Lipid and lutein recovery from desertic microalgae in saline wastewater combined to abiotic stressors for sustainable antioxidant and biodiesel production

Freshwater salinisation is a serious global issue affecting natural resources availability and food production. Salinity-based cultivation systems are considered promising approaches to generate valuable microalgal biomass for energy and food purposes, even though salt stress can compromise growth efficiency and bioproducts productivity markedly. Herein, a single-stage cultivation of two native microalgae in saline wastewater combined to abiotic stress factors was studied. The physicochemical responses of each microalgae including biomass growth, biochemical composition and antioxidant activities were evaluated. The results showed that all the combinations enhanced microalgal growth performance efficiently, with lipids and antioxidant productivities increasing in a simultaneous manner. The biomass contents and productivities were found to vary within the range of 0.58–2.02 g_dw L ^{̶ 1} and 40.50–189.00 mg_dw L ^{̶ 1} d ^{̶ 1}, respectively. The highest lipid accumulation was obtained in the culture of Selenastrum sp. KCC3, under the synergistic effect of 11 g salt L ^{̶ 1} and nitrogen deprivation (36.59 %, dw), as well as in the mixotrophic cultures of Chlorella sorokiniana KCC4 (35.83 %, dw). The lipid productivity varied between 12.50 and 65.66 mg_dw L ^{̶ 1} d ^{̶ 1}, while production of lutein was maximal at 2.04 mg g_dw ^{̶ 1} in Selenastrum sp. and achieved an optimal value of 1.56 mg g_dw ^{̶ 1} under moderate light stress culture of Chlorella sorokiniana. Abiotic factors were also effective in increasing the antioxidant levels and activities of algal extracts, whereas the composition of fatty acid for biodiesel production was also influenced under salt stress. The whole findings provide a promising salinity stress-induced strategy for efficient biorefining of desertic microalgae.