Abatement of Polychoro-1,3-butadienes in Aqueous Solution by Ozone, UV Photolysis, and Advanced Oxidation Processes (O₃/H₂O₂ and UV/H₂O₂)

Abstract

The abatement of 9 polychloro-1,3-butadienes (CBDs) in aqueous solution by ozone, UV-C(254 nm) photolysis, and the corresponding advanced oxidation processes (AOPs) (i.e., O₃/H₂O₂ and UV/H₂O₂) was investigated. The following parameters were determined for 9 CBDs: second-order rate constants for the reactions of CBDs with ozone (k_O₃) (<0.1-7.9 × 10³ M^-1 s^-1) or with hydroxyl radicals (k_^•OH) (0.9 × 10⁹ - 6.5 × 10⁹ M^-1 s^-1), photon fluence-based rate constants (k') (210-2730 m² einstein^-1), and quantum yields (Φ) (0.03-0.95 mol einstein^-1). During ozonation of CBDs in a natural groundwater, appreciable abatements (>50% at specific ozone doses of 0.5 gO₃/gDOC to ∼100% at ≥1.0 gO₃/gDOC) were achieved for tetra-CBDs followed by (Z)-1,1,2,3,4-penta-CBD and hexa-CBD. This is consistent with the magnitude of the determined k_O₃ and k_^•OH. The formation of bromate, a potentially carcinogenic ozonation byproduct, could be significantly reduced by addition of H₂O₂. For a typical UV disinfection dose (400 J/m²), various extents of phototransformations (10-90%) could be achieved. However, the efficient formation of photoisomers from CBDs with E/Z configuration must be taken into account because of their potential residual toxicity. Under UV-C(254 nm) photolysis conditions, no significant effect of H₂O₂ addition on CBDs abatement was observed due to an efficient direct phototransformation of CBDs.