Carbonate ions in wastewater can interfere with the reactions in advanced oxidation processes. In the present study, the effects of carbonate ions on the degradation of a polyazo direct dye, the Sirius Red F3B (SRF3B), using persulfate (PS) oxidation catalyzed by Fe-0 aggregates (PS/Fe-0) was investigated. Results of this study indicated that the oxidation power of the PS/Fe-0 process was inhibited in the dye solutions containing carbonates, and the efficiency of SRF3B decolorization decreased with increasing concentration of Na2CO3. A short period of ultrasound (US) irradiation can significantly enhance the destruction of dye molecules. Complete decolorization of a 25 mg/L SRF3B solution containing 1 x 10(-3) M carbonate, 5 x 10(-3) M PS, and 1.5 g/L Fe-0 was achieved within 5 min in a PS/Fe-0/US system augmented with 5 min of US irradiation (60 kHz, 106 W/cm(2)). The operating cost to complete removal of the dye was estimated at 2.79 USD/m(3). Higher PS dosage and US power further minimized the interference from carbonate ions. A two-step reaction model, including a slow surface heterogeneous and a fast homogeneous aqueous reactions was proposed for the system. The presence of Fe2+ and Fe3+ ions identified using X-ray photoelectron spectroscopy, suggests a direct oxidation of the dye on the surface of the Fe-0 aggregates. (C) 2016 Elsevier B.V. All rights reserved.