Polychloro-1,3-butadienes (CBDs) are problematic groundwater contaminants. In this study, the abatement of nine CBDs (6 tetra-CBD isomers, 2 penta-CBD isomers, and hexa-CBD) by ozone, UV-irradiation, and the advanced oxidation processes (AOPs) thereof (i.e., O3/H2O2 and UV/H2O2) was investigated. The following key parameters for the CBDs for respective treatment options were empirically determined: second-order rate constants for the reaction of CBDs with ozone (kO3) (&lt;0.1 – 7.9×103 M-1s-1) or hydroxyl radical (kOH) (0.9×109 – 6.5×109 M-1s-1), photon fluence-based rate constants (210 – 2730 m2 einstein-1), and quantum yields (0.03 – 1.23 mol einstein-1). The kO3 could be predicted by a previously developed quantum molecular model using the natural bond orbital (NBO) energy for 6 tetraCBDs within a factor of 4 of the experimental kO3, while an error of more than 2 orders of magnitude was obtained for 2 pentaCBDs and hexaCBD. The abatement of the CBDs by the different treatment options in a natural groundwater was also investigated. For ozonation, an ozone dose of 0.5 gO3/gDOC led to a complete abatement of the tetraCBDs, whereas pentaCBD (50%) and hexaCBD (~10%) were abated only partly. This is consistent with the magnitude of the determined second order rate constants, kO3 and kOH. The H2O2 addition for ozonation (i.e., O3/H2O2) led to slightly decreased abatement efficiencies for several tetraCBDs but significantly reduced the formation of bromate that is a potentially carcinogenic by-product formed during ozonation. For a typical UV dose for disinfection (~400 J/m2), CBDs could be photodegraded by 10-90%. The CBDs with E/Z configuration were found to undergo photoisomerization. Therefore, not only the abatement of parent CBDs but also the formation of photoisomers needs to be taken into account for such CBDs since the photoisomers may also be toxic based on the similar chemical composition. The H2O2 addition did not lead to a significant effect on the abatement of CBDs during UV-based treatment because the direct phototransformation of CBDs was an efficient process.

Abatement of polychoro-1,3-butadienes in aqueous solution by ozone, UV-photolysis, and advanced oxidation processes (O3/H2O2 and UV/H2O2)

253rd National Meeting (2017)

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