Microalgal Heterotrophic and Mixotrophic Culturing for Bio-refi ning: From Metabolic Routes to Techno-economics

In comparison with conventional photo-autotrophic cultivation, heterotrophic and mixotrophic cultivations of microalgae offers a feasible strategy to produce biomass and valuable chemicals through biorefi nery processes. Supplementing microalgae cultures with organic carbon sources increase the biomass production and lipid/carbohydrate contents in cells. Consequently, this yields high productivity of biorefi ned products such as biodiesel, ethanol, starch and polyunsaturated fatty acids. Nevertheless, the addition of an organic carbon source imposes the necessity to pre-produce them and increase the cost and susceptibility of the cultures to microbial contamination. This chapter reviews the aspects related to the heterotrophic and mixotrophic cultivation of microalgae. These include advantages and limitations, metabolic routes of organic carbon assimilation, alternative carbon sources and main considerations for cultivation systems. It provides a comprehensive review of cultivated species, organic carbon sources and recently achieved productivity metrics. The chapter includes discussions regarding the main commercial products obtained using these cultivation modes and a simplifi ed techno-economic analysis of the full biorefi nery operation. The overarching aim of the chapter was to depict the main challenges for commercialization of chemical products using heterotrophic/mixotrophic cultivation of microalgae and identifi es the promising research lines to achieve the same.