Microalgae Culture Medium Recycling: Improved Production of Biomass and Lipids, Biodiesel Properties and Cost Reduction

The reuse of the culture media after biomass growth can be a cost-effective strategy for large-scale microalgae production, especially when the target product is biofuel. Therefore, this study aimed to investigate the effect of recycling the microalgae Tetradesmus obliquus culture medium, focusing on the improved production of biomass and lipids, biodiesel properties, and cost reduction. The experiments were carried out in duplicate and three sequential steps with successive recycling (50% of the clarified medium and 50% of the standard). It was found that cells from recycled cultures had a similar overall performance as those from the fresh medium (standard). From this verification, the main findings of this research pointed out that (i) the consumption of the nutrients was efficient, with values in the order of 99% nitrate, 20% phosphate, 64% total iron, and 9% potassium; (ii) the average contents of biomass and lipids in the recycled medium increased around 20% to 24%, respectively, concerning the standard; (iii) the polyunsaturated fatty acids pool present in the microalgal oil dropped from 20.71 to 9.78% in the recycled culture, which represents a high-quality feedstock for biofuel; and (iv) the biodiesel properties evaluated, including iodine and saponification values, were 48 g I 2 100 g −1 and 254 mg KOH/g oil −1 , respectively. Finally, this recyclability bioprocess can reduce overall costs by about 34%, thus improving the economic viability of microalgae production.