AUTHOR=Villanova Valeria , Roques Jonathan Armand Charles , Forghani Bita , Shaikh Kashif Mohd , Undeland Ingrid , Spetea Cornelia 

TITLE=Two-phase microalgae cultivation for RAS water remediation and high-value biomass production

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1186537

DOI=10.3389/fpls.2023.1186537

ISSN=1664-462X

ABSTRACT=<p>The overall goal of this study was to provide solutions to innovative microalgae-based technology for wastewater remediation in a cold-water recirculating marine aquaculture system (RAS). This is based on the novel concept of integrated aquaculture systems in which fish nutrient-rich rearing water will be used for microalgae cultivation. The produced biomass can be used as fish feed, while the cleaned water can be reused, to create a highly eco-sustainable circular economy. Here, we tested three microalgae species <italic>Nannochloropis granulata</italic> (<italic>Ng</italic>), <italic>Phaeodactylum tricornutum</italic> (<italic>Pt</italic>), and <italic>Chlorella sp</italic> (<italic>Csp</italic>) for their ability to remove nitrogen and phosphate from the RAS wastewater and simultaneously produce high-value biomass, i.e., containing amino acids (AA), carotenoids, and polyunsaturated fatty acids (PUFAs). A high yield and value of biomass were achieved for all species in a two-phase cultivation strategy: <italic>i)</italic> a first phase using a medium optimized for best growth (f/2 14x, control); <italic>ii)</italic> a second “stress” phase using the RAS wastewater to enhance the production of high-value metabolites. <italic>Ng</italic> and <italic>Pt</italic> performed best in terms of biomass yield (i.e., 5-6 g of dry weight, DW.L<sup>-1</sup>) and efficient cleaning of the RAS wastewater from nitrite, nitrate, and phosphate (i.e., 100% removal). <italic>Csp</italic> produced about 3 g L<sup>-1</sup> of DW and reduced efficiently only nitrate, and phosphate (i.e., about 76% and 100% removal, respectively). The biomass of all strains was rich in protein (30-40 % of DW) containing all the essential AA except Methionine. The biomass of all three species was also rich in PUFAs. Finally, all tested species are excellent sources of antioxidant carotenoids, including fucoxanthin (<italic>Pt</italic>), lutein (<italic>Ng</italic> and <italic>Csp</italic>) and <italic>β</italic>-carotene (<italic>Csp</italic>). All tested species in our novel two-phase cultivation strategy thus showed great potential to treat marine RAS wastewater and provide sustainable alternatives to animal and plant proteins with extra added values.</p>