The removal of biocide 4-chloro-3-methyl phenol (CMP) was investigated by heterogeneous Fenton-like system using nanoparticulate zero-valent iron (nZVI) as catalyst. The properties of nZVI before and after reaction were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of pH value, initial concentration of CMP, nZVI dose and hydrogen peroxide (H2O2) concentration were determined. The experimental results showed that lower pH value and CMP concentration brought faster degradation rate. With the initial pH value of 6.1 and initial CMP concentration of 0.7 mM, the optimal dosage of reagents were 0.5 g nZVI/L and 3.0 mM H2O2. At pH 6.1, the degradation of CMP followed two-stage first-order kinetic that composed of an induction period (first-stage) and a followed rapid degradation stage (second-stage). According to the effects of scavengers n-butanol and KI, hydroxyl radicals ((OH)-O-center dot), especially the surface-bounded center dot OH, had a dominant role in the oxidation of CMP. The degradation intermediates. carboxylic acids and chloride ion produced during the reaction process were monitored by high performance liquid chromatography (HPLC), liquid chromatography/mass spectrometry (LC/MS) and ion chromatography (IC). On the basis of these findings, the possible mechanistic steps of CMP degradation were proposed. (C) 2010 Elsevier B.V. All rights reserved.