Red algae grown in wastewater from fish-farming facilities could become sustainable salmon feed

Dulse, or Palmaria palmata in Latin, is a red algae.

Researchers have found that it can be cultivated in discharge water from salmon farming. The results show that for every kilogram of fish feed used in RAS salmon farming, 257 grams of dulse can be grown.

The Norwegian land-based salmon industry uses around 100,000 tonnes of feed annually. The nutrients in discharge water could therefore cover the needs of a substantial Norwegian seaweed industry.

"Could be a win-win"

“I think this could be a win-win for salmon producers, new businesses, and the environment,” says researcher Philip James.

James and his colleagues have cultivated this algae in discharge water from land-based salmon production using so-called Recirculating Aquaculture Systems (RAS).

These are closed farming systems that recycle water.

They have investigated which environmental conditions are necessary to produce dulse with good growth rates and a strong red colour.

This is what the researchers found

In the trial, discharge water from SalMar’s land-based facility was used to grow dulse. The results show that:

• Dulse grew best in water consisting of 50 per cent discharge water from this RAS facility. This is compared to seawater, 25 per cent, and 100 per cent discharge water from RAS.
• Results show that a dilution of 50 per cent provided the best removal of ammonia and nitrate for this facility. For the removal of phosphate, however, somewhere between 25 and 50 per cent RAS water was most efficient.
• Dulse grew just as well in water with a salt content ranging from brackish water to seawater, equivalent to 10 to 32 grams of salt per kilogram of seawater respectively.

Read more about the research project here.

Great potential for food production

“This underlines the potential for both macroalgae cultivation and utilising RAS nutrients in discharge water as a valuable resource,” James says.

He notes that challenges still remain.

In future projects, the researchers will test dulse grown in RAS discharge water to see if there are nutritional benefits, as well as any potential harmful compounds.

This content is paid for and presented by Nofima The Norwegian Institute of Food, Fisheries and Aquaculture Research

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