OPTIMIZATION OF ULTRASONIC IRRADIATION AS AN ADVANCED OXIDATION TECHNOLOGY

The optimization of ultrasonic irradiation as an advanced oxidation te chnology can be achieved by adjusting the ultrasonic frequency and sat urating gas during sonolysis. The sonolytic production of hydrogen per oxide (H2O2) and hydroxyl radical ((OH)-O-.) has been investigated at the ultrasonic frequencies of 20, 40, 80, and 500 kHz, respectively, i n the presence of four different saturating gases (i.e., Kr, Ar, He, O -2) at each frequency. H2O2 was measured with a Kl dosimeter, and the formation of (OH)-O-. was monitored by trapping with terephthalic acid . Both the applied frequency and the physicochemical properties of the saturating gases influence the sonochemical rates of production of (O H)-O-. and H2O2. At 20 kHz, the rate contants for the production of H2 O2 vary over an order of magnitude as a function of the nature of the dissolved gas (0.0508 and 1.31 mu M min(-1)). Similar trends are obser ved for the production of (OH)-O-. at the same frequencies and under a n identical set of saturating gases. The highest rates of production o f H2O2 (PH 7, 2.94 mu M min(-1)) and (OH)-O-. (pH 11, 0.391 mu M min(- 1)) are observed during sonolysis of Kr-saturated solutions at 500 kHz . Sonolysis of He-saturated solutions at 20 kHz results in the lowest rates of production of H202 (0.0508 mu M min(-1)) and (OH)-O-. (0.0310 mu M min(-1)). Decreasing differences among the saturating gases at h igher frequencies are attributed to changes in bubble dynamics and the rmodynamics as the resonant bubble radius decreases from 177 mu m at 2 0 kHz to 7 mu m at 500 kHz.