The feasibility of ultrasonic stimulation on microalgae for efficient lipid accumulation at the end of the logarithmic phase

The microalgae Scenedesmus quadricauda were treated by ultrasound (200 W, 40 kHz) at the end of the logarithmic phase to investigate the effects on stimulating lipid accumulation. Firstly, the microalgae were treated by ultrasound for different times of 0, 5, 10, 15, 20 and 40 min, and then cultivated for 2 days. Although the biomass concentration did not increase, the maximum lipid content of 37.8% dry weight (DW), showing a significant improvement of 57.5%, was obtained after ultrasonic exposure for 20 min. Secondly, the cultivation of the microalgae at the end of the logarithmic phase was continued for a different number of days (1, 2, 3, 4, 5 and 6) after ultrasonic stimulation for 20 min to check the variation of biomass, lipid and other compositions accumulation. The results indicated that a maximum lipid content of 38.9% DW was obtained on day 2, showing an excellent performance. The improved fatty acid in microalgae cells was also analyzed after ultrasonic treatment. This study efficiently increased the accumulated lipid of microalgae by ultrasonic treatment at the end of the logarithmic growth phase without decreasing the biomass, which might be a useful method in practice.