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 (CO 3 2− , HCO 3 − , Cl − , Br − , PO 4 3− , HPO 4 2− , H 2 PO 4 − , NO 3 − , SO 4 2− 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. HCO 3 − /CO 3 2− and NOM inhibited the BTEX oxidation and the inhibiting effects became more pronounced as the HCO 3 − /CO 3 2− /NOM concentration increased. SO 4 2− , NO 3 − , PO 4 3− and H 2 PO 4 − did not affect the BTEX oxidation while HPO 4 2− 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, HCO 3 − , CO 3 2− , H 2 PO 4 − , 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.