Kinetic modelling of UVC and UVC/H2O2 oxidation of an aqueous mixture of antibiotics in a completely mixed batch photoreactor

The removal kinetics of an aqueous mixture of thirteen antibiotics (i.e., ampicillin, cefuroxime, ciprofloxacin, flumequine, metronidazole, ofloxacin, oxytetracycline, sulfadimethoxine, sulfamethoxazole, sulfamethazine, tetracycline, trimethoprim and tylosin) by batch UV_C and UV_C/H₂O₂ processes has been modeled in this work. First, molar absorption coefficients (ε), direct quantum yields (Φ) and the rate constants of the reaction of antibiotics with hydroxyl radical (k_HO•) (model inputs) were determined for each antibiotic and compared with literature data. The values of these parameters range from 0.3 to 21.8 mM^-1 cm^-1 for ε, < 0.01 to 67.8 mmol·E^-1 for Φ and 3.8 × 10⁹ to 1.7 × 10¹⁰ M^-1 s^-1 for k_HO•. Second, a regression model was developed to compute the rate constants of the reactions of the antibiotics with singlet oxygen (k¹_O₂) from experimental data obtained in batch UV_C experiments treating a mixture of the antibiotics. k¹_O₂ values in the 1-50 × 10⁶ M^-1 s^-1 range were obtained for the antibiotics studied. Finally, a semi-empirical kinetic model comprising a set of ordinary differential equations was solved to simulate the evolution of the residual concentration of antibiotics and hydrogen peroxide (model outputs) in a completely mixed batch photoreactor. Model predictions were reasonably consistent with the experimental data. The kinetic model developed might be combined with computational fluid dynamics to predict process performance and energy consumption in UV_C and UV_C/H₂O₂ applications at full scale.