Growth of microalgae using CO2 enriched air for biodiesel production in supercritical CO2

The optimum conditions for lipids productivity and CO2 fixation of two freshwater strains, namely Chlorella sp. and Pseudochlorococcum sp. and a marine strain; namely Nannochlorpsis sp. have been determined in this work. The species were grown autotrophically under aeration with different CO2 concentrations, ranging from 0.04 to 2% (v/v). The growth was tested in nitrogen sufficient and deficient media at different salinities (0.49-680 mM) and temperatures of 27 and 31 degrees C. The optimum CO2 enrichment was found to be 1% (v/v) in both media. Nitrogen starvation resulted in an increase in lipid 'contents, but at lower growth rate, which resulted in a lower overall lipid productivity. The experimental data were used to determine the kinetic parameters of Haldane model. The Chlorella sp. grew well at salinity levels of up to 460 mM. The highest CO2 biofixation rate was observed when Chlorella sp. was grown at 27 degrees C in seawater (230 mM NaCl). Lipids were extracted from harvested marine strain, Nannochlorpsis sp., and enzymatically trans-esterified to produce biodiesel in supercritical CO2 (SC CO2) medium. It was found that the conversion of biodiesel produced from microalgae lipids was 35% higher than that achieved using lamb fat in a similar system. (C) 2014 Elsevier Ltd. All rights reserved.