Seaweed harvest

Is seaweed the future of fuel?

Image credit: AtSeaNova

A growing band of scientists and engineers wants to feed and fuel the world with seaweed.

Off the most westerly tip of Norway, sheltered among rocky outcrops, lies a small farm that is growing quite a different kind of crop. Home to an underwater forest of massive, brown leathery seaweed, the floating plantation – set up by Belgium-based AtSeaNova – provides a brief glimpse into a burgeoning industry that could solve many of the world’s big problems.

“From our point of view, our future lies in seaweed,” says AtSeaNova business manager Adrián Martínez. “Population growth, dwindling energy sources and the need to get more protein and nutrients from food – be it plants or animals – per square metre, means now is the moment to look at seaweed more seriously.”

Without a doubt, the future of this type of aquaculture holds great potential. Already a multi-billion-dollar industry, seaweed, also known as macroalgae, is used in many food, fertiliser, animal feed and cosmetic products. For example, the slimy alginate extracted from the cell walls of seaweed is widely used as an emulsifier or gelling agent in ice-creams and salad dressings and also in the production of paper, textiles and pharmaceuticals.

Yet despite its mass appeal, a mighty 95 per cent of global seaweed production takes place in Asia, with the macroalgae typically grown on twine and ropes in small, labour-intensive farms, in lagoons and sheltered waters. Across Europe, seaweed harvests are dominated by wild seaweed, dredged mechanically, and sometimes unsustainably, from seabeds. But not for much longer.

The last decade has seen a surge in seaweed aquaculture, driven by a rising interest in using the aquatic plant as a biofuel. It’s easy to see why.

Unlike land-based biofuels, such as corn and sugar cane, seaweed does not compete for land and fresh water with other food or non-food crops. What’s more, the US Department of Energy (DoE) has estimated that if enough algae could be grown as a biofuel to replace all petroleum-based fuel in the US, it would require less than 0.5 per cent of the area of that sprawling nation. That’s about half of the land area of Maine and around one-seventh of the area needed to harvest US-grown corn.

At the same time, seaweeds grow very quickly, have a high polysaccharide content – both crucial for biomass used in biofuel production – and could represent a colossal carbon sink, by absorbing carbon dioxide from the sea during photosynthesis.

As Martínez puts it: “Seaweed needs almost nothing – it doesn’t need fresh water, you don’t need to add fertilisers or extra nutrients into the sea; it really is a sustainable resource for bioenergy.”

However, where’s the seaweed stampede? Despite serving food and pharmaceutical sectors, the industry still needs some work if it’s going to make it in bioenergy.

Ocean life is rough, and high capital and production prices mean algae costs more per unit mass than most land-based biofuel sources. Meanwhile, businesses have yet to find a cost-effective way to convert seaweed into a commercial fuel. Yet this is where the growing band of modern seaweed farmers and developers, such as AtSeaNova, are helping.

AtSeaNova’s western Norway farm is just one of many pilot farms springing up across the oceans. For its part, the company has trialled small-scale seaweed farms in Denmark, France, Scotland, Sweden, Morocco, Indonesia, Sri Lanka and more. Here, a vast range of red, green and brown seaweeds are farmed using novel seeding, growing and harvesting equipment designed to ease growth and boost yields.

“Our aim has been to unlock the potential of seaweed,” says Martínez. “We’ve been finding ways to replace today’s manual production and optimise mechanisation and crop quality.”

At the heart of AtSeaNova’s technologies lie 2D textile cultivation substrates, ‘AlgaeTex’, a range of twines, ropes, sheets, ribbons and nets based on synthetic fibres such as nylon and polyester, as well as bio-fibres. Typically, most seaweeds are seeded on twine, nursed in a hatchery and then attached to thicker rope and deployed at sea. However, AtSeaNova’s substrates bypass the nursery and allow juvenile seaweeds to be directly seeded onto the textile structure using a binder, before being sent out to sea to grow.

According to Martínez, the choice of substrate depends on seaweed type and growing conditions, with a view to nurturing the healthiest seaweed at the highest possible yield. “We developed sheets that can occupy more surface area in the sea than, say, ropes,” he says. “Our tests show these yield up to eight times more seaweed than your traditional long [rope] line.

“However, we also discovered that in some regions where we installed our sheet substrate it collected sediment, which damaged the seaweed, and this is why we developed nets,” he adds.

Clearly, direct seeding and greater yields are a win-win for seaweed production, but there’s much more to growing this crop than a substrate. As Martínez highlights, AtSeaNova’s substrates are critical, but are just one part of its ‘turnkey’ seaweed farms.

