Using ultraviolet absorbance and color to assess pharmaceutical oxidation during ozonation of wastewater

The reduction of ultraviolet (UV) absorbance at 254 nm (UV₂₅₄) and true color were identified as appropriate surrogates to assess the oxidation of six pharmaceuticals (i.e., carbamazepine, meprobamate, dilantin, primidone, atenolol, and iopromide) during ozonation of wastewater. Three tertiary-treated wastewaters were evaluated during oxidation with ozone (O₃) and O₃ coupled with hydrogen peroxide (O₃/H₂O ₂). The correlation between pharmaceutical oxidation and removal of UV₂₅₄ was dependent upon the reactivity of each specific compound toward ozone, as measured by the second-order rate constant (k″ _O3). Oxidation of compounds with k″_O3 > 10 ³ M^-1 s^-1 correlated well (R² > 0.73) with UV₂₅₄ reduction between 0-50%. Oxidation of compounds with apparent k″_O3 < 10 M^-1 s^-1 resulted primarily from hydroxyl radicals and correlated well (R² > 0.80) with the UV₂₅₄ reduction of 15-65%. The removal of true color also correlated well (R² > 0.85) with the oxidation of pharmaceuticals during the ozonation of two wastewaters. These correlations demonstrate that UV₂₅₄ reduction and true color removal may be used as surrogates to evaluate pharmaceutical oxidation in the presence or absence of dissolved ozone residual during advanced wastewater treatment with O₃ or O ₃/H₂O₂. The use of online UV₂₅₄ measurements would allow wastewater utilities to optimize the ozone dose required to meet their specific treatment objectives.