Oxidation of Parachloronitrobenzene in Dilute Aqueous Solution by O3 + UV and H2O2+ UV : A Comparative Study

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Abstract
This laboratory study was designed to investigate the degradation of 4-chloronitrobenzene ([CNB] = 2.4 × 10−6 mol L−1; pH = 7.5) by H2O2/UV and by O3/UV oxidation processes which involve the generation of very reactive and oxidizing hydroxyl free radicals. The effects of the oxidant doses (H2O2 or aqueous O3), liquid flow rate (or the contact time), and bicarbonate ions acting as OH· radical scavengers on the CNB removal rates were studied. For a constant oxidant dose, the results show that the O3/UV system appears to be more efficient than the H2O2/UV system to remove CNB because of the greatest rate of OH· generation by ozone photodecomposition compared to H2O2 photolysis. However, for a given amount of oxidant decomposed, the H2O2/UV oxidant system was found to be more efficient than O3/UV. Moreover, high levels of bicarbonate ions in solution (4 × 10−3 mol L−1) significantly decrease the efficiency of CNB removal by H2O2/UV and by O3/UV oxidation processes.

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