Enhanced ozonation degradation of para-chlorobenzoic acid (pCBA) with the addition of peroxymonosulfate (PMS) was investigated in aqueous solution. The results demonstrated that the addition of PMS could accelerate the decomposition of O-3 by 50 times compared to that of O-3 alone, and the effect was comparable to that of hydrogen peroxide. The degradation of a typical organic contaminant pCBA, was significantly enhanced by the addition of O-3/PMS. The mechanism behind the synergistic effect was preliminarily explored by the addition of hydroxyl and sulfate radical (SO4 center dot-) scavengers. The degradation of pCBA by O-3/PMS could not be completely inhibited by tert-butanol, whereas it was inhibited by the addition of methanol, indicating that the effect of O-3/PMS was primarily due to the production of a greater amount of SO4 center dot-. The addition of O-3/PMS had a selective effect on various contaminants. The enhanced degradation of pCBA by O-3/PMS was also observed in actual water samples, and provided some impetus for practical applications of the developed system. (C)2014 Elsevier B.V. All rights reserved.