Experimental investigation of direct saline water application for effective biorefinery from newly isolated freshwater microalgae

The expanding extent of freshwater scarcity and salinisation has encouraged a growing use of saline footprints as an alternative for microalgae cultivation to ensure water security and preserve natural resources for generations. Native microalgae, being highly adapted to adverse environmental conditions, are more attractive for the sustainable production of biofuels and high-value compounds in arid areas where conventional crop fail to face salt stress. The current study reports for the first-time a direct cultivation in saline water (11 g L-1 NaCl) of Coelastrella sp. KCC1, Chlorella sp. KCC2, Selenastrum sp. KCC3 and Chlorella sorokiniana KCC4 isolated from Algerian desert for biomass production and concomitant product accumulation. The growth patterns in terms of biomass production and specific growth rate indicated high performance of Coelastrella sp. (1.26 g L-1, 0.38 day(-1)) and Selenastrum sp. (1.085 g L-1, 0.4 day(-1)). The latter had the highest efficiency for phosphorus consumption (92.84%), while Chlorella sp. showed the best nitrate assimilation (34.91%). Biochemical screening revealed higher accumulation of carbohydrates (33.31-38.75% of dry weight (DW)) mainly in Chlorella sorokiniana, while Coelastrella sp. was the main lipid producer (31.60% DW) with a favourable saturated and monounsaturated fatty acids profile (63.46%) and suitable biodiesel properties. Supramolecular solvents technique enabled the extraction of high carotenoid content in Chlorella sorokiniana (2.03 mg g(DW)(-1)) and maximum polyphenol content in Coelastrella sp. (15.95 mg GAE g(DW)(-1)), in agreement with stronger antioxidant activities. These results appoint the isolated algae as very promising for effective biorefinery in saline water conditions.

Automated summary

The cultivation of various desert algae in saline water conditions has been successfully carried out in this study, showing their potential for sustainable production of biofuels and high-value compounds. These algae exhibited high growth performance and accumulation capabilities, making them suitable for cultivation in salt-stressed environments.