Ozonation of 14C-labeled micropollutants - mineralization of labeled moieties and adsorption of transformation products to activated carbon

Ozonation transformation products (OTPs) are largely unknown compounds that are formed during the ozonation of micropollutants, and it is uncertain to which extent these compounds can be removed by subsequent adsorption to activated carbon. Thus, C-14-labeled micropollutants were ozonated to generate C-14-labeled OTPs, for which the adsorption of the sum of all C-14-labeled OTPs to activated carbon could be determined, based on the adsorption of the labeled carbon. Further, (CO2)-C-14 traps were used to examine the mineralization of C-14-labeled moieties during ozonation. (CO2)-C-14-formation revealed a partial mineralization of the C-14-labeled moieties in all compounds except for propyl-labeled bisphenol A and O-methyl-labeled naproxen. A similar degree of mineralization was noted for different compounds labeled at the same moiety, including the carboxylic carbon in diclofenac and ibuprofen (similar to 40% at 1 g O-3/g DOC) and the aniline ring in sulfamethoxazole and sulfadiazine (similar to 30% at 1 g O-3/g DOC). Aromatic ring cleavage was also confirmed for bisphenol A, sulfamethoxazole, and sulfadiazine through the formation of (CO2)-C-14. The adsorption experiments demonstrated increased adsorption of micropollutants to powdered activated carbon after ozonation, which was connected to a decreased adsorption of dissolved organic matter (DOM). Conversely, the OTPs showed a substantial and successive decline in adsorption at increased ozone doses for all compounds, likely due to decreased hydrophobicity and aromaticity of the OTPs. These findings indicate that adsorption to activated carbon alone is not a viable removal method for a wide range of ozonation transformation products.