The algal carbon diet: Repurposing volatile fatty acids into sustainable lipids

• This review examines mixed VFAs from real wastes as carbon sources for microalgae. • Various treatment strategies can be used to ‘’Turbocharge’’ VFA accumulation. • Microalgae are rich in lipids and carbohydrates, ideal for biofuel production. • CRISPR/Cas9 is a breakthrough technology for increasing lipid content in microalgae. • The review underscores the circular bioeconomy as a key approach to replace finite energy. Volatile fatty acids (VFAs) generated through dark fermentation (DF) are emerging as a sustainable and cost-effective carbon source for microalgae cultivation and for the production of sustainable lipids and/or biodiesel within the circular bioeconomy framework. The current review examines the effects of the combined VFAs derived from real wastes on the growth performance and lipid accumulation of various microalgae strains. This understanding is critical for maximizing lipid productivity using microalgae. This review synthesizes current research on the role of VFAs in enhancing lipid accumulation for sustainable biodiesel production. Effective treatment strategies for organic waste are crucial for improving hydrolysis efficiency and producing high VFAs in the DF. Therefore, the review discusses the current emerging pretreatment methods, considered as advanced, hybrid, or process-intensification pretreatments for enhancing VFA production, relevant to the sustainable microalgae cultivation. Similarly, the environmental variables that affect VFA production, namely, temperature and pH, are elaborated. Additionally, this study underscores the advancements and role of CRISPR/Cas9 applications for genetically modifying and improving lipid content in microalgae. Furthermore, the review discusses the importance of integrating VFA-producing industries with microalgae cultivation systems to promote sustainable waste valorization and advance biofuel production in the future. The results of this review article reveal that researchers have used freshwater microalgae to produce lipids. Therefore, further research should be carried out on the lipid and/or biodiesel production potential of marine microalgae as well. In conclusion, identifying novel freshwater and marine microalgae species from diverse and underexplored aquatic environments, including lakes, rivers, wetlands, coastal waters, estuaries, and extreme habitats, and scaling up their lipid and/or biodiesel production are essential for developing sustainable alternatives to finite energy resources and for environmental protection.