Unexpectedly Enhanced Organics Removal in Persulfate Oxidation with High Concentration of Sulfate: The Origin and the Selectivity

Massive anions in high saline wastewater are primary factors that restricted the efficiency of pollutant degradation in advanced oxidation processes (AOPs). Herein, we reported the influence laws of different anions at high concentration on the electron-transfer process in the activation of persulfate, and especially, the sulfate anion exhibited the excellent promotion effect. Depending on the ionic charge, polarizability, and size, the anions exerted diverse effects on the dispersed phase and zeta potential of carbonaceous catalysts, which further embodied in the removal of pollutants. Based on the differences of reaction rate constant in water solution and high saline solution, the order was ClO4- < NO3- < Cl- < SO42- < CO32-, obeying the Hofmeister series. The enhancement of the sulfate anion was widely confirmed with different carbonaceous catalysts and pollutants with various structures. It could be attributed to the higher oxidation capacity, the faster interfacial electron transfer, and the better catalyst dispersion in the high sulfate environment. On the other hand, the decrease of zeta potential of the catalyst induced by sulfate reinforced the electrostatic attraction or repulsion with pollutants, which caused the selectivity of the sulfate promotion effect. Overall, this study provides new insights into the mechanism of influence of anions on AOPs, which refreshed the cognition of the role of sulfate on pollutant degradation, and helps guide the treatment design of high salinity wastewater.