Ultrasound-enhanced activated sludge for selective fermentation to improve bioenergy extraction efficiency from microalgae

Selective fermentation effectively addresses issues such as the high energy consumption associated with traditional microalgae cell disruption methods, while maintaining high efficiency. In this study, ultrasound was employed to enhance microbial activity and improve the selective fermentation capacity of Chlorella. The results indicated that, compared to the control group, the ultrasound pretreatment group achieved a 199 % and 152 % increase in the first-order degradation rates of carbohydrates and proteins, enabling ethanol-based fermentation. After 16 h of fermentation, the hydrogen production rate of the ultrasound pretreatment group reached 4.91 mL/g_microalgae, and the lipid extraction was 0.46 g/g_microalgae, which were 2.3 and 1.35 times higher than those of the control group, respectively. The biodiesel quality was significantly improved, meeting the biodiesel standards of various countries. High-throughput sequencing results revealed that ultrasound pretreatment enhanced microalgae production capacity by stimulating the activity of functional microorganisms, such as hydrogen-producing bacteria, during the fermentation process.