Influence of persulfate (PS) on the sonochemical degradation of naphthol blue black (NBB) was examined.

For the first time, the sonolytic decomposition of PS was proved.

The positive effect of PS on NBB degradation decreased with increasing power.

PS enhanced effect was more remarkable at 20 kHz than that observed at 585 kHz.

Theoretical and experimental measurements was made for interpreting the positive effect of PS.