Enhancement in the partial nitrification of wastewater sludge via lowintensity ultrasound: Effects on rapid start-up and temperature resilience

The partial nitrification process can reduce the aeration energy consumption in bioreactors by 25%. Low-intensity ultrasound (0.25 W.mL(-1)) was applied during the partial nitrification process to evaluate its effects on start-up and temperature resilience. Ultrasound application led to rapid start-up of the partial nitrification process (within 18 d) with a nitrite accumulation ratio of above 80% at 18 degrees C. Moreover, when the temperature was increased to 28 degrees C, the partial nitrification process was effectively maintained with a nitrite accumulation ratio of above 80%. Ultrasonic treatment for a long duration had a positive effect on ammonia oxidizing bacteria of the genus Nitrososphaera, whereas the population of nitrite oxidizing bacteria, Nitrospira, decreased. The temperature resilience of Nitrososphaera was also enhanced. These findings indicate that ultrasound induces rapid start-up of the partial nitrification process and enhances the temperature resilience of Nitrososphaera.