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.