A ‘sea tractor’ harvests and replants carbon-capturing seaweed at this floating farm

posgter-sea6-energy A ‘sea tractor’ harvests and replants carbon-capturing seaweed at this floating farm. (Photo by Sea6 Energy)

Source: Fast Company

Date: 12 July 2021
  • Seaweed farming could be a potent weapon in the fight against climate change. But can it scale?

In a series of floating seaweed farms off the coast of Bali, Indonesia, a catamaran travels back and forth through lines of dangling red algae. Custom technology on board automatically harvests and replants the seaweed, which quickly grows several feet long. The system is designed to help the tiny seaweed industry scale up—and to capture some of seaweed's potential to help fight climate change.

"Agriculture on the sea is in its infancy," says Shrikumar Suryanarayan, cofounder and managing director of Sea6 Energy, the India-based company that designed the "Seacombine," the tractor-like machine now in use at its Indonesian seaweed farm. 

The company just announced a new $9 million funding round, led by Aqua-Spark, an investment firm focused on sustainable aquaculture. There's growing interest in seaweed farming now in part because of seaweed's ability to absorb carbon: Macroalgae like seaweed can grow as quickly as two feet a day, sucking up CO2 much faster than trees (and unlike forests, seaweed doesn't face risks from drought or fire). 

While some projects aim to permanently sequester that carbon by sinking seaweed to the ocean floor, the algae can also be used to make products, from fish feed to human food. Grown at a large scale, seaweed could replace some of the crude oil used to make jet fuel or plastic. But it's been so expensive to grow that it can't compete with fossil fuels.

Floating seaweed farms off the coast of Bali, Indonesia. (Photo: Sea6 Energy)

Right now, some seaweed is cultivated for use in additives like carrageenan, an ingredient used as a stabilizer in ice cream, toothpaste, and other products. But the process of farming is labor-intensive. "It's very manual, with a lot of labor involved, and the areas in which [seaweed] can be grown are limited to shallow and calm waters where people can walk out," says Suryanarayan. Though methods vary depending on the type of seaweed (and some seaweed is gathered from the wild), farmers typically have to attach pieces of seaweed to rope lines or nets by hand, wait for them to grow, and then manually harvest and "re-seed" the lines.

Seaweed farming avoids some of the costs of land-based agriculture—growers don't need to pay for irrigation or use fertilizer or other soil amendments. The main cost is labor. And while the manual process provides more jobs, it means that the industry can't easily grow. There's also only a limited area, very close to coastlines, where it's possible to operate.

Roughly a decade ago, while teaching at a university in India, Suryanarayan began thinking about seaweed as he considered the potential of biofuels. India is one of the world's largest consumers of crude oil, almost all of which is imported. Biofuels made from plants could be a replacement, but to completely replace oil, the plants would have to be grown on a massive scale—around a billion tons of biomass a year. "A billion tons of biomass is the entire agricultural output of India," he says. There was no feasible way to produce it without disrupting the food supply. Seaweed, grown in the ocean, wouldn't have the same problem. It just needed to be cheaper to produce.

"We quickly realized that there were two things that we need to meet if this was ever going to be viable," he says. "One is that it had to be grown at scale. And it had to be extremely cheap and cost effective."

Seaweed (Photo: Sea6 Energy)

The company is still working on reducing the cost of its system, and hasn't started trying to manufacture biofuel. But it's already selling another seaweed-based product called a biostimulant that farmers can add to soil to help plants grow faster; in tests on cornfields in Iowa, farmers saw yields grow by 10%. For farmers, it's a way to earn more. But the product also has a climate benefit, as the plants absorb more CO2 without any extra input. Another seaweed-based product can be added to animal feed to improve health, so farmers can use fewer antibiotics. (A different type of seaweed, not currently grown by Sea6, can be added to cattle feed to reduce methane in cow burps, another driver of climate change.)

Within three or four years, the company aims to expand and lower the cost of production enough that it's feasible to make bioplastics from seaweed. Eventually, Suryanarayan says they also hopes to be able to produce biofuel that could be used in airplanes or cargo ships, both of which can't easily run on electricity. Biofuels could potentially be produced from seaweed grown locally in Pacific island nations, so cargo ships crossing the Pacific could stop to refuel. And India could potentially wean itself off crude oil. "I think this is definitely within sight," says Suryanarayan. "We have the technology, we have the ability. We need the capital."

The new round of funding is a start. Seaweed "is a potential incredible solution," says Amy Novogratz, founder and managing partner at Aqua-Spark. "We just need to put more resources behind it and learn more about producing that the amounts we need in a way that works."

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