Comparative study of H₂O₂ and O₃ effects on radiation treatment of TCE and PCE

The effects of H₂O₂ and O₃ on the decomposition of trichloroethylene (TCE) and perchloroethylene (PCE) by gamma-rays (γ-rays) were investigated in this work. The combined γ-rays/O₃ process showed a synergistic effect and enhanced the removal of TCE and PCE compared with γ-rays alone, but, the γ-rays/H₂O₂ process did not increase the removal. This interesting result was successfully identified by an electron paramagnetic resonance spectroscopy/spintrapping method that can quantify hydroxyl radicals, which is directly related to the efficiency of TCE and PCE decomposition. For γ-rays/H₂O₂ system, there was no difference of hydroxyl radical production between γ-rays alone and γ-rays/H₂O₂. This indicates γ-rays cannot activate H₂O₂ to produce hydroxyl radicals and this causes no increase of TCE and PCE removals. To the contrary, the production of hydroxyl radicals was obviously increased in the case of γ-rays/O₃ process. This suggests additional hydroxyl radicals are produced from the reaction of O₃ with the irradiation products of water such as hydrated electrons, hydrogen atoms, etc. and this accelerates the removal of TCE and PCE.