Advanced oxidation of pharmaceuticals by the ozone-activated peroxymonosulfate process: the role of different oxidative species

Given the need for innovations in advanced oxidation processes to deal with challenges such as center dot OH scavenging, this paper addresses the removal of pharmaceuticals with a large variety in ozone reactivity (k(O3) = 0.15-3 x 10(5) M-1 s(-1)) by use of the novel ozone -activated peroxymonosulfate (O-3/PMS) process. A clear improvement in removal efficiency (up to 5 times higher) is noticed as a result of the generation of SO4 center dot-radicals, mainly for slow-ozone reacting compounds (k(O3) <= 250 M-1 s(-1)) and in the presence of a center dot OH scavenger. Depending on the target compound, SO4 center dot-are assessed to contribute for 50-90% to the overall removal of the micropollutants, both in single-compound and mixture experiments. Ozone-based PMS activation occurs at neutral to alkaline pH and, in the presence of a center dot OH scavenger, removal efficiencies during O-3/PMS are up to 3 times higher than with the O-3/H2O2 process. In optimizing the O-3/PMS process, a trade-off has to made between the desired removal and the PMS:O-3 ratio. A molar ratio of 1:10 already results in a clear benefit compared to the ozonation process. Further increase of the PMS content up to a 1:1 ratio improved the removal by an additional factor of 1.3-1.5.