Low-strength ultrasonication positively affects methanogenic granules toward higher AD performance: Hydrolytic enzyme excretions

In our previous studies, enhanced methane (CH₄) production using low-strength ultrasonication was achieved and the results were evidenced by physico-chemical and molecular biological approaches. As a final continuation study, the effects of low-strength ultrasonication on the activities of hydrolytic enzymes (amylase, cellulase, and protease) were investigated on methanogenic granules given that hydrolysis regulates the whole anaerobic digestion (AD) process. Up to 213% enhanced hydrolytic enzyme activities were observed, and they seem to be highly related to the enhanced CH₄ production. However, the effects of ultrasonication on the distribution (liquid- and solid-phases) of hydrolytic enzymes were negligible. Enzymatic activation by low-strength ultrasonication was hypothetically caused by acoustic streaming, presumably enabling to overcome the masking effect, substrate inhibition and spatial constraint.