Degradation of binary mixtures of water pollutants in a photocatalytic microreactor: Competitive kinetics with explicit radiation absorption effects

Abstract

The photocatalytic degradation of 17-α-ethinylestradiol (EE2) and phenol in aqueous solutions was studied using a continuous flow, planar microreactor under simulated sunlight. A TiO2 thin film was employed as photocatalyst. The degradation rates of single compounds and binary mixtures were well described by the Langmuir-Hinshelwood equation, including competitive terms for the companion pollutant and the intermediate products, and the effect of photon absorption by the photocatalyst. The absorbed radiation in the microreactor was calculated from the optical properties of the TiO2 film and the application of the Net Radiation method. The estimation of the kinetic parameters was carried out by numerical integration of coupled mass balance equations for EE2 and phenol employing the Runge-Kutta method, and adjusting the kinetics parameters with a nonlinear least-squares solver. The objective of this routine was to minimize the sum of the squares of the differences between the simulated and experimental outlet concentrations of EE2 and phenol under different operating conditions. Using this approach, intrinsic kinetic parameters were obtained. The model was able to predict the degradation of both organic pollutants under different inlet concentrations, irradiation levels, and fluid flow rates. This methodology can be extended to assess the simultaneous degradation of multi-component systems.