The degradation of p-chloronitrobenzene (pCNB) in different systems including ozone alone, ozone together with zero-valent zinc (Zn(0)) and Zn(0) bubbled with air instead of ozone was investigated. The results demonstrated that the degradation of pCNB by ozone alone was weak. However, the coexistence of Zn(0) and ozone exhibited a significantly synergistic role in pCNB degradation and approximately 98% of the initial pCNB (10 mg/L) was removed within 18 min. The degradation efficiency of pCNB was related to Zn(0) dosage and ozone flow amount, and the optimum conditions were 0.5 g/L and 4.8 mg/min, respectively. pCNB could be effectively degraded in the initial pH range of 4-10, but a higher or a lower pH was not beneficial to the removal of pCNB. Accompanying anions also affected pCNB degradation. Chloride and sulfate slightly improved pCNB degradation, whereas bicarbonate and phosphate markedly suppressed the degradation of pCNB. The reuse of Zn(0) (4 cycles) for pCNB ozonation indicated that the catalytic activity of Zn(0) maintained high and stable. The experiments of free radical scavengers (tert-butyl alcohol and p-benzoquinone) corroborated the dominant active species responsible for pCNB degradation by a combination of ozone with Zn(0) was OF rather than OH. Based on the results obtained in this study, it can be concluded that ozone activated by Zn(0) is an effective and promising approach to degrade organic contaminants. (C) 2015 Elsevier B.V. All rights reserved.