Chemistry of persulfates in water and wastewater treatment: A review

Persulfate decontamination technologies either utilizing radical driven processes or direct electron transfer are very powerful tools for the treatment of a broad range of impurities, including halogenated olefins, BTEXs (benzene, toluene, ethylbenzene and xylenes), perfluorinated chemicals, phenols, pharmaceuticals, inorganics and pesticides. Furthermore, the reactivity of persulfates is extremely dependent on the related activation techniques and the composition of the treated water matrix. Direct reactions of peroxydisulfate (PDS) or peroxymonosulfate (PMS) are rather slow and mostly unsuitable for pollutant degradation. However, PDS or PMS decompose at elevated temperatures under UV radiation, and radiolysis treatment as well as in presence of reduced metal ions to form sulfate radicals (SO4−). (SO4−)-based oxidation can also form secondary oxidants for instance carbonate radicals, hydroxyl radicals, superoxide radicals or singlet oxygen which can influence both transformation efficiency and product formation. The formation of such species is extremely subjected on the water matrix composition and can hardly be predicted. One important aspect in dealing with PDS or PMS is their analysis, which is often prone for interference by other matrix components and hampered by the low stability of PDS and PMS in aqueous systems. Numerous methods for analysis of PDS and PMS are available. The present work also provides an overview on these methods.