Seaweed Cultivation Enhanced by Residual Water from Food Industry

Food processing water is an excellent fertilizer for land-based seaweed cultivation. Not only does the seaweed grow faster, but its protein content increases as well. In this way, process water can transition from a cost to a resource in the food industry.

Can macroalgae, such as sea lettuce, become a competitive source of protein in future foods, as soybeans do today? Seaweed has a lower protein content than soybeans by nature, but with fertilizer, that difference is reduced.

According to a scientific paper published by researchers from the University of Gothenburg and Chalmers University of Technology, process water from food production can be used as an excellent fertilizer in seaweed cultivation. With the addition of process water, the seaweed grew more than 60% faster, and the protein content quadrupled.

"Soybeans have a protein content of around 40%. We increased the protein content of the seaweed to more than 30% by using process water "says Kristoffer Stedt, a doctoral student at the University of Gothenburg's Department of Marine Sciences.

We already know that algae grow better near fish farms in the sea because of nutrients in fish faeces that spread in the water. Process water from food industries is frequently high in nitrogen and phosphorus.

Different Food Manufacturers

The researchers tested four different types of seaweed and added process water from a variety of food producers, including the herring industry, salmon farming, shellfish processors, and an oat milk manufacturer. The seaweed cultivation received a certain amount of process water with controlled nitrogen content. The researchers analyzed the results after eight days.

"To achieve completely vegan cultivation, we included oat milk. And it turned out that all of the different types of process water worked well as seaweed fertilizer "Stedt explains. Food production necessitates large amounts of water, and managing the process of water is currently an expense for producers. This water, however, has the potential to be a valuable resource.

"We believe that land-based cultivations of algae, such as sea lettuce, could be established near a herring factory, for example. The cultivation of seaweed can remove a large portion of the nutrients from the process water. This brings us closer to a sustainable approach, and the companies now have a stronger footing "Stedt explains.

No off-taste for Seaweed

The researchers were concerned that the process water would contaminate the seaweed. Not everyone will enjoy herring-flavored sea lettuce. However, test panels found no impact on the taste of the seaweed from the process water.

Kristoffer Stedt and his colleagues plan to scale up their seaweed cultivation experiments in the future. They plan to use process water from the herring industry, which has yielded promising results and will concentrate on the species Ulva fenestrata (sea lettuce).

"As a first step, we need to conduct tests in larger volumes in a controlled environment." However, we believe that this could be a new source of protein in the future. It could also be a completely circular system if we used cultivated seaweed as feed for land-based salmon culture and used the process water to fertilize the seaweed cultivation," Stedt says.

Need for New Protein Sources

By 2050, there will be an estimated 10 billion people on the planet, and there will be a high demand for sustainably produced food protein. Seaweed production tripled between 2000 and 2018, reaching 32 million tonnes. Almost all of it is made in the Far East.

Researchers from the University of Gothenburg and Chalmers University of Technology are collaborating on processes that can generate a new Swedish marine protein source in a resource-efficient manner through both seaweed cultivation and processing in the CirkAlg research project.

"In addition to increasing the protein content of the seaweed with process water, we are investigating several methods for extracting the proteins from the algae for use in other foods, similar to how protein is extracted from soybeans today. However, this presents a problem because the protein in seaweed is more tightly bound than in soybeans" according to Ingrid Undeland, a food science professor at Chalmers' Department of Biology and Biological Engineering. She is also the CirkAlg coordinator.

(Source: University of Gothenburg)