Seaweed harvest

Image credit: AtSeaNova

These installations are based on traditional fish farms, but are easier to assemble and quick to deploy, comprising robust moorings and flexible polyethylene supports that can withstand rough seas. One significant structure off the coast of Asturias, Spain, sitting in depths of around 15m, comprises six rows of seaweed, spans 154m by 50m and can withstand recurrent waves of up to 8m. According to Martínez, more farms will follow soon – and this is just the beginning of what lies in store for seaweed farming.

Marine biologist Neil Sims is working with tropical macroalgae just off the west coast of Hawaii’s Big Island. Heading up aquaculture research and development business Ocean Era, he is adamant the tropics are the place to cultivate seaweed.

“Away from the tropics, if you’re culturing something that photosynthesises in the ocean, then the challenge is that you have very limited light for about half of the year,” he says. “This makes your algae production highly seasonal, so for food, feed or energy, the entire processing cycle becomes very annualised and less efficient. But here in the tropics you can have continuous production.”

With this in mind, Ocean Era is developing the ‘Blue Fields’ offshore macroalgae farm, with support from the DoE’s Advanced Research Projects Agency (ARPA-E) Mariner programme (Macroalgae Research Inspiring Novel Energy Resources). Here, Sims and colleagues intend to efficiently grow native seaweeds, known as limu, along a long-line that is anchored to the seabed via a single-point, swivel mooring, as used in the oil and gas shipping industry.

As Sims points out, the long-line macroalgae array with its single-point mooring has two key benefits. First, the mooring only has a single point of failure, the swivel. And second, thanks to the swivel point, the macroalgae farm will always align itself with the downcurrent flow of nutrients, ensuring these are more evenly dispersed across the seaweed.

“If you use a typical grid array that is fixed in its location, then the current will come and wash around that grid but often only in certain directions, making nutrient distribution really inefficient,” says Sims. “But [with the swivel mooring], we hope to get a better distribution of nutrients.”

Yet the delivery of nutrients hardly ends here. Just as still waters run deep, so do the nutrients in the tropical Pacific Ocean. As Sims puts it: “We can have all-year-round production, but the challenge in the tropics is that it’s a desert out there. Tropical surface waters are nutrient-poor, which is why you don’t get kelp growing in the tropics.”

Finding a way to get the all-important deep-sea nitrogen and phosphorous up to the clear blue, shallow waters where the macroalgae will grow isn’t easy, or necessarily cheap, but Sims and colleagues have devised what they believe is a cost-​effective method.

Nutrient upwelling occurs naturally when winds push surface water away from the shore and deeper water rises to fill the gap. Working with Hawaii-based firm Makai Ocean Engineering, Sims and colleagues are set to build a small, prototype wave-driven upwelling system, in which wave energy drives a pump that pulls up the deeper seawater, and nutrients, to the offshore seaweed array.

The team hopes to test the upwelling system with a 10m by 40m offshore seaweed array, some 120m deep, in the coming months. As Sims highlights: “We’ll be getting the macroalgae sporelings onto lines and we’ll then deploy an offshore array and run some trials, monitor nutrient levels and algae growth rates.

“We’ve got the permits to move forward and will soon be increasing our understanding of exactly how macroalgae grows,” he adds.

At the same time, Ocean Era is pursuing that all-important problem of how to cost-​effectively convert seaweed into a commercial biofuel. Sims explains: “There’s a whole range of complex carbohydrates in seaweed, which are very difficult to break up – this is why it piles up on beaches and takes months and months to rot.”

Given this, the marine biologist is collaborating with other Hawaii- and US mainland-based researchers on adapting the microbiome of a seaweed-eating fish, Kyphosus, to improve the biodigestion of seaweeds. “We’re going to try to work out a more efficient means of macroalgae biodigestion,” he says. “It’s astonishing to me that people haven’t looked at this biological model before.”

California-based Marine BioEnergy is also getting ready to launch a macroalgae array in the open ocean, on the far side of Catalina Island, south-west of Los Angeles. However, instead of bringing the nutrients to the seaweed, this company is taking the seaweed – in this case, giant kelp – to the nutrients.

Marine BioEnergy co-founder and ex-Nasa Jet Propulsion Lab engineer Brian Wilcox decided that upwelling was incredibly capital-intensive, so instead devised a system to tow farms of giant kelp down to deeper waters using unmanned submarine drones. Here, two leading underwater drones will tow rows of Macrocystis pyrifera, fixed to an array of hose lines, downwards at around 0.25m/s. Meanwhile, two drones fixed to the back end of the array will maintain its tension.

Programmable floats, also fixed to the array, are used to maintain overall depth. These can be flooded with water via the hoses to alter the buoyancy of the entire set-up. In this way, the entire farm can be submerged and surfaced steadily and simultaneously, rather than being left to waft through the water depths like a piece of fabric.

