Food process water may hold key for seaweed aquaculture

Researchers from the University of Gothenburg have found that seaweed grown in process wastewater from the manufacturing and processing of foods can increase the nutritional profile of seaweed. In this way, process water can go from being a cost to becoming a resource in the food industry.

The aquacultural growing of seaweed has been suggested as a useful way of providing a source of protein; with the right growing conditions it can have the same percentage of protein as soy beans and it is easy to grow.

Previously, it has been demonstrated that algae grown near fish farms will have high levels of protein due to the nutrients introduced into the water as a fertiliser through the fishes’ faeces. The researchers thought this may be the case near food processing plants too, where the discarded wastewater is also high in nitrogen and phosphorus as is the case with water near fish farms.

This hypothesis was tested by growing various species of seaweed in processed water from several different kinds of food producers. Water from the herring industry, salmon farming, shellfish processors and oat milk production were used, with the latter being due to it being a vegan product.

The research showed the use of the water sourced from various industries acted as a fertiliser on the seaweed. All but one of the four species of seaweed saw a higher rate of growth from the water and they all had notably higher levels of protein. The various waters had different effects on the plants but protein content was increased by four times in some of the samples.

The scientists will be further studying the effects in the future and want to ensure that the seaweed’s taste has not been negatively impacted, as this may cause an issue with using it in food. Ultimately, though, there is a possibility that seaweed grown using this water could be a healthy, efficient way of obtaining protein.

“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,” said Kristoffer Stedt, a doctoral student at the Department of Marine Sciences at the University of Gothenburg and the study’s lead author.

Research will continue at larger scales in the future to assess the viability of using the food processing water at industrial levels.

“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 fertilise the seaweed cultivation.”

The full paper, published in Algal Research, is available here: https://doi.org/10.1016/j.algal.2022.102647.

Image credit: Kristoffer Stedt, University of Gothenburg