Effect of different iron concentrations on growth, lipid accumulation, and fatty acid profile for biodiesel production from Tetradesmus obliquus

Abstract

The present study investigated the effect of ferric iron on growth and lipid content of the green microalga Tetradesmus obliquus as a promising feedstock with favorable features for biodiesel production. The microalga was isolated from a freshwater body and cultured for 20 days in five types of modified BG11 medium with different concentrations (0, 10⁻⁴, 10⁻³, 10⁻², 10⁻¹ mmol L⁻¹) of ferric iron. The algae grown in medium supplemented with 10⁻² mmol L⁻¹ ferric iron had the highest specific growth rate of 0.36 ± 0.04 day⁻¹ and remained in the exponential growth phase over the next 6 days compared with those grown in medium without iron supplementation. The peak of lipid content (34.19 ± 1.93% dry weight, DW) and biomass productivity (459.20 ± 2.37 mg L⁻¹ day⁻¹) was obtained in the media supplemented with 10⁻² and 10⁻¹ mmol L⁻¹ ferric iron, respectively. The highest proportion of saturated fatty acids and the lowest proportion of unsaturated fatty acids were also achieved by adding 10⁻¹ mmol L⁻¹ ferric iron to the growth medium. These findings may lead to a two-step process for lipid production from T. obliquus, in which biomass should be separated from the culture supplemented with 10⁻² mmol L⁻¹ ferric iron concentration to achieve the maximum algal biomass in the first step and then inoculated to the culture supplemented with 10⁻¹ mmol L⁻¹ ferric iron concentration to reach the highest lipid productivity in the second step, leading to optimization of lipid production from T. obliquus. Although the quality of biodiesel produced from T. obliquus met the specification of the European biodiesel standard (EN14214) in all media, ferric iron supplementation could be used to optimize the lipid characteristics of T. obliquus for biodiesel production.