Biological fixation of carbon dioxide by microalgae and application for biodiesel production

Abstract

Due to negative impacts of global warming and potential depletion of petroleum, research for alternative fuels is an emerging issue all over the world. Biodiesel derived from biomass such as animal fat and vegetable oil is a potential substitute for petroleum-based diesel because it has similar combustion properties to petroleum-based diesel with mitigating the carbon dioxide. Especially, microalgae have been paid much attention as biomass feedstock for biodiesel production because they have high growth rate and need low land-use compared with conventional biomass. They can also fix $CO_2$ directly from exhaust gas of industrial facilities. Several studies have shown that quantity and quality of lipids of microalgae can vary as a result of changes in nutrient media characteristics (concentration of nitrogen, phosphates, and iron). Recently, microalgal cultivation in various temperatures to produce biodiesel has been studied, and it was shown that temperature has an effect on microalgal growth rate and lipid contents. At relatively higher or lower temperature, there is a tendency of lipid content increase and growth rate decrease. Therefore, after microalgal cultivation at optimum temperature until stationary phase for high growth rate, temperature shock in a certain range can increase microalgal lipid content. In this study, N. oculata was cultivated in batch-type photobioreactor (PBR) to fix $CO_2$ and produce biodiesel. Optimum microalgal culture conditions such as $CO_2$ concentration, flow rate, initial nutrient concentration, and light intensity were investigated for high growth rate. Based on optimum culture conditions, column-type PBR with water jacket which can control temperature was developed, and total lipid content was investigated in PBR under alternating temperatures. And N. oculata was cultured at mixotrophic condition adding yeast extract for high lipid productivity. In addition, oil extracted from microalgae was analyzed to evaluate quality of...