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/spin-trapping 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.