World attention in renewable energy sources, such as biofuels, has been increasing since the decline in petroleum supplies. In the quest to find a viable and sustainable resource for biofuel, recent studies have shown that microalgae can be used as feedstock in biodiesel production. This study was undertaken to screen marine microalgae for biodiesel, to upscale microalgae culture for biomass, to extract fatty acids for biofuel, and to determine biodiesel productivity from different microalgal strains. Two of seven screened marine microalgal strains, Thalassiosira sp. and Nannochloropsis sp., were cultured in the laboratory. Starting with the same cell concentration, the cell density of Thalassiosira sp. in a Walne medium, either with free air bubbling or with an air/CO2 mixture, was less than Nannochloropsis sp. Thalassiosira sp. and Nannochloropsis sp. had high specific growth rates of 0.17 and 0.19, and cell densities (in 10 days) at 0.49 g/l and 2.63 g/l, respectively. To release oils from inside the cells, a sonication method seemed to be effective for disrupting microalgae, followed by Soxhlet extraction using a chloroform/methanol solvent to extract more fatty acids. Biodiesel productivity of Thalassiosira sp. was 150 μl/l culture/d. This is higher than other biodiesel feedstock like palm oil.
