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

Valeria Villanova; Jonathan Armand Charles Roques; Bita Forghani; Kashif Mohd Shaikh; Ingrid Undeland; Cornelia Spetea

doi:10.3389/fpls.2023.1186537

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

Front Plant Sci. 2023 Jun 12:14:1186537. doi: 10.3389/fpls.2023.1186537. eCollection 2023.

Authors

Valeria Villanova^{1

2}, Jonathan Armand Charles Roques^{1

3}, Bita Forghani⁴, Kashif Mohd Shaikh¹, Ingrid Undeland⁴, Cornelia Spetea¹

Affiliations

¹ Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.
² Department of Biological, Chemical and Pharmaceutical Sciences and Technologies (STEBICEF), University of Palermo, Palermo, Italy.
³ SWEMARC, The Swedish Mariculture Research Center, University of Gothenburg, Gothenburg, Sweden.
⁴ Department of Life Sciences-Food and Nutrition Science, Chalmers University of Technology, Gothenburg, Sweden.

Abstract

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 Nannochloropis granulata (Ng), Phaeodactylum tricornutum (Pt), and Chlorella sp (Csp) 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: i) a first phase using a medium optimized for best growth (f/2 14x, control); ii) a second "stress" phase using the RAS wastewater to enhance the production of high-value metabolites. Ng and Pt performed best in terms of biomass yield (i.e., 5-6 g of dry weight, DW.L^-1) and efficient cleaning of the RAS wastewater from nitrite, nitrate, and phosphate (i.e., 100% removal). Csp produced about 3 g L^-1 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 (Pt), lutein (Ng and Csp) and β-carotene (Csp). 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.

Keywords: Carotenoids; Chlorella; Nannochloropsis; PUFA; Phaedactylum tricornum; RAS wastewater; proteins; two-phase cultivation.

Grants and funding

This research was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 844909, The Swedish Research Council for Sustainable Development FORMAS (2020-00867 and 2018-01839), Stockholm, Sweden, the Royal Swedish Academy of Agriculture and Forestry (KSLA), Stockholm, Sweden (VAT2020-0007), The Birgit och Birger Wåhlströms Minnesfond för den bohuslänska havs-och insjömiljön, Stockholm, Sweden, STINT, Stockholm, Sweden (mobility grant for internationalization, MG2019-8483), SWEMARC, the Swedish mariculture research center, strategic funding university of Gothenburg, Gothenburg, Sweden, JSPS KAKENHI Grant Numbers JP20KK0244 Tokyo, Japan. KS was a recipient of a postdoctoral fellowship from the Carl Tryggers Foundation CTS20:406.