Cultivation of Freshwater Microalgae in Wastewater Under High Salinity for Biomass, Nutrients Removal, and Fatty Acids/Biodiesel Production

Purpose Microalgae show growth and fatty acids (FAs) accumulation up to a certain level which is dependent on species and type of cultivation conditions. Application of abiotic stress on microalgae can induce nutrient uptake and enhance biocomponent accumulation. Methods In the current study, freshwater microalgae ( Chlorella sorokiniana GEEL-01 and Desmodesmus asymmetricus GEEL-05) were investigated for growth, nutrient removal, and FAs composition during cultivation in municipal wastewater under high NaCl concentration (150 to 600 mM) along with control (w/o NaCl addition). Results The growth of both microalgae declined upon an increase in NaCl concentration in the wastewater. GEEL-05 showed higher growth of 0.572 OD 680 nm at 150 mM NaCl, followed by 0.40 and 0.174 OD 680 nm in 300 and 450 mM NaCl, respectively. Both microalgae were completely inhibited at 600 mM NaCl. GEEL-01 and GEEL-05 removed 60–80% total nitrogen (TN) up to 450 mM NaCl concentration. Both strains totally removed the total phosphorus (TP) after 8 days of cultivation from wastewater having up to 300 mM NaCl, while 40–80% TP was removed under 450 mM NaCl. FAs profiling of microalgal strains varied under different NaCl concentrations. GEEL-01 had high palmitic acids (33%) at 300 mM NaCl, high oleic acid (28 and 37%) at 300 and 450 mM NaCl and high linoleic acid (23%) at 450 mM NaCl. Whereas, GEEL-05 showed high palmitic acid (51.59%) at 450 mM NaCl and high oleic acid (30%), at 150 mM NaCl. The improved FAs content also resulted in better biodiesel properties. Conclusion Both microalgae survived under high salinity having NaCl up to 450 mM in wastewater with high nutrient removal and improved FAs profile which indicated their use in wastewater treatment coupled with quality biodiesel production. Graphical Abstract