Growth, lipid extraction and thermal degradation of the microalga Chlorella vulgaris

The microalga Chlorella vulgaris was cultured in a combined medium obtained by mixing standard Jaworski medium with a solution from the modified Solvay process that contained only NaHCO3 and NH4Cl. Cell number, pH and nitrogen content were monitored throughout growth. Lipids were extracted from lyophilised biomass using CHCl3-MeOH. A combination of grinding, microwave treatment and sonication proved to give the best lipid extract yield. Freeze-dried algal biomass was also utilised for thermal degradation studies. The degradation exhibited three distinct regions - primary cell structure breakage paralleled by evaporation of water, followed by two predominant exothermic degradation processes. The latter were modelled using nth order apparent kinetics. The activation energies of the degradation processes were determined to be 120-126 kJ/mol and 122-132 kJ/mol, respectively. The degradation model may be readily applied to an assortment of thermal algal processes, especially those relating to renewable energy.