Enhanced degradation of Orange II using a novel UV/persulfate/sulfite system

UV-activated persulfate (PS) systems have been widely employed to remove organic contaminants. However, the heavy use of persulfate may lead to secondary pollution. Here we proposed a novel UV/PS/sulfite oxidation process, in which sulfite would not only promote but also partially replace persulfate to produce sulfate radicals. We tested this system using Orange II as a model compound. Results show that the use of sulfite improves the degradation of Orange II. For instance, increasing the molar ratio of sulfite to persulfate in the range of 0.05-0.5 enhanced the removal efficiency by 21.7%. Compared to the UV/PS system, the presence of sulfite can achieve a 33.4% higher performance. We also found that the absence of dissolved oxygen remarkably inhibited the oxidation of Orange II. SO4 center dot-, SO5 center dot- and HO center dot were identified in the UV/PS/sulfite system, and SO4 center dot- and HO center dot should be primarily responsible for Orange II removal.