Growth kinetics and metabolic characteristics of five freshwater indigenous microalgae for nutrient removal and biofuel generation: a sustainable approach

The isolation, screening, and diversified biocomponent analysis of microalgae species is essential for categorizing its potential applications. In the present study, several microalgal species were isolated from freshwater samples collected from three geographically distant cities, Lanzhou Shi Chuang Xian Dai Cheng in Gansu Province (103.75 E, 36.09 N), Datong Children Park in Shanxi Province (113.29 E, 40.08 N), and Jinan Quenching Park in Shandong Province (117.02 E, 36.65 N), China. The screened species were identified and further evaluated for their growth kinetics, metabolic characteristics (such as proteins, carbohydrates, and lipids/fatty acids), and nutrient uptake. The molecularly identified microalgae species were Chlorella vulgaris GEEL-10, Tetradesmus obliquus GEEL-11, Desmodesmus communis GEEL-12, Chlorella sorokiniana GEEL-13, and Scenedesmus quadricauda GEEL-14. Among the identified strains, C. vulgaris GEEL-10 (2.12 OD 680nm ), T. obliquus GEEL-11 (2.01 OD 680nm ), and D. communis GEEL-12 (2.15 OD 680nm ) showed the highest growth. Microalgae D. communis GEEL-12 achieved the highest nitrogen (N) 89.86% and phosphorus (P) 99.78% removal. T. obliquus GEEL-11 showed 89.37% and 64.43% of N and P removal, respectively. The lipids (21.75–35.67%), proteins (18.08–24.35%), and carbohydrates (33.98–46.33%) content in five microalgal species was accumulated in high fraction. The saturated fatty acids (such as C16:0 and C18:0) composition of the investigated microalgal species was also high which favor the quality evaluation parameters for biodiesel generation. These results indicated the potential applications of five microalgae (especially GEEL-11 and GEEL-12) for bioethanol, higher alcohols, and biodiesel/oil production along with nutrient removal. Graphical Abstract