Decomposition of 2-chlorophenol in aqueous solution by ultrasound/H₂O₂ process

Several authors have indicated that ultrasound is effective in oxidizing organic contaminants in water and in wastewater either as the sole means of treatment or in combination with ozonation and UV irradiation. In this work we decomposed 2-chlorophenol (2-cp) in aqueous solution with ultrasound and H₂O₂. The experiment was conducted with a sonicator (Microson XL-2020) operated at 20 kHz. The double amplitude at the tip of the standard horn (12.7 mm) was adjusted to 0, 72 and 120 μm, corresponding to power input 0, 125 and 160 W. The initial concentration of aqueous 2-cp solution was 100 mg/l, treated in the system with 0, 100, 200 and 500 mg/l H₂O₂ individually. The volume of solution was 1 l in a mixing flask, and was circulated to the sonication cell at the rate 500 mL/min. Oxygen was continuously purged into the flask. The temperature of solution was kept constant at 25°C and pH was controlled at 3, 5, 7, 9 and 11. The results showed the decomposition of 2-cp was effective at increased amplitude of ultrasound and concentration of H₂O₂, and smaller pH. At reaction duration 360 min, 2-cp decomposition with 500 mg/l H₂O₂ was found with 57% improvement over the control, i.e. without H₂O₂ addition. The pH, controlled below the pKa of 2-cp (8.49 at 25°C), had significantly better decomposition of 2-cp than at greater values. The decomposition rate of 100 mg/l 2-cp was 99% at 120 μm double amplitude with H₂O₂ (200 mg/L) and pH 3, after 360 min of reaction. The removal of total organic carbon was found to be only 63%. From analysis of the experimental results, the data on 2-cp decomposition appeared to follow pseudo-first-order reaction kinetics. The squared correlation coefficient, R2, of the model was greater than 0.9 for various pH values.