Comparison of different advanced oxidation processes involving ozone to eliminate atrazine

The oxidation of the herbicide atrazine by advanced oxidation processes (AO P) has been studied. The experiments were carried out in a tubular photorea ctor, 2.5 L capacity, capable of providing good contact between the liquid and gas reactants. The decomposition rate of atrazine was determined at dif ferent pH using UV radiation, Hydrogen Peroxide, Ozone, Ozone/UV, Ozone/H2O 2, H2O2/UV and Ozone/H2O2/UV processes. The effect of three different pH va lues was studied (4.7, 6.8, 11.7). In the experiments with hydrogen peroxide an excess of 10 times the concent ration needed for the total oxidation of atrazine was employed (C-H2O2 cong ruent to 0.025 mol/L). A positive effect of increasing pH was observed in all cases except when us ing UV/H2O2 and UV/H2O2/O-3 at pH 11.8, and when H2O2/O-3 was used at pH 10 .1. In these cases the pH showed a negative effect due to the presence of c ompetitive reactions that consume hydroxyl radicals. The combined processes may have a synergistic effect on the degradation rate because of the forma tion of very reactive hydroxyl radicals. The UV/H2O2 treatment at pH 6.8 sh owed the fastest degradation rate. The measurement of total organic carbon (TOC) showed that no mineralization was produced from the beginning of the experiment to the total elimination of atrazine by any method employed.