Aromatic Compound Degradation in Water Using a Combination of Sonolysis and Ozonolysis

The combination of sonolysis and ozonolysis as an advanced oxidation process was investigated to gain insight into factors affecting enhancement of the combined system. Sonolysis, ozonolysis, and a combination of the two were used to facilitate the degradation of three known organic contaminants, nitrobenzene (NB), 4-nitrophenol (4NP), and 4-chlorophenol (4-CP), in water. Experiments were performed at frequencies of 20 and 500 kHz. At 20 kHz, there appeared to be an enhancement due to sonolytic ozonation, while at 500 kHz, an apparent retardation was seen. The catalytic effects of NB, 4-NP, and 4-CP degradation at 20 kHz increased with decreasing kO3 of the compounds, whereas retardation at 500 kHz was correlated with increasing kO3. The correlation of apparent rate enhancement at 20 kHz and retardation at 500 kHz with kO3 is consistent with a pathway involving the thermolytic destruction of ozone to form atomic oxygen. Atomic oxygen then reacts with water vapor in cavitation bubbles, yielding gasphase hydroxyl radical. Enhancement in loss of total organic carbon (TOC) by sonolytic ozonation was considerable at both 20 and 500 kHz with all three compounds. In addition, intermediate product formation was observed.