Agricultural and food processing operations typically generate a lot of wastewater. It has significant potential to pollute land, air and water due to its high chemical oxygen demand (COD) and 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 – from the herring industry, salmon farming, shellfish processors and an oat milk manufacturer. A certain amount of process water with controlled nitrogen and phosphorus content was then added to the water used to grow four different varieties of sea lettuce at an onshore seaweed farm.
After eight days, 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 more than 60% faster and the protein content quadrupled with the addition of process water. In addition, the test panels did not note any impact on the taste of the algae from the process water.
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 over 30%”, says Kristoffer Stedt, a PhD student in the Department of Marine Science at the University of Gothenburg.
Going forward, the team will focus on scaling up 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 cultivated algae as feed for salmon farming on land and used the process water to fertilize the algae culture.
“We think you could have land-based algae crops, like sea lettuce, near a herring plant, for example. Algae cultivation can clean much of the nutrients from the process water. It brings us closer to a sustainable approach, and companies have another leg to stand on,” said Stedt.