Successful growth of coastal marine microalgae in wastewater from a salmon recirculating aquaculture system

As global demand for seafood increases, recirculating aquaculture systems (RAS) have gained prominence for sustainable fish rearing. The sustainability of RAS still requires improvement, particularly managing the fish waste. Here we investigated the growth and nutrient removal capabilities of three microalgal species (Isocrysis galbana, Phaeodactylum tricornutum and Skeletonema marinoi) in aquaculture wastewater (AWW) mixed at different concentrations with cultivation medium. All three microalgae showed growth in different concentrations of the AWW obtained from an Atlantic salmon RAS facility in Agder, Norway. The average growth rates for I. galbana, S. marinoi and P. tricornutum at 75% AWW concentration were 0.31± 0.00 day^-1, 0.34 ± 0.00 day^-1, 0.25 ± 0.02 day^-1, respectively. All three species effectively contributed to nitrate, ammonium and phosphate removal. When cultivated in 75% AWW, the microalgae achieved nearly complete removal of nitrite, nitrate, and phosphate, while approximately 90% of ammonium was also removed. Our results confirm the viability of AWW for microalgal cultivation on a laboratory scale suggesting this presents a sustainable route to further develop a circular bioeconomy in aquaculture.