In this study, persulfate (PS) activation by nano-Fe-0 was used to degrade dichlorodiphenyltrichloroethane (DDT), and the mechanism of this process was elucidated with EPR, GC-MS and free-radical quenching studies. It was found that DDT was degraded efficiently in PS/nano-Fe-0, and GC-MS analysis showed that benzoic acid, benzyl alcohol, dichlorobenzophenone and 2,2-bis(p-chlorophenyl)-ethane were the dominant products of DDT degradation, while only dechlorination products (DDD and DDE) were observed in nano-Fe-0 without persulfate. EPR results showed that persulfate activation by nano-Fe-0 led to the production of more sulfate radicals and hydroxyl radicals, which accounted for DDT degradation. But the free radical quenching studies suggested that the addition of ethanol to PS/nano-Fe-0 favored the reductive dechlorination of DDT, which was ascribed that the formed ethanol radical ((CH)-C-center dot(CH3)OH) enhanced the reductive dechlorination of DDT. Furthermore, the nano-Fe-0 loading not only affected the degradation efficiency of DDT, but also influenced the intermediate product distribution of DDT degradation in the PS/nano-Fe-0 process. (C) 2016 Elsevier B.V. All rights reserved.