Anaerobic digestion of microalgae is essential for making microalgal biodiesel sustainable. This process helps manage residual biomass and reduces the need for fertilizers by converting algal biomass into methane. However, microalgae pose challenges due to low biodegradability, high protein content leading to ammonia toxicity, and the presence of sodium in marine species. Strategies like physico-chemical pretreatment, co-digestion, and controlling composition can enhance methane yield. When lipid content is below 40%, anaerobic digestion of whole biomass is optimal for energy recovery. The study highlights the importance of addressing ammonia and sodium toxicity, improving digestion efficiency through pretreatment, and considering the energy balance of lipid recovery. Biogas purification using microalgae can enhance methane content and reduce CO₂, making the process more efficient. Overall, anaerobic digestion is a key step in making microalgal biodiesel sustainable by improving energy efficiency and reducing environmental impact.Anaerobic digestion of microalgae is essential for making microalgal biodiesel sustainable. This process helps manage residual biomass and reduces the need for fertilizers by converting algal biomass into methane. However, microalgae pose challenges due to low biodegradability, high protein content leading to ammonia toxicity, and the presence of sodium in marine species. Strategies like physico-chemical pretreatment, co-digestion, and controlling composition can enhance methane yield. When lipid content is below 40%, anaerobic digestion of whole biomass is optimal for energy recovery. The study highlights the importance of addressing ammonia and sodium toxicity, improving digestion efficiency through pretreatment, and considering the energy balance of lipid recovery. Biogas purification using microalgae can enhance methane content and reduce CO₂, making the process more efficient. Overall, anaerobic digestion is a key step in making microalgal biodiesel sustainable by improving energy efficiency and reducing environmental impact.