turn the climate crisis around,” she says.