Optimizing algal lipid production and its efficient conversion to biodiesel

Abstract

We report here the successful combination of a two-step algal growth protocol, maximizing lipid yields with a single-step, and efficient extraction/transesterification procedure for the production of biodiesel. As a part of a global effort to find green renewable energy sources, our research focused on defining the optimal conditions for growing oil-rich microalgal biomass and its direct conversion to biodiesel. The influence of temperature, nutrient limitation and light intensity on biomass production was analyzed in three microalgal species: Chlorella sp., Isochrysis sp. and Phaeodactylum tricornutum. The temperature was found to dramatically affect the algal growth rates, reaching up to 2–3-fold higher rates on the “optimal combinations” than under initial conditions. The effects of temperature, light intensity and nutrient-deficient conditions on triglyceride levels in algal cells were measured by Nile red staining. In Chlorella sp. and P. tricornutum, the highest lipid content was obtained at 20ºC, under high and low light intensity, respectively, and in Isochrysis sp. at 25ºC and intermediate light intensity. A synergistic effect appeared only in Chlorella sp., where the lipid content reached 62% of the dry biomass. The three species were grown under the conditions we found optimal for oil yield. The dry biomass was converted directly into biodiesel without first extracting the lipid phase. The direct transesterification process was performed at 60°C using an SrO catalyst and MW radiation, yielding 99.5% conversion of lipids to biodiesel in 5 minutes.