A certain amount of process water with a controlled content of nitrogen was added to the seaweed cultivation. The result showed that the seaweed grew up to 60% faster, and the protein content quadrupled. Photo: Kristoffer Stedt
A scientific article from researchers at the University of Gothenburg and Chalmers University of Technology shows that process water from food production can serve as an excellent fertilizer in seaweed cultivation. The seaweed grew more than 60% faster, and the protein content quadrupled. In this way, process water can go from being a cost to becoming a resource in the food industry.
“The protein content of soybeans is about 40%. By using process water, we have increased the protein content in the seaweed to more than 30%,” says Kristoffer Stedt, a doctoral student at the Department of Marine Sciences at the University of Gothenburg.
We already know that algae grow better in the vicinity of fish farms in the sea due to nutrients in fish feces that spread in the water. Process water from food industries is often rich in nitrogen and phosphorus in a similar way.
Testing using different food producers
The researchers tested four different types of seaweed and added process water from several different food producers — from the herring industry, salmon farming, shellfish processors, and a manufacturer of oat milk. This water, with a controlled content of nitrogen was added to the seaweed cultivation. After eight days the researchers analyzed the results.
“We included oat milk to achieve cultivation that was completely vegan. And it turned out that all different types worked well as fertilizer for the seaweed,” says Mr. Stedt.
Food production requires large amounts of water and taking care of the process water is currently a cost for producers. This study shows the used water can be turned into a valuable resource. “We think that you could have land-based cultivations of algae, such as sea lettuce, near a herring factory, for example. Seaweed cultivation can cleanse large portions of the nutrients from the process water. That brings us closer to a sustainable approach, and the companies have another leg to stand on,” he says.
No off-taste for the seaweed
The researchers were worried that the seaweed would be tainted by the flavor of the particular water used. Not everyone may appreciate herring-flavored sea lettuce. But test panels did not note any impact on the taste of the seaweed.
In the future, Mr. Stedt and his colleagues will focus on scaling up the experiments with seaweed cultivation. They will use water from the herring industry, which showed very promising results, and focus on the species Ulva fenestrata (sea lettuce).
“We need to conduct tests in larger volumes as a first step in a controlled environment. But we believe that this may be an alternative source of protein in future foods. It could also be a completely circular system if we used cultivated seaweed as feed for salmon culture on land and used the process water to fertilize the seaweed cultivation,” he said.
In the research project, the scientists are collaborating on practices that can generate a new Swedish marine protein source in a resource-efficient manner through the entire system of production, from cultivation to final product.
“In addition to boosting the seaweed’s protein content using process water, we are also looking at several ways to extract the proteins from the algae for use in other foods in the same way as protein is extracted from soybeans today. However, this presents a challenge, because the protein in seaweed is bound more tightly than in the soybeans,” says Ingrid Undeland, a professor of food science at the Department of Biology and Biological Engineering at Chalmers.
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