Bioprocess strategies for enhancing lipid content in microalgae to improve biofuel production

• Provides an integrated review of the entire microalgae biofuel chain, from genetic and environmental interventions to downstream processing. • Compares regulatory vs. enzymatic genetic strategies and environmental stress conditions with mechanistic schematics. • Discusses techno-economic challenges such as TRL gaps, scalability, and cost barriers. • Mention future opportunities through systems biology, AI-driven modeling, and smart biorefineries for real-time optimization. Microalgae have emerged as promising candidates for third- and fourth-generation biofuels due to their ability to efficiently fix CO₂, accumulate high lipid content, and adapt to extreme environments with minimal resource input. This review critically examines recent advances across the entire microalgae biofuel production chain. It highlights key species with high lipid productivity and strong environmental tolerance, including those capable of thriving in wastewater, saline, and acidic conditions. The review further synthesizes current strategies for enhancing lipid accumulation, encompassing both genetic interventions and environmental manipulations. Innovations in post-harvest processing—such as integrated fermentation, thermochemical conversion, and anaerobic digestion—have also demonstrated improvements in overall biofuel yield and energy recovery. Despite these advancements, challenges related to scalability, cost-effectiveness, and industrial CO₂ integration remain significant barriers to commercialization. This review underscores the importance of continued efforts in strain engineering, direct CO₂ utilization from industrial emissions, and life cycle sustainability assessments, while also highlighting emerging opportunities through systems biology, AI-driven modeling, smart biorefineries, and circular bioeconomy integration to enhance the overall viability and environmental performance of microalgae biofuels in meeting future global energy demands.