The processing of foods typically generates a lot of wastewater, which has to be cleaned up before being released back into local waterways. According to new research, however, that water could first be put to use as a very effective fertilizer for farmed seaweed.
In a study conducted by scientists from Sweden's University of Gothenburg and Chalmers University of Technology, "process water" was collected from four sources: a salmon farm, a factory that processed herring, another one that processed shellfish, and – as a vegan option – a manufacturer of oat milk.
That nitrogen- and phosphorus-rich water was subsequently added to the water used to grow four different varieties of sea lettuce, in a land-based seaweed farm.
After just eight days, it was found that all types of process water drastically boosted the growth rate and protein content of all varieties of sea lettuce – on average, the seaweed grew over 60 percent faster, and its protein content quadrupled. Importantly, use of the process water didn't affect the taste of the plants.
And while sea lettuce is eaten as a food in its own right, its boosted protein content could also allow it to serve as an added source of protein in other foods, much like soybeans are now. According to the scientists, the protein content of the boosted sea lettuce is over 30 percent, as compared to about 40 percent in soybeans.
It is hoped that once further research has been conducted, a win-win scenario could result. On the one hand, seaweed farms would be able to produce much more of a higher-value product. On the other, food processing companies could actually sell their process water to those farms, instead of having to clean it. It's even possible that in a circular arrangement, farmed fish could be raised on feed made from algae that was grown using their farms' own wastewater as fertilizer.
"We think that you could have land-based cultivations of algae, such as sea lettuce, near a herring factory, for example," said lead scientist Kristoffer Stedt, a doctoral student in U Gothenburg's Department of Marine Sciences. "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."
A paper on the study was recently published in the journal Algal Research.
Source: University of Gothenburg
