Abstract
In the present study, the marine microalga Tisochrysis lutea was cultivated mixotrophically in F2 growth medium with sodium acetate as exogenous carbon source. The medium was composed of different concentrations of nitrogen to determine the impact of nitrogen depletion on cellular growth and chemical composition. Nitrogen depletion led to severely decreased growth and protein content. However, mild nitrogen depletion (0.22 mM NaNO3) led to maximum lipid yield. The fatty acid methyl ester profile also showed increased unsaturation as the nitrogen content decreased. Growth in nitrogen-free medium increased the proportions of mono- and poly-unsaturated fatty acids, while the proportion of saturated fatty acids decreased. Growth under all tested nitrogen levels showed undetectable fatty acids with ≥4 double bonds, indicating these fatty acids had oxidative stability. In addition, all tested nitrogen concentrations led to specific gravity, kinematic viscosity, iodine value, and cetane number that meet the standards for Europe and the U.S.A. However, growth in the presence of nitrogen deficiency enhanced the higher heating value of the resulting biodiesel, a clear advantage from the perspective of energy efficiency. Thus, mixotrophic cultivation of T. lutea with nitrogen limitation provides a promising approach to achieve high lipid productivity and production of high-quality biodiesel.
Highlights
Extensive use of petroleum to produce fuel oil and its derivatives is not sustainable in the long-term because of resource depletion and increasing levels of greenhouse gases [1,2]
Dry microalgal biomass typically contains about 50% carbon and 10% nitrogen, and their typical responses to nitrogen deficiency are drastic declines in dry weight (DW) and growth [14]
68.4% lower than that of the control medium (0.187 d−1 ). These results indicated a close relationship between nitrogen deficiency and the inhibitory effect
Summary
Extensive use of petroleum to produce fuel oil and its derivatives is not sustainable in the long-term because of resource depletion and increasing levels of greenhouse gases [1,2]. There is increasing attention on research initiatives that are developing renewable, sustainable, and environmentally friendly sources of energy [4,5]. In this context, biodiesel is a widely recognized and promising replacement for fossil fuels whose use may mitigate the effects of greenhouse gas emissions [6]. Biodiesel is produced by transesterification of animal fats or vegetable oils in the presence of a suitable catalyst, resulting in production of glycerol and esters [7]. Many recent studies have focused on biodiesel production from oleaginous microalgae because of their high lipid content, fast growth, and minimal requirements for land
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