Amphidinium carterae growth in hydroponic wastewater. A sustainable approach to a microalgae-based process promoting a circular bioeconomy

Hydroponic cultivation is being increasingly used worldwide for horticultural production. However, this technique consumes large quantities of freshwater and produces significant amounts of wastewater. Effluent wastewater from hydroponic cultures may contain high nitrogen (N) and phosphorus (P) concentrations, thus contributing to soil, surface, and subsurface water pollution if directly discharged into the environment; it also potentially leads to ecosystem degradation. In the present work, a synthetic hydroponic effluent wastewater was formulated to evaluate the potential of a marine microalga to remove the main nutrients (N and P) and to test its suitability for sustainable, large-scale cultivation. The marine dinoflagellate microalga Amphidinium carterae successfully removed 100 % of the N and P from the hydroponic wastewater. The formulation yielded comparable biomass yields (0.5 g L^-1) to those of the same culture grown in a control medium but considerably increased the production of carotenoids (40 %), polyunsaturated fatty acids (17 %), and, significantly, amphidinols (56 %). Hence, the use of A. carterae to treat and valorise hydroponic effluents shows significant promise, supporting further investigation into utilizing hydroponic wastewater from different origins to cultivate marine microalgae that can then be used to produce agricultural bio-based fungicides and other bioproducts in line with the principles of the circular bioeconomy.