Impacts of inorganic anions and natural organic matter on thermally activated persulfate oxidation of BTEX in water

The present study investigated the impacts of water matrix constituents (CO32−, HCO3−, Cl−, Br−, PO43−, HPO42−, H2PO4−, NO3−, SO42− and natural organic matters (NOM) on the oxidation of a mixture of benzene, toluene, ethylbenzene, and xylenes (BTEX) by thermally activated persulfate (PS). In the absence of matrix constituents, the BTEX oxidation rates decreased in the following order: xylenes > toluene ≈ ethylbenzene > benzene. HCO3−/CO32− and NOM inhibited the BTEX oxidation and the inhibiting effects became more pronounced as the HCO3−/CO32−/NOM concentration increased. SO42−, NO3−, PO43− and H2PO4− did not affect the BTEX oxidation while HPO42− slightly inhibited the reaction. The impacts of Cl− and Br− were complex. Cl− inhibited the benzene oxidation while 100 mM and 500 mM of Cl− promoted the oxidation of m-xylene and p-xylene. Br− completely suppressed the benzene oxidation while 500 mM of Br− strongly promoted the oxidation of xylenes. Detailed explanations on the influence of each matrix constituent were discussed. In addition, various halogenated degradation byproducts were detected in the treatments containing Cl− and Br−. Overall, this study indicates that some matrix constituents such as NOM, HCO3−, CO32−, H2PO4−, Cl− and Br− may reduce the BTEX removal efficiency of sulfate radical-based advanced oxidation process (SR-AOP) and the presence of Cl− and Br− may even lead to the formation of toxic halogenated byproducts.