Advanced oxidation of phenolic compounds

Phenol degradation with a UV/H2O2 advanced oxidation process (AOP) was studied in a completely mixed, batch photolytic reactor. The UV irradiation source was a low-pressure mercury vapor lamp that was axially centered and was immersed in the phenol solution. The effects of hydrogen peroxide dosage, initial phenol concentration, H2O2/phenol molar ratio, pH, and temperature have been investigated. The experimental results indicate that there is an optimum H2O2/phenol molar ratio in the range of 100-250. A sufficient amount of hydrogen peroxide was necessary, but a very high H2O2 concentration inhibited the photoxidation rate. The second-order reaction rate constants were inversely affected by the initial phenol concentration. No pH effect was observed in the pH range of 4-10. A detailed reaction mechanism was proposed. The reaction products include hydroquinones, benzoquinones, and aliphatic carboxylic acids with up to six carbon atoms. A kinetic model, which employs the pseudo-steady state assumption to estimate hydroxyl radical concentration and assumes constant pH was developed to predict phenol oxidation kinetics and product distribution. (C) 2000 Elsevier Science Ltd. All rights reserved.