The removal of Acid Orange 7 by zero-valent iron (Fe-o) activated sodium persulfate (Na2S2O8, PS) in the presence of ultrasonic irradiation (US) was performed in this study. The effects of persulfate concentration, zero valent iron addition, ultrasonic power and initial pH on the decolorization rate of Acid Orange 7 were investigated. The results showed that the decolorization rate increased with an increase in persulfate concentration from 0.1 to 0.5 g/L, an increase in zero valent iron amount from 0.1 to 0.5 g/L, and an increase in ultrasonic power from 40 to 60 W. But further increase in persulfate concentration, zero valent iron addition and ultrasonic power would result in an unpronounced increase of decolorization rate. The optimal initial pH for decolorization was found as 5.8. The maximum decolorization efficiency of 96.4% was achieved within 20 min with persulfate concentration of 0.3 g/L, zero valent iron concentration of 0.5 g/L, initial pH value of 5.8 and ultrasonic power of 60 W. (C) 2013 Elsevier B.V. All rights reserved.