Innovative microalgae-based bioremediation of desalination brine coupled with biomass valorization

Although desalination of seawater is essential for water security in arid regions, the discharge of hypersaline brine remains a major environmental challenge due to its high salinity and elevated ion concentrations. This study investigates the potential of the halotolerant microalga Dunaliella salina for sustainable brine valorization through optimized cultivation and lipid recovery. Colony assays confirmed growth tolerance across 20-110 ppt salinity, with an optimum range of 50-60 ppt, aligning closely with brine salinity (49.9 ppt). Nutrient supplementation experiments identified phosphorus as the most limiting factor. Combined phosphorus and nitrogen enrichment achieved a maximum biomass yield of 1.44 g L -1 and biomass productivity of 0.112 g L -1 d -1 , surpassing the standard f/2 medium by ∼16.7%. Biochemical analysis revealed balanced macromolecular composition, with slightly elevated lipid content (261 mg g -1 dw) under brine conditions, compared to 251.2 mg g -1 dw in f/2 medium. Importantly, fatty acid methyl esters (FAMEs) productivity increased by 29.6% using brine, accompanied by a shift toward higher saturated and monounsaturated fatty acids. Fuel properties of brine-derived biodiesel fully complied with the recommended international standards, with a high cetane number (54.45) and reduced iodine value (106.7 g I 2 per 100 g). These findings confirm that desalination brine, when strategically supplemented with nutrients, provides a sustainable medium for cultivating D. salina , coupling biomass with high-quality biodiesel production. This dual benefit highlights the potential of integrating algal biotechnology into brine management strategies, advancing circular bioeconomy and renewable energy goals in arid regions.