High-performance activation of ozone by sonocavitation for BTEX degradation in water

This work presents a novel advanced oxidation process (AOP) for degradation of emerging organic pollutants - benzene, toluene, ethylbenzene and xylenes (BTEXs) in water. A comparative study was performed for sonocavitation assisted ozonation under 40-120 kHz and 80-200 kHz dual frequency ultrasounds (DFUS). Based on the obtained results, the combination of 40-120 kHz i.e., low-frequency US (LFDUS) with O₃ exhibited excellent oxidation capacity degrading 99.37-99.69% of BTEXs in 40 min, while 86.09-91.76% of BTEX degradation was achieved after 60 min in 80-200 kHz i.e., high-frequency US (HFDUS) combined with O₃. The synergistic indexes determined using degradation rate constants were found as 7.86 and 2.9 for LFDUS/O₃ and HFDUS/O₃ processes, respectively. The higher extend of BTEX degradation in both processes was observed at pH 6.5 and 10. Among the reactive oxygen species (ROSs), hydroxyl radicals (HO^•) were found predominant according to scavenging tests, singlet oxygen also importantly contributed in degradation, while O₂^•- radicals had a minor contribution. Sulfate (SO₄^2-) ions demonstrated higher inhibitory effect compared to chloride (Cl^-) and carbonate (CO₃^2-) ions in both processes. Degradation pathways of BTEX was proposed based on the intermediates identified using GC-MS technique.