A comprehensive dynamic kinetic model for the UVC/H₂O₂ process: application to zinc bacitracin degradation in...

A dynamic kinetic model is presented for the UVC/H₂O₂-driven process. The model comprises 103 reactions, including background species, such as HCO₃^-/CO₃^2-, NO₂^-, NO₃^-, SO₄^2-, Cl^-, and H₂PO₄^-/HPO₄²/PO₄^3- anions, and effluent organic matter (EfOM) was validated based on experimental data obtained for the photooxidation of the nonribosomal peptide antibiotic zinc bacitracin (Zn-Bc, 34 μmol L^-1). The set of ordinary differential equations for 38 species was combined with the molar balances describing the recirculating tubular photoreactor used. Predictions for the photolytic and UVC/H₂O₂ processes confirmed the good agreement with experimental data, enabling the estimation of fundamental kinetic parameters, such as the direct photolysis quantum yield (Ф_{254 nm, Zn-Bc} = 0.0143 mol Einstein^-1) and the second-order rate constants for the reactions of Zn-Bc with HO^•, HO₂^•, and O₂^•- radicals (2.64 × 10⁹, 1.63 × 10³, and 1.49 × 10⁴ L mol^-1 s^-1, respectively). The predicted optimum process conditions correspond to [H₂O₂]₀ = 6.8 mmol L^-1 and a specific photon emission rate of 11.1 × 10^-6 Einstein L^-1 s^-1. Zn-Bc photooxidation was significantly impacted by wastewater constituents, particularly EfOM and HCO₃^-/CO₃^2- (i.e., alkalinity), resulting in a degradation rate about 32% lower compared to that obtained in deionized water. In particular, EfOM acts as a strong radical scavenger and inner filter. In addition, simulations pointed out the continuous tubular photochemical reactor as the best configuration for treating Zn-Bc-containing wastewater. This study hence provides a comprehensive modeling approach, especially useful for predicting the effect of complex water matrices on the performance of the UVC/H₂O₂ treatment process.