Kinetics of Photooxidation of Dihydric Phenols in the Presence of Hydrogen Peroxide and Potassium Persulfate

Abstract

Wastewater treatment to remove organic ecotoxicants is one the most important problems today. Scientists’ efforts throughout the world are focused on searching for effective and harmless technologies for the removal and/or complete degradation of organic pollutants. One of the solutions is the use of UV lamps in combination with various oxidants. UV irradiation is widely used in various branches of industry, especially in water treatment. Photolysis methods are environmentally clean and are included in handbooks of the best available technologies. Experiments performed in this study were aimed at revealing kinetic relationships of the photochemical degradation of dihydric phenols in aqueous solutions under the action of active species. All the processes were performed using a flow-through laboratory installation. A 9 W, 254 nm OSMAR special ozone-free bactericidal lamp (Finland) was chosen as a UV radiation source. The residence time of the model solution in the reactor was varied from 20 to 120 s. Quantitative determination of dihydric phenols was performed by the spectrophotometric method. Hydrogen peroxide (3% solution) and potassium persulfate were chosen as oxidizing additives. The potential of the UV radiation and oxidative treatment for efficient removal of dihydric phenols from water was evaluated. Photooxidation of pyrocatechol, resorcinol, and hydroquinone in aqueous solution in the presence of hydrogen peroxide and potassium persulfate was performed. The oxidants were taken in amount from stoichiometric to fivefold excess relative to the stoichiometry. The photochemical degradation of dihydric phenols can be performed with up to 99% efficiency. At the phenol : oxidant molar ratio of 1 : 5, the photooxidation rate increases by a factor of 3–5. The degradation involves the breakdown of the benzene ring, and the main degradation products of dihydric phenols are monobasic carboxylic acids and formaldehyde.