Photochemical oxidation of phenol and chlorophenol by UV/H2O2/TiO2 process: A kinetic study

In the present work, the photochemical oxidation of phenol and chlorophenol aqueous solutions in a batch recycle photochemical reactor using ultraviolet irradiation, hydrogen peroxide and TiO₂ (as photocatalyst) was studied. The study showed that the combined treatment process was the most effective process under acidic conditions and showed a higher rate of degradation of phenol and chlorophenol at a very short radiation time. The reaction was found to follow the first order kinetics and was influenced by the pH, the input concentration of H₂O₂ and the dosing amount of the TiO₂ photocatalyst. The results indicate maximum 74.6% and 79.8% degradation of phenol and chlorophenol respectively within 90 minutes of radiation time. The experimental results showed that the optimum conditions were obtained at a pH value of 4, with H₂O₂ concentration ranging from 200-550 ml/L, and TiO₂ dosing ranging from 1-2 g/L for UV/H₂O₂/TiO₂ combined system. The reactions were accompanied by the reduction of COD and generation of Cl^- ion, which reached its maximum value at a short reaction time. Finally a rough comparison of energy consumption shows that UV/H₂O₂/TiO₂ process reduced the energy consumption by 40-50% compared with the UV/H₂O₂ and UV/TiO₂ processes.