Sonocatalytic oxidation processes for the removal of contaminants containing aromatic rings from aqueous effluents

The effect of low frequency (20 kHz) ultrasonic irradiation on the removal of sodium dodecylbenzene sulfonate (SDBS), phenol, 2-chlorophenol and 3,4-dichlorophenol from aqueous solutions has been investigated. Sonolytic degradation of SDBS (at an initial concentration of 1 g/l) results in the formation of lower molecular weight compounds and is accompanied by low total oxidation rates. In parallel, water sonolysis results in the formation of hydrogen peroxide. Several heterogeneous catalysts (three noble metals and a metal oxide) were tested with respect to their effect on SDBS sonolysis. Of these, a CuO.ZnO supported on alumina catalyst appears to enhance both SDBS fragmentation and total oxidation rates as well as hydrogen peroxide formation. Phenolic compounds (at an initial concentration of 0.1 g/l) are only partially removed by ultrasonic irradiation with 2-chlorophenol being more susceptible to degradation than phenol and 3,4-dichlorophenol. However, the presence of Fe2+ ions at concentrations as low as about 10(-3) g/l generally increases the rate of the uncatalysed sonolytic degradation. This is attributed to iron being capable of readily decomposing hydrogen peroxide in a Fenton-like process to form reactive hydroxyl radicals as well as being an effective oxidation catalyst. (C) 2003 Elsevier B.V. All rights reserved.