Traditionally, biodiesel is produce

Traditionally, biodiesel is produced via transesterification reaction of lipids and oils. The microalgal biomasshave to be dewatered by drying before extraction oflipids. Consequently, the lipids in microalgal biomasshave to be extracted before transesterification. This iscalled three-step method. Alternatively, the wet microalgal biomass can be used in lipid extraction step withoutdrying step. Recently, the direct transesterification reactions of wet microalgal biomass into biodiesel havebeen developed to reduce the number of unit operations and overall production cost of microalgae-basedbiodiesel. The transesterification reaction can be catalyzed either by homogeneous or heterogeneous catalysts, and these catalysts are acid, alkaline, andenzymes [118e123]. Fig. 6.2 shows biodiesel