Enhanced activity of methanogenic granules by low-strength ultrasonication

In this study, low-strength ultrasonication was applied at various ultrasonication densities (UDs) (0–0.1 W/mL) and ultrasonication time (UT) (0–30 min) to methanogenic granules on the purpose of increasing their activity, and eventually, enhancing the performance of upflow anaerobic sludge blanket reactor (UASBr). Batch test results showed that 5 min of ultrasonication at 0.05 W/mL was found to be the optimal conditions, resulting in the increase of dehydrogenase activity and adenosine triphosphate content by 257%, and 374%, respectively, compared to the control. These increments were confirmed by specific methanogenic activity test. When ultrasonication (UD 0.05 W/mL, UT 5 min) was irradiated every 8 h during the continuous operation of UASBr, it caused a gradual drop of methanogenic activity, complete loss after 20 days. At further operation, UT was decreased to 1 s but irradiated every 1 min, which resulted in a 43% higher specific CH4 production rate.

► Ultrasonicator was installed inside the UASBr and irradiated to the granules.
► 0.05 W/L, 1 s per 1 min of ultrasonication were applied to methanogenic granules.
► Forty-three percentage of CH4 production enhancement was observed during the continuous operation.
► It was attributed to the increase of the dehydrogenase activity and ATP content.
► In addition, propagation of acoustic waves possibly accelerated the mass transfer.