Unlocking the potential of microalgae cultivated on wastewater combined with salinity stress to improve biodiesel production.

Microalgae have the potential as a source of biofuels due to their high biomass productivity and ability to grow in a wide range of conditions, including wastewater. This study investigated cultivating two microalgae species, Oocystis pusilla and Chlorococcus infusionum, in wastewater for biodiesel production. Compared to Kühl medium, KC medium resulted in a significant fold increase in cellular dry weight production for both O. pusilla and C. infusionum, with an increase of 1.66 and 1.39, respectively. A concentration of 100% wastewater resulted in the highest growth for O. pusilla, with an increase in biomass and lipid content compared to the KC medium. C. infusionum could not survive in these conditions. For further increase in biomass and lipid yield of O. pusilla, different total dissolved solids (TDS) levels were used. Maximum biomass and lipid productivities were achieved at 3000 ppm TDS, resulting in a 28% increase in biomass (2.50 g/L) and a 158% increase in lipid yield (536.88 mg/g) compared to KC medium. The fatty acid profile of O. pusilla cultivated on aerated wastewater at 3000 ppm TDS showed a high proportion of desirable saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) for biodiesel production. Cultivating microalgae in wastewater for biodiesel production can be cost-effective, especially for microalgae adapted to harsh conditions. It could be concluded that O. pusilla is a promising candidate for biodiesel production using wastewater as a growth medium, as it has high biomass productivity and lipid yield, and its fatty acid profile meets the standard values of American and European biodiesel standards. This approach offers a sustainable and environmentally friendly solution for producing biofuels while reducing the environmental impact of wastewater disposal.