1. Biodiesel from Microalgal Oil Extraction

The rapid development of the modern society has resulted in an increased demand for energy, and consequently an increased use of fossil fuel reserves. Burning fossil fuels is nowadays one of the main threats to the environment, especially due to the accumulation of greenhouse gases in the atmosphere, which are responsible for global warming. Furthermore, the continuous use of this non-renewable source of energy will lead to an energy crisis because fossil fuels are of limited availability. In response to this energy and environmental crisis, it is of extreme importance to search for different energy supplies that are renewable and more environmentally friendly. Microalgae are a promising sustainable resource that can reduce the dependence on fossil fuel. Biodiesel production through microalgae is actually highly studied. It includes several steps, such as cell cultivation and harvesting, oil extraction and biodiesel synthesis. Although several attempts have been made to improve biodiesel yields from microalgae, further studies are required to optimize production conditions and to reduce production costs.

This chapter reviews recent developments on oil extraction for biodiesel production. Two different processes are distinguished: (i) an indirect route, in which microalgal oil is recovered in an appropriate solvent and then converted into biodiesel through transesterification; and (ii) a direct route, in which the production of biodiesel is performed directly from the harvested biomass. Both routes, direct and indirect, should be preceded by cell wall disruption because this step facilitates the access of solvents to microalgal oil. The most advantageous disruption methods for lipid extraction are enzymatic and pulsed electric field disruption because enzymes present higher selectivity towards cell walls. In addition pulsed electric field requires less energy than other disruption methods.