Freshwater microalgae-based wastewater treatment under abiotic stress

Wastewater treatment by microalgae is an eco-friendly and sustainable method for pollutant removal and biomass generation. Microalgae production under abiotic stress (such as salinity/salt stress) has an impact on nutrient removal and fatty acid accumulation. In this study, a freshwater microalgal strain (Desmodesmus communis GEEL-12) was cultured in municipal wastewater with various NaCl concentrations (ranging from 25-150 mM). The growth kinetics and morphological changes of the microalgae were observed. The nutrient removal, salinity change, fatty acid composition, and biodiesel quality under various groups were also investigated. The maximum growth of D. communis GEEL-12 was observed in the control group at 0.48 OD680nm. The growth inhibition was observed under high salt conditions (150 mM), which showed poor tolerance with 0.15 OD680nm. The nitrogen (N) and phosphorus (P) removal significantly decreased from 99-81% and 5.0-5.9% upon the addition of 100-150 mM salt, respectively. Palmitic acid (C16:0) and stearic acid (C18:0) were the most common fatty acid profiles. The abundance of C18:0 enhanced from 49.37%-56.87% in D. communis GEEL-12 upon high NaCl concentrations (100-150 mM). The biodiesel quality index of D. communis GEEL-12 under 50-75 mM salt concentrations reached the levels advised by international standards.