Aqueous Metronidazole Degradation by UV/H2O2 Process in Single-and Multi-Lamp Tubular Photoreactors: Kinetics and Reactor Design

A kinetic model was developed to predict the removal of aqueous metronidazole utilizing the UV/H 2 O 2 process. The rate constant for the reaction between metronidazole and hydroxyl radicals was determined to be 1.98 × 10 9 M −1 s −1 . The model was able to predict an optimal initial H 2 O 2 dose and the inhibitory effects of high H 2 O 2 doses and bicarbonate ions in the aqueous solution. Simulations were performed for three different photoreactors treating a 6 μM solution of metronidazole at various influent H 2 O 2 doses and photoreactor radii. The predicted removal rates of metronidazole were 4.9−13% and 14−41% for the single-lamp and multilamp photoreactors, respectively. Selection of a photoreactor radius for maximum metronidazole removal varied with influent H 2 O 2 concentration. The lowest operational cost of $0.05 per mmol removed was projected for the multilamp photoreactor. Operationally, it was cost-effective to utilize higher UV lamp output (36W), while keeping influent H 2 O 2 concentration low (25 mg/L).