“We would surface the farms during the day so the kelp can absorb sunlight and then take the farms down below the thermocline – some 200m deep – at night to absorb the nutrients,” says Marine BioEnergy president and co-founder Cindy Wilcox. “We keep repeating this and harvest the kelp four times a year... we can also use the drones to submerge farms to avoid ships and storms.”

Like Ocean Era, Marine BioEnergy received funds from ARPA-E’s Mariner programme for proof-of-concept experiments on test-rigs, which have shown that giant kelp not only survives repeated depth cycling, but thrives. Some 40 kelps were repeatedly plunged to 80m depths at night-time and resurfaced during the day. While four kelps were initially lost in the first week during a storm, after nine weeks, the remaining 36 showed rapid growth, yielding four times more biomass than control kelp grown in a natural kelp bed.

Marine BioEnergy intends to repeat this experiment soon and will then seek further government and investment funds to scale operations. “We shouldn’t be replacing petroleum with products grown on land such as corn and sugar cane that compete for agricultural land and fresh water,” says Wilcox. “We’ve got all of this open ocean available which is a massive space, and should use it.”

What about the impact of such endeavours on the marine environment? Surely bringing farms of seaweed into the sea holds unknown ecological consequences, including disrupting food chains?

Wilcox says that as of yet she and colleagues don’t know of any problems, and highlights that seaweed farms will be absorbing huge amounts of carbon dioxide from the ocean. She also points out that the seaweed could be sequestered to the ocean subduction zones to mitigate climate change and ocean acidification.

Similarly, Sims says: “There is growing awareness of the massive catastrophic challenge of ocean acidification, and macroalgae should be used a tool to counter this. What better way to take carbon dioxide out of the water biologically?”

He also points out how offshore aquaculture tends to act as a ‘fish-​aggregating’ device, and says the farms are usually “spectacularly successful” with local fishermen.

At the same time as AtSeaNova, Ocean Era and Marine BioEnergy, and many more small-scale seaweed farm developments start to scale activities, other key players are working out how best to monitor and maintain these growing areas of cultivation. Erin Fischell, an assistant scientist at the Woods Hole Oceanographic Institution (WHOI), points out: “Macroalgae needs to scale up to the point where it’s economically feasible for biofuel, and to do this we are going to have thousands of hectares of farms.”

As this happens, cultivators will need more and more data on, say, water-nutrient content and seaweed growth rates, which will raise the costs of today’s labour-intensive farms. Given this, Fischell and colleagues have been developing autonomous underwater observation systems for monitoring large-scale seaweed farms with minimal human intervention.

“The ocean gets pretty rough out there and surface vehicles aren’t going to cut it, but underwater vehicles are somewhat isolated from this,” says Fischell.

The WHOI systems are implemented across two REMUS 100s (Remote Environmental Monitoring UnitS), dubbed Snoopy and Darter. These would typically be used in 100m water depths, to monitor fisheries, pipeline and the like. To cater for future seaweed farms, both Snoopy and Darter have had facelifts.

“We’re using broadband split-beam echo-sounders to provide scattering information, which will tell us where the lines and seaweed are, as well as any fish that are hanging around,” says Fischell. “We’ve also added a suite of environmental sensors, including dissolved oxygen, nitrate and salinity sensors, and what we call KelpCam, which is our 360-degree camera.

“We are operating in murky and turbid New England waters, so acoustics is our go-to quantitative measurement,” she adds. “Our general approach has been to throw everything and the kitchen sink at this, as we don’t yet know what information is most valuable to the farmers.”

Snoopy and Darter typically run for around eight hours and, so far, have been collecting vast swathes of data on Saccharina sugar kelp farms in Maine, New England. To deal with the data deluge, Fischell and colleagues have developed data management, feature extraction and processing chain tools, some of which use machine learning, to process data sets and generate maps that will be useful to farmers.

The WHOI researchers are not alone in their preparations for large-scale seaweed farming. In Japan, the Ariake Sea Fisheries Cooperative has joined forces with NTT Docomo and other Japan-based organisations to monitor the sprawling edible Nori seaweed farms, just off the Japanese island of Kyushu. In a similar vein to Fischell and colleagues, they are developing a system of buoys and, in this case, air drones to collect data that could boost yields, predict disease and reduce manual labour.

When might we see the high-tech seaweed farm in action? The WHOI researchers intend to continue with their test runs over the coming months, but as Fischell highlights, scale must come before full implementation.

“The reality is that right now it’s at least five years until any kelp farm is going to want an autonomous underwater vehicle,” she says. “But then you don’t build the space shuttle when you first put together a rocket - this is a journey and most engineering happens this way.”

Sign up to the E&T News e-mail to get great stories like this delivered to your inbox every day.

Recent articles