Selecting nitrobenzene (NB) as the model pollutant, this paper investigated the efficiency and mechanism of the degradation of NB in aqueous solution by O3/H2O2. The effects of pH value, H2O2 dose and the inhibitor or accelerant of •OH on the removal rate of NB were studied. H2O2 could obviously improve the ozonation decay rate of NB below pH 7. When H2O2 dose increased from 1.0 mg/L to 4.0 mg/L, the removal rate of NB was remarkably enhanced. However, as H2O2 dose increased from 4.0 mg/L to 20 mg/L, the removal efficiency of NB decreased. Different masses of H2O2 were yielded in different reaction phases of the single ozonation system. Both single ozonation systems and H2O2-catalysed ozonation could not observably reduce the TOC. During the process of NB degradation, organonitrogen was almost completely converted to nitrate and the pH value reduced significantly. Results of HPLC-MS and GC-MS showed that the main intermediate products were phenolic compounds and carbonyl compounds. Finally, a possible reaction pathway of the catalytic ozonation of NB is proposed. It had been found that the catalytic ozonation of NB could be divided into two steps. First, hydroxyl radical attacked phenyl ring, and then the ring opened, forming into various aliphatic compounds or being mineralized to inorganic compounds.

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