Oxidation of organic pollutants over MnO2 in cold water assisted by peroxydisulfate.

[Display omitted] • The two-component oxidant system persulfate + MnO 2 is active at low temperatures. • MnO 2 is a primary oxidant rather than a catalyst. • Persulfate acts as a secondary oxidant which re-oxidizes MnO x. • The advantage of MnO 2 over direct persulfate oxidation is highest at low temperatures. • Singlet oxygen 1O 2 does not play a major role in the oxidation process. MnO 2 can be used in advanced oxidation processes to activate peroxydisulfate (PS) and generate reactive species such as sulfate radicals (SO 4 •-), hydroxyl radicals (•OH) and singlet oxygen (1O 2) for the abatement of organic water contaminants. Alternatively, one can use MnO 2 as particulate oxidant which, in contrast to PS, is active already at low temperatures. This low-temperature activity is particularly attractive for in situ groundwater treatment. The roles of PS and MnO 2 as oxidant and catalyst, respectively, may invert: MnO 2 functions as primary oxidant and PS works as re-oxidant of reduced Mn-oxides. In this way, the limited oxidation capacity of particulate MnO 2 can be overcome. So far, such reaction systems have not been extensively explored. In the present study, the degradation of 4-hydroxybenzoic acid (HBA) by PS + MnO 2 was studied under various experimental conditions, by varying reaction temperature (15–45 °C), reagent concentrations, and water matrix. Both PS and MnO 2 alone have the ability to effect the oxidation of HBA. In the co-presence of PS and MnO 2 , a fast removal of HBA from water was achieved even at low temperatures (half-life of HBA about 0.5 h with 2.4 g L-1 MnO 2 at 25 °C), owing to a synergic effect between the two components. Quenching experiments indicate that the primary HBA oxidation step is a heterogeneous reaction on the MnO 2 surface rather than a homogeneous reaction driven by SO 4 •- or 1O 2 , as frequently reported in literature. This is in line with results from the PS driven oxidation of perfluorooctanoic acid which is not significantly enhanced in the presence of MnO 2. [ABSTRACT FROM AUTHOR]