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·−, SO5·− and HO· were identified in the UV/PS/sulfite system, and SO4·− and HO· should be primarily responsible for Orange II removal.