Challenges and opportunities to increase economic feasibility and sustainability of mixotrophic cultivation of green microalgae of the genus Chlorella

Green microalgae belonging to the genus Chlorella have long been used as health foods and additives for human consumption, as well as animal feed. These photosynthetic microorganisms have also found application in the bioremediation of wastewater and bio-mitigation of CO₂. In the last decades, Chlorella microalgae have attracted considerable attention due to their great potential as feedstock for production of biofuels and high-value products. This review explores key aspects related to the cultivation of different Chlorella species under mixotrophic conditions. Common organic compounds and cheap substrates used for mixotrophic microalgal growth are presented. Bottlenecks and strategies to increase economic feasibility and sustainability of mixotrophic cultivation of Chlorella for future commercial production are also discussed. In this sense, the use of wastewater as a nutrient source for microalgae cultivation seems to be a promising alternative to improve the sustainability and economic feasibility of microalgae production systems. However, since wastewater presents a complex composition, methods to minimize the risk of contamination should be developed. Additionally, the screening of novel mixotrophic species of Chlorella capable of both assimilating a wide range of organic compounds from wastewater and accumulating high content of molecules of interest (e.g., lipids) would be highly recommended.