Agricultural and food processing operations typically generate a large amount of wastewater. It has a significant potential for soil, air and water contamination due to its high chemical oxygen demand (COD) and large volume. Sewage must be cleaned before it is discharged into local waterways.
New research has shown that process water from food production can serve as an excellent fertilizer in algae cultivation.
In their study, researchers from the University of Gothenburg and Chalmers University of Technology collected process water from several different food producers, the herring industry, salmon farming, seafood processors and an oat milk manufacturer. Next, a certain amount of controlled nitrogen and phosphorus process water was added to the water used to grow four different varieties of sea lettuce in an onshore seaweed farm.
After eight days, the researchers analyzed the results and found that all types of treatment water significantly increased the growth and protein content of all varieties of sea lettuce. Algae grew over 60% faster and protein content quadrupled with the addition of process water. Additionally, the test panels noticed no impact on the flavor of the algae.
The researchers also think it could be an alternative source of protein in future foods. “The protein content of soybeans is around 40%. By using process water, we have increased the protein content of the algae to more than 30%,” says Kristoffer Stedt, PhD student at the Department of Marine Science at the University of Gothenburg.
Going forward, the team will focus on expanding algae cultivation experiments. They will use process water from the herring industry, which has shown very promising results, and will focus on Ulva fenestrata (sea lettuce). It could also be a completely circular system if we used farmed algae as feed for farmed salmon on land and used the process water to fertilize the algae culture.
“We think you could have algae cultures on land, like sea lettuce, near a herring plant, for example. The algae culture can clean a lot of the nutrients from the process water. This brings us closer to a sustainable approach,” says Stedt.