Utilization of Saline Water Enhances Lipid Accumulation in Green Microalgae for the Sustainable Production of Biodiesel

The main objective of this research was to determine the effect of salinity on growth, and production of bio-relevant molecules, from green microalgae: Oedogonium, Cladophora, Ulothrix, and Spirogyra using response surface methodology (RSM) together with central composite design (CCD). Investigated algal biomass decreased (4-–fivefold), whilst carbohydrates decreased ranging from (0.14–0.19 mg/g), proteins (28–36%), and chlorophyll by (17–50%) using a treatment 100 mM of NaCl. The reduction in carbohydrates, proteins, and pigments was accompanied with a significant increase in lipids ranging from 33 to 80% at 100 mM NaCl. Saturated fatty acids were increase from 34.3 to 49.5%, PUFAs from 12.0 to 27.9% while MUFAs decreased from 52.8 to 19.4% at 80 mM of NaCl. Biodiesel-related values including iodine value (less than 120 g I2/100 g), saponification value (161–209 mg/KOH/g), cetane number (greater than 47 except for Cladophora sp.), cold filter plugging point (− 13.84 to − 16.39 °C), density (0.86–0.88 gcm−3), kinematic viscosity (3.5–3.9 mm2/s), oxidative stability (46–382 h at 110 °C), and heating value (36 to 41 MJ/kg) were in the satisfactory ranges of biodiesel standards EN 14,214 & ASTM D6751-02. Our results indicate that the investigated green algal species can produce large lipid yields and biofuels using brackish, saline water in contrast to conventional and current systems.