FAME Productivity and Biodiesel Potential Based on Fatty Acid Composition of Chlorella vulgaris and Scenedesmus obliquus Cultivated in Urban Wastewater Under Mixotrophic and Nitrogen-Limited Conditions
Abstract
Microalgae-based wastewater treatment represents a sustainable approach for simultaneous nutrient removal and biodiesel feedstock production. This study evaluated the growth, total organic carbon (TOC) removal, FAME productivity, fatty acid composition, and predicted biodiesel properties of Chlorella vulgaris and Scenedesmus obliquus cultivated in urban wastewater and synthetic medium under photoautotrophic and mixotrophic conditions, with and without nitrogen limitation using a two-stage cultivation strategy. S. obliquus showed greater adaptability to urban wastewater, with better growth and the highest TOC removal efficiency (92%) under mixotrophic cultivation with nitrogen limitation. Nitrogen limitation significantly enhanced FAME productivity in both species, with increases of 43.06–79.35% for C. vulgaris and 48.11–69.98% for S. obliquus relative to the corresponding photoautotrophic cultures. Fatty acid analysis revealed higher saturated fatty acid contents in C. vulgaris and higher polyunsaturated fatty acid levels in S. obliquus. Based on the fatty acid composition, C. vulgaris showed lower predicted iodine values and greater predicted oxidative stability than S. obliquus. The predicted cetane numbers were below the minimum values cited in international biodiesel specifications, while predicted kinematic viscosity was within the ranges reported by ASTM D6751 and EN 14214. However, the predicted cold filter plugging point (CFPP) values of 14.9–15.0 °C indicated limited suitability for low-temperature applications, and oxidative stability met the cited EN 14214 threshold only for some C. vulgaris treatments. These results indicate the potential of urban wastewater as a culture medium for sustainable microalgal FAME production and as a feedstock source for biodiesel applications, particularly when combined with fatty acid profile optimization or blending strategies.