COMPARATIVE EFFECTS OF THE TIO2-UV, H2O2-UV, H2O2-FE2+ SYSTEMS ON THE DISAPPEARANCE RATE OF BENZAMIDE AND 4-HYDROXYBENZAMIDE IN WATER

The kinetics of disappearance of benzamide (BZA), chosen as a model water organic pollutant was studied under various treatment conditions. Under illumination at wavelengths greater-than-or-equal-to 220 nm with the same radiant flux, the effects of H2O2 ([H2O2]o/[BZA]o = 8.3) and TiO2 (Degussa P-25 ; 2.5 gL-1) used as a photocatalyst are comparable, whereas the direct photolysis eliminates BZA very slowly. The Fenton reagent (H2O2 - Fe2+; [H2O2]o/[BZA]o = 8; [Fe2+]o/[BZA]o = 0.9 ; pH = 3.4) does not destroy BZA efficiently. In all cases, hydroxybenzamides (HBZA) are the main aromatic intermediates. Additional aromatic intermediates were detected under the treatment conditions that do not involve TiO2, which may be caused by different mechanisms. Also, no mineralization of the nitrogen atom of BZA to nitrate was observed at least in the first stages of the H2O2 - UV treatment. The Fenton reagent is efficient to destroy 4-HBZA. However, the maximum concentration of the main aromatic intermediate, parabenzoquinone (pBQ), is higher than during the photocatalytic treatment and pBQ remains after the elimination of BZA, whereas in the presence of TiO2 all aromatics disappear within about the same time. In short, this study shows that the photocatalytic treatment of water is more general and efficient than the Fenton reagent and compares well with the H2O2 - UV System at least for the pollutant and the conditions chosen.