Effects of operating parameters on sonochemical decomposition of phenol

Ultrasonic removal of phenol under irradiation at 20, 300 and 520 kHz was investigated to assess the impacts of operating parameters on the efficiency of the systems. It was found under our experimental conditions that 20 kHz was the least effective frequency for ultrasonic decomposition of phenol, owing to the low volatility of phenol and the slow rate of OH radical ejection to the bulk solution at this frequency. Assessment of relative rates of destruction and ultrasonic yields showed that maximum efficiency was accomplished with 300 kHz employed in a reactor enclosed with an ultrasonic energy of 14.7 W. The same reactor and frequency was found to provide maximum ejection of hydroxyl radicals to the solution. Impacts of pH and initial concentration on the efficiency of phenol removal were such that acidic pH and high concentrations accelerated the process as related to the increased likelihood of phenol at these conditions to approach the cavity sheath. Separate injection of equivalent volumes of air and argon into the reactors showed that the decomposition was enhanced in the presence of air by virtue of the production of additional reactive species via the reaction of nitrogen with molecular oxygen. (c) 2006 Elsevier B.V. All rights reserved.