Oxidation of priority and emerging pollutants with persulfate activated by iron: Effect of iron valence and particle size

Abstract

Persulfate (PS) activated with iron to generate sulfate radicals was employed in the oxidation of Diuron (selected as an example of priority pollutant), Caffeine and Ibuprofen (examples of emerging pollutants whose consumption is widespread). The effect of iron valence (0, 2 and 3) and particle size of Zero-Valent Iron (ZVI) was studied in a batch isothermal reactor at 20°C. The efficiency of the process was evaluated in terms of pollutant and TOC removal, as well as oxidant and iron consumption. Moreover Microtox standard procedure was employed in ecotoxicity measurements.When Fe2+ was employed as PS activator, an undesired reaction consumed both Fe2+ and SO4-. However, in case of ZVI, the release of Fe2+ to the media occurs at the particles surface through acid corrosion and reaction with PS. This allows a controlled production rate of SO4- through a slow release of Fe2+ by selecting the proper particle size, which helps minimizing this undesirable reaction increasing the efficiency of the oxidant. Better results were obtained with ZVI than with Fe2+ especially when regeneration of Fe3+ to Fe2+ through oxidation intermediates did not occur.A kinetic model capable of describing the evolution of pollutant, oxidant, and iron concentrations (at the different oxidation stages) as well as the mineralization was proposed and validated.