Valorisation of seawater desalination brine via cultivation of a halotolerant microalga in bubble column photobioreactors

This study investigated the valorisation of seawater desalination brine (61 g L^-¹) by cultivating the halotolerant microalga Prymnesium parvum in 10-L bubble column photobioreactors, previously acclimated to a broad salinity range (5-61 g L^-¹). Under optimized nutrients and irradiance, brine-based cultures achieved biomass yields (1.9 gL^-¹) comparable to seawater controls. Salinity altered biomass composition, increasing saturated and monounsaturated fatty acids (up to 83 % of total fatty acids) and reducing polyunsaturates, suggesting membrane remodelling. Carotenoid content increased by 25 % under salinity-induced stress. Methanolic extracts and solvent fractions showed strong bioactivity. CH₂Cl₂ and BuOH fractions inhibited >85 % of cancer cell growth across lines; several fractions also exhibited antimicrobial and antiphytopathogenic effects. These findings highlight P. parvum's potential for integrated brine management while generating valuable microalgal biomass, reducing freshwater use and supporting circular bioeconomy. However, further research is needed to assess limitations and validate techno-economic feasibility at larger scale.