Diverse cultivation temperatures and nitrogen supplementation levels alter biomass, lipid, and fatty acid productivity in the native microalgae for biodiesel application

Microalgae have emerged as potential and sustainable sources for biodiesel production due to their high lipid composition, rapid growth, and minimal resource inputs for cultivation. However, technical and economic challenges hinder commercial biodiesel production. Therefore, this study aims to evaluate the effect of nitrogen sufficient/deficient concentration as well as cultivation temperatures (20 °C, 25 °C, 30 °C, and 35 °C) on the biomass, lipid accumulation, and fatty acid composition of a microalga, Nannochloropsis sp., for biodiesel application. The test alga is known for high lipid productivity and is stress-tolerant. This work suggests that biomass yield can be maximized at 25 °C in nitrogen-replete conditions because of a maximal growth rate, biomass density, and chlorophyll content. Yet, when nitrogen-depleted conditions are present at 35 °C, lipid production shifts to a maximum due to the temperature and nutrient stress. Under these conditions, the temperature stress combines with nitrogen deficiency to substantially improve productivity with a biodiesel yield of approximately 70 % and a maximum lipid content of approximately 27 %, which were above the control condition. Additionally, there was a significant increment in saturated fatty acids of approximately 45 %, while that of monounsaturated fatty acids increased by approximately 40 % under nitrogen-depleted conditions, improving the oxidative stability of the biodiesel. This research emphasizes a sustainable and economically viable approach to cultivating the test alga in outdoor cultivation for pilot-scale mass production of biomass for biodiesel